700 Volt surges reported from a commercial site

[Cracker]

Although I joined sometime ago and have read afew threads, this is my first post on the forum.

I've just had a call from a client reporting that they're getting sustained surges of 700V in an industrial type plant. This is blowing various VFDs they are using, apparently. Most time the voltage sits at about 400V.

They have a 315KVA mini-sub, council supplied, on the property which then feeds a 450-amp/400V possible load. A typical council supply to commercial properties.

I haven't been to site so the fault they're reporting is second-hand knowledge. They have, however, told me that their neighbours are experiencing the same problem, which leads me to believe it's a supply problem on the HV/MV side. I'd assume this is a council problem and is also outside my skill set. I don't know whether HV fluctuations are handled by the mini-sub or not.

My question is how to fix? They'll contact the council but is there something I can install inside the property to stop the damage?

Is there some sort of large surge arrstor/capacitor I can install on the incoming supply to remove these surges, even if they are for long periods of time?

This is uncharted water for me but I need a solution and am hoping you guys can help.

[Justloadit]

There are maybe 2 ways for protection , depending on the application or physical size, as this will have a bearing on cost.
Voltage Monitor
This is a voltage monitor which checks the incoming voltage and if with in the window switches a contactor on, and allows the load to be connected.
Constant voltage transformer
This is a special transformer that maintains the output to the load at a constant voltage. But as any piece of equipment there are limits.

[ANU]

Please contact me . I have a client who is an experienced & qualified electrical contractor.
anitag@mweb.co.za

[GCE]

Hi

I would stick a voltage recorder on the LT side and see what is actually happening before making a decision - If the voltage spike is short you may get away with good quality surge arrestors - If not then go with the above suggestion of contactors and voltage monitors - Problem is that it causes chaos with production .

I have used auto tap transformers on a small scale , 5Kva , but a quick spike still gets through before the change - There are a number of systems available but on 315Kva will start at R600K to purchase

I would also check that the earthing , mainly earth to neutral from the star point is still intact and has no loose connections . You will get an elevated voltage between earth and neutral.
My theory is that when something funny happens that cannot be explained , check the neutrals .

With the neighbours also experiencing problems it could be MV side but then again somebody could have gone through the area and stolen all the earth to neutral bridge points or the earthing in the area has become a problem.

We recently had the neutral conductors and earth wires stolen from multiply sub stations in the area over a period of a week or two at random intervals.

[Cracker]

Thanks for the replies.

I've spoken with the clinet and we'll start with the voltage recording and take things from there.

[SiyaM]

Although I joined sometime ago and have read afew threads, this is my first post on the forum.

I've just had a call from a client reporting that they're getting sustained surges of 700V in an industrial type plant. This is blowing various VFDs they are using, apparently. Most time the voltage sits at about 400V.

They have a 315KVA mini-sub, council supplied, on the property which then feeds a 450-amp/400V possible load. A typical council supply to commercial properties.

I haven't been to site so the fault they're reporting is second-hand knowledge. They have, however, told me that their neighbours are experiencing the same problem, which leads me to believe it's a supply problem on the HV/MV side. I'd assume this is a council problem and is also outside my skill set. I don't know whether HV fluctuations are handled by the mini-sub or not.

My question is how to fix? They'll contact the council but is there something I can install inside the property to stop the damage?

Is there some sort of large surge arrstor/capacitor I can install on the incoming supply to remove these surges, even if they are for long periods of time?

This is uncharted water for me but I need a solution and am hoping you guys can help.

This is very strange and interesting. I wonder if that surge is not from a sensitive earth fault. This can only be possible if it's an underground cable network where sensitive earth fault protection on Mv networks is not activated. It can only be a feed from the primary side of the MV trfr because I don't see it coming from the secondary windings.
Please share your findings.

Regards
S.Mjali (Pr Techni Eng)


Sent from my SM-G955F using Tapatalk

[ians]

Put an online ups on the control circuits (it gets expensive...but so does replacing VFD's)...it will regulate the voltage on the control side (the part that blows) ...install a 3 phase trip connect...this device will monitor the voltage and drop out the contactor if a surge voltage is detected...very handy in locations where they steal the neutral cable which causes the voltage to spike...which could be the problem...a loose neutral connection

Surge protection is not designed for over voltage.

You need to install a logger...without recorded data you have no idea what is actually going on.

[GCE]

Hi Cracker

Did you ever do a voltage recording and find the problem ?

[Jackt]

A bit late to post now, but the recorder must be able to log voltage events.
A short surge or dip will not be detected by standard voltage recorders.

[Cracker]

Nope, I didn't do the voltage recording.
The client hasn't taken it any further.
Which is a pity, because I wanted to see what these voltage recorders do. I'd found a company that does data logging and besides the voltages, I wanted to see the amp draw over time, etc.

But, next year, when they're in full swing again, maybe they'll start losing VSDs again and revisit the problem.

[GCE]

Thanks Cracker

We have a similar complaint after finishing a MV reticulation job.We have an Eskom 11Kv incoming along with a Genset feeding a step up transformer to 11Kv
The Eskom and Genset 11Kv feeds onto an Automatic transfer switch which then feeds the ring with 4 x 200Kva minisubs fitted with Class 1&2 combined surge arrestors
If Eskom falls away the genset automatically takes over the 11Kv feed.
We are switching the MV 1 000 m away from the minisub and I would not expect any type of switching spike to have an effect on the LT supply

The electrical contractor doing the LT works is having a problem with a Dali interface "blowing " when we switch between supplies.We have checked our side and don't find anything but when I looked at his panel I see all sorts of basic mistakes just waiting to go wrong including his class 2 surge arrestors being wired with 2,5sqmm wire - I am no expert in surge arrestors but it just seems wrong when you are 10m away from a 200Kva minisub with a 125Amp feeder CB.He does appear to have a 20Amp CB protecting the surge arrestors which to me is also incorrect.

[Cracker]

I'm no SPD fundi at all but on our site, fed from a 320Kva minisub, I initially installed DehnGard? Class 2 SPDs. these are fed directly from the busbars with 16mm conductors for live, neutral and earth and are located as close as possible to the busbars. No o/load protection is fitted other than the 450amp main switch.

Should this be different? I don't know yet, will wait and see what the data logging company suggests. This is their speciality besides the logging.

But 20amp breakers protecting an SPD sounds wrong, I'd say there should be no protection at all. Don't quote me on this though, I'm not sure.

Maybe your LT guy should fit class 3 protection directly on his Dali interface ..................

[Jackt]

Cracker, I sent you a PM.

If the voltage quality is costing the client money, I'd recommend installing a power quality meter on the supply to the problem area.
Once again it must record events and some statistics of the event.
(I normally set this at recording any event above or below 10% of nominal)

I've had cases of recording so long with a portable instrument that the customer could have installed a permanent meter at that cost. and still not had any events occur.