Sparking from the transformer floating neutral

veera1257

In our solar plant we are using Bonfiglioli INVERTER which requires floating neutral for transformer. Now we installed Air-conditioner for our inverter room and we took phase from t/f LV phase and neutral from floating neutral. And it worked fine for few days and now sparking is coming from the neutral terminal when AC is ON, though there is no loose connection.

What could be the reason..

Cariboocoot

Re: Sparking from the transformer floating neutral

Welcome to the forum.

I think we need a few more details, such as what power standard this is running (230 VAC 50 Hz or 240 VAC 60 Hz). It sounds like 240 VAC 60 Hz "split phase" and you are trying to run the A/C from Neutral and L1 or L2.

The "floating neutral" doesn't make much sense; usually it will be bonded to ground. This sounds like it might be an MSW type inverter. When you say sparks are coming from the neutral terminal, under what circumstances? Sparks have to go from somewhere to somewhere; they won't occur randomly. Is this happening when the unit is unplugged or plugged in? I'd hate to think there was arcing going on while in use; that is not safe at all!

BB.

Re: Sparking from the transformer floating neutral

Assuming you are in Northern India (Delhi or there about)?

So, assuming 230 VAC 50 Hz power--Either ungrounded or undetermined ground reference 220 VAC output?

Is this an off grid/backup AC inverter (and battery bank) or is this a "Grid Tied" inverter (solar panels>AC inverter>AC Mains and no battery bank)?

In any case, what do you mean by a "sparking neutral"?

There is arcing from series connection failures (arcing across a lose terminal/electrical connection), and there are arcs from "fault" connections (hot to earth/ground, Hot to Return, etc.).

In general, AC power "fault" connections should trip a circuit breaker (i.e., a short circuit on the AC output).

Series connections will not trip a circuit breaker (in the US/Canada, we are starting to see requirements for "arc fault" breakers that detect the electrical "spectrum" from arcs (bad connections) which will trip an Arc Fault type breaker.

As Marc "Cariboocoot" says--There is something very wrong and unsafe here. It sounds like a series arc (loose connection)--Which can easily start a fire in your wiring insulation.

If you are having something else arcing (say "neutral" or even a "Hot" wire to metal ground--That is something else. In the US, all AC wiring is rated up to 600 VAC operation (and 1,800 VAC "high-pot" tested against insulation failures--I.e., it should take >>600 VAC to "punch through" or "flash over" your insulation).

Be really careful here--Most AC meters are only good for ~600 VAC maximum--If you have >1,800 VAC on your branch circuit, somebody could easily be killed trying to do fault isolation.

-Bill

veera1257

Re: Sparking from the transformer floating neutral

Cariboocoot wrote: »

Welcome to the forum.

I think we need a few more details, such as what power standard this is running (230 VAC 50 Hz or 240 VAC 60 Hz). It sounds like 240 VAC 60 Hz "split phase" and you are trying to run the A/C from Neutral and L1 or L2.

The "floating neutral" doesn't make much sense; usually it will be bonded to ground. This sounds like it might be an MSW type inverter. When you say sparks are coming from the neutral terminal, under what circumstances? Sparks have to go from somewhere to somewhere; they won't occur randomly. Is this happening when the unit is unplugged or plugged in? I'd hate to think there was arcing going on while in use; that is not safe at all!

We installed a stabilizer for Air conditioner(A/C rating 230vAC 50HZ 1.5KW). And stabilizer out put was 200V.However A/C is working fine .And the problem is that we are getting intermittent sparks from the neutral at Transformer side.

You can suggest us to connect neutral to earth as we generally do.But as far as solar inverters are concerned we should not do that as per NEC guidelines and inverter manual.And I am running A/C from L1 and Neutral.Intermittent sparks are occurring when its compressor is ON.Also note that there is no ground fault( we checked and confirmed)

veera1257

Re: Sparking from the transformer floating neutral

We installed a stabilizer for Air conditioner(A/C rating 230vAC 50HZ 1.5KW). And stabilizer out put was 200V.However A/C is working fine .And the problem is that we are getting intermittent sparks from the neutral at Transformer side.

You can suggest us to connect neutral to earth as we generally do.But as far as grid tied solar inverters are concerned we should not do that as per NEC guidelines and inverter manual.And I am running A/C from L1 and Neutral.Intermittent sparks are occurring when its compressor is ON.Also note that there is no ground fault( we checked and confirmed)

For your information T/F LV out put is 330V (L-L)

BB. wrote: »

Assuming you are in Northern India (Delhi or there about)?

So, assuming 230 VAC 50 Hz power--Either ungrounded or undetermined ground reference 220 VAC output?

Is this an off grid/backup AC inverter (and battery bank) or is this a "Grid Tied" inverter (solar panels>AC inverter>AC Mains and no battery bank)?

In any case, what do you mean by a "sparking neutral"?

There is arcing from series connection failures (arcing across a lose terminal/electrical connection), and there are arcs from "fault" connections (hot to earth/ground, Hot to Return, etc.).

In general, AC power "fault" connections should trip a circuit breaker (i.e., a short circuit on the AC output).

Series connections will not trip a circuit breaker (in the US/Canada, we are starting to see requirements for "arc fault" breakers that detect the electrical "spectrum" from arcs (bad connections) which will trip an Arc Fault type breaker.

As Marc "Cariboocoot" says--There is something very wrong and unsafe here. It sounds like a series arc (loose connection)--Which can easily start a fire in your wiring insulation.

If you are having something else arcing (say "neutral" or even a "Hot" wire to metal ground--That is something else. In the US, all AC wiring is rated up to 600 VAC operation (and 1,800 VAC "high-pot" tested against insulation failures--I.e., it should take >>600 VAC to "punch through" or "flash over" your insulation).

Be really careful here--Most AC meters are only good for ~600 VAC maximum--If you have >1,800 VAC on your branch circuit, somebody could easily be killed trying to do fault isolation.

-Bill

Cariboocoot

Re: Sparking from the transformer floating neutral

Well there's no ground fault because there's no ground. Hard to have a fault with something that isn't there.
There is no NEC requirement forbidding N-G bond; quite the opposite. But I can believe that your inverter does not allow one. That is the mark of a poor quality inverter.
I don't know what the 'stabilizer' is of which you speak: autotransformer for balancing the load on the two legs of the inverter? That definitely will not operate correctly without an N-G bond.

I see you now use the term "grid-tie inverter". So that would be panels feeding an inverter directly and that inverter's output going to the main service panel which is also fed by the utility, correct? In such an instance the N-G bond would be at the service panel and no additional bond would be used.

You seem to have quite a few variations in Voltage from 330 to 200. That is indicative of a problem right there. Is the grid Voltage stable? Is that what your stabilizer is for: to give a consistent Voltage from an inconsistent grid? If so and you have the GTI connected to back feed the stabilizer that won't work as the GTI will try to match the V of whatever it is connected to and the stabilizer will isolate it somewhat from the grid preventing the grid from 'clamping' the GTI's output Voltage to a fixed value.

Likewise if the GTI is connected directly to the grid and the grid Voltage is unstable then the GTI will be cutting in and out according to the variations in grid Voltage; every time it goes out of range the GTI will shut down. A set up like that is fairly useless and the fault is with the grid. As such it isn't something you can correct.

We have heard a lot about the quality of India's power grid. Frankly, it's scary. It's the sort of system that causes people to buy batteries if they actually want to keep the power on and consistent.

Still, arcs occur from one point to another. They do not occur on solid connections. Can you provide wiring diagrams and/or pictures? It may help us to see what is going on and possibly offer a solution.

BB.

Re: Sparking from the transformer floating neutral

I agree with Marc, still don't understand your setup.

In any case, you can only have sparks if there is a voltage differential across (or through) and insulator or poor electrical connection.

Not sure that the balance of your system is responsible for the sparks. Turn off the power (check with meter) and carefully disconnect the electrical connections around the area that is arcing. Check for browning (overheating due to poor connections) and pits (arc endpoints).

-Bill