Changyuan Shenru ISA-387G Transformer Differential Protection Device

The ISA-387G is a transformer differential protection device that utilizes independent dual CPU system technology.

ISA-387GA can connect to 3 sets of CT currents
ISA-387GB can connect to 4 sets of CT currents

1 Basic Configuration

Protection Functions:
? Independent differential current starting element
? Differential instantaneous protection
? Composite ratio differential protection
? CT break alarm and differential blocking
? Differential current over-limit recording element
? Long-term differential current over-limit alarm
? Two-stage overcurrent protection for the second/third/fourth sides (optional)

2 Differential Protection Wiring and Current Calculation
The ISA-387G device is suitable for three-winding and two-winding transformers with various wiring methods. The interface provides a transformer wiring configuration function, and the software adaptively processes protection logic based on the transformer wiring method.
To simplify field wiring and improve inrush current restraint characteristics, this device requires that the CTs on all sides of the transformer be connected in a Y configuration, and that all sides' CTs be connected with the same polarity, meaning that the current flowing into (or out of) the transformer is considered the positive direction. The device internally performs phase correction for the current on the Y side of the transformer, achieving the same effect as connecting the CTs in a Δ configuration. For retrofit projects in older stations, if the CTs on the Y side of the transformer were originally connected in a Δ configuration, they are generally required to be modified to a Y configuration.