difference amongs PT,CVT,IVT 1

[Yogi3377]

HELLO ALL

MY QUESTION IS WHAT IS DIFFERENCE AMONGS PT, CVT AND IVT USED IN SWITCHYARD.CAN WE USE CVT INPLACE OF PT AND IVT,VISEVARSA.DEEPLY EXPLAINATION .

THANKS IN ADVANCE

 

[rterickson]

See this for PT vs. CVT, courtesy Ritz Instument Transformer (now Areva):

I am not familiar with the term IVT (inductive type?).

 

[scottf]

That looks to have been written by a really smart guy!

 

[DTR2011]

I will take a guess that "IVT" is Current and Voltage Transformer (integrated in one unit).

 

[scottf]

IVT normally stands for inductive voltage transformer...same thing as VT or PT.

 

[DTR2011]

Further to the OP questions,the term "PT", (Potential Transformer) has been replaced by "VT", (Voltage Transformer), both being the same thing, an inductive (wire wound) device. I am not sure when this occurred, or in what standard.

As the attachment describes, there are some limitations to exchanging a VT with a CVT. The attachment describes a CCVT, which has the ability to couple a communications signal on the line, used primarily for distance relay station to station communications, although there are other applications, such as blocking and direct transfer trip, etc. A CVT is the same without the additional components required to couple a communications signal. As noted, one concern of using a CVT in place of a VT is the performance under fault conditions (transient response). Most modern digital/numerical distance relays have a function which, when enabled, can compensate for this.

 

[rcw retired EE]

Scott- I agree that summary was written by a good engineer. I assume the fact that you probably had something to do with this document has no bearing on your opinion of the author?

 

[scottf]

rcwilson...yes, I wrote it and therefore consider it top-notch

smallgeek...you're correct on the transient response issue. However, in actual practice, it rarely is an issue now, since the burden presented by electronic relays and meters is so low. Transient response performance improves as the burden is reduced. Also, as you mentioned, most relays can compensate for CVT transient response when set accordingly.

There is not uniformity in using CVT or CCVT. Most tend to use the terms interchangeably and use the term with or without "carrier accessories" to indicate if they can be used for power-line carrier coupling or not. BUt technically CCVT = coupling capacitor voltage transformer and CVT = capacitor voltage transformer. In reality, they are both the same devices, just carrier accessories include a drain coil, carrier ground switch, and choke coil.