ECN Forum Forums General Topics of the Trade Non-US Electrical Systems & Trades 11 kV Voltage Regulator

We have a problem with the Voltage regulator in Piha. This one is actually a bank of two auto transformers which can step up or down and regulate the feeder voltage within ± 10%, over 16 steps either way.
The set up is for one regulator in the red phase and one in the blue phase ( 2 wattmeter method ).
Some photo's are in the photo gallery to give an idea of the set up.
It must have gone with a good bang. 2 * 11kV Lightning arrestors were blown off the pole and one 3 kV arrestor across the series winding gone up in fire as well.
No thunder or lightning prior to the faillure which happened last week wednesday.

These units are put at the end of long 11 or 22 kV feeder lines where the voltage can be down by 8 to 10 % and this way it can be boosted to avoid voltage complaints.
These areas don't have the population base to warrant a 7.5 MVA substation.

The LV voltages were with the bypass switch closed down to around 211 Volts instead of a normal 235 Volts.

Today we tested the replacement spare unit with the winding ratio tester, in the workshop and got a heavy hiab in to put the unit in service position on the pole platform, with traffic management in place.

Tomorrow will be the livening up and complete commisioning because this afternoon the weather turned to custard.

Interesting to disassemble the unit and see what was wrong with it.

I wonder if these arrangements are used in other countries around the world as well.

It has been quite on the non US forums hence this post about some local utility work in New Zealand.

Regards, Raymond

Gidday Ray,
I know exactly what you mean.
I have mis-givings about using auto-transformers at these voltages, even though we use them like this.
Even when they were used in motor starters they used to give untold problems.
We lost a whole sub-station here out in the sticks once because of one of those things.

Auto transformer regulators like that are use here in rural Ontario Canada, usually on sets of three. Lightening arrestors are usually installed on adjacent poles though.

The replacement unit is in service since last Thursday and the voltages in Piha are fine now 235 / 408 volts.

We usually have 3 LA's at the incoming 3 phases (line side of the bypass ABS switch)
Then 2 LA's at the outgoing 2 phases (load side off regulator).

The 3 kV LA's are across the tapchanger (S and L terminals) of the regulator.
The one blown off above the regulator must have exploded when something internally went wrong (open circuit).

When the unit is detanked I will take a few piccies and will post these and let you know.

I put a couple of pics up in the photo galleries of the internal of the auto TX.

An internal spring broke which is part of the switching mechanism and supposed to flick the contacts from one tap to another in a snap type action.
The contacts didn't close properly and it started arcing, hence fluctuating voltages.

I think it is repairable. Up to the asset owner to decide if the TX is toast or reco.

Cool pictures. Do you work for some kind of contractor? I see from your pictures that your work is extremely varied.

Yesterday we dropped off a malfunctioning 7200v recloser at the repair place, that was fun to look around. It was actually a converted school gymnasium, and it was filled end to end with reclosers (and a few regulators) in various stages of repair.

I work for Siemens and we are contractors to Vector (POCO) in Auckland and work in the electrical distribution industry.

I cover almost all the aspects of electrical work. Electrician, line mechanic, faultman, fault location, HV , LV substations and repair work.

Also when involved in certain jobs I like to see what caused a particular fault and see if improvements can be made to prevent the same failure in future again.

Regards, Raymond