The capacitive-coupled potential transformer (CCPT) or Capacitive Voltage Transformer is a Voltage Transformer with a capacitive circuit as shown in the figure below.
The two Capacitor C1 and C2 here acts as a voltage divider circuit and lower the high voltage to 11 KV than this 11 KV voltage across the Capacitor C2 is fed to a voltage transformer.
This voltage transformer step down this voltage to few hundred volts i.e. 110 or 100 volt. This low voltage 110 or 100 across secondary terminals of voltage transformer is fed to meters and protective relays for metering and protection respectively.
Application: Just as voltage transformer, for metering and protection (CVT steps down the high voltage to low voltage. Meters and relays are fed with this low voltage obtained by CVT)
A tuning reactor was used to increase energy transfer.
Pros and cons of CVT: CVT or CCPT vs Conventional PT
- Low cost. CVT is widely used in 220 KV , 400 KV or higher voltage level because of its low cost(cost is low as compared to conventional voltage transformer because the voltage is reduced substantially by capacitor voltage divider circuit to just 11 KV and only 11 KV voltage transformer is needed which is cheap)
- Less effect of ferroresosnance due to lower flux density
- Good for protective relaying.
- Not good for revenue metering as the accuracy drift over time and with temperature
- Poor transient response -when a fault reduces the line voltage, the secondary output does not respond instantaneously due to the energy-storing elements. The higher the capacitance, the lower is the magnitude of the transient response.