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:

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.