How to Control a 3-Phase Motor Using a Motor Protector?

Electrical Technology

Wiring and Controlling of a 3-Phase Motor Using Manual Motor Protector Circuit Breaker

Abstract: Controlling a three-phase motor while ensuring its safety is a crucial aspect of industrial applications. One effective method of controlling a motor and providing protection is by using a motor protector. This article provides a comprehensive guide on how to control a three-phase motor using motor protection circuit breaker, highlighting its key features, installation process, and the benefits it offers in terms of motor protection.

Three-phase motors are widely used in industrial settings due to their efficiency and reliability. To ensure safe and optimal operation, it is important to control the motor and provide protection against various electrical faults. A motor protector, also known as a motor protection relay or motor circuit breaker, is specifically designed to protect motors from overloads, short circuits, phase imbalances, and other potentially damaging conditions. This article aims to provide a detailed overview of how to control a three-phase motor using a manual motor protector, highlighting its importance and benefits.

Table of Contents

Toggle

Features and Functionality of a Motor Protector

A motor protector is a specialized device that offers several key features to control and protect a three-phase motor effectively. The following are the primary features and functions provided by a motor protection CB:

Overload Protection: Motor protectors monitor the motor’s current and detect excessive current flow that could lead to motor damage. They provide overload protection by tripping the motor circuit in such situations.
Short Circuit Protection: In the event of a short circuit, where a high current flows due to a fault, the motor protector quickly interrupts the circuit to prevent further damage to the motor.
Phase Imbalance Protection: It detects phase imbalances in the three-phase power supply. Excessive phase imbalances can lead to motor overheating and premature failure. The protector disconnects the motor from the supply if a severe phase imbalance is detected.
Ground Fault Protection: They can also detect ground faults, which occur when one of the motor’s current-carrying conductors comes into contact with the ground. Ground faults can cause electrical shocks and damage the motor. The motor protector detects and responds to ground faults by tripping the circuit.
Motor Control: They offer control functionality, including start, stop, and reset functions. These controls allow manual operation of the motor, enabling easy and convenient management.
Monitoring and Diagnostics: Some motor protectors provide advanced monitoring and diagnostic features. These include temperature sensing, motor load monitoring, and communication capabilities to relay information to a central control system.

In the following wiring tutorial, we have used the ABB MS116 manual starter AKA motor protection circuit breaker or manual motor protector which manually switch ON and OFF three phase motors with additional protection such as short circuit, overload and phase failure washout using fuse.

Additionally, the MS116 motor protector provides the following features.

Manual Motor Starter: The MS116 is a manual motor starter, meaning it requires manual operation for starting and stopping the motor. It is equipped with a rotary handle for manual control.
Thermal Overload Protection: The MS116 incorporates a bimetallic thermal overload relay. This relay monitors the motor’s current and protects it against overloads by tripping the starter if the current exceeds the specified threshold.
Motor Disconnect Function: The MS116 provides a motor disconnect function, allowing quick and safe isolation of the motor from the power supply. This feature is useful during maintenance or in emergency situations.
Phase Loss Protection: Some variants of the MS116 have built-in phase loss protection, which detects and protects against the loss of one or more phases in the power supply.
Adjustable Current Range: The thermal overload relay in the MS116 is adjustable, allowing customization of the overload protection to match the motor’s specific current requirements.
Trip Indication: The MS116 features a visible trip indication mechanism, which provides visual feedback when the overload relay trips. This helps in identifying and troubleshooting overload events.

Components Required

Three-Phase Motor
Motor Protector (ABB MS116)
Contactor
MCCB – 3P, 400V
MCB – 2P, 230V
ON/OFF Push buttons
400V – Three Phase AC Supply
230V Single Phase AC Supply
Wires, cables, switches and indicators: Manual control switches (such as start, stop, and reset buttons) and indicator pilot lights (for status indication).

Wiring & Installation Process

To control a three-phase motor using a motor protector, the following steps outline the installation process for the the given wiring and control diagram below.

Click image to enlarge

Step 1: Motor and Power Connections

Connect the three-phase power supply lines (L1, L2, L3) to the 3-poles MCCB and motor protector’s input terminals (1L1, 3L2, 5L3), ensuring proper phase sequence.
Connect the motor’s three phases (U1, V1, W1) to the output terminals of the motor protector (2T1, 4T2, 6T3).
Connect the grounding wires to the designated grounding terminals.

Step 2: Control Circuit Connections

Connect the control circuit wires to the motor protector’s control terminals. Connect the control switches, such as start, stop, and reset buttons, to the appropriate control terminals on the motor protector as follow.
Connect the terminal 1 of NC – OFF push button to the 230V single phase phase supply from 2-poles circuit breaker
Connect the terminal 2 of NC – OFF push button to the 13-NO terminal on contactor and terminal 1 of NO – ON push button.
Connect the 2 of NO – ON push button to the A1 and 14-NO terminals of contactor.
Connect the Neutral from 2-poles CB to the A2 terminal of contactor.

Step 3: Configuration

Configure the motor protector’s settings based on the motor’s specifications and protection requirements. This includes setting the appropriate overload and phase imbalance thresholds.

Step 4: Testing and Commissioning

Verify all wiring connections and ensure there are no loose or damaged connections.
Test the motor protector’s functionality by activating the control switches and observing the motor’s response.
Conduct thorough testing to ensure that the motor protector effectively detects and responds to overload, short circuit, phase imbalance, and ground fault conditions.

Safety Considerations

Disconnect the power supply before performing any wiring connections or maintenance tasks.
Use appropriate personal protective equipment (PPE) when working with electrical systems.
Ensure proper grounding of the motor protector and the motor according to local electrical codes and regulations.
Confirm that the motor connections match the corresponding terminals on the motor guard starter.
Ensure proper tightening of the connections and use appropriate wire sizing to handle the motor’s current.
Use appropriate wire sizes and connect the start, stop, and reset buttons to their respective terminals on the DOL starter.

Benefits of Using a Motor Protector

Controlling a three-phase motor using a motor protector offers several significant benefits:

Motor Protection: A motor protector safeguards the motor against a wide range of electrical faults, such as overloads, short circuits, phase imbalances, and ground faults. This protection extends the motor’s lifespan and minimizes downtime due to motor failures.
Enhanced Safety: They provide an extra layer of safety by detecting and responding to potentially hazardous conditions. This helps prevent accidents, electrical shocks, and fires caused by motor malfunctions.
Convenience and Control: it offers integrated control functions, enabling easy manual operation of the motor. With start, stop, and reset buttons conveniently located on the protector, motor control becomes straightforward.
Diagnostic Capabilities: Advanced motor protectors often include monitoring and diagnostic features, allowing users to track the motor’s performance, temperature, and load conditions. This information facilitates preventive maintenance and timely troubleshooting.
Cost Savings: By protecting the motor from damage, motor protectors help avoid costly repairs, motor replacements, and production losses resulting from motor failures. The investment in a motor protector can yield substantial long-term cost savings.

Summary

Controlling a three-phase motor using a motor protector is essential for ensuring safe and reliable operation while providing effective protection against electrical faults. The features and functionalities offered by motor protection circuit breakers, such as overload protection, short circuit protection, phase imbalance detection, and control capabilities, make them an integral part of motor control systems.

By following the installation process and considering the benefits of motor protection, industries can significantly enhance the performance, safety, and longevity of their three-phase motor applications.