Phase Sequence Relay Wiring Diagram and Connection

In this article, we are going to see the Phase Sequence Relay Wiring Diagram and Connection Procedure. A Phase Sequence Relay is also known as a Phase Rotation Relay or Phase Sequence Corrector. It is basically a special type of protective device that is used to monitor and control the sequence or order in which the phases of a three-phase power supply are connected.

The primary function of a Phase Sequence Relay is to ensure that the phases are connected in the correct sequence (L1, L2, L3). It is widely used to prevent motor damage or improper operation of three-phase equipment. If the phase sequence is incorrect, the relay will either trigger an alarm or disconnect power to prevent damage to equipment.

Phase sequence relays are commonly used in industrial electrical systems to protect equipment that relies on the correct phase sequence for proper functioning. For example, if phase sequence changes in the three-phase power supply to the motor. the motor will start rotating in the opposite direction and it can put the whole system in trouble.

Wiring Diagram

Here, in the below wiring diagram, you can see the connection of a Phase Sequence Relay with a DOL Starter and Motor that will help you to easily understand the working principle of the relay.

Components Used

• A Phase Sequence Relay
• A DOL Starter Circuit(built with a Contactor, OLR, and push-button switches)
• A Three-phase Motor

Connection Procedure

1. Connect the DOL Starter and Motor as the normal procedure we follow. If you don't know how to connect DOL starter then read this article.
2. Now, Connect all Three Phases from the power supply to the three-phase input terminals of the phase sequence relay by properly following R, Y, B or L1, L2, L3.
3. You will see in the DOL starter circuit, the input terminal of the NC push button switch is connected to any phase terminal of the power supply.
4. So, disconnect that input terminal of the switch and connect it to the NO terminal of the sequence relay.
5. Then, connect the Common terminal of the phase sequence relay to any phase terminal of the power source.
6. Now, connect the NC terminal of the phase sequence relay to the phase terminal of an indication lamp.
7. Connect the neutral terminal of the indication lamp directly to the neutral terminal of the power source.

Operation Procedure

Here, we don't need to operate the Phase Sequence Relay manually, it will operate automatically. We just need to operate the DOL starter. When we push the start switch the motor will start running and when we push the stop switch the motor will stop rotating.

Working Principle

The working principle of the Phase sequence relay is very simple. When the power supply to the sequence relay and all the phases are in the correct sequence, the relay will keep closing its NC contact. As the contactor is connected through the NC contact, the contactor will get a power supply and the motor will run. But when the three-phase sequence gets incorrect, the relay will make its NC contact to NO and it will disconnect the power supply to the contactor so the motor will stop running.

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