ASL-446H Differential Line Protection

Description

Overview of differential line protection

• The ASL-446 digital line differential protection device is a relay used for phase fault protection of short transmission lines, and it supports differential line protection for short-circuit faults on lines of various voltage levels.

Differential protection relay function

• Differential instantaneous overcurrent protection
• Line current differential protection
• CT disconnection

Communication Mode

• Optional: RS-485, CAN bus, Ethernet, IEC 60870-5-103 (IEC-103)

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

Event Logging, Fault Recording

• The recorded events include protective action events and device malfunctions;
• Record the type of protection trip, the time of the trip, and the operating parameters at the time of the trip;
• The fault recording data includes: the time of the protection operation, the type of protection operation, and the rms values before and after the recording was initiated;
• Data length of the fault recording: 2 cycles before the fault and 4 cycles after the fault;
• 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.

Working Principle of Line Differential Protection

• It compares current magnitudes and phase positions at two terminals of protected line via real-time data exchange. Under external fault or normal load condition, the differential current is nearly zero;
• internal short-circuit creates obvious differential current to trigger rapid breaker trip. It also equips CT disconnection lockout to avoid false operation.

Setting List of Transmission Line Differential Protection

No.	Display Name	Range	Step	Remarks
1	Differential Instantaneous Trip Setting
1.1	Differential Instantaneous Trip Protection	1/0	—	Differential instantaneous trip: Enable(1) / Disable(0)
1.2	Instantaneous Trip Setting Value	0.40～99.99A	0.01A
2	Differential Protection Setting
2.1	Differential Protection Enable/Disable	1/0	—	Differential protection: Enable(1) / Disable(0)
2.2	CT Broken Line Blocking Differential	1/0	—	CT broken line blocking differential: Enable(1) / Disable(0)
2.3	Differential Setting Value	0.50～99.99A	0.01A
2.4	Restraint Setting Value	0.50～99.99A	0.01A
2.5	Differential Current Setting Value	0.50～99.99A	0.01A
2.6	CT Broken Line Setting	0.50～99.99A	0.01A
2.7	Slope Coefficient	0.30～0.70	0.01
2.8	Balance Coefficient	0.100～1.999	0.001
3	General Setting
3.1	Control Circuit Broken Line	1/0	—	Control circuit broken line alarm: Enable(1) / Disable(0)
3.2	Display Current Angle	1/0	—	Display current angle: Enable(1) / Disable(0)
3.3	Current Corresponding to 1A	1/0	—	Set (1) as 1A / Set (0) as 5A
3.4	Interlock C6-C7	1/0	—	Enable(1) inter-tripping / Disable(0) inter-tripping
3.5	Rated Current	0.50～99.99A	—	Secondary rated current of local line side

Outline and Installation Dimensions

   

FAQ

Q：line differential protection vs distance protection

A:Short-distance line differential protection compares current vectors at both line ends to identify internal faults with absolute selectivity, while distance protection judges fault location by measuring line impedance and acts according to fault distance.

Q：What is the difference between line differential protection and transformer differential protection?

Line differential protection simply compares the current amplitude and phase at both ends of the line without considering transformation ratio and inrush current. By contrast, differential protection of transformer, also known as protection of a transformer, requires compensation for transformation ratio and phase deviation, as well as inrush current blocking, leading to more complex setting logic.