SGB-SMIT Group is able to deliver Cast Resin Transformers (from production sites in Germany, Malaysia, the USA, China, Czech Republic, France and India) with capacities up to 25 MVA and applied voltages up to 40,5 kV. Our offer includes converter transformers, distribution transformers and special transformers.
With more than 30 years experience in the construction of cast resin transformers, SGB-SMIT Group has worldwide expertise, and this is expressed in remarkably high quality coefficients such as mean time between failures (MTBF) of over 2,400 years.
Transformers which are part of a semiconductor inverter installation must be specially dimensioned. This also applies for use in power supply with increased harmonics-strain, for example, in office blocks or computer centres. Here single-phase loads with power supply units cause a great deal of harmonics.
In the operating-rated current or in the transformer’s rated power, the true values of the fundamental wave and the harmonics are to be included. (Radix from quadratric additions of the values.) This means that the effective capacity decreases in accordance with the harmonics ratio. (With a B6 wiring ca.5%.) At the same time when operating converters, load losses increase due to the frequency-dependance of the additional losses. Additional losses occur both through eddy currents and through flux leakage in the windings and iron pieces.
With converter transformers special attention must be paid so that the amount of additional losses at 50 Hz (see test certificate) is as low as possible (reduced additional losses). With a transformer with normal additional losses it can lead to excessively high heating when operating with loads that cause harmonics. This then affects the service life.
With the SGB calculation model, both additional losses and thermal strain of the winding are ascertained. Heating is adopted in such a way that the converter can be dependably supplied.
SGB manufactures converter transformers for 6-/12-/18- und 24-pulse operations. Thereby moulded, low-vibration, high voltage layer winding with regard to short cycles of operation, quick variable loads, short-time overloads and commutation processes is particularly suitable. This is especially important with inverters with a voltage immediate circuit.
Details on harmonics for standard application as follows:
Converter transformer K-Factor calculation (PDF, 1 KB)
Converter transformer K-Factor calculation Dynavert 6-pulse (PDF, 14 KB)
If your applications differ from this, we request you to inform us of the values. Please also bear in mind that noise values can increase markedly as regards 50Hz.
Being offshore SGB Safe System
SGB cast-resin transformers are characterized not only by their high reliability, but also by extremely high operator safety and good environmental compatibility. Development of the "SGB Safe System" sets new standards for the new Megawatt Class for off-shore installation.
When building transformers for wind parks, a number of factors must be considered, in addition to their economic efficiency:
"Safe System" means that the transformer is accommodated in a protective housing with integrated cooler. The heat generated by the transformer losses is routed to the cooler in the internal cooling circuit.
In the cooler, this waste heat is transferred to the external coolant (air or water). The recooled air is routed back to the transformer via the internal cooling circulation.
Optimizing the cooling system helped reduce weight considerably (pic. 2). The cooling system is designed so that only a small part of the transformer's power loss is issued to the nacelle of the wind power plant via the housing.
The transformer is hermetically sealed against the external salty, corrosive cooling air and against the wind power plant. Thus, it not only complies with the requirements acc. to DIN EN 50308, but also extends the maintenance intervals, as no salt can get deposited on the transformer.
For the inner and outer cooling circuit, two redundant fans are provided, one of which always ensures operation at approx. 90% of the rated power. The fans are decoupled via non-return valves. The fans are connected via plugs mounted externally on the housing.
The service life of the fans, which can be exchanged during operation, is over 5 years. The volumetric flows are recorded via a ring testing circuit and can be read on site or transmitted to the control room on site. The tubular cooler was manufactured of highly resistant Al Mg 4.5 Mn. Condensate and cleaning water are discharged to the outside.
The metallic housing, which can be disassembled (type of enclosure: IP44), protects operators against touching electrically active parts.
All parts are connected to the signal ground. The inspection parts are integrated in the wind power plant's interlocking system. The inverter is supplied via a fused outgoing feeder cabinet.
The winding temperatures are integrated into plant operation and enable a controlled reduction of the system load or temperatures in case of overload or excess temperatures. Moreover, once the admissible winding temperatures are exceeded, the system is switched off via PTC sensor and tripping devices. All control units are accommodated in a housing recess. The operating states can be read through a glass safety port. All messages are transmitted to the control room via connectors. The safe earthing of the deenergized transformer is effected by an earthing switch with leading auxiliary contacts. When the transformer voltage is "on", the auxiliary contacts trips the MS feeder circuit-breaker.
Moreover, a capacitive testing and monitoring system has also been provided. The earthing switch is also integrated into the wind power plant interlocking system. Surge arresters are provided on the HV and LV end in order to protect the transformer against the consequences of lightning.
To account for the installation of the wind power plant off-shore, safety precautions were taken which exceed the regulations by far.
SBG cast-resin transformers have a much lower fire load than comparable oil transformers. Thus, dry-type transformers do not contribute essentially to fire incidents. The behaviour in fire is judged according to EN 60726.
The properties "flame resistant" and "self-extinguishing" essentially contributing to protect the operators. As the transformer insulation consists of solids, there is no risk of fire carryover by liquid escaping at high pressure and high temperature. Moreover, the transformer is integrated in the fire extinguishing system of the wind power plant. Sensors detect typical decomposition products which are produced at a very early stage. As the transformer is located in the housing, extinguishing is very efficient.
An incident on the transformer always gives rise to an arc. An arc sensor ensures that the plant is switched off quickly. Should excess pressure arise nevertheless, it is discharged via pressure relief valves in the outer cooling circuit and from here to the outside. The service ports are secured by multiple interlocks.
These safety devices detect the fault more quickly than the short-circuit tripping of circuit-breakers, and much earlier than temperature sensors. These are provided for overload protection.
Taking into account marked and rapid power fluctuations SGB cast-resin transformers are particularly well suited for operation involving high and rapid power fluctuations.
The HV winding is cast in moulds under vacuum using epoxy / glass fiber insulation. The glass fibres embedded in epoxy can absorb the forces which are exercised by the expansions of the conductor material and the resin due to the load variations.
Considerable mechanical loads occur during installation of a transformer in the nacelle and during transport. These loads were calculated by means of the finite-element method and verified at IABG, Ottobrunn.
Contrary to oil-insulated transformers, the dry-type transformer distinguishes itself by the tight fit of the windings and that the supporting structure is visible, and can easily be retightened, if necessary, with spring elements.
To account for the safety aspects of an off-shore plant, during the routine test, the transformers are additionally loaded until they reach their limit temperature, and are subsequently subjected to an impulse voltage test with subsequent PD measurement.
The SGB Safe System meets all requirements of off- shore applications and proved it in practice.
The SGB-Safe-System corresponds to the "Guideline for Certification of Offshore Wind Turbines". This was confirmed by Germanischer Lloyd in the Statement of Compliance 72943.
New cooling for on-shore transformers
With its Jet System, SGB offers an optimized solution for wind energy plants for on-shore installation.
It is produced for the power range from 1.6 MVA to 4 MVA and for a maximum operating voltage of Um 36 kV.
The design can be adapted for installation in the tower as well as in the nacelle.
In addition to life-cycle costs, the following factors were given especial consideration in the course of development:
In this context, the SGB resin-encapsulated transformer is accommodated in a proven protective housing IP44. The cold supply air is routed directly to the housing from outside via a supply air box and a piping system. The cooling air is routed directly into the transformer winding ducts via an air guide plate.
The exhaust air heated by the transformer losses is blown directly into the open air via a piping system which also accommodates a low-noise fan and an exhaust air box. This makes up a defined cooling system which can be tested in the scope of a factory test and ensures that the measured values are also reached after installation within the wind energy plant.
No-load losses and the low load losses up to 30% nominal power can be dissipated without switching the fan ON. In case of a higher load, the fan is activated via temperature sensors in the windings.
The optimized design of the cooling system makes for considerable material and space savings. The targeted air supply keeps the heating of the windings low. The transformer has been designed for climate class C2 and for a temperature range from + 40 to – 25°C. Temperatures between –50°C and + 50°C can be covered in exceptional cases.
In accordance with the environmental class E2, the transformer was tested successfully at KEMA in a climatic chamber with moisture precipitation and a conductivity of the water of 0.5 to 1.5 S/m. If the environmental conditions exceed these requirements, the feed air box can be equipped with appropriate filters.
Thanks to the high reliability of SGB resin-encapsulated transformers, the risk involved is very low. Due to the low fire load and the fact that no coolant is used, the transformer does not contribute essentially to fire incidents.
The dismountable housing of galvanized sheet steel protects the staff against touching live parts. All components are connected to the plant's grounding system. In case of faults, the hot gases can escape via the ventilation and deaeration lines. Arc monitoring sensors signal malfunctions occurring, thus allowing the plant to be switched off extremely quickly. This reduces possible risks and damage considerably. Fire gases are also routed out of the plant via the supply and exhaust air lines, thus satisfying the requirements of EN 50308.
The temperatures of the windings are integrated within the plant control system and, on being exceeded, cause the plant to be deactivated.
Wind energy plants are often built and operated on spurs remote from the large consumption and conventional power generation centers. Due to the continuously rising proportion of wind energy in consumption networks, the demands on grid operators as regards the electrical properties are also on the increase.
Depending on the prevailing conditions in the countries concerned, voltage fluctuations resulting from the power characteristics of wind parks and the behaviour in case of fault have to satisfy different requirements. A certain amount of inductive and capacitive reactive power must be provided.
As transformers are the link connecting the grid to the wind generator, the conditions for connection to the power system have a considerable effect on the transformer's design and thus the costs of manufacturing. Overvoltages on the transformer due to higher mains voltage or capacitive loads, result in over-excitation and thus cause the core to heat up to inadmissibly high temperatures.
This can be compensated by a reduction of induction, i.e. the enhanced use of magnetic sheet metal. It should also be possible to provide the rated power of the wind energy plant at undervoltage. Thus, the transformer must be operated continuously at approx. 10% higher current. This also means extra material outlay.
By optimizing the cooling of the transformer, through ducts in the windings and the design of the magnetic core, we have managed to reduce this additional extra expense considerably.
As wind energy plants are exported in high quantities, the stress imposed by transport, especially over the last few meters, must be considered. We know from experience that the risks are higher than those caused by vibration in the wind energy plant and can realistically be compared to those caused by serious earthquakes.
Thus, the cores of SGB transformers used for wind energy plants are not only secured by gluing the core plates and bandages, but also by pins passed through the core yokes.
Moreover, clamping of the glass-fibre reinforced HV winding and the LV winding glued with Prepreg is effected by a support system with cup springs.
The targeted cooling within the Jet System permits material savings and provides a proven, reliable and low-cost version of safe interfacing of wind energy plants to supply grids.
SGB-SMIT cast resin transformers are designed and manufactured as standard in accordance with IEC 60076-11.
In line with the value-added chain at SGB-SMIT, the tests specified in the standard are performed in our own, modern test area:
SGB-SMIT is the first transformer manufacturer world-wide with internal C2/C3 and E2/E3 testing facilities!
External special tests:
Detailed measurements in external institutes
Moreover, we have performed detailed measurements for important technical areas together with external institutes:
SGB-SMIT cast resin transformers are delivered in over 50 countries – of course, design, manufacture and testing are based on the standards relevant in these countries such as ANSI, IEEE, GOST etc. Project-related acceptance/verification tests by classification institutes such as Lloyd‘s Register, DNV, Bureau Veritas or other external inspection agencies such as TÜV-Süd are part of our day-to-day business.
Based on a precise analysis according to automotive standards, all relevant production parameters of each transformer are recorded continuously and compared online to the set-point values. The next production step only follows if everything is found to be correct.
This system makes it possible to achieve a uniform level of quality over large production quantities at all locations of the SGB-SMIT Group on an international basis.
Type: Three Phase Cast Resin Transformer
Material of HV winding: Aluminium/copper
Material of LV winding: Aluminium/copper
Frequency: 50 Hz
Max. installation height: < 1000 m above sea level
Highest voltage of equipment Um HV: 7,2 kV 12 kV 17,5 kV 24 kV 36 kV
Power frequency withstand voltage: 20 kV 28 kV 38 kV 50 kV 70 kV
Impulse withstand voltage (peak): 40 or 60 kV 60 or 75 kV 75 or 95 kV 95 or 125 kV 145 or 170 kV
Highest voltage of equipment Um LV: 1,1 kV
Power frequency withstand voltage: 3 kV
Environmental, climate and fire class: E1 on request E2; C2; F1
Max. ambient temperature: 20°C yearly average / 30°C daily average / 40°C max. ambient temperature
Winding temperature rise: 100 K
Connection group: Dyn 5
Tappings (HV side): ± 2 x 2,5 %, ± 5 %
Insulation class: F
Requirements / standards: IEC 60076-11 for dry-type transformers with high voltage for equipment up to and including 36 kV
Equipment and accessories: 2 PTC sensors per phase for alarm and trip, lifting lugs, earthing terminal, rating plate, carriage with rollers for bi-directional movement, tappings reconnectable by links, coating of core and clamping bar: RAL5013
For specifying cores for cast resin transformers, no-load losses, noise and no-load current are essential quality features which are, in many cases, of decisive importance. Thus, the core design is an important engineering task. This includes the precise geometrical design, determination of the material properties of the magnetic sheet to be used and many details, including design measures such as those to control vibrations, slanting positions and other mechanical requirements.
Today, transformer cores are produced on special machines which manufacture complete cores in accordance with our specifications out of prefabricated and precisely pre-measured sheet coils. To this effect, SGB-SMIT deploys top-quality specialists and cooperates with these experts very closely in long-term partnerships. Our logistics concept means that material is supplied daily on a just-in-time basis.
Core lamination with high-temperature resistant varnish is suitable for all – even extreme – installation conditions. This provides not only corrosion protection, but also enhances the core‘s stability, as the SGB-SMIT varnish penetrates between the individual laminations, bonding them to one another.
The core is fastened by a holding frame which consists of upper and lower steel clamps and flat tie bars resting directly against the core. The tie bars consist of non-magnetic flat steel and connect the lower and upper steel clamps via forces. The holding frame is designed so that the laminations are largely kept free of traction and pressure strain, as this is the only way to ensure that they retain their excellent loss- and noise-related properties. The lower yoke rests, supported by moulded parts of glass-fibre reinforced plastic, on the lower chassis beams to which bi-directionally adjustable rollers can be fastened. Depending on the requirements at the site of installation, various fastenings can be selected such as additional foot bridges, skids, vibration-reducing elements etc.
The high voltage winding (HV winding) is the heart of the cast resin transformer. It embodies the enormous technical know-how of SGB-SMIT.
Cast resin transformers are characterized by the conductors of the HV winding being embedded completely in an enclosed cast resin body with a smooth surface. Even if not specified so explicitly by the standard, this can be achieved in production of high voltage applications only using vacuum-encapsulated moulds. To this effect, the SGB-SMIT production technology and the materials used feature important USPs (USP = unique selling proposition) which distinguish them on the one hand from other cast resin transformers in terms of technology and, on the other hand, make them a highly reliable and extremely safe solution.
Thermal reserves allow for overload
In this regard, SGB-SMIT cast resin transformers are not only one step ahead of oil transformers, but also of cast resin transformers made according to conventional technology. These use a continuously wound coil whose conductor consists of an aluminium coil and the winding/layer insulation of foil. The insulation corresponds only to insulation class F and even this qualification is only reached in conjunction with the entire insulation system - without thermal reserves.
This is completely different in the case of SGB-SMIT cast resin transformers, as SGB-SMIT uses forthe double-layer winding insulated profile wires whose primary insulation consists either of highlyheat-resistant polyesterimide varnish with a temperature index of 200°C or a Nomex thread covering of temperature class C (220°C). As SGB-SMIT cast resin transformers are utilized, due to their design, mainly according to temperature class F (155°C), primary insulation features considerable temperature reserves.
Ensuring a long service life
Cast resin transformers must dissipate the thermal loss produced in the windings to the cooling air via the coil surfaces. The coils are dimensioned so that the over temperatures admissible due to the
insulation class are not exceeded.
Cooling of conventional technology cast resin transformers with continuously wound coil is only possible via the two inside and outside surfaces of the cylindrical coil. To provide the required surface, the coils must be larger than required by the electrical parameters in many cases. The double-layer winding technology chosen by SGB-SMIT, on the other hand, permits straightforward introduction of additional cooling ducts within the coil. Thus, the cooling surface is gained and the design of the coils is ideal in view of their mechanical dimensions.
SGB-SMIT cast resin coils can even feature multiple cooling ducts.
SGB-SMIT cast resin transformers ensure a uniform temperature distribution within the coil in line with a reasonable material utilization. The optimized coil permits temperature reduction for the HV winding and additionally a uniform temperature distribution for the entire transformer.
Reliable handling of high surge voltages
Only SGB-SMIT cast resin transformers feature vacuum-encapsulated high voltage coils whose winding is designed as a double-layer winding. This means safety in the handling of surge voltages as are caused by lightning strikes or by vacuum circuit-breakers.
Reliably resistant to temperature shocks
During transport, cast resin transformers are subject to mechanical and – especially during operation – strong thermal shock stress. Thus, the transformer‘s capability of handling steep or extreme temperature increases safely is paramount. This feature depends decisively on the design of the cast resin composite material, the matrix, into which the conductors are encapsulated.
For the usual cast resin transformers, this composite material consists of an epoxy resin which is mixed by over 70% with a mineral based filler, primarily quartz powder. Such composite material can only reach the tensile strength of the epoxy resin, i. e. approx. 50 N/mm.
Quite the opposite is the case with SGB-SMIT. Here, the composite system consists of a glass-fibre reinforced epoxy resin between the layers and on the surface, with a high tensile strength in the range of 120 N/mm. The advantage of the composite system chosen by SGB-SMIT has proved its worth in various tests. The thermal shock tests according to IEC 60076-11, which are required for climate classification C2, based on a temperature of -25°C, were passed successfully by SGB-SMIT cast resin coils even at an initial temperature of -50°C.
The low voltage winding of SGB-SMIT cast resin transformers are almost always designed as foil winding.
The benefits of this form of winding are self-explanatory:
Exceptions exist, for technical reasons, only in case of minor ratings below 250 kVA and for higher system
voltages (> 3.6 kV). For more than 40 years SGB-SMIT has been producing foil windings for distribution transformers and cast resin transformers. This long expertise ensures quality features.
Temperature monitoring via PTC (resistors whose resistance changes quickly once the operating temperature is reached) is provided in general for each cast resin transformer. As the LV and HV windings are thermally balanced, the thermistors are located on the LV winding for reasons of insulation. They offer special protection of the vacuum-encapsulated high voltage windings against inadmissibly high temperatures which may occur in situations of overload, insufficient cooling and high ambient temperatures. Subject to customer‘s request, PT100 and core monitoring by PT100 or PTC are also possible. Non-contact temperature monitoring is also available.
As a rule, two systems are installed:
For details of the marshalling panels please remove the following design:
Transformers are capital goods with a service life of many decades; thus, the purchaser should not only focus on the comparison of acquisition prices, but also and especially of the presumable maintenance costs and those resulting from no-load losses (iron core) and load losses (windings).
SGB-SMIT offers different loss variants from normal to highly reduced values.
Higher acquisition costs due to higher outlay for laminations and winding materials coincide with lower operating costs.
It is relatively straightforward to evaluate idle losses, as these are incurred at a constant level over the entire service life of 8,760 hours/year. Evaluation of the load losses which exhibit quadratic growth or decline according to the load is slightly more difficult.
The use of transformers with reduced no-load losses is also profitable as it helps reduce noise Emission.
The following parts can possibly be used as options:
As standard we offer earthing switches from the company Driescher. If you prefer other makes, we can naturally also use these.
With the assembly of transformers directly on the ground or on non-insulated running rails, oscillations from the transformer can give off unwelcome noises and vibrations in the surrounding area. For active interference suppression, special transformer stock can be used and can also be re-fitted at any time.
Fixed ball point
Fixed ball points can be included optionally 20 mm or 25 mm
Remote-reading indicator thermometer
As a further monitoring system we offer a remote-reading indicator thermometer-monitoring from JUMO:
SGB-SMIT cast resin transformers make minimum demands on the site of installation. This results from the above-mentioned regulations regarding groundwater protection, fire protection, functional integrity in DIN VDE 0101, DIN VDE 0108 and ELT Bau VO (Body of regulations for the building trade).
With SGB-SMIT cast resin transformers, no measures are required for water protection.
If however, the cast resin transformer with a rated voltage of over 1 kV is to be used for facilities accommodating crowds of people according to DIN VDE 0108 and ELT Bau VO, the additional requirements specified in these bodies of regulations apply.
SGB-SMIT cast resin transformers feature the degree of protection IP 00 and are intended for indoor installation. The cast resin surface of the transformer winding is not safe to touch in operation.
Cast resin transformers can be located in the same room as medium- and low voltage switchgear, thus permitting electrical connection over an extremely short distance. As in this case, no additional measures are required for oil collecting pans or fire protection, considerable costs can be saved for transformer cells as far as buildings are concerned. In case of outdoor installation, a housing is mandatory. To this effect, the IP type of enclosure of the housing must be specified by the customer.
Especially extreme installation conditions on site must be taken into account when planning switchgear. Thus, special measures are required e. g. in case of utilization of a cast resin transformer at altitudes above 1,000 m due to the low air density. SGB-SMIT cast resin transformers are specially designed for utilization of cast resin transformers in ships, excavators, seismic areas, wind power plants etc. where increased mechanical strain is involved. SGB-SMIT also takes extreme temperature conditions into account in individual cases such as installation in especially cold or tropical areas, and the transformer design is adapted to local conditions accordingly.
Moreover, SGB-SMIT cast resin transformers feature the decisive advantage that all components are always visible, permitting any mechanical damage to be detected and repaired immediately.
With exceptionally restricted circumstances, for example, like these found in protective enclosures, minimum distances (see table) must be heeded in order to prevent voltage flashovers.
(May differ according to customers‘ requirements!)
The place at which the cast resin transformer is installed must be adequately ventilated because with each transformer operation, heat loss occurs which must be discharged from the transformer chamber. In so doing it is worth checking whether the possibility is given for natural airing and ventilation. If dimensions of a chamber or enclosure do not guarantee proper cooling, the air rate must then be guaranteed via forced ventilation. Therefore it is immaterial whether the transformers are operated as self-cooling with the cooling method AN or with attached fans for increased capacity.
Therefore the ventilation system must be assessed for maximum heat loss arising which is made by iron core no-load losses and the heat energy caused by the coils. In order to achieve natural air circulation, it is important that the additional air entrance port is always arranged below and with a maximum height up to the beginning of the low voltage coil, in order to further the chimney effect and the circulation of the air flow in the channel between the low and high voltage coil. With regard to the planned openings of additional air – intake and extracted air – outtake, it is important that the lower opening under the transformer is preferably all the way around, whereby the upper opening must normally show a cross section around 10 to 15 % higher in order to take the lower density of extracted air into consideration and consequently prevent heating.
The necessary volume for perfect cooling can be calculated as follows:
Q = Pt / (1.15 x ΔO) [m³ / s ]
Effective area of the lower opening can be calculated as follows:
S = 10 x (Pt / ((H x ΔO³)0,5))[m²]
Pt: total losses discharged in kW
ΔO: Temperature gradient in °C between additional air and extracted air / experience value 15 K
Q: Air change in m³
H: Distance in meters between the axis of the transformer and the axis of the upper opening of the booth
S: Effective area in m² of the lower additional air opening (without bars)
Noises occur as a result of magneto-striction of laminations. With distribution transformers it depends on induction and not on strain. Harmonics in voltage, which occur for example as a result of converter operation, heighten the noise. Operational noises of the cast resin transformer permeate on site as airborne sound and mechanical vibration, whereby for each form of sound other measures for noise reduction are adopted.
The airborne noise is heightened in a transformer chamber as a result of reflection on walls and ceilings. This increase depends on the total area of the chamber, the area of the transformer and the noise-absorption coefficient of the construction material used for ceilings and walls. This increase in operational noises as a result of reflection can be greatly reduced by lining the transformer chamber with slag wool. Furthermore the sound pressure level in the chamber is reduced outwards through the walls. This insulation is so much greater the thicker a bricked wall is for example. However what is crucial is that outside the transformer chamber the sound pressure level steadily decreases with distance.
Transformer noises are also carried over the contact areas of the transformer, down to the ground, on the walls and other parts of the transformer chamber, the so-called mechanical vibration. This method of noise transmission can be reduced or prevented through mechanical vibration insulation of the transformer. The intensity of the main outbound operational noises from the transformer can not thereby be reduced although mechanical vibration insulation can contribute greatly towards optimising the insulation of the chamber and can therefore, for example, do without noise absorption lining with slag wool on the walls.
Special transformer supports see to mechanical vibration insulation of SGB transformers. Equally expansion straps can be interposed, for example on site, on the low voltage connection, in order to protect the low voltage connection against mechanical voltages and transmission of mechanical vibration.
If nothing else is demanded from the customer, the cast resin transformers are installed on a chassis roller according to transformer capacity. The noises associated with the transformer operation and vibrations caused are not however always negligible. As a possible step for mechanical decoupling of the transformer from the basis of the site is the use of vibrastops from Kächele or Gummi Technik Wager und Wagner. Transformer supports of both manufacturers do not differ purely visually, however Kächele’s supports are harder and more expensive. In many cases special rubber material from ISOLOC is used, normally IPL 20 material The advantage of this material essentially lies in the fact that absorption material out of sheet material can also be produced for larger transformers. It is then used if the transformer is installed without a chassis.
The previously mentioned transformer supports are restricted in dimensions and maximum permitted loads. For instance the maximum permitted weight for transformer supports from a certain manufacturer is 3000N, which corresponds to a permitted transformer total weight of 30000/10 x 4 = 12000 kg. Cast resin transformers with this weight have a capacity of ca. 5000 kVA.
With installation of the transformer on a rubber support, deflection is to be taken into consideration as the position of the connections can change somewhat as a result. This is critical when connecting transformers to existing railing systems. Subsequently a calculation model for deflection of a rubber support is illustrated:
Total mass of transformer : Number of support points = Strain (F) per support (e.g. 22500 N : 4 = 5500 N)
From the strain F per transformer support in Newtons, the statistical deflection can be calculated in millimeters. This is obtained from the table of the support manufacturers, whereby the mechanical vibration absorption value is then also given in decibles, which depends on the particular transformer support used. The bigger the strain per support, the greater the deflection.
Internal studies in our test room have revealed that the effectiveness in terms of the noise insulation performance is in the region of ca. 1 dB(A), when the cast resin transformer is installed on an appropriate support. It is to be noted however that transmission of vibrations made from the transformer is suppressed better on the whole with a metal rubber deadener in transition, as is the case with noise and vibration deadeners.
When supporting the transformer directly on the ground or on non-insulated running rails, outbound vibrations from the transformer emit unpleasant noises and unwelcome vibrations into the environment.
It is sensible to use transformer supports for active interference suppression and protection of both people and the environment. An upgrading of available installations is possible at any time.
Noise and vibration deadener
Range of application using the example of the noise and vibration deadener EK 290 from Langmatz for transformers with maximum 10000 N ultimate load:
Safeguarding rollers as well as deadening noise and vibration for transformers. The vibration deadeners bring about a deadening of the mechanical vibration transmission of at least 20dB for the main parasitic frequency of 100 Hz with transformers. A deadening is brought about as a result of the constructional separation of the top and bottom section with a special deadening element. The rubber is compressed with the weight of the transformer so that a lateral oscillation deadening and a horizontal deadening arise as a result. Strain of deadener per roller: max. 10000 N
Roller diameter of transformer: 125 – 160 mm
Width of roller: 64 mm
For transformers without rollers, the version with the deadener top and bottom section can be used.
Naturally for other ultimate loads, the corresponding noise and vibration deadener must be used.
Basically it must be pointed out that with increased mechanical strains which occur, for example, in ships, excavators, wind turbines, earthquake areas etc, additional design features are required. This distinguishes SGB Cast Resin Transformers among other things, which have proven themselves worldwide under the most diverse conditions of installation.
Reducing noises from transformers radiating into the circumambient air is becoming more and more important. SGB Cast Resin Transformers are therefore provided both with normal execution in accordance with the German Institute for Standardisation 42 523 and with reduced losses and noises. Apart from the choice of induction and the core material the type of mortise and tenon joint of legs and yokes used by SGB in the "step lap" procedure has a favourable effect on noise properties and on transformer losses.
For specific values for noise for cast resin transformers in an AN operation without enclosure, in practice, the possibilities are:
A – Evaluated sound pressure level LPA in dB
A –Evaluated sound power level LWA in dB and associated measurement surface LS in dB.
Sound power is a measurement for the amount of noise which is produced and generated from a noise recorder. Sound power characterises the noise of the recorder and unlike the sound pressure level does not depend on the measuring position or acoustics in the surrounding area.
The definition of these values and type and how noise measurement is to be carried out is defined in the German Institute for Standardisation 45 635/Part 30. Important terms in this context are:
Reference plane (from the thread measure, which includes the heat radiating surface)
Length of measuring path lm in m
Measurement area S in m²
As with dry-type transformers, but not oil-filled transformers with their scoop-proof vessels, a distance of 0.3m can be measured from the vessel, for safety reasons with cast resin transformers, the measurement is made at a distance of 1 m from the reference plane.
LWA and LPA with LS have the set combination in the German Institute for Standardisation 45 635/Part 30:
LWA = LPA + LS
LS = 10 lg S/S0 dB
S = (h + 1) + lm an S0 = 1 m²
lm = 4 MA + (DWA + 2)π
MA = Dual spacing in m
DWA = Coil outer diameter in m
h = Height of core with clamping bar in m (including castors)
When operated, transformers cause electric and magnetic fields. These electromagnetic fields can attain values to whose assessment the following basis applies:
The Federal Immission Control Act
With the coming into effect of the 26th decree on the 1st January 1997 of the implementation of the Federal Immission Control Act (26. BImSchV), low frequency installations with 50-Hz-fields at the place of influence have to abide by the threshold values of 5 kV/m for electrical field strengths and 100 µT for magnetic induction. Place of influence is the place with the greatest exposure at which not only a sojourn from people is to be expected. The electric field outside the cast resin transformer and its connections are hardly effective outside the transformer booth. The protective enclosure of SGB Cast Resin Transformers acts as a Faraday cage. This also applies as far as possible to ceilings and walls in the transformer booths provided that these do not consist of electrical insulating material. The magnetic transformer scatter fields can give rise to disturbances, which in essence consist of three sources.
The no-load field issues mainly at the top and bottom ends of the coil and from the impact points of the iron core. However the no-load field is clearly smaller than the scatter field from the load current-carrying coils. In the literature for instance, factor 10 is mentioned. Separate measurements have resulted in a magnetic leakage flux density at least four times smaller. Therefore you can disregard the no-load scatter field for calculations.
Like each current-carrying conductor, discharges, like connection cables and busbars set up a scatter field. At every point in the chamber this depends on the vectorial sum of the field strengths caused there by the single current-carrying conductors. With conductor set-ups in which the total currents appear as neutral, like outward and return conduction in the AC circuit or three phases with the three-phase current system, the resultant field is all the more smaller the closer these conductors are together. The load current-carrying coils constitute the largest part of the scatter field, which is overlaid by fields of the low voltage-sided discharges.
These scatter fields were recorded by SGB measurements in order to determine the field and with action a reduction occurs in the fields. For instance, the connected low voltage outgoing circuits were set up point-symmetrically at a 1000VA cast resin transformer, so that the field capacity was able to be minimised as much as possible by means of the cable and at the same time, by using a very simple and assembly friendly aluminium shield box, demonstrating that you could reduce the distance for a lower deviation of the flux density in all directions (x - direction, y - direction, z - direction). Equally recommended for the connection of the transformer is field compensation by means of a double low voltage conduction with point-symmetrical phase sequence, were it to be required.
Transformers are regarded as passive elements in accordance with IEC 60076 with regard to electromagnetic interference emission and interference immunity and a CE marking is not permissible.
In accordance with measurements and calculations, the magnetic field around SGB Cast Resin Transformers as well as SGB oil distribution transformers is significantly below the threshold value, which the 26th decree for the implementation of the Federal Immission Control Act (26. BImSchV) of 16.12.96 stipulated. Capacity transformers are basically exempt from this decree as capacity transformers are to be seen as components of a total system or of an installation. Measures are to be sought to reduce the critical field strengths as well as adherence to threshold values in a system or installation which essentially determine the whole field configuration.
SGB had already started with the calculation and measurement of the electromagnetic field well before this date in order to determine the field around a transformer and to try out measures to reduce the field. Under defined measurement conditions the magnetic field of a cast resin transformer is circa 5 μ , for example, 630 kVA/20 kV-0,4 kV in accordance with separate measurements with a distance of 2 m to the cast resin surface of the coil. With an oil transformer of the same capacity it is less than 2 μ with a distance of 1.7m to the geometric centre. It is evident that the partly magnetic fields by means of currents in the coil in this voltage level (0.4 kV) fall significantly below the permitted 100 μ. Disturbances on the display may arise from 1 μ onwards. Further technical disturbance limits are:
Pacemarkers 50 Hz, 4 - 6 µT
Hearing aids 50 Hz, 2 - 20 µT
ECG 50 Hz, 0,4 µT
Pay attention however to the contribution of the current flow in the low voltage connections, e.g. busbars or feed lines. The magnetic field around the feed lines decreases only with the reciprocal value of the square number of the distance, by contrast, around transformers, with the reciprocal value cubic from the distance. It is simply because the current flow in transformers is restricted in a limited space and in feed lines in one dimension expands at will.Therefore the magnetic field around low voltage connections dominates the level of the entire field e.g. in a supply station. A range of measures to optimise the laying of busbars and feed lines, e.g. the batch of outbound connections,have a great effect in reducing induction. The manufacturers of transformers can already create an "interface" for the connection of such optimum laying in the design.
The 26th decree applies to the "fixed installations for the transformation and transmission of electricity". In its area of application it includes "electrical transformation installations including switch bays with a frequency of 50 Hz and high voltage of 1kV or more". As capacity transformers are to be seen as components of a total system, i.e. an appropriate installation, they are exempt from this decree.
The cast resin transformer must be connected to the earthing (potential equalisation). For this purpose a connection for the earthing at the chassis is available as standard. Customer requests can naturally be taken into consideration, like for example, earthing at the clamping bar.
Connection of earthing and short circuit equipment:
For this purpose fixed ball points of 20mm or 25mm diameter can be attached to the conductor connection straight or angled. There is also the opportunity to attach earthing switches to the high voltage connection side on the transformer or over the course of the high voltage cable connection on the wall.
The earthing and the potential equalisation on the transformer must be connected and checked correctly. Please bear in mind here the torque of the fixing screws and the minimum cross-sections of the potential equalisation conductors. The cross-section of the potential equalisation conductor must be at least half as big as the largest protective earthing conductor cross-section of the installation, but at least 6 mm² copper for mechanical reasons. For potential equalisation conductors, 25 mm² copper is mentioned for non-electrical installations as a satisfactory upper limit. Other than that the whole protective earthing conductor of 50 mm² is to be chosen as a cross-section for the potential equalisation conductor.
Assignment of the minimum cross-sections of protective earthing conductors and neutral conductors to the cross-section of the outer cable in accordance with the Association for Electrical, Electronic & Information Technologies 0100, part 540:
PEN-conductor >= 10 mm² Cu or >= 16 mm² Al, in accordance with article 8.2.1 of the Association for Electrical, Electronic & Information Technologies 0100, part 540. Unprotected movement of Al conductors is not permitted. Use bare conductors chiefly from a cross-section of the outer cable of >= 95 mm².
If the capacity of a transformer is not sufficient you can then connect several transformers in parallel. In addition the momentary values of the voltages must be equal and the transformers must change their voltages with strain to the same extent. In distribution networks rotary current transformers for example are operated in parallel in order to supply the low voltage network from the high voltage network. With a voltmeter the low voltage side is checked to see whether the parallel connection was correctly made.
If a parallel connection is made, before connection you have to check to see if the high and low voltage cables are connected to all transformers at the same phases and that the switch links are at the same position, so that equal voltage is available at all phases and all instruments and at the output the same stress ratio exists. In addition it is necessary to make a conductive connection between the secondary sides of the transformer with a metal rail in order to be able to compare more easily the voltages of the phases. If there is a neutral conductor it is beneficial to employ a metallic connection. With a voltmeter the value of the potential difference must also be checked. If the measured value is zero this means that all requirements are met for a parallel connection and the high voltage switches can be closed.
To connect rotary current transformers in parallel the following requirements are to be met in accordance with the German Institute for Standardisation and the Association for Electrical, Electronic & Information Technologies 0532:
The high and low voltages must be equal so that the transmission of open circuit voltages is equal as much as possible.
The short circuit voltages of transformers should differ by 10% at most from each other. Thereby you can avoid the transformer with the small short-circuit voltage getting too large a current and being overloaded. If the difference is bigger then inductances can be preceded to increase the short-circuit voltage.
The ratio of rated outputs should be less than 3:1. With larger rated output ratios, equalising currents are able to flow and bring about a phase shift between the output voltages.
The coefficient of vector groups must be equal so that phasing of the output voltages corresponds and no short-circuit occurs.
By way of exception rotary current transformers must be connected in parallel and their coefficient differs by 6, for example Dy5 and Dy11. In addition however the connections must be duly alternated. A check of the phasing is then essential.
The Cast Resin Transformer shall be suitable for continuous indoor operation in a tropical climate on a 3 phase distribution system with solidly earthed neutral. It shall be of a short circuit, impulse and moisture prove design.
The cast resin transformer shall be designed, manufactured and tested according to the latest edition of International Electrotechnical Commission (IEC) Standard 60076- 11. It shall be compact and suitable for easy installation on site.
The transformer shall be suitable to operate in a enclosure of the protection class IP20 and IP 23 without derating. For installation of the cast resin transformer in an enclosure of higher protection class the transformer shall be adopted accordingly.
In general the insulation level of the cast resin transformer used in public and in industrial systems shall comply to the requirements of IEC 60076-11 as follows
The relevant figures shall be selected according to the system voltage of the grid. Transformer with an insulation level differing from the above shall be considered separately on request.
The HV and the LV winding shall be of insulation class F in respect of mechanical and electrical strength (Partial Discharge Test).The maximum continuos operation temperature shall be within the limit of the maximum system temperature according to IEC 726, i.e. 155°C. The maximum temperature rise shall be limited to 100 K at 40°C ambient.
The core laminations shall be made of cold rolled grain oriented high quality silicon steel with non hygroscopic insulation material ”Carlite” covering both sides. The mitred interleaved joints of the limbs and yokes shall be executed in the STEP LAP stacking process. The flux density shall be selected in the way that the core material used is efficiently operating.
The clamping structure of the core and coil arrangement shall be of robust construction to withstand the stress to which it may be subjected during transport, installation and service.
The clamping frame shall respect the requirements of high voltage equipment. Tie rods shall be located next to the lamination. Lifting lugs capable to carry the weight of the transformer shall be provided at the core frame.
An adequate painting shall cover the complete core and the clamping structure and shall protect it against corrosion.
The conductor material used at the HV windings shall be of high grade copper or aluminium. Enamel insulated wire and fibre glass insulated wire shall be allowed. The material used for insulation and reinforcement shall be of fibre glass and of pure epoxy resin. Filler shall not be allowed.
The HV winding shall be wound in a multi layer winding technique and shall be in such a way that a linear potential distribution during impulse stresses is achieved.
The resonance frequency of the winding shall be below 20 kHz to avoid resonance with the switching impulse of VCBs and over stress of the insulation.
The winding process must position each winding accurately in order to minimise and control the electric stress on the insulation material.
Cooling ducts formed in the HV winding shall minimise the temperature gradient in the coil and get the cooling most efficient.
The HV coil shall be moulded and cast under vacuum with epoxy resin to ensure complete void-free resin impregnation throughout the entire insulation system. The flexibility of the resin shall be such that the formation of cracks shall be avoided during short circuit stresses and temperature shocks. Penetration of moisture shall be avoided by the vacuum cast process.
The termination of the HV feeder cable shall be made directly at the HV coils.
The HV winding shall be equipped with tappings preferable at -5 -2,5 0 +2,5 +5 % of the rated voltage.
The tappings shall be inter connectable by links which shall be located at the dom of the HV winding and shall form part of the delta connection.
The conductor material used at the LV windings shall be of high grade copper or aluminium formed as a foil. The width of the foil shall form the height of the winding (foil winding).
Epoxy resin pre impregnated solid multi layer type insulation material of Class F shall be used for insulation. After thermal treatment, the winding shall form a solid structure which shall be ; capable to withstand the stress occurring during a short circuit.
The LV winding shall not be wound on the core to create a cooling duct between core and LV winding Cooling ducts formed in the LV winding shall minimise the temperature gradient in the coil and get the cooling most efficient.
Rectangular section terminals shall be rigidly fastened to the upper clamping structure and avoid displacement at a short circuit.
Pre set PTC sensors shall be provided and attached to each of the LV winding as close as possible to the hottest spot.
The PTC sensors shall be selected in order to protect both, HV and LV windings.
The transformer shall be made for AN cooling.
On request the transformer shall be equipped with fans in order to achieve 40 % uprating . The fans shall be temperature controlled by means of temperature sensors which shall be installed at the LV winding of the middle leg.
The transformer shall be provided with the following accessories:
Each transformer shall be routine tested according to IEC 60076-11. Test report to
Acording SGB Standard.
12 months from delivery ex works
Ventilated enclosures of adequate protection for indoor installation shall be supplied The transformer and the enclosure shall create a compact unit. In order to minimise the space required the HV XLPE cables shall be connected direct to the transformer coils inside the enclosure. Gland plates with cable glands shall be provided at top or bottom. Removable panels shall allow access for cable termination and to the reconnection links.
The LV terminals shall be designed in the way to allow the termination of ample nos. of cables.
In order to minimise the space required the LV terminals shall be placed inside the transformer enclosure.
On request HV and LV cable box shall be provided. Enclosures of IP20, IP21, IP23, IP30, IP31, IP33 degree of protection are available and have to be selected according to the local protection requirements.
SGB Cast Resin Transformers comply with the relevant national, European and international standards of the customer’s order.
The following requirements are also worth considering when setting up and operating installations.
Further hints for planning and explanations can be obtained:
AGI-Worksheets J11 or J12 (structural execution, space for transformers) VDI 2078 (Calculating the cooling load in air-conditioned spaces) Worksheets J11 and J12 can be ordered at the following Internet address:
The tender or contract documentation and specifications are decisive in the specific execution of cast resin transformers. The actual measurements such as width, height and weight of the transformer naturally depend upon the relevant customer order. Consequently the types of transformers shown in the selection table with their actual dimensions and weights may differ.
The following constructional principles can be applied in the installation of dry-type transformers in buildings, which are in force in accordance with DIN VDE 0101 as enclosed electrical production sites with an installation height of up to 1000 m. The information relates to dry-type transformers with a rated power of 400 kVA up to 2500 kVA and a rated voltage up to 20 kV.
It is generally said that the installation of the transformer depends upon the type of electrical connections (cable or railing system), position of the cable entry point, position of the switchgear to the transformer chamber (transformer and switchgear can be placed in one chamber), transport conditions, required space and accessibility. When planning transformer chambers, you can possibly consider the option that transformers of a greater capacity can be upgraded later.
Position of a transformer chamber
The chamber in which a transformer is installed, ought to be free from both ground and high water, turned away from the sun and access for means of transport, operation and fire fighting must be ensured. That is precisely why the chamber should preferably be on the ground floor or platform height. Furthermore any obstruction of free movement of traffic in exits and stairs due to fire and smoke must be avoided. The additional air openings should be aligned towards the north, the area away from the sun. Also avoid the use of piping for fluids, combustible gases and also cables in transformer chambers.
Knowing the measurements of the transformer to be used, i.e. length, height and width, is vital for the dimensions of the chamber. The chamber length and width should amount to the transformer length or width plus twice 80 cm (ambulatory measurement). The ambulatory measurement of 80 cm is recommended as the width for the all-round ambulatory around the transformer for installation or maintenance work, measured from the outer edge of the transformer. With noise-insulated installations the chamber measurements are to be extended accordingly.
The chamber height complies with the maximum height of the transformer, the voltage and protection distances of electrical connections, the type of ventilation of the transformer chamber and the height of the used air opening. The height of the chamber should be at least 50 cm higher than the maximum transformer height.
With a transverse arrangement the door opening should be twice 10 cm transport safety distance plus transformer length and with arrangement lengthways, the door opening should be twice 10 cm transport safety distance plus transformer width. For the height of the door, transformer height plus 20 cm transport safety distance applies.
Windows, doors, ventilation openings
Windows should be avoided in transformer chambers. If this is not possible, then any access must be made difficult. Doors must open outwards, on the door outside a high voltage danger sign must be attached and the door locks must be used in such a way that any unauthorized entry is prevented at all times. However without a key it must be possible to open the door from inside with a handle or something similar, even if it is locked from the outside. Ventilator openings for the transformer chamber are provided, for example, with grates. These are used as it is difficult for foreign matter to infiltrate, people will not be put in danger and snow and rain will not be able to get in. Protective grates must be secured so that they are not moved or taken off.
Cable glands and cable supporting frames
An opening of 80 x 20 cm is recommended for the cable gland with transformers up to 630 kVA and with 800 kVA to 2500 kVA transformers, an opening of 140 x 20 cm. The loading assumptions for the cable supporting frames are to be considered and also ensure that there is adequate fastening.
Electrical installation for lighting and ventilation
Installations for lighting, ventilation etc in the transformer chamber should be arranged in such a way that they can be operated safely when the transformer is being used and there is as little risk as possible due to any arcing fault or mechanical effects.
Again, always refer to the worksheets AGI J11 and AGI J12, which give helpful constructional planning principles.
The requirements of SGB cast resin transformers concerning conditions of installation at site are marginal. This is due to the regulations mentioned for ground water protection, fire prevention, functional preservation according to DIN VDE 0101, DIN VDE 0108 and ELT Bau VO. With SGB Cast Resin Transformers, no protective measures for the prevention of water pollution are necessary. However with the transformer being executed with insulating fluids like, for example, mineral oil or silicone oil, drip pans and collecting pits would be essential, however, discharge of fluid from the collecting pit must also be prevented. Equally the Water Management Act and German Land regulations must be observed.
With protective measures for fire prevention and functional preservation in accordance with DIN VDE 0101, the following conditions must be met:
These three conditions mentioned do not apply when fast-acting protection is available.
When installing in an open-air installation, no measures are necessary for fire prevention and functional preservation with SGB Cast Resin Transformers.
Should the cast resin transformer however be equipped with rated voltage above 1 kV for installations for crowds of people in accordance with DIN VDE 0108 and Elt Bau VO , the following additional demands arise:
SGB Cast Resin Transformers comply with the most defined classes E2 and C2.
Air moisture, condensation, pollution and ambient temperature are environmental conditions for dry-type transformers. These factors are of importance not only during operation but also during storage before installing the transformer.
With regard to air moisture, condensation and pollution, three different environmental classes are defined.
Condensation does not appear on the transformer, pollution is negligible. This condition is normally met with installation in a dust-free and dry interior.
Occasional condensation can appear on the transformer (for example if the transformer is turned off). Pollution in a confined area is possible.
Frequent condensation or considerable pollution or a combination of both factors.
The climate class takes the lowest ambient temperature into consideration.It is distinguished between two climate classes:
The transformer is suitable for operation with ambient temperatures not below –5°C , but can be exposed during transport and storage to ambient temperatures of up to –25°C.
The transformer is suitable for operation, transport and storage with ambient temperatures up to –25°C.
The necessary classes regarding environment and climate must be defined by the operator.
The necessary fire class must be defined by the operator. However SGB Cast Resin Transformers comply strictly with the most defined class F1.
Two fire classes are defined:
No specific fire risk is to be taken into account. With the exception of the features available as a result of the design of the transformer, no special measures have to be provided in limiting the fire hazard. Nevertheless the emission of toxic materials and smoke which impedes sight must be cut to an absolute minimum.
By this we mean transformers, which take into consideration the dangers starting from fires. It is necessary to limit the fire hazard. The emission of toxic materials and smoke which impedes sight must be cut to an absolute minimum.
SGB Cast Resin Transformers are therefore safe to operate both with damp condensation and being exposed to dirt. However maintenance intervals should be adapted to environmental conditions. That is to say with considerable pollution we recommend the coil surfaces be cleaned.
Equally they are suitable for open-air installation for temperatures up to -25°C in an IP 23 protective enclosure with a special coating and comply with a large part of fire prevention.
As SGB Cast Resin Transformers only have cast resin parts in low and high voltage coils, the fire load is defined for the most part as these components. It should be indicated using the example of a 1000 kVA –execution and likened to liquid-cooled transformers. In the latter case, for the sake of simplicity, the fire load of the coil and supporting insulation is disregarded and only the insulation fluid is taken into consideration.
In the laboratories of ALLIANZ AG the cast resin moulding material from a SGB transformer coil as well as samples from all insulants were carbonised and the fire gases analysed. There were no halogens, such as fluorine, bromine and chlorine in the moulding material. Dioxin formation can therefore be ruled out. Sulphur dioxin does also not occur, as P-moulding materials contain no sulphur. Apart from trace contents of other hydrocarbons, the smoke gas is composed practically of carbon monoxide, carbon dioxide, steam and carbon black. That means it is a question of the same waste products which arise with each combustion, like for example, wood and paper. Corrosivity of the combustible products was analysed by the Allianz Centre for Technology in Munich in accordance with the VDE-directive 0472, Part 813. The result of the analysis proves that the cast resin moulding material used by us is technically free from sulphur and halogen and consequently does not lead to corrosion in this respect.
AZT Investigation Report (PDF, 65 KB)
For many years cast resin transformers have been used as a safe means of production and with the correct specification and installation, they are the equal of oil transformers in every way in their durability. To this day however cast resin transformers are not suitable for any exposed open-air installation. For this they require a protective enclosure. With the vents in the enclosures, moisture, salt content, aggressive gases and dust can reach the transformer. If the cool air is polluted considerably it possibly must be filtered.
Climatic conditions such as extreme cold in winter or strong sunshine in summer must also be taken into consideration. Equally in air-conditioned chambers make sure that the cooled air from the air conditioning is not blown directly onto the hot transformer coils. This extreme difference in temperature can lead to cracks forming in the moulded coils, which, at worst, may lead to malfunction of the cast resin transformer.
Cast resin transformers are designed in accordance with the relevant standards for the following cool air values:
The cool air temperature does not exceed
and does not exceed
The monthly and annual mean values are defined in chapter 3.12 of IEC 60076-11.
The average monthly temperature is half the total of the mean values of the daily maxima and the mean values of the daily minima during a certain month, calculated over many years. The average yearly temperature is one twelfth of the total of the average monthly temperature.
In standard operations the normal service life consumption of the transformer is attained in the process. For service life consumption, the average yearly temperature and strain are crucial. If the ambient temperatures differ from standard operations in the annual mean, then the power rating of the transformer will naturally change in form so that with a reduction of the ambient temperature in the annual mean, a greater power rating of the transformer is possible and with an increase of the ambient temperature in the annual mean, the power rating of the transformer would decrease. This correlation can be seen in the following table.
On certain conditions each cast resin transformer can be overloaded, just like liquid-filled types.
The temperature monitoring system which brings about the shutting down of the transformer with a fixed rated response temperature limits the overload capacity with cast resin transformers.
Our choice of rated response temperature comes from the heating permitted in the low voltage coil. Including the hotspot rate at the measuring point depending on the heating of the coil it is 120° - 150° C, based on the required maximum coolant temperature of 40°C in accordance with VDE 0532, Part 6.
If in a practical operation, the strain under the rated power and the coolant temperature are below 40 °C, then coil temperatures below the threshold values permitted arise as a result. This extent can be exploited for overloads until the fixed response temperature of the thermistor is obtained. The height and duration of the overload are determined through the preceding preload, the actual ambient temperature and the coil time constant. The diagram stated below for a 630 kVA cast resin transformer shows this correlation, based on a coolant temperature of 20 °C and different permanent preloads.
From this it follows that the transformer can be operated with a 100% permanent preload, still about 27 minutes with 130% of its rated power until the temperature monitoring system responds. As the "coil time constant" parameter depends very much on the required technical data and constructive execution, universal overload diagrams are not indicated. On request we can issue them as such whereby all interpretation-specific parameters are taken into consideration.
We have deliberately only shown the overload capacity for the temperature produced with temperature monitoring. As a result we do not exploit a more comprehensive extent* above the threshold temperature as is proposed in IEC/VDE in guidlines on strain for dry-type transformers currently under discussion. Hereby prevent uncontrolled overloads from leading to such thermal strains as it can lead to an abnormally short service life.
To calculate the service life of cast resin transformers you start with the thermal ageing of the cast resin compound insulation in the coils. The thermal effect basically changes the chemical constitution and reduces significant electrical and mechanical features such as partial discharge use, disruptive discharge voltage, tensile strength, elongation etc. These ageing properties can be deduced from the thermal resistance diagram of the relevant insulation system in accordance with DIN / IEC 216 or VDE0304 guidelines. Example of a thermal resistance diagram for temperature index or limiting temperature 155° C and half life temperature interval 10 K. Subsequently, in accordance with standardised definitions, for lower limiting values of the relevant test features from the regressing laws on Arrhenius, you obtain temperature index or the limiting temperature and the half life temperature interval. The resultant limiting temperature is based on an underlain service life of 20,000 hours. The half life temperature interval in Kelvin lets you know the temperature level from which a halving or doubling of the service life arises, based on the limiting temperature calculated (Montsinger-Rule). For cast resin compound mould material a value of 8 – 10 K is expected. Provided that a cast resin transformer is constantly operated with an aforementioned temperature, in theory you can expect a service life of at least 2¼ years (which is equivalent to about 20,000 hours). In practice however long-term usage with limiting temperature, i.e. nominal load and 40°C coolant temperature, is unusual. For an estimation of the service life you must take into consideration the daily and annual fluctuations of the coolant temperature with an average of 20K. Analogously you can also calculate an equivalent permanent load for the customer induced load fluctuation. If these are accepted with a relatively high value of, for example, 88 %, a reduction in heat of 20K will come about, as heating measurements have shown. Together with the average coolant temperature all in all this means a lower temperature load around 40K compared to the limiting temperature of the insulant. With an assumed half life temperature interval of 10K you can already calculate a service life of 36 years, based on 2¼ years with limiting temperature, in these cases without partially interpreted safety margins being taken into consideration.
On the strength of their high dependability Cast Resin Transformers are in every type of power generating installation and/or power distribution as any malfunction here can have dramatic & costly consequences.
Cast Resin Transformers within industrial applications increase the reliability of plants and at the same time contributes to the safety as no oil has been used.
Wherever trouble-free operation of complete infrastructure is dependent upon the reliability of fewer individual components, specific quality benchmarks are set. For this reason on the strength of their exceptional dependability, Cast Resin Transformers are preferred thanks to the unique winding concept.
Wherever trouble-free operation of complete infrastructure is dependent upon the reliability of fewer individual components, specific quality benchmarks are set. For this reason on the strength of their exceptional dependability, Cast Resin Transformers are preferred thanks to the unique winding concept.