Phase loss detection of three-phase three-wire circuit

电工新手求指导

Phase loss detection of three-phase three-wire circuit [Copy link]

 

I am going to make a soft start switch for a three-phase circuit recently, which needs to realize the phase loss detection function. How to achieve the phase loss detection of three-phase power in the case of three-phase three-wire (that is, without ground wire)? Please guide me, thank you very much!

maychang

For three-phase three-wire systems, if one phase is missing, two line voltages will be very low and only one line voltage will be roughly normal.

电工新手求指导

maychang posted on 2020-4-1 13:13 In a three-phase three-wire system, if one phase is missing, two line voltages will be very low (close to zero), and only one line voltage will be roughly normal.

How should the related circuit be designed? I want to pass the signal to the microcontroller after detection, but how should this signal come from? I am not very good at designing this part of the circuit. I hope the experts can give me some guidance. Thank you

maychang

If it is not required to determine which phase is missing, three voltage transformers can be used, and the three secondary terminals can be connected in series and then connected to the detection circuit. Since the vector sum of the three-phase voltage is zero, the vector sum of the three secondary voltages connected in series is zero when the three phases are normal. If it is not zero, it can be determined that the phase is missing.

maychang

New Electrician Seeking Guidance Posted on 2020-4-1 14:06 How should the relevant circuit be designed? I want to pass the signal to the microcontroller after detection, but how should this signal come from? This part of the circuit is not...

The three voltage transformers have their primary terminals connected to the three phase lines respectively, and detect whether the three secondary voltages are normal (obviously three detection circuits are needed to determine whether the voltage is normal).

huo_hu

Similar projects I have done

The transformer solution above has a voltage detection function, but the problem is that when one phase of voltage is missing, the transformer is in series and the voltage is not 0, but approximately half of the standard value. Due to the different impedance, it is not a complete half. This is more troublesome. It depends on whether your project can accept the situation where low voltage is not considered.

In addition, the power transformer connected in parallel in the three-phase circuit will also cause abnormal status when a phase is missing.

If your project also requires phase detection, it will be better to combine it with phase detection.

电工新手求指导

huo_hu posted on 2020-4-1 19:04 I have done similar projects. The transformer solution above has both voltage detection function, but the problem is that when one phase voltage is missing, the transformer becomes series connected...

Phase detection is not required. However, whether this abnormal state will affect the subsequent circuit needs to be considered. Do you have any relevant circuit diagram for reference?

电工新手求指导

maychang posted on 2020-4-1 14:24 Three voltage transformers, the primary is connected to the three phase lines respectively, and the three secondary voltages are detected to see if they are normal (obviously three detection circuits are needed to determine the voltage...

Is it feasible to use the method of comparing phase voltages? For example, to check whether the voltages between AC and BC phases are consistent?

maychang

A novice electrician is looking for guidance. Posted on 2020-4-2 12:06 Is it feasible to use the method of comparing phase voltages? For example, to detect whether the voltages between the AC and BC phases are consistent

The voltage of three-phase three-wire power supply is regulated, and it can be judged as abnormal if it is lower than a certain value. For example, the voltage of single-phase mains power is regulated to +7% to -10%, and that of 10kV and below is +7% to -7% of the rated value, and so on. In abnormal conditions of the power system, the receiving end should not exceed +10% to -10%. If you measure that the voltage of a phase exceeds this range, you should judge that the power supply is abnormal, and you don't even need to compare.

If you want to compare and detect whether the voltages between the AC and BC phases are consistent, you must obviously use AD conversion to get the value before you can compare. If you use analog circuits to compare, it is better to use a microcontroller with AD to compare the difference between the three voltages.

maychang

A novice electrician is looking for guidance. Posted on 2020-4-2 12:06 Is it feasible to use the method of comparing phase voltages? For example, to detect whether the voltages between the AC and BC phases are consistent

If you only need to determine whether there is a phase loss (an abnormal and quite extreme state), as mentioned above: the secondary of three voltage transformers are connected in series, and the voltage vector sum is zero when the three phases are balanced. If you require a pure analog method, use a comparator to detect the three-phase voltage vector sum, and it can be judged as abnormal when it is greater than a certain value.

电工新手求指导

maychang posted on 2020-4-2 12:30 If you only need to determine whether there is a phase loss (an abnormal and quite extreme state), as mentioned earlier: the secondary terminals of three voltage transformers are connected in series, and the three phases are balanced.

That's right, the simpler the circuit, the better. If you design it according to your idea, can you draw a sketch for me when you are free? My foundation is relatively poor, and I don't understand it very well just by looking at the text. I hope the master can forgive me.

maychang

New electrician seeking guidance Posted on 2020-4-2 12:56 That's right, the simpler the circuit, the better. If you design it according to your ideas, can you draw a sketch for me when you are free? The basics are...

Draw a sketch, you should also make it clear which one you want, right? I and the 6th floor have already proposed several options.

huo_hu

Do you want to detect the three-phase voltage value?

涛子哥

You can try using a voltage comparator to achieve this function. Our company specializes in low-voltage electrical appliances. We have detection chips and voltage comparators. The voltage comparator is low-cost and easy to implement. You can give it a try.

电工新手求指导

Tao Zige published on 2020-4-3 09:31 You can try to use a voltage comparator to achieve this function. Our company is engaged in low-voltage electrical appliances. We use detection chips and voltage comparators. ...

Received Tao Ge's suggestion! I'll give it a try

电工新手求指导

huo_hu posted on 2020-4-3 02:05 Do you want to detect the three-phase voltage value?

No need for testing, just make a preliminary judgment on the phase loss

maychang

A novice electrician is looking for guidance. Posted on 2020-4-3 13:56 It is not necessary to test. Just make a preliminary judgment on the phase loss.

If we only need to determine if a phase is missing, we can use the three-phase voltage vector sum to achieve this, which is the simplest.