HomeFAQIncorrect phase sequence

Incorrect phase sequence

Incorrect phase sequence is a human error which can be corrected by testing before putting the motor into service. It is not worth to invest on the auto adjustment of the phase sequence. If you really want it, I can suggest to use a VFD and operate it at a fixed speed, selection of phase rotation can be done by a change of one parameter setting and you also can apply physically motor shaft direction sensor to feedback to the VFD.

Incorrect phase sequence of power supply to a motor can occur in different situations:
- Cut & re-join of power cable.
- Removal and re-installation of motor.
- Error by motor repair shop.

Ways to reduce/avoid incorrect phase sequence of the motor's power supply:

- Ensure proper markings/identification of cable terminations and leads.

- If you are commissioning or re-commissioning a motor, you can do pre-measurement of phase rotation by using a motor rotation meter. It will help you to confirm motor rotation before the uncoupled test runs. This can avoid embarrassment and time spent to do correction when many parties could be waiting and looking at you.

Identifying the phases is one of the easiest job. Even one that is not electrician but who has a common sense can do this. First, de-energize and separate the installation you want to identify. Than... apply voltage on each power cable end and find it on the other end. Or, apply voltage on 2 cable ends and find it on other ends. This will identify 2 cables (phases). After that apply voltage on other 2 cables and you will identify each one at this moment.

Although, I tend to believe that the problem is at the motor connection since the maintenance of the power transformers and substations should always end with phase identification. Otherwise major problems could develop. And, the easiest and fastest way to solve this problem is by checking the sense of rotation and after that, if not correct, changing 2 cables at the motor connection.

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