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GE 872256-QL21B170D
Product Name: GE Multilin QL21B170D Digital Line Protection Relay
Product Overview: The 872256-QL21B170D is a GE Multilin QL21B series digital line protection relay with a 170 V DC control power supply. It is designed for medium-voltage (6 kV–35 kV) distribution system feeder protection, providing comprehensive overcurrent, ground fault, and voltage protection functions.
Detailed content
Technical Specifications:
- Product Model: QL21B170D
- Control Power Supply: 170 V DC
- Rated Current (In): 5 A / 1 A (selectable via CT ratio)
- Rated Frequency: 50 Hz / 60 Hz
- Overcurrent Protection: 3-stage (50/51, 50N/51N)
- Ground Fault Protection: 12 programmable ground fault curves
- Voltage Protection: 27/59 overvoltage, 27/59 undervoltage
- Communication Interfaces: RS-485 (Modbus RTU); Ethernet (optional)
- Auxiliary Contacts: 4 NO + 4 NC (programmable)
- Accuracy: Current measurement ±0.5%; Voltage measurement ±0.5%
- Time Accuracy: ≤1 ms
Functional Features:
- Three-stage overcurrent protection (50/51 timed overcurrent, 50N/51N ground overcurrent)
- 12 programmable ground fault curves covering high-impedance ground fault detection
- Directional overcurrent protection (optional) for feeder direction discrimination
- Auto-reclosing (ARC) supporting single or multiple reclosing operations
- Fault recording (fault waveform capture before and after event)
- Sequence of Events (SOE) with 1 ms resolution
- Energy metering (optional) for forward/reverse active/reactive energy
Performance Parameters:
- Overcurrent operating time: 15 ms to 999 s (programmable)
- SOE resolution: 1 ms
- MTBF: ≥100,000 hours
- Dielectric strength: 2 kV AC / 1 minute
- Insulation resistance: ≥100 MΩ at 500 V DC
- Operating temperature: -20°C to +70°C
- Front panel protection rating: IP51
Material & Structural Characteristics:
- Housing: Flame-retardant ABS engineering plastic, UL94 V-0
- Front panel: Brushed aluminum alloy, wear-resistant
- Terminal block: Flame-retardant PA66 nylon, high-temperature resistant
- PCB: FR-4 double-sided with conformal coating (three-proof)
- Display: Backlit LCD screen
Structural Features:
- Panel-mount design with cutout dimensions per IEC 60255
- Front panel LCD displays current, voltage, power, and protection status
- Four LED indicators: Run, Alarm, Trip
Working Principle: The relay continuously samples current and voltage signals via CTs and VTs, processes them through its protection algorithms, and executes trip commands when fault conditions are detected. It records fault waveforms and sequence-of-event logs, communicates via Modbus RTU (RS-485) or optional Ethernet, and provides programmable auxiliary contacts for control and alarm functions.
Installation Requirements:
- Panel-mount in accordance with IEC 60255 cutout dimensions
- Provide 170 V DC control power supply
- Connect CT secondary circuits (5 A or 1 A selectable)
- Connect VT inputs for voltage protection functions
- Terminate RS-485 or Ethernet communication as required
Usage Notes:
- Configure protection settings, ground fault curves, and autoreclose parameters per system requirements
- Verify CT ratio selection (5 A or 1 A)
- Regularly review fault records and SOE logs for system diagnostics
