Description
The Low Voltage Motor Protection Relay is designed to provide integrated protection, monitoring and control for low-voltage three-phase AC motors. It is typically available in models rated from 0.4 kV to 690 V, with current ranges covering a few amperes up to several hundred amperes. The relay supports multiple control modes, including direct-on-line starting, star-delta starting, soft starter control and variable frequency drive coordination. It also offers configurable protection functions such as overload, phase loss, phase imbalance, locked rotor, undercurrent, overcurrent and earth fault, along with RS-485 or Modbus communication for remote monitoring and parameter setting.
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?
Integrated Motor Protection
Unlike a simple overload relay that only responds to excessive current, a low voltage motor protection relay combines overload, phase loss, phase imbalance, locked rotor, undercurrent, overcurrent, earth fault and temperature-related protection in one device. It also separates alarm and trip thresholds, giving warning before a fault escalates.
Motor Monitoring and Measurement
The relay continuously measures three-phase current, voltage, phase status, motor operating condition and fault information. Engineers can see whether the motor is running normally, lightly loaded or approaching an overload. When a fault occurs, the relay records the fault type and measured values at trip, shortening troubleshooting.
Motor Control and Communication
It also serves as a control interface, supporting local panel control and remote control via digital inputs or communication. With RS-485 or Modbus, it connects to a PLC or SCADA system for start/stop commands, parameter settings and real-time data, reducing field wiring and integrating the motor into plant-wide monitoring.
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.
The low‑voltage motor protection relay provides comprehensive motor protection modes for fault response and abnormal condition handling.
| 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 |
The low voltage motor protection relay combines multiple electrical protection functions in one device, reducing the need for separate protection components in low-voltage motor control applications.
Control Mode
The low‑voltage motor protection relay supports multiple motor control modes for flexible startup management and field application adaptation.
|
|
|
| Direct Start |
Two-way Start |
Two-speed Start |
| Star-Delta Start |
Protection Mode |
Undervoltage Restart |
| Power-on Auto Start |
|
|
Measurement Function
The low voltage motor protection relay provides motor operating measurements for protection monitoring and maintenance.
| 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
The low‑voltage motor protection relay provides complete motor management functions for event recording and operation data statistics.
| 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
The low‑voltage motor protection relay provides standard communication interfaces for data transmission and remote monitoring.
Dimensions and Cutout Sizes
Low Voltage Motor Protection Relay Applications
The relay can be applied to low-voltage motor protection and control systems in industrial facilities, motor control centers, water treatment systems, pumping stations, fans, compressors, conveyors and other motor-driven equipment.
| 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
Q:What Is a Low Voltage Motor Protection Relay?
A:It is an intelligent protection device designed for low‑voltage motors. It provides measurement, multiple protection modes, motor control, event logging and communication functions to safeguard motors against electrical faults and support on‑site maintenance.
Q:What Motors Can a Low Voltage Motor Protection Relay Protect?
A:It is suitable for most low‑voltage AC asynchronous motors, including direct‑start, two‑way, two‑speed and star‑delta starting motors, widely used in pumps, fans, compressors and conveyor equipment.
Q:What Protection Functions Are Integrated into the Relay?
A:Typically for LV systems up to 690V AC. The working current can be adapted via external current transformers to cover small to large‑capacity motors according to project requirements.
Q:What Protection Functions Are Integrated into the Relay?
A:It integrates overload, locked‑rotor, phase loss, phase unbalance, short‑circuit, earth‑fault, overvoltage, undervoltage, under‑load, start‑timeout and external fault protection for comprehensive motor safety.
Q:What Is the Difference Between a Motor Protection Relay and an Overload Relay?
A:Traditional overload relays only offer simple thermal overload protection. The intelligent motor protection relay adds abundant protection, real‑time measurement, fault records, multiple startup control and industrial communication for full‑range motor management.
Q:Can the Relay Be Used for Three‑Phase Motors?
A:Yes. This relay is specially developed for three‑phase low‑voltage AC motors, supporting three‑phase current & voltage monitoring and all three‑phase related protection logic.
Q:Does the Relay Support Communication With PLC or SCADA Systems?
A:Yes. It supports Modbus‑RTU and Profibus‑DP interfaces. Real‑time measurement data, fault information and running status can be uploaded to PLC or SCADA for centralized monitoring.
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