What is Phase Sequence Meter?
Phase Sequence Meter is an electromagnetic test and measurement instrument that indicates the phase sequence in a given three-phase electric circuit. Simply said, the phase sequence meter has the ability to show the direction or rotation of the three-phase motors. This portable and sturdy induction instrument is most commonly found in a form of a small electric motor which contains aluminum disk. The purpose of the aluminum disk is to indicate the phase sequence by rotating upon a given magnetic field in which three currents run in three windings. This induction test and measurement instrument has three terminal marks to which the phase sequence corresponds.
Types of Phase Sequence Meters
There are two general types of phase indicators.
- Rotating type – The phase rotation meter works on the same principle as induction motors. If you understand the way the three-phase motor operates, you will have no problem understanding the working principle of a phase rotation meter.
In short, the three-phase motor needs three-phase power supply that comes in a certain sequence. Usually the phase supply that comes to the rotating motor has a phase sequence of RYB. This is when the three-phase motor rotates in a clockwise direction. If the three-phase supply comes in a reversed sequence, then the motor will rotate counter clockwise direction. EMF is a rotating magnetic field that is produced by the coils that receive the three-phase supply.
The phase rotation meter contains three separate coils that are connected in 10 degrees apart in space. Their ends are connected to three terminals (in star path) that are marked with the characters RYB. Furthermore, there is the aluminum disk that is connected to each of the top of the three coils. This disk of the phase rotation meter rotates in the direction of the phase sequence of the supply, which is shown by an arrow that rotates in the direction of the disk rotation.
- Static type – Static type features one inductor connected to a phase B and two lamps connected to two different phases, R and Y . There are also resistors connected to both lamps, which main function is to control and maintain needed voltage and currents and to prevent breakdown. Depending on the phase sequence, one lamp dims while the second one glows.
The phase rotation meter is most commonly used type. This instrument is indispensable piece of equipment for checking new electrical connections in different applications. Furthermore the phase rotation meter is used for tracking the electrical connection during both, the installation and the maintenance of the electrical connection. You can use it for wiring switchboards when three-phase supply is a matter of concern. Also by checking the sequence, this device is used for checking the rotation in 3 phase rotating motors.