Transformer Differential Protection｜87T

Description

Product Overview

• The AST-441H Digital Transformer Differential Protection｜87T and Control Unit is suitable for transformer protection in substations with voltage levels of 110kV and below.

Product Functions (ANSI)

• Transformer High-Speed Differential Protection 87T-HI / 87HS
• Transformer Differential Protection Relay 87T
• CT Open-Circuit Detection and Excessive Differential Current Alarm
• Overcurrent-start fan

Communication Features

• Optional: RS-485, CAN bus, Ethernet, IEC 60870-5-103 (IEC-103)
• The transformer differential protection device transmits real-time data, including measurement data, waveform data, fault and alarm signals, as well as all protection settings, configurations, and coefficients; it also allows for remote online modification of settings and activation/deactivation of protection functions.
• The transformer differential protection device receives commands from the master station, which primarily include remote control, system synchronization, setting adjustments, and data read/write commands.

Event Logging, Fault Recording

• Event logs include protection trip events and device self-test faults
• Record the type of protection trip event, the time of the trip, and the operating parameters at the time of the trip; record the type and time of device self-test faults
• The fault recording data includes: the time and type of the protection operation, as well as the rms values before and after the recording was initiated.
• Data length of the fault waveform recording: 2 cycles before the fault and 4 cycles after the fault for each channel, totaling 192 data points per channel
• The SOE can retain 48 sets of data after a power loss, and the fault report can retain 16 sets of data after a power loss.

Monitoring Features

• Transformer differential protection devices are capable of measuring analog quantities such as current, voltage, and frequency.
• Collect position signals (such as circuit breaker, energy storage, isolating switch, and remote/local) and other digital signals
• Control Functions of Circuit Breakers

General Technical Data

Power supply

• Ripple coefficient: not more than 5%;
• Tolerance: -20% to +15%;
• Rated operating voltage: AC/DC 220 V

AC circuit

• AC current In: 1 A/5 A (specify when ordering)
• Rated AC voltage: 100 V or 100 V
• Frequency: 50 Hz (customizable according to project requirements)

Power consumption

• DC power supply circuit: During normal operation, no more than 25 VA; when the device is activated, no more than 30 VA
• AC voltage circuit: When the rated voltage is 100 V, no more than 1 VA per phase
• AC current circuits: When the rated current is 1 A, no more than 0.5 VA per phase; when the rated current is 5 A, no more than 1 VA per phase

Output contacts

• In a DC circuit with a voltage not exceeding 250 V, a current not exceeding 0.5 A, and a time constant of 5 ± 0.75 ms, the breaking capacity of the output contacts of the transformer differential protection device is 50 W, and the allowable closing current does not exceed 5 A;
• In AC circuits with a voltage not exceeding 250 V, the device’s output contacts have a breaking capacity of 50 W and a maximum allowable make current of 5 A.

Insulation properties

• The transformer differential protection device meets the requirements for insulation resistance, dielectric strength, and impulse voltage specified in the IEC standards.

Main Functional Specifications

• Protection response time (including the response time of the output relay): Average error in response time: not more than 35 ms;
• Precision operating range: Minimum precision current: 0.08 In, Maximum precision current: 20 In
• Current setting error: When the current exceeds 1.00 A, the error shall not exceed ±2.5%; Voltage setting error: shall not exceed ±3%
• Measurement accuracy: Current (I)/Voltage (U): Class 0.2; Power (P)/Reactive power (Q): Class 0.5
• Remote signal resolution: no more than 2 ms

Setting Table

No.	Display Name	Range	Step	Remark
1	High-speed Differential Setting
1.1	High-speed Differential Protection	1/0	—	Enable(1) / Disable(0)
1.2	High-speed Differential Setting Value	0.40～99.99A	0.01A
2	Differential Protection Setting
2.1	Differential Protection Enable	1/0	—	Enable(1) / Disable(0)
2.2	CT Broken Circuit Blocking Differential	1/0	—	CT break blocking function: Enable(1) / Disable(0)
2.3	Differential Current Setting	0.50～99.99A	0.01A
2.4	Restraint Current Setting	0.50～99.99A	0.01A
2.5	Differential Bias Current Setting	0.50～99.99A	0.01A
2.6	CT Broken Circuit Threshold	0.50～99.99A	0.01A
2.7	Harmonic Restraint Coefficient	0.10～0.70	0.01	Second harmonic restraint ratio
2.8	Slope / Ratio Restraint Coefficient	0.30～0.70	0.01
2.9	Balance Coefficient	0.100～1.999	0.001
3	Overcurrent Fan Control
3.1	Overcurrent Fan Start	1/0	—	Enable(1) / Disable(0)
3.2	Ventilation Time Delay	0.00～999.99s	0.01s
3.3	Fan Start Current Setting	0.5～99.99A	0.01A
4	General Setting
4.1	Motor Differential Mode Selection	1/0	—
4.2	HV Side Y/△-11 Connection	1/0	—
4.3	HV Side Y/△-01 Connection	1/0	—
4.4	Secondary Wiring Mode	1/0	—	Delta/Y(1) / Y/Y(0)
4.5	Control Circuit Break Alarm	1/0	—	Alarm enable(1) / disable(0)
4.6	Current Angle Display	1/0	—
4.7	Secondary Current Rated	1/0	—	1A input(1) / 5A input(0)
4.8	Inter-tripping C6C7	1/0	—	High-speed & differential trip C06C07(1)
4.9	Rated Secondary Current	0.50～99.99A	0.01A	HV side CT secondary rated current

Outline and Installation Dimensions

   

FAQ

Q：What is the scope of protection provided by a transformer differential protection device?

A:Transformer differential protection primarily protects the internal components of the transformer. When a turn-to-turn short circuit or a phase-to-phase short circuit occurs inside the transformer, the corresponding protection function in the transformer differential protection device will trigger an alarm and trip the circuit.

Q：How to Select a Transformer Differential Protection Device?

A:When selecting a transformer differential protection device for differential protection of transformer and differential protection for transformer applications, three key points should be noted: first, consider the transformer’s capacity, as larger capacity requires more advanced device functions; second, identify whether the transformer is two-winding or three-winding, since the suitable protection device differs by transformer type; third, refer to relevant industry standards and verify compliance with international norms such as IEC and IEEE.