How capacitor voltage transformer (CVT) can be useful for power system? and how it is different from potential transformer

What is a capacitor voltage Transformer

The capacitor voltage transformer is very useful in the power system, it can step down extra high voltage signals to low voltage signals. It has three parts, two capacitors in which the splitting of transmission line signal takes place, then it has an inductive element to tune the device to line frequency and then a transformer it can isolate or step down the voltage level which could be easily measured by the measuring instrument, it would be helpful for the protective relays too.

CVT’s are single phase device which can be used for measuring voltages which are more than 100 kilovolts so it could step this high voltage into a low voltage thus it could be measured by the instruments

It is also useful in communication systems, if the CVT is combined with the wave traps then it can be used to filter high-frequency communication signals from power frequency

Why do we need CVT?

To measure voltages above 100KV we must use a highly insulated transformer, but it is highly expensive when it is compared to the normal transformer. So we can use a CVT instead of a highly insulated transformer and we could reduce the cost

Difference between capacitor voltage transformer and potential transformer

A CVT is used to measure high voltage in lines, PT is connected to bus bar it is also used to measure the voltage

The main difference is in its usage

  • CVT can be used in high voltage values but PT can’t be used for that
  • CVT is used in line circuit while PT is used in bus circuit
  • CVT is a capacitor voltage transformer while PT is a potential transformer
  • CVT usage starts from 132KV while PT can be used up to 132KV
  • Both of them step down transformers
  • CVT can be used for carrier communication purpose while PT can’t do that
  • In CVT capacitor acts as a potential divider
  • CVT is constructed by using a series of capacitor
  • It is referred to as magnetic transformer because its mode of operation is magnetic
  • CVT can be tuned to the fundamental frequency of the line
  • PT uses windings to step down the voltage
  • CVT can be used to reduce the voltage from 400kv

Working of a CVT

It is a capacitor coupled voltage transformer, it is made up off two capacitor sets which act as a voltage divider and it can bring down the line voltage to around 12kv and then it is fed to a small transformer. CVT can be used for extremely high voltage levels above 230Kv. It can be also used for the purpose of deriving, metering, relaying and protection signals. High voltage is applied to the capacitors in series and an inductor is in parallel to the capacitors which will be the primary winding of the CVT. The secondary winding terminals at different tapping points are bought out to a small junction box and then it is wired for different functions.

Advantages of CVT

  • Design is very simple and it could be easily installed
  • It can be used as a voltage measuring device and also could be used as a coupling condenser for power line carrier communication
  • It can provide isolation between high and low voltage terminal
  • It is not frequency dependent while voltage distribution