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Low Voltage Motor Protection Relay
Overview of Low Voltage Motor Protector
This series of Low Voltage Motor Protector are low-voltage AC motor protection and control devices independently developed by our company, suitable for motors with rated frequency 50Hz, AC voltage up to 690V and rated current up to 800A.
Protection Configuration（ANSI）：51,51LR,46,47,37,51LR,50,50N/51N,51G,59,27,48,60,49
Communication Mode
Optional: RS-485, CAN bus, Ethernet, IEC 60870-5-103 (IEC-103), IEC 61850
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Description
Overview of Low Voltage Motor Protection Relay
The Low Voltage Motor Protection Relay is a digital protection and control device designed for low-voltage AC motors. It integrates motor protection, measurement, control, fault recording and communication functions for motors operating at up to 690V and rated currents up to 800A.
Key Protection Functions
- Overload protection
- Locked rotor protection
- Phase loss protection
- Phase unbalance protection
- Short circuit protection
- Earth fault protection
- Overvoltage protection
- Undervoltage protection
- Underload protection
- Start timeout protection
What Is a Low Voltage Motor Protection Relay?
A low voltage motor protection relay is a digital protection device used to monitor the electrical and operating conditions of low-voltage motors and protect them against overload, phase loss, locked rotor, short circuit, earth fault, voltage abnormalities and other operating conditions.
Compared with a conventional thermal overload relay, a digital motor protection relay can integrate multiple protection functions, measurement, event recording, control and communication in one device.
Low Voltage Three-Phase Motor Protection Relay Features
- Built-in multiple protection functions; users can easily enable/disable protection, set alarm or tripping modes with simple selection.
- Supports various control modes including protection mode, direct start, two-way start, two-speed start and star-delta start. Different control logics can be switched conveniently with high flexibility and universality.
- Equipped with optimized start-up protection, it automatically identifies start-up process and accurately distinguishes starting current from fault current.
- Built-in 4-20mA analog output to realize transmission output of multiple measured variables.
- Stores 8 groups of detailed fault records with complete fault information.
- Supports 8 groups of digital input status records, 8 start records and 8 stop records.
- Adopts Chinese LCD display for intuitive viewing of parameters, data and operating status.
- Equipped with 5 programmable digital inputs and 4 programmable relay outputs.
- Flexible installation and compact dimension, suitable for installation in 1/4 drawer cabinet.
Low Voltage Three-Phase Motor Protection Relay Features
- Built-in multiple protection functions; users can easily enable/disable protection, set alarm or tripping modes with simple selection.
- Supports various control modes including protection mode, direct start, two-way start, two-speed start and star-delta start. Different control logics can be switched conveniently with high flexibility and universality.
- Equipped with optimized start-up protection, it automatically identifies start-up process and accurately distinguishes starting current from fault current.
- Built-in 4-20mA analog output to realize transmission output of multiple measured variables.
- Stores 8 groups of detailed fault records with complete fault information.
- Supports 8 groups of digital input status records, 8 start records and 8 stop records.
- Adopts Chinese LCD display for intuitive viewing of parameters, data and operating status.
- Equipped with 5 programmable digital inputs and 4 programmable relay outputs.
- Flexible installation and compact dimension, suitable for installation in 1/4 drawer cabinet.
Low Voltage Motor Protection Functions
| Protection Function | Purpose |
|---|---|
| Overload Protection | Protects the motor against excessive thermal loading |
| Locked Rotor Protection | Detects stalled or locked rotor conditions |
| Phase Loss Protection | Detects loss of one phase |
| Phase Unbalance Protection | Detects abnormal three-phase current imbalance |
| Short Circuit Protection | Detects severe current faults |
| Earth Fault Protection | Detects motor earth leakage/fault conditions |
| Overvoltage Protection | Protects against excessive voltage |
| Undervoltage Protection | Protects against low voltage |
| Underload Protection | Detects abnormal low-load operation |
| Start Timeout Protection | Detects abnormal motor starting |
| External Fault Protection | Receives external protection/fault signals |
Control Mode
| Direct Start | Two-way Start | Two-speed Start |
| Star-Delta Start | Protection Mode | Undervoltage Restart |
| Power-on Auto Start |
Measurement Function
| Three-phase Current | Three-phase Voltage | Frequency |
|---|---|---|
| Active Power | Reactive Power | Power Factor |
| Active Energy | Thermal Capacity | Unbalance Degree |
| Positive & Negative Sequence Current | Residual Current Value |
Management Function
| DI & DO Status | 8 Fault Records | 8 DI State Change Records |
|---|---|---|
| 8 Start Records | 8 Stop Records | Real-time Starting Current |
| Real-time Starting Time | Total Start Times | Total Trip Times |
| Total Running Time | Total Stop Time |
Communication Function
| Modbus-RTU | Profibus-DP |
|---|
Dimensions and Cutout Sizes
Technical Specifications
| Item | Specification |
|---|---|
| Rated Motor Voltage | AC380V or AC660V, 50Hz |
| Rated Motor Current | 0.1A ~ 800A |
| Insulation Resistance | ≥100MΩ |
| Controller Auxiliary Power Supply | |
| Operating Range | AC/DC 80～270V |
| Power Consumption | 5VA |
| Operating Environment | |
| Ambient Temperature | -20℃～+60℃ |
| Relative Humidity | ≤93%RH |
| Storage Temperature | -40℃～70℃ |
| Protection Grade | IP66 |
| Other Requirements | No explosive medium, corrosive gas or conductive medium that damages metal and insulation on site |
| Protection Action Accuracy | |
| Current/Voltage Startup Value | ±1% of set value |
| Thermal Capacity Accumulated Value | ±1% of set value |
| Time Delay Action Time | ＜2s: ±100ms; ≥2s: ±5% of set value |
| Control Relay Output | |
| Contact Capacity | AC250V/5A (resistive), AC250V/3A (AC15) |
| Max Breaking Voltage | AC400V |
| Max Breaking Capacity | 2000VA |
| Signal Relay Output | |
| Contact Capacity | AC250V/3A (resistive), DC30V/3A (resistive) |
| Max Breaking Voltage | AC300V |
| Max Breaking Capacity | 750VA |
| Analog Output | |
| Output Type | DC 4～20mA, RL≤350Ω |
| EMC Electromagnetic Compatibility | |
| Electrostatic Discharge | Severity Level Ⅲ |
| Electrical Fast Transient Burst | Severity Level Ⅲ |
| Surge Immunity | Severity Level Ⅲ |
| Damped Oscillatory Wave Immunity | Severity Level Ⅲ |
| Radiated Radio Frequency Field Immunity | Severity Level Ⅲ |
| Conducted Radio Frequency Immunity | Severity Level Ⅲ |
| Power Frequency Immunity | Class A |
| Conducted Emission Test | 150kHz-30MHz |
| Radiated Emission Test | 30MHz-1000MHz |
| Dielectric Withstand Voltage | |
| Between Power Supply and Input | AC2kV/1min |
| Between Power Supply and Output | AC2kV/1min |
| Between Input and Output | AC2kV/1min |
FAQ
Q1. What is a low voltage motor protection relay?
A digital protection device designed to protect low voltage motors against electrical faults such as overload, short circuit, phase loss, unbalance, and earth faults, while also providing monitoring and control functions.
Q2. What voltage and current ranges does the relay support?
It typically supports AC voltage up to 690V and current ranges from 1A to 800A (or higher with external CTs) – please refer to the specific model’s datasheet for exact ratings.
Q3. What protection functions are integrated?
Common functions include overload protection, short circuit protection, phase loss protection, phase unbalance protection, earth fault protection, locked rotor protection, and under/over voltage protection.
Q4. Does it support three-phase motor protection?
Yes. It is designed for three-phase AC motors and provides comprehensive protection for all three phases.
Q5. Can it protect against motor overload and locked rotor?
Yes. It includes thermal overload protection with adjustable trip curves, as well as locked rotor protection that trips when starting current persists beyond the allowable time.
Q6. Does it provide phase loss and phase unbalance protection?
Yes. It continuously monitors phase currents and trips when a phase loss or excessive unbalance (typically >10-15%) is detected.
Q7. Does the relay support earth fault protection?
Yes. It supports earth fault protection, typically using core balance CT (zero-sequence CT) or residual current calculation.
Q8. Can it monitor motor current, voltage and power?
Yes. It provides real-time monitoring of current, voltage, active power, reactive power, power factor, and energy consumption.
Q9. Does it support Modbus RTU or SCADA communication?
Yes. It supports Modbus RTU over RS-485 as standard, enabling seamless connection to SCADA and PLC systems for remote monitoring and control.
Q10. What is the difference between a digital motor protection relay and a thermal overload relay?
A thermal overload relay is an electromechanical device that provides basic overload protection using bimetallic elements, while a digital motor protection relay is microprocessor-based and offers multiple protection functions (overload, short circuit, phase loss, unbalance, earth fault, etc.), precise adjustable settings, real-time monitoring, communication capability, and fault recording – providing far more comprehensive protection and intelligence.
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xiao zhang –
It monitors overload, open-phase and overcurrent faults for motors, cuts off power promptly to avoid equipment damage, compact and easy installation for low-voltage cabinets.
Jack –
Simple menu navigation reduces training time for new users.