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What Is a Capacitor Voltage Transformer?

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  • Written By: Alexis W.
  • Edited By: Heather Bailey
  • Last Modified Date: 17 December 2014
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A CVT, or capacitor voltage transformer, is a transformer circuit used in high-voltage applications. The capacitor voltage transformer is used as a means of delivering a filtered, low-voltage signal to the protected relay portions of the attached electrical circuitry. These transformers are mostly used within the high-voltage circuitry as measurement devices and as a means of protecting specific parts of the circuitry.

The main function of a capacitor voltage transformer is to systematically step the amount of signal it receives upon input. It steps this signal down to an amount that is within the parameters set by the smaller components of the circuit. These parameters are usually meters or other measurement devices that are used to record the amount of signal received by and output through the circuit in its entirety.

Another form of capacitor voltage transformer is one that is either attached to or run in sequence with something called a capacitance coupled voltage transformer, or CCVT. These types of transformers are used in the same manner, however, they are able to handle much higher amounts of input signal. They are also able to distribute the lower amounts of output signal to multiple locations within the circuit at the same time.

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These coupled capacitors are used much more sparingly, as their design entails a higher cost. Often, they prove to be uneconomical for the function they provide. In general, this means that a CCVT is not typically connected to any circuit that processes less than 100 kilovolts.

The basic construction of a capacitor voltage transformer consists of two different capacitors and four main terminals. The first capacitor is actually a large sequence of smaller capacitors that have been run in sequence. This allows for the even distribution of the signal across the circuit, as well as for the rapid decrease of the input signal’s power. The four main terminals are an input and a ground terminal and at least two output terminals that are used to connect the transformer to the protected hardware or circuitry.

The two capacitor units are used to decrease and divide the amount of input signal that is applied to them. They are then connected to an inductive element that is used as the means of tuning the signal to the desired frequency for the correct output terminals, after they pass through a transformer. The transformer is used to lower the input signal even further after it’s been divided, before the signal is dispersed amongst the more delicate elements of the high-voltage circuit.

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anon270015
Post 4

@nony: If the transformer went bad you wouldn't have any power coming to your house. It would result in an open in the electrical grid. Another transformer parallel to the one that failed would pick up the load.

anon242889
Post 3

Question. Can a ccvt be considered a source of power (backfeed)connected to a transmission line under clearance? Should there be a grd switch or open secondary switch associated with the ccvt?

NathanG
Post 2

@nony - That would be bad news – but I think that other equipment in the substation would trip, like circuit breakers and stuff, to prevent your house from getting fried.

I’ve heard of power outages happening, but never of a house getting zapped. I don’t doubt that it could happen; I just believe that there a lot of other protections in the power utility’s infrastructure to keep that from happening.

There’s an awful lot of voltage riding on those wires for the utilities not to have some sort of fault protection in place.

nony
Post 1

While I am sure that all the equipment in a power company’s substation is important, I believe that the transformer is one of the most important pieces of equipment.

Its job is to reduce the high voltage coming out of the substation so that it's low enough to supply energy to your house. What would happen if the transformer went bad?

You’d have a very big spike of electricity coming into your house, possibly frying your appliances and causing other damage as well.

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