ABB Protection Relay REX 521

ABB Protection Relay REX 521

Product positioning and purpose

REX 521 is a high-performance digital protection relay launched by ABB, designed specifically for medium voltage (MV) power systems, suitable for the protection, measurement, and control of equipment such as substations, transmission and distribution lines, transformers, motors, and busbars. Its modular design supports multiple standard configurations and can flexibly adapt to scenarios such as radial networks, ring networks, and compensating grounding systems, meeting the needs of selective protection, automatic reclosing, and synchronous inspection.

Core functional features

Multi dimensional protection function

Overcurrent protection: Supports three-stage non directional/directional overcurrent protection (3I>, 3I>>, 3I>>>), and can be configured with IDMT (inverse time limit) or DT (definite time limit) characteristics.

Ground fault protection: Non directional/directional ground fault protection (Io>, Io>>, Io>>and directional versions), suitable for different grounding systems (isolated, resistive, resonant grounding).

Voltage and frequency protection: overvoltage/undervoltage (3U>, 3U<<), frequency abnormality (f1, f2) protection, to prevent equipment damage caused by grid voltage fluctuations or frequency offset.

Motor and special protection: thermal overload (3Ithdev>), start-up supervision (Is2t n<), phase sequence protection (3I()), etc., designed specifically for motor drive systems.

Accurate measurement and monitoring

Real time measurement of three-phase current/voltage, power, energy, and harmonics (supporting THD/TDD analysis) with an accuracy of ± 1%.

The disturbance recording (DREC) function can capture fault waveforms, support pre triggering and multi cycle recording, and facilitate fault analysis.

Flexible control and communication

8-channel programmable digital input/multi-channel relay output, supporting circuit breaker control, interlocking logic, and alarm signal output.

Compatible with communication protocols such as Modbus and DNP 3.0, it can be connected to substation automation systems (SCADA) for remote monitoring.

Hardware specifications

Hardware version

Basic: Basic protection function, suitable for simple distribution networks.

Medium: Increase directional protection and support more complex grounding systems.

High/Sensor: Advanced features including synchronization check, motor protection, etc. Some configurations support sensor input.

Rating

Current input: 1A/5A (measurement), 0.2A/1A (ground fault).

Voltage input: 100V/110V/115V/120V (phase voltage/line voltage).

Auxiliary power supply: DC 24-250V or AC 24-240V.

Output Relay

High speed trip relay (HSPO1): 4 normally open+4 normally closed, contact capacity 5A/250V AC.

Power output relay (PO1-PO3): 3 sets of conversion contacts, capacity 10A/250V AC.

Signal output relay (SO1-SO2): 2 sets of conversion contacts, capacity 5A/250V AC.

Protection function parameters

1. Overcurrent protection

Three stage non directional:

3I>(low setting): Starting current 0.10-5.00 x In, operating time 0.05-300s (supports IDMT/DT characteristics).

3I>>(high setting): starting current 0.10-40.00 x In, operating time 0.05-300s.

3I>>(instantaneous): starting current 0.10-40.00 x In, instantaneous action (<40ms).

Directional overcurrent:

3I>-->/3I>>-->: Starting current 0.05-40.00 x In, basic angle adjustable from 0 ° to 90 °, supporting forward/reverse action.

2. Ground fault protection

Non directional:

Io>(low setting): Starting current 1.0-500% In, operating time 0.05-300s seconds.

Io>>(high setting): Starting current 0.10-12.00 x In, operating time 0.05-300s seconds.

Io>>(instantaneous): Starting current 0.10-12.00 x In, instantaneous action.

directional:

Io>-->/Io>-->/Io>>-->: Starting current 1.0-500% In, basic angle -90 ° -60 ° adjustable, supports Uo/Io phase judgment.

3. Voltage protection

Overvoltage:

3U>(low setting): starting voltage 0.10-1.60 x Un, operating time 0.05-300s.

3U>>(high setting): starting voltage 0.10-1.60 x Un, operating time 0.05-300s.

Undervoltage:

3U<(low setting): starting voltage 0.10-1.20 x Un, operating time 0.1-300s.

3U<<(high setting): starting voltage 0.10-1.20 x Un, operating time 0.1-300s.

4. Other protections

Frequency protection (f1/f2): frequency range 25-75Hz, df/dt detection accuracy ± 100mHz/s.

Motor protection:

Thermal overload (3Ithdev>): Dual time constant model, temperature range -50 ° C-150 ° C.

Start supervision (Is2t n<): Start current 1.0-10.0 x In, start time 0.3-250s.

Phase sequence protection (3I()/U1U2<>_1): detects phase sequence reversal or imbalance, with an operation time of 0.1-10 seconds.

Measurement and monitoring parameters

Electrical Measurement

Current/Voltage: True RMS measurement with an accuracy of ± 1% (within the rated range).

Power/Energy: Fundamental active power (kW), reactive power (kVAr), accuracy ± 0.5%.

Frequency: Measurement range 10-75Hz, accuracy ± 10mHz.

Disturbance Record (DREC)

Record length: up to 1066 cycles (21.3s at 50Hz), supporting pre triggering (0-100%).