In conjunction with thyristor or diode rectifiers, these transformers form the link between the AC and the DC systems of the industrial plant. Their development and construction requires extensive experience as well as deep theoretical knowledge.
We manufacture transformers for electrolytic plants. In this case both bridge and double star with interphase transformer circuits are frequently used. Coarse voltage regulation is often obtained by means of an on-load tap-changer (OLTC) operating on taps made on primary windings. We design the cooling system of a rectifier transformer with particular attention to the current harmonics arising from the rectifier operation, which can otherwise cause very high eddy current losses. This becomes very important in transformers for electrolytic plants and for SCR power circuits, where high values of delay angle determine very fast commutations.
In small oil immersed units natural cooling (ONAN) is utilized. In larger units cooling is mostly obtained by forced circulation of either oil and water (OFWF) or oil and air (OFAF) in a cooler connected by oil pipes to the transformer tank.
The cooler acts as a heat exchanger with the heat flowing from either the oil to the water (OFWF) or the oil to the air (OFAF). In the case of OFWF cooling, two coolers are usually provided. Each of them is rated for the full transformer losses, so that the transformer can be kept running at its full load in the event of a failure of either a cooler itself or its auxiliary equipment.
DC Current 105 kA
Secundary voltage regulation 26 V to 360 V with 33 position OLTC
Rated power 2x26.000 kVA
24 pulse reaction (12 pulse with 4 units in parallel)