suppliers of voltage sensors

[stevenal]

Can anyone direct me to a supplier of voltage sensors for 69 and 115kV lines? Don't need the accuracy of VTs. Main use will be to drive SCADA animation showing whether line segments are energized. Looked at Lindsey insulators, but they are not available at the voltage needed. Non-contact devices would be okay if they can ignore the state of 12.5kV underbuild. Thanks.

 

[Runsor]

Try googling "Nortroll voltage indicators"

 

[stratford]

On site and on our 400kV switchyard we use TRENCH voltage and current transfomers, type VEOS 420. Very reliable at the moment.

 

[scottf]

At 69 and 115 kV, there really isn't a more cost-effective voltage measuring option that coupling capacitor voltage transformer. S&C makes a resistive voltage divider, but it can cost more than a relay accuracy CCVT and offers less accuracy and a lower burden rating, and is a bit more difficult to apply.

CCVT manufacturers in the US are AREVA/Ritz and Trench.

(disclaimer...I work for one of these companies)

 

[slavag]

Hi Scottf.
What is benefit of resistive voltage divider for 69 and 115kV in this case? not cost, not accuracy, difficult to apply.
To be sure I'm not work for S&C and it's not sales discussion. Only technical arguments.
I work with voltage divider only once in MV swg 12.5kV and not so happy,
small size yes ( cost I don't know), but used it for protection and synchro application is so difficult.

 

[scottf]

Advantage used to be cost, but from I've seen there's not too much difference now. Not stating that as fact, just what I've seen in the market place.

I can't really think of any advantage of resistive dividers over CCVTs, outside of maybe power quality measurements. We make a device now that can be added to a CCVT that allows it to measure harmonics accurately, but it does cost more.

Also, resistive dividers are a bit lighter than CCVTs, but I can't imagine too many situations where that really makes a difference in substation applications.

Also, our company does make resistive dividers too, although not as standardized as S&C.

 

[slavag]

Hi Scottf.
I aslo would like ask your ( stevenal sorry, it's other thread,but I'm use good connection now with Scottf and don't want open new thread) opinion about benifits of current sensors (rogovsky coil). I know several companies provide them for the MV swg. Are some companies have current sensors also for HV.
What is a benefits of current sensors ( not saturated it's clear)?
Thanks.
Slava

 

[scottf]

Rogovsky coils aren't used too often for HV applications...in fact I don't recall that we've ever built one for the North American market. We have built a few 345 kV CTs with Linear Couplers.

In general, the one advantage of a Rogovsky coil to a normal CT is the fact that it doesn't saturate. Outside of that, there is no clear application advantage. Another might be that in theory, they should be cheaper to produce since they don't require a core, however, the pricing is more market driven than cost driven for these type devices. That would change if they started being used more. Also, there is potentially added cost due to the processing equipment mentioned below.

The disadvantages are that the output signal needs to be processed electronically (normally), which is another source for failure/mis-operation. Also, I don't quite believe in their use for metering applications (although some will tell you it works), especially for low current levels. They also can't drive very high burdens, so application considerations are a bit different than for normal CTS.

In my opinion, with the burdens of electronic relays all by being negligible, the main burden on the CT is now reduced to the leads alone.

In the IEEE world, C800 is the normal protection accuracy for HV units. The normal lead budens would rarely exceed 2 ohms. This means that at 2 ohms burden, the CTs would be roughly linear up to 80 times rated current. For most applications, this really ought to be way over what is really needed. For a 2000:5A C800 CT, that means that the CT will be "linear" up to 160 kA on the primary!

 

[ScottyUK]

Rogowski Coils can certainly be made to metering standard, and given some decent low noise design on the signal conditioning and integrator they should be the equal of a CT for metering applications. The company linked below did some which were calibrated traceable to the NPL. Shame us protection people are such a conservative bunch or there might be a few more out there. I have some (ok, quite a few) misgivings about taking a signal of a few hundred uA through a substation environment and relying on it for protection. I think this is probably instinctive rather than based on facts, but I don't like doubt eating away in the back my mind about whether a protection scheme will work or not.

The other big advantage that Rogowski Coils have over iron-cored CTs is their immunity to DC fields, which I guess is back to saturation in a different guise.

http://www.rocoil.co.uk

And some applications which they have been used for:

http://homepage.ntlworld.com/rocoil/Applications.PDF

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Sometimes I only open my mouth to swap feet...

 

[scottf]

ScottyUK-

You're quite correct that Rogowski coils can be made for metering applications, i.e. to meet metering standards. The problem is that they have a tough time for ranges outside of the normal standard (e.g. down below 10% of rated current). The output becomes such a low level that it is very prone to noise issues. Also, you have to worry about the meter/coil interface. Most are made to take 1A or 5A type inputs.

Also, these type coils are very much affected by the position of the primary conductor...at least for metering applications.

Where you said DC fields above, did you mean DC offset? I can't imagine too many MV or HV power applications where DC field would be of concern.

 

[stevenal]

Not really looking for a fault locater or VT (capacitive or otherwise). Here is one that might do the job:

http://seecoswitch.com/sensorvs.htm

Even this sounds like the accuracy far exceeds our need, since what we need is simply an energized/deenergized indication. Any other suppliers of similar products?