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Generator Relay & Generator Protection Relays

Generator relays, also known as generator protection relays, monitor generators for electrical faults and abnormal operating conditions. Generator protection relays primarily include generator differential protection, stator ground fault protection, and rotor ground fault protection to ensure the safe operation of the generator.

generator backup protection relay

Generator Relay & Generator Protection Relays

A generator relay is an intelligent protection device for generator sets. Also referred to as a generator protection relay. It collects real-time electrical quantities such as voltage, current and excitation, and rapidly identifies faults including short circuits, rotor earth faults and loss of excitation via built-in algorithms.

It sends alarm or tripping signals instantly to isolate faults and prevent generator burnout. Integrated with measurement, fault recording and communication functions, it connects to station monitoring systems to guarantee safe and stable operation of generators and power grids.

Professional generator protection relays for all generators with full protection functions. Stable quality, quick delivery and full technical support.
Feel free to ask for catalog, specs and bulk pricing. Looking forward to your cooperation.

RelayProtect provides a complete range of generator protection relays designed for hydroelectric generators, diesel generators, and industrial power generation systems.

Our generator protection relay products include generator differential protection relay (87G), rotor earth fault protection relay (64R), generator transformer protection relay (87GT), backup protection relay and multifunction generator protection devices.

These protection relays help detect electrical faults, protect generator units, and ensure safe operation in power plants and industrial applications.

Generator Relay Protection Functions List

ANSI Protection Function Main Purpose
87G Generator Differential Internal stator faults
64R Rotor Earth Fault Rotor insulation / ground fault
64S Stator Ground Fault Stator earth faults
50/51 Overcurrent Phase faults / backup
32 Reverse Power Prevent generator motoring
40 Loss of Excitation Detect excitation failure
46 Negative Sequence Protect against unbalanced current
24 Overexcitation V/Hz protection
27/59 Under/Overvoltage Voltage abnormality
81 Frequency Under/overfrequency

Product Listing

Our generator relay range covers primary and backup protection for hydroelectric, diesel, gas and industrial generators, including differential, rotor earth fault, reverse power, overcurrent and generator-transformer protection.

Product Name Primary Application Key Features
400V Low Voltage Generator Protection Relay Low-voltage grid-connected generation (small hydro, diesel, biogas, factory emergency power) Compatible with 400V systems; grid-connected safety protection; simple parameter setting; strong anti-interference
400V Low Voltage Hydroelectric Generator Protection Relay Small hydro unit control and protection Supports auto start, excitation, voltage regulation, grid synchronization, power regulation; integrated voltage/current/frequency/temperature protection; RS485 communication
Generator Backup Protection Relay Backup to main protection; covers internal defects and external line faults Graded coordination settings; monitors stator, rotor and grid-side faults; time-delayed operation
Voltage Injection Rotor Earth Fault Protection Relay (64R) Rotor insulation monitoring and ground fault protection Low-frequency AC injection; no blind zone; supports single-point alarm, two-point trip, fault location; monitors even without excitation voltage
Ping-Pong Type Rotor Earth Fault Protection Relay (64R) Rotor insulation monitoring and ground fault protection Ping-pong alternating measurement; locates ground fault points; prevents two-point earth fault damage
Generator Integrated Protection Relay Integrated protection for low-voltage captive units (small hydro, gas generators) Integrates differential + backup protection; supports fault recording, event logging, remote communication; flexible trip logic setting
Generator Transformer Protection Relay (87GT) Complete protection for generator-transformer units Simultaneously provides generator main/backup protection and transformer differential/backup protection; widely used in large/medium thermal and hydro power plants
Generator Differential Protection Relay (87G) Primary protection for stator winding phase-to-phase short circuits Compares current difference between two sides; instantaneous tripping; prevents winding burnout

Types of Generator Protection Relays

Relay Type ANSI Code Application
Generator Differential Relay 87G Internal generator fault
Rotor Earth Fault Relay 64R Rotor insulation monitoring
Generator Transformer Relay 87GT Generator-transformer unit
Reverse Power Relay 32 Prevent motoring
Loss of Excitation Relay 40 Excitation failure
Overcurrent Relay 50/51 Backup protection

Applications of Generator Protection Relays

Application Typical Relay
Hydropower Plant 87G + 64R
Diesel Generator Set 50/51 + 32
Industrial Power Plant Multifunction Relay
Generator Transformer Unit 87GT
Microgrid Complete Protection Package

Why Choose Our Generator Protection Relays?

  1. We possess mature and stable core algorithms, covering a full range of solutions including injection-type and ping-pong rotor earth fault protection, generator differential protection and generator-transformer integrated protection, compatible with 400V low-voltage small hydropower stations, diesel backup generators and large & medium-sized power stations.
  2. The protection system features precise hierarchical logic with fast response of main protection and well-coordinated backup protection, effectively eliminating hazards such as unit short circuit, insulation breakdown, reverse power transmission and islanding operation.
  3. Our devices boast strong anti-interference capability and wide-temperature design, capable of stable long-term operation under harsh conditions including humid outdoor environments and intense electromagnetic interference.
  4. One-click parameter setting and intuitive visual HMI are available. Equipped with standard RS485 communication interface, the products can be seamlessly connected to SCADA and remote monitoring systems for easy installation and commissioning.
  5. Customized functions and cabinet specifications are available on demand. We provide one-stop services including technical clarification, setting guidance and after-sales technical support to meet bidding and complete set supporting demands for domestic and overseas projects.

Generator Protection Relay-FAQ

Q1: What are generator protection relays?

A: Generator protection relays are intelligent electronic devices that continuously monitor a generator’s electrical parameters (current, voltage, frequency, etc.) to detect faults and abnormal conditions. When a fault is detected, they issue a trip command to disconnect the generator from the grid, preventing catastrophic damage to the machine.

Key roles:

  • Measure via CTs and PTs

  • Detect internal/external faults

  • Trip circuit breakers

  • Communicate with SCADA systems

Q2: What types of generator protection relays are available?

A: Common types include:

Type Protection Function ANSI Code
Generator Differential Relay Stator internal fault protection 87G
Rotor Earth Fault Relay Rotor insulation monitoring 64R
Stator Ground Fault Relay Stator winding ground fault 64S
Overcurrent Relay Backup protection for overload/faults 50/51
Reverse Power Relay Prevents motoring 32
Loss of Excitation Relay Excitation failure detection 40
Negative Sequence Relay Unbalanced load protection 46
Overexcitation Relay V/Hz protection against core saturation 24
Voltage Relay Over/under voltage protection 27/59
Frequency Relay Over/under frequency protection 81
Generator Transformer Relay Generator + transformer unit protection 87GT
Backup Protection Relay Comprehensive backup protection 441H
Low Voltage Generator Relay 400V generator protection –

Q3: What is 87G generator differential protection?

A: 87G is the primary high-speed protection for detecting internal stator winding faults in generators.

How it works:

  1. CTs are installed at both ends of the stator windings (neutral side and line side)

  2. Under normal conditions, currents at both ends are equal → differential current = 0

  3. During an internal fault, currents become unequal → differential current appears

  4. The relay issues an instantaneous trip command

Key features:

  • Dual-slope characteristic for stability during external faults

  • High sensitivity for internal faults

  • CT saturation detection to prevent false tripping

Q4: What protection functions does a generator need?

A: Depends on the generator’s size, type, and criticality. Three tiers:

Tier Functions ANSI Codes Best For
Basic Overcurrent protection 50/51 Small, non-critical generators
Advanced Basic + Differential protection 50/51 + 87G Medium industrial generators
Complete Advanced + Rotor earth fault + Loss of excitation + Reverse power 87G + 64R + 40 + 32 Large, utility-critical generators

Additional functions as needed: 64S (stator ground), 46 (unbalance), 24 (overexcitation), 27/59 (voltage), 81 (frequency).

Q5: How to select a generator protection relay?

A: Based on three key factors:

1. Generator Type

Type Key Protection Focus
Hydro Loss of excitation (40), frequency (81), reverse power (32)
Diesel Reverse power (32), unbalance (46), overcurrent (50/51)
Gas Overfrequency, overcurrent, differential (87G)

2. Voltage Level

Voltage Recommended Relay
400V Basic relay with overcurrent (50/51)
6.6kV Standard relay with differential (87G)
11kV Advanced relay with full protection suite
13.8kV High-end relay with SCADA communication

3. Protection Tier

If your generator is… Choose…
Small or non-critical Basic (50/51)
Medium-sized Advanced (50/51 + 87G)
Large or critical Complete (87G + 64R + 40 + 32)

Q6:What is a generator relay?

A generator relay is a protective relay used to monitor a generator’s electrical parameters and detect faults or abnormal operating conditions. It may provide functions such as differential protection, overcurrent protection, reverse power protection, loss-of-excitation protection, rotor earth fault protection and voltage or frequency protection. In power systems, the terms generator relay and generator protection relay are often used to describe the same type of protective device.

Q7: What does a generator relay protect against?

A generator relay can protect against internal winding faults, rotor and stator ground faults, overcurrent, reverse power, loss of excitation, negative-sequence current, overexcitation, abnormal voltage and frequency conditions. The required protection functions depend on the generator type, rating and application.

General Equipment & System Integration Inquiry

Whether you need individual protection relays, control panels, or a complete secondary system integration, please fill in the form below. We provide technical parameters, competitive quotations, engineering drawings, and on-site support. Our expert team is ready to assist you within 24 hours.
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High Quality

Stable performance, reliable design, ensuring safe operation for power system protection and grid stability.

Fast Delivery

Timely delivery to support your urgent orders and project schedules efficiently and professionally at any time.

Best Warranty

Professional Warranty: Reliable after-sales support for stable relay protection and long-term customer satisfaction.