Overvoltage Problem in Residential Unit

Only a well trained person examining the failed hardware can possibly attest to the nature of the hardware failure, but it seems to me a very remote possibility that any measurement instrument could cause an overvoltage condition. I would more likely suspect one of a variety of likely intermittent conditions coincided to produce your failure. Here are a few possibilities:

• Lightening induced voltage spike occurred somewhere on the power grid. This residence happened to just lose the return to earth potential lottery.
• Loose connection on one phase of a three phase motor somewhere in the grid that is moving a large mass.
• Insulation/isolation breakdown of a step down transformer in the grid powering this residence. This can come from anything from varnish cracking, oil loss in the transformer, to a now dead animal that bridged from the low voltage line to the high voltage line.

This sounds like a 230Y/415 3Φ system; say A,B,C,N. If phase A and N are shorted, then voltages B-N and C-N go to 415. In other words, an overvoltage condition on phases B and C.

Sorry but to me that doesn't follow unless the N-E bond is lost at the time of the fault and then restores it's self after the fault.

Sorry to shoot at your theory especially as I can't think of an alternative other than lightening.

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In some areas, the code requires that the null have a separate barker. You have surge and C phase and null O, trips the barkers. If the AC was working at the time, the barker did not trip nor the command turn off the contactor and in the compressor the coil OB gets burned out, between O and B will be 400 volts.

Dwar Jerybaciu,

About your view pertaining to the aircon problem, it seems very possible as the aircon outdoor condensor and surge arrestor was burnt out. Similar incidents were also experienced in our local industry.

Will appreciate if you can explain and give more details about the cause that you have mentioned?

Thanks.

For overvoltage to occur, as LAA Lucke was writing, one of the phases shorted to the neutral temporarily. Fore this to occur, one of the possibilities require that at the time of the surge, at least one try phase motor has to run, with inadequate protection (factories, trying to save costs, make the automation as cheap as possible). Consider that an appliance has o short and the breakers (fuses) for that phase and the null tripped (supply C and O outside). That motor that was running with 3 phases will run with only 2. If the protection that that motor is inadequate, then one of the coils can burn out and intrerrupts the contact between B and null (O) before the protection brakes the supply (A and B) to the motor. If the barker for phase B does not trip, then between B and (O) you will have 400 volts, because (O) is through the coil AO in contact with phase A. Of course, when that happened, everything that is ON and hooked up on phase B is toasted, which in turn, tripe the breakers for A and B. You can say this if only on one phase has its consumers burned out.

Yes, you are right. All aircon PCB board, surge arrestor, fluorescent ballasts, lamps, home appliances etc were burnt.

There are a total of 8 units on a floor sharing the same incoming source but only 1 unit is affected. During the site investigation, it observed the LED light (varh/Imp) of the concerned KWH meter was litted very brightly and remained ON for 20sec duration, abnormal to the rest of the KWH meters for other apartment. The KWH meter brand is Elster 1700.

This incidents also happened in our local industry since 2010 before Christmas.

We do not know how to solve this problem and it become an open verdict case.

May you share with us how to resolve it in your country?

Thanks.

The cods differ from country to country, and you MUST follow them. Personally what I do is put a transformer 1:1 that will supply the three phase consumers. This way I will have galvanic separation, and if this happened again I will know that the problem comes from the supplier.

Are u using any mcb's or mccb's for protection and isolation of power to your residential unit. if you are using so there is a chance of opening or improper closing of neutral contact in any one of the MCCB. In this sutuation there is a chance for such high voltage.once switching off and on may solve this problem. if you are not using any mccb's (4pole). there is chance for drop in insulation resistance for any one of the phase and neutral.

Dear All,

I like to express my great appreaciation for the spontaneous comments and views posted pertaining to this issue.

I will like to update that we have taken up the issue with the utility provider regarding to possiblity of direct digital kWh meter failure causing the current issue.

We have received the incident log data of the concerned meter, with mutiltple fault log indicating "Phase Fail", coinciding with our power outage and site investigation activities.

We will like to seek advice from the forum on the following:

1. As reflected in the incident data log, the definition of "Phase Fail" is denote as any one or more phase voltages supply to meter are <80% of rated voltage (230V/per phase)/missing phase voltage supply to meter.

We will like to ask whether "Phase Fail" should also include over-voltage as our electrical appliances should not have destroyed due to undervoltage scenario?

2. During our site investigation, we observed that the LED light (varh/Imp) of the concerned meter was litted very brightly and remained ON for 20sec duration, abnormal to the rest of the meters for other apartment.

We will like to ask about the possible explanation to this abnormal phenomenon.

For discussion purpose only, the concerned meter is from Elster.

Thank you while we look toward for all comments and views to the issue, hopefully a closure to the matter.

We will update if we have further progress.

If a supply phase shorted to the neutral wire, upstream of the meter, and the neutral connection, upstream, failed, then the meter will record a phaise fail. But the problem is that the voltage downstream will experience high values (400V) between the other 2 phases and the supposed neutral wires.

1: The overvoltage is not sensed by the meter since there was none: The phase to phase voltage is still the same (400V). The neutral is missing --> the voltage experienced by the different appliances will no longer be pinned to 220 or 230V. It will float from o to 400V, depending on the appliances that were connected and ON at the time.

If as confirmed, the wiring in the buildings was safe without any faults, then the problem is still with the supply company.