ISA-381G Station Service Transformer Protection and Control Device

Changyuan Shenru ISA-381G Station Transformer Protection, Measurement and Control Device

The ISA-381G device implements protection, measurement and control, and operational functions for station/grounding transformers (supports 220V voltage monitoring).
ISA-381G Model and Function Description Table
Model Function Description
ISA-381GA Suitable for small resistance grounding systems, supports 220V voltage monitoring
ISA-381GB Suitable for ungrounded systems, supports 220V voltage monitoring
ISA-381GC Suitable for ungrounded systems or small resistance grounding systems

Protection Principles
Phase Current Over-Limit Recording Element
The phase current over-limit recording element has an independent over-limit threshold setting d797, and records the over-limit condition of each phase current separately, generating independent phase current over-limit records, including the start time, duration, and maximum current of the over-limit condition for each phase.
1) Per-phase recording facilitates detailed and comprehensive documentation of disturbance processes.
2) This record is not used for alarms, only for disturbance analysis.
3) The device interface provides a function to view phase current over-limit records.
4) The setting of d797 should avoid the maximum load current value (to prevent unnecessary frequent recording) and ensure sufficient sensitivity for smaller fault currents.
Three-Stage Overcurrent Protection
Three-stage overcurrent protection includes instantaneous overcurrent, Stage I overcurrent, and Stage II overcurrent protection. Each can be independently enabled or disabled, with current and time settings adjustable independently. The principles of the three stages are the same; Figure 4-2-1 shows the logic diagram for Stage I overcurrent protection.
Low-Voltage Side Zero-Sequence Overcurrent Protection
The low-voltage side zero-sequence protection includes two independently configurable definite-time zero-sequence overcurrent protections and one inverse-time zero-sequence overcurrent protection. The logic for Stage I and Stage II zero-sequence overcurrent protections is identical, except for setting codes and event codes. The logic is shown in Figure 4-2-2.
Low-Voltage Side Inverse-Time Zero-Sequence Overcurrent Protection
The ISA-381GA/B/C devices each include one inverse-time zero-sequence overcurrent protection, offering three operating characteristics: general inverse-time, very inverse-time, and extremely inverse-time. If all three are enabled simultaneously, the priority from highest to lowest is: extremely inverse-time > very inverse-time > general inverse-time.
High-Voltage Side Zero-Sequence Overcurrent Protection
Note: In "Configuration" - "Manufacturer Settings" - "Zero-Sequence Current Collection Method," the high-side zero-sequence current 3Iol and 3Iog can be set to "self-generated" or "external input." The default is "external input." When set to "self-generated," the protection zero-sequence current is synthesized from the three-phase protection currents. For telemetry, 3Iol in the 381GB is also synthesized from the three-phase protection currents, while the 381GC uses the three-phase measurement currents for synthesis.
1) Zero-Sequence Overcurrent Protection for Small Resistance Grounding Systems (ISA-381GA/ISA-381GC)
For small resistance grounding systems, the ISA-381GA/ISA-381GC devices provide three-stage high-voltage side zero-sequence overcurrent protection as backup protection for bus ground faults. The principles of the three stages are the same; Figure 4-2-6 shows the logic for Stage I zero-sequence overcurrent protection.