How to Decrease High Voltage Due to Interference

and what are you monitoring?

HI,

Nice question ,but u did not mention at which time the interference is happen, because during nights all the factories surrounding may shut down. so during night you may observe over voltage ....

My monitoring is used to control on/off ACB, generators, ATS, boilers, air-compressors and show alarms if there are problem about those devices. Over voltage happens on all of day.

What is the intended voltage on that one phase?

And what kind of power system are we talking about--I'm guessing this is (hmm, can't remember a good name for it)--the typical US system with two hot lines of 120 VAC each with a current carrying neutral from the center tap of the supply transformer (thus providing 240 VAC "phase to phase" and 120 VAC phase to ground)?

And if the intended voltage of the system is 120 VAC, what does the 250 VAC voltage look like--is it a nice continuous sine wave, or is it a bunch of spikes?

If it's a nice continuous sine wave (or even a fairly nice one with spikes, but the underlying sine wave is 250 volts (RMS--i.e., as read on a typical AC voltmeter), you've got something wired up wrong.

If it's a bunch of spikes, then I wouldn't expect you to read 250 VAC with a typical voltmeter. But, if it is a bunch of spikes averaging out to 250 VAC, wow!

If you are just seeing spikes up to 250 volts (or somewhat higher) on an oscilloscope (which I suggest you use (in addition to a voltmeter) to look at the 250 volts, you might try some surge suppression.

Not a lot of detail here, but it sounds like you are using some type of electronic monitoring system, a programmable logic controller or something similar.

If that is the case, the only vulnerable component is the power supply. PLC's, computers and other electronics operate on low voltage DC. The incoming line is transformed, rectified and filtered to get the exact system voltages needed. A power conditioner on the AC line input to the monitoring system will provide the protection you seek.

Thanks to Jack, I agree If high volatage happens constantly, I will use a step-down transformer, but as mentioned above high voltage happens sometimes due to interference. How to decrease the interference.

If it is really not just overvoltage by the transformer tap selection, you have two choices:

1,. The overvoltage does not really damages anything. You then need to adjust to that.

2,. The voltage really need to be adjusted, as the equipment requires it

3,. Yo need to figure out, which

best regards

Levente

What sort of "interference" is suspected? Descriptions thus far are vague.

If voltage should be 240 and it's 250 volt.

10 volts is reasonable line regulation.

My guess is some single phase equipment is turning on and causing one line to go high and is also giving what appears to be interference.

i will explain my problem for all of you. I am working monitoring system for my customer's factory but the voltage at the factory is high 250 VAC and it happens sometimes, so when I turn on power then many relay of trip ACBs in monitoring panel on and monitoring alarm ACBs trip but in reality the ACBs in Panel not trip. I measure at two point of coil of relays, the value is 168 VAC and I think there is interference on the voltage. I do not understand this problem.

Please explain that problem for me. Thank you very much.

INTERFERENCE IS USUALLY 'HIGH IMPEDANCE' AND WOULD NOT CAUSE A PERMANENT VOLTAGE RISE.Otherwise you have discovered 'perpetual motion'.

penttijp

I would like to help you but I really dont understand your english... the grid voltage is of (value) ?; you get over voltages just in one pair of relays ?; the alarms ring but there is not a cause for alarm ?; seriously, I cant understand...

Re: the voltage at the factory is high 250 VAC

What is the voltage supposed to be?

Among other things, you should get (or borrow) an oscilloscope and look at the line voltage with an oscilloscope. Tell us what you see. (If you are not sure how to use an oscilloscope, get some help.)

Let's go back to another basic concept:

When did the problem start or when was it noticed?

How long has this been going on?

Is this why the customer called you or was it a related problem?

Was it unrelated but something you happened to notice?

Before the problem started what was the last thing that was touched/adjusted/installed/messed with?

I am guessing wildly here, because you simply have not given enough valid information, as others have mentioned one way or another, but reading between the lines, I suspect that you have 3 phase power and one phase is high. Am I right?

The reason usually for this to happen is if the single phase loads are unbalanced.

By the way, did you compare phase to ground with phase to neutral voltages on each phase? The results might be interesting as you might have a bad earth to neutral connection as well.....or it was completely forgotten. But it may only be made once usually at the secondary of the transformer.....or substation.

I would guess that the loads are only unbalanced and a clamp ammeter will quickly discover that, then you need to do a little load balancing if 10 volts difference is unacceptable (assuming 240 phase to neutral is your requirement!)

After read Andy's explain. I check the load current of three phase on the Multimeter then I noticed first phase current is 20A, second one is 10A and third one is zero, so there are unbalance load and I think grounding system of factory is not good so there are leaking current on the neutral line that I measured it.

Are there other way except improve grounding system?

Thank you all of you.

Re-read Andy's response. You haven't yet determined that you have a ground problem, so far you've only determined you have an unbalance problem. See what you can do to balance the loads.

If you can't, you might need to use a regulating transformer, as someone else has suggested.

But, in any event, again as suggested by Andy, you might have a grounding problem and should check into that as well.

Grounding and bonding should be common to the three phases, i.e., back at the service. Depending on the size of your distribution bus, it is not likely to produce such varied results. Check your balance, back to basics, i.e., resistive/reactive loads.

Isolating transformers/secondary unit substations may also be good half-splitting points to check.

Check the history of the site. Are there logs with daily readings showing a long downhill slide to poor power factor? Was this a sudden shift indicating fault or a recent installation/replacement of equipment?

You have a total load of 30 amps, so you need to remove 10 amps of load from the 20 amp phase and put it on the unloaded phase.

That will fix most problems.

Also do a continuity check between ground and neutral, the easiest was is with power on (do be careful!) measure the volts difference between ground and neutral, more than a few volts is generally considered too much, but local electrical laws must be followed.

I understand this problem.

Thanks to all of you

Hi Andy,

I have no against on your suggestion as it is also the best solution. However we must consider some points that sometimes we transfer some load to other phase and become, balance later on when some load come off and some will come on you have again in the same situation of unbalance phasing as the load didn't comes on line at the same time. we will usually encounter this in most cases where most of the load are single phase.

I am wondering why the OP worried about interference while he need only to monitor on/trip/off loads in the factory. which he must be using independent dry contact relay to get individual load activities???

Thanks and kind regards

Roman

Buy a constant voltage transformer with a good level of isolation.

The transformer is one step up from an isolation transformer in that it provides a well regulated AC output in-spite of a widely varying input voltage. They generate a lot of heat but provide a very well regulated output voltage.

They are not very common but most major electronic distributors sell them.

Dave