optical current and voltage transformers? 1

[CONSTANG]

Can somebody offer an explanation of functionality?
Eventual characteristics, relevant schematics?
Or may be a site to check out?
Thanks... I really appreciate your inputs..

 

[jwerthman]

Check out this site for info:

http://www.nxtphase.com

 

[scottf]

Nxtphase has a lot of information on their site, but they really don't have many units installed. ABB has been in the optical IT game the longest.

There has been a fair bit of negative experiences in the US market of the past few years in terms of reliability in the field. The big push for optical units came from a percieved advantage in terms of accuracy and dynamic current range for CT metering applications. A few of the conventional IT manufacturers (Ritz, Trench) introduced conventional core/coil CTs that outperform optical CTs in terms of accuracy and range, without the reliability concerns. This really set the optical guys back, as all this came about during the big generation boom over the last few years.

From a price/performance/reliability perspective, it's tough to beat some of the newer conventional designs.

The one big advantage of optical units is in the measuring of harmonics, but unfortunately, that's just not normally a big factor in transmission metering points.

 

[twosockets]

scottf,

I agree with you. I have had less than good experience with optical current transformers and would not recommend them.

Would very many people be interested in high voltage CTs that are accurate (+/- .15% or better) down to <1% of rating? These would be especially important for tie points where currents can be quite small for considerable periods of time.

 

[scottf]

twosockets-

Ritz makes a CT called an ERCT (extended-range current transformer) that is available for transmission metering applications (69 kV to 765 kV). The design has 3 available ranges from 0.25A-750A to 1A-4000A, all with a 0.15B1.8 accuracy rating.

They are great for type of generation or intertie metering. I know some folks are using them for all transmission metering applications.

 

[twosockets]

Scottf,

Do these CTs from Ritz have a dynamically compensated core? A dynamic range of 1 to 4000 Amps @ +/- .15% is extraordinary!

 

[scottf]

No...no compensation...no electronics. A purely core/coil device. Based on what I've seen, there is no equal in terms of accuracy and range. For IPP applications at 230 kV and above, most folks use the type that goes from 0.25A to 750A, so they can meter both the full generation load and the auxilary load from the high side.