A DC transformer in this case refers to the traditional 50/60 Hz three phase transformer used for many years for high power requirement. These low frequency transformers are high power machines capable of long duty cycles. These tend to be large transformers due to their power ratings and applications.
DC LOW FREQUENCY TRANSFORMER
Typical applications are large ring projections, flash-butt and rim welding.
This class of transformer can deliver outputs up to:
Secondary Amperage: 1 KA up to 1000 KA
KVA Range: 10 to 3000 KVA
Secondary Voltages: 0.5 - 50 V
Primary Input: 200- 800 V
Frequency: 50/60 Hz
References: RWMA Resistance Welding Manual- 4th Edition
Roman Manufacturing Inc.