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I am Vango from Ethiopia. Am junior electrical engineer. While working today I've faced some problem. That is when incoming voltage drops below 380 V, I mean when it is about 370 V, motor stops immediately and it won't start again till the voltage reaches 380 V. So It is interrupting our production. What shall I do?

winny
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Vango raggar
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    Supply cables too long? Supply voltage variation? Other equipment starting? So many possibilities, what have you checked? – Solar Mike May 11 '22 at 05:59
  • Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking. – Voltage Spike May 11 '22 at 06:10
  • It could be the motor contoroller has an undervoltage detection and turns everything off when the votlage drops, doesn't turn it back on until voltage is correct. The problem is either your voltage is not reliable enough (which could be caused by many many different things), or your undervoltage detection is set to high (but there are saftey concerns about changing this without knowing the system fully). – Puffafish May 11 '22 at 06:39
  • @SolarMike The problem am facing is voltage supply is variable, that is from power supplier company. Most of the time I get voltage around 390 but. sometimes it drops to 375 or below. At that time motors couldn't start because of the low voltage than desired one. – Vango raggar May 11 '22 at 06:40
  • So, do what one company I worked at did: have your own power station, even then they had to draw from the grid for start-up... – Solar Mike May 11 '22 at 06:44
  • @SolarMike is there any way to fix such a problem? Or any device which can improve such a voltage drop?? – Vango raggar May 11 '22 at 06:53
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    "have your own power station". – Solar Mike May 11 '22 at 06:55
  • You say this is happening "today"; is this a new problem that's only just started? – Hearth May 11 '22 at 13:02
  • @Hearth It's not first time. The problem was there before I join them – Vango raggar May 11 '22 at 13:57

3 Answers3

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I think what you are looking for is called a Servo Controlled Voltage Stabilizer, e.g. implemented as variable transformer that automatically adapts its transforming ratio in order to compensate input voltage variations.

Curd
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The problem am facing is voltage supply is variable, that is from power supplier company. Most of the time I get voltage around 390 but. sometimes it drops to 375 or below. At that time motors couldn't start because of the low voltage than desired one.

It appears that the motor under-voltage tripping device is to be appropriately set.

Generally, the drop-out voltage can be set at 80–95% of the operating voltage and the drop-out time between 0.1 to 20 seconds.

The drop-out time setting eliminates nuisance tripping caused by momentary voltage fluctuation.

vu2nan
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You need to find out why your power line voltage is so low. I believe the nominal voltage should be 440 VAC. If you are getting below 370, your power grid is dangerously close to failing.

I assume that your 370 number is measured under no load conditions, and reflects the voltage available. Certainly, as you have described it, the 380 number is no-load by definition. If so, either the power provider is not doing its job of regulating the voltage, or the total load on the system is so great that you're getting into brown-out conditions.

If the 370/380 number is not the no load voltage, but rather reflects voltage under load, this suggests that your facility has been wired with wiring which is under-sized for the required loads. If this is the case, you'll need to spend some money to rewire your production line with smaller-gauge wiring. You'll also need to pay attention to the possibility that your wiring will catch fire. You have not mentioned what "production" means in your case. It's possible that you're talking about a facility which is using multiple loads, and this particular motor is just the one that trips first, while the facility as a whole is actually responsible for the low voltage. Has your plant been expanding recently, so more loads have been added without upgrading the wiring? Is the plant electrical system protected by fuses/circuit breakers which are sized for the nominal (as opposed to the real) loads, or have any such protections been bypassed in the name of getting things to work without spending all the money needed to upgrade the wiring?

If the issue is a failure of the power grid, caused either by excessive load or incompetent administration, your only hope is to buy a voltage regulator which will boost the voltage you're getting to the nominal 440.

And don't think about trying to defeat the undervoltage lockout on the motors, either. As the voltage drops, for the same load a motor will draw more current and experience greater internal heating. With no under-voltage protection you run a real risk of damage to the motor or even fire.

WhatRoughBeast
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