After the switchgear and other variable power distribution equipment or line transformation and maintenance, it is necessary to check the phase sequence of the power supply. Otherwise, the phase sequence of the original power supply may be reversed, and all three-phase asynchronous motors on the line are reversed, causing serious consequences.
Before the transformer or generator is running in parallel or connected to the grid, it is necessary to check the phase sequence. Otherwise, if the phase sequence is mistaken, it will cause huge current impact on the transformer and generator, causing huge damage to the equipment and the power grid, even making the transformer. The generator was burned.
The method for judging and measuring the phase sequence of the three-phase power supply is as follows:
In the power supply and use regulations, the phase sequence marks of transformers, generators, motors, busbars in the switchgear, and power supply lines are specified. According to these regulations, the phase sequence of the three-phase power supply can be roughly discriminated.
The phase sequence markings of transformers, motors, generators and power lines are shown in Figure 1 . The colors of U , V , W ( u , v , w ) or L 1 , L 2 , L 3 are yellow, green, and red, respectively, and the neutral line N is light blue. Â
The phase sequence of the busbars in the switchgear is arranged as follows (in the face of the switchgear or the front view of the device).
1 Busbars arranged up and down: U , V , W phase, should be from top to bottom.
2 Horizontally arranged busbars: U , V , W phase, should be from inside to outside.
3 The busbar of the down conductor: U , V , W phase, should be from left to right.
It should be pointed out that the phase sequence discrimination described above is inaccurate in many cases. This is because the installation is not standardized, and the phase sequence may be reversed after the maintenance. Therefore, in order to accurately determine the power supply, the instrument test must be used.
The most commonly used is the phase sequence meter, which is suitable for three-phase AC power supply with a power frequency of 100~500V . When in use, the three terminals on the surface of the U , V , W lead (yellow, green, red) are respectively on the three power lines to be tested. Press the button (for a few seconds). If the aluminum disk rotates in the clockwise direction, the three power cables connected are in positive phase sequence; if the aluminum disk rotates counterclockwise, it is reverse phase sequence. Â
If there is no phase sequence table, it can also be checked by the bulb method. As shown in Figure 2 , two identical 220v bulbs ( 15~40w ) H 1 , H 2 and a capacitor C ( 0.22~0.47 μ F , 400v ) are connected into a star, and the three lead wires of 1 , 2 and 3 respectively Connected to the three-phase power supply under test, the two lamps will have different illumination levels, one brighter and one darker. If one phase of the junction capacitor is used as the U phase, the one phase that emits light is the V phase, and the other phase is the W phase.Aspire Vape pen, Manufacture Aspire Vaporizer, Aspire Vape pod
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