Determination of the same phase sequence for two 380V low-voltage AC circuits

Use a multimeter to measure on the upper side of the two incoming circuit switches; the circuits with a voltage of zero are in the same phase. Then, arrange the two circuits on the upper side of the switches in the same phase sequence.

In fact, there are 4 methods; if you get one right, can your friends get them all correct? Thank you all for your participation! :handshake :victory:

I have encountered situations with two power supply lines, not from the same system, and the voltage across those two phases reached as high as 140V

You are absolutely right; based on the voltage values you measured, it can be determined that the high-voltage ratings of the high-voltage sides of these two power transformers are different. For example, one transformer has a rating of 35KV/0.4KV, while the other has a rating of 10KV/0.4KV. The voltage across these same phases is 140V. In my question, it refers to transformers whose voltage levels, turns ratios, connection groups, and short-circuit impedances are all the same for these two low-voltage circuits.

A phase sequence chart can be used to directly determine whether the phase sequences are consistent.

The second method has already been answered on the 7th floor; who else can come up with the remaining two methods? You might want to ask an experienced electrician around you – perhaps that will help clear things up in your mind. :handshake :victory:

It can be determined using a phase sequence meter.

Standing on an insulating board, use two test pens with both hands to make measurements; the test pen does not light up for phases that are the same.

Master Zhang suggested the third method, but his description of the brightness of the test lamps was somewhat inaccurate; in fact, both lamps shine whether they are in phase or out of phase. It’s just that when the lamps are out of phase, their brightness is higher than when they are in phase. The key to successful measurement using this method is that the human body must be effectively insulated from the ground, as mentioned correctly in the first sentence on page 10. There is one last measurement method; let’s do our best! ! ! Tip: The last method is the most traditional one. Thank you once again to everyone for their active participation and support! ! !

It can be measured using a 380V bulb. :victory:

There’s an error on the 2nd floor! I’m dizzy! The two power supplies come from completely different transformers and are not part of the same power grid either. Otherwise, what’s the point of having two power supplies? This post was last edited by rhymebus on 2009-2-23 12:39]

I have a simple trick: find a small 380V motor and connect it separately to see which direction it rotates! It’s not that complicated!

Just check it with a phase sequence meter or use a multimeter to determine it; there’s no need to complicate things for such a simple issue!

The last method was given on the 12th floor, but it is safer to use a suitable resistor for voltage division and then connect a 12V low-voltage AC incandescent lamp in series. In the past, due to backward economic and technical conditions, each electrician in factories had few multimeters available. Older electricians came up with this method for use in practical work to solve real-world problems; such homemade tools demonstrate the ingenuity of our older generation of electricians. Many complex problems actually involve many of the simplest basic principles. If you have a clear understanding of these basic concepts, I believe that when faced with problems, you can recall the solutions by thinking calmly. The 4 answers are as follows: 1. Phase sequence meter, 2. Multimeter, 3. Voltage tester, 4. Resistor and light bulb. Thank you again to everyone for participating! ! ! This post was last edited by jsnjhu on 2009-2-23 21:11]