3-phase Electricity Problems

[naammanow]

Maybe there is an electricity expert here that can help me? I am having 3-phase electricity system to my house with a 50 Kv transformer. From the transformer the electricity cables are going underground into the house. Once entering the house it goes to the main board which is protected with a W-OP4 Digital Phase Protector. This should trip the main switch in case of over/under voltage or unbalanced voltage. It has a set time delay of between 1 to 5 seconds, now set @ 5 seconds. Well it does not.

An animal walking/playing on the lines got electrocuted resulting in the main switch tripping. However it did not switch off everything quick enough. The water heater was blown almost of the wall, the garage door unit blown as well as several light bulbs/units, fridge, water pipes. All in all a huge mess.

I used to have a flat that had a “Safety Cut” box that tripped the switch should there be a fault somewhere and was measured in Millie Seconds and worked very well. However, as it a huge power from the 3-phase that system cannot be used, I was told.

Anybody has any solutions as I have been told that animals like mine (a sort of huge rat) snakes etc can quite often go up on the wires with dire results for themselves and my house? And why did my “state of the art” phase protector not protect the house and its effects as it should? Any answer will be truly appreciated. Thanks, John

[Crossy]

According to the website http://www.wipelectric.com/en/product.php?id=1&h=1 this unit is intended to protect from phase-loss, under voltage and over voltage, typical issues with 3-phase that can cause damage to motors etc. These events have to last a relatively long period (seconds) before damage is caused.

It is not intended as a surge protector, for this you need a device called a MOV (Metal Oxide Varistor). A MOV provides protection within microseconds.

It would appear that you had a large, very high-power surge caused by the demise of the unfortunate critter. It had sufficient energy to destroy the water heater so it's highly likely that even a MOV (which is intended to handle lightning surges) would have been destroyed although it may have absorbed sufficient energy to limit the damage.

The surge, which the W-OP4 likely detected, would have caused the damage almost instantaneously, certainly long before the unit had chance to operate.

Not sure how you can protect against a recurrence of this event

EDIT I also note that the W-OP4 has a contact rating of only 5A, so it's likely driving an auxiliary contactor which will slow the action even more

[InterestedObserver]

Sounds like your system is not properly grounded? If not then you could have experienced tempory line voltage (380V) on the neutral connection which should have been at ground potential (0V). That alone would blow out most electrical equipment, along with the critter.

[Rimmer]

Which wires did your 'animal' play on? I also have a 50kva transformer leading to an underground NYY cable and thence to a TP distribution board. The only 'wires' in my system that an animal could play on are the HT cables just outside my wall all the rest are enclosed or underground. If a rat should climb one of the HT poles and play with the HT, the fuses protecting the transformer will presumably clear.

[Crossy]

the fuses protecting the transformer will presumably clear.

Nah, the rat will clear first

I was wondering the same, maybe the critter got between the 25kV incomer and the LV side (would be bigger than a rat though), that would lead to interesting effects that no protection system could mitigate

[naammanow]

Thanks for the feedback. I have the High Voltage cables running from the road, about 200 meters to the house. 3 cables and one wire that is for the lighting protection. When the cables are coming towards the transformer they run pretty far apart, about 80+ cms I would think. I suppose the animal must have gone towards the transformer, jumped somehow and created the shortcut and fried. I have the grounding form the transformer and also from the pole on which it is based. I am going to increase this grounding I think with another 4 copper rods of 3 mtr lengths in a square of about 3 mtrs wide hoping that the current will go into the ground before hitting my main breaker. The digital phase protector I have set now at 2 seconds (before was at 5) The fault registered on the unit was "set unbalanced voltage" (whatever that means!?) I will also check the grounding of all the cables in the house I think; the main board is earthed of course as are all the sockets etc. I am including some pictures of the 3-phase and the transformer and inlet before the wiring goes underground.

Not sure what you mean Crossy by "I also note that the W-OP4 has a contact rating of only 5A, so it's likely driving an auxiliary contactor which will slow the action even more" - maybe care the explain, thanks. You also think the an additional (or instead) MOV might be better? Regarding the animal, what to say, it was charbroiled, hairless (by now) stiff like a board and about 40 cms long - long tail. Maybe a full proof protection with overhead wiring cannot be guaranteed. It's just that we're worried stiff, especially with the shattered bulbs blowing in the bedroom of our one year old son. Any bang, and whow, we're up and running!

[Rimmer]

the fuses protecting the transformer will presumably clear.

Nah, the rat will clear first

Instant fricassee of rat. Baldrick would approve!!

[naammanow]

some picts as promised

[powderpuff]

Crossy is on to something here. Most protection you add at load center is designed to protect DOWNSTREAM of the load center. The protection you needed was near to the transformer. Nes Pas?

[Rimmer]

A lot of the HT poles on the golf course where I live have an upside down cone made from mesh on the poles to stop rats climbing up them.

[InterestedObserver]

Crossy is on to something here. Most protection you add at load center is designed to protect DOWNSTREAM of the load center. The protection you needed was near to the transformer. Nes Pas?

The OP was using over/under and phase unbalance voltage protection. Typically this type of protection would monitor from the upstream source (transformer) to the point of protection (W-OP4). The long time delay, 5 seconds, is what caused the transient over voltage to cause all the damage. Surge suppressors would have helped, provided their capacity was great enough and the system ground was adequate.

Edited May 1, 2010 by InterestedObserver

[david96]

There should be surge protection (lightning arresters) at each of the the HV terminals of the transformer.

There should be 3 HV fuses protecting the transformer.

Are there any HRC fuselinks on the LV side of the transformer?

Is the LV neutral of the transformer earthed?

On the LV side it would be recomended that surge protection be installed one on each phase at the main switchboard, these should be protected by an MCB.

The "phase protection (failure) relay" is a device that operates if one or more phases fail, if phases become imbalanced (%) or the phase rotation is incorrect (R. W. B. )

Functions are dependant on the specific type. Available in DIN rail mounting.

The N0/NC contact is connected to operate a secondary device such as a contactor which switches the load to be protected. May be time delayed usually to prevent operation on transient system voltage events.

In the event of the fault on the HV as you mentioned was on the load side of the HV fuses

an HV fuse may have cleared the fault first, causing the voltage to be lost on one phase

thus operating the PFR.