Coupling Capacitor Voltage Transformer (CCVT)

 In an electrical power substation, Capacitor Voltage Transformer in combination with Wave

Trap is placed at the sending and receiving ends of the substation. Capacitor is behaving as

coupling capacitor. The carrier equipment is connected to the transmission line through

coupling capacitor which is of such capacitance that it offers low reactance (Xc =

1

2πfcC

) to

the carrier frequency (PLCC signal). This coupling capacitor allows carrier frequency signals

to enter the carrier equipment but does not allow 50Hz power frequency currents to enter

the carrier equipment. To reduce impedance further, low inductance is connected is

connected in series with coupling capacitor to form a resonance at carrier frequency.

Accuracy Class:

Measuring voltage transformers

Standard accuracy class may be one of 0.1, 0.2, 0.5, 1 or 3. The recommended class of

accuracy will depend upon the type of metering.

Protection voltage transformers

Generally, a measuring voltage transformer may also be used for the purpose of protection.

A protection transformer, however, is assigned an accuracy class of 3 or 6, which defines

the highest permissible percentage voltage error at any voltage between 5% of the rated

voltage up to the voltage obtained by multiplying the rated voltage by the rated voltage

factor of 1.2, 1.5 or 1.9. And when the secondary has a burden between 25% and 100% of

the rated burden at a p.f. of 0.8 lagging.

This accuracy class is followed by a letter ‘P’ such as 3P and 6P etc.

Burdens

The standard ratings, at 0.8 p.f. lagging, may be 10, 15, 25, 30, 50, 75, 100, 150, 200, 300, 400 or 500 VA / phase or

as the auxiliary circuit may demand. This is the maximum burden the transformer may have to feed at a time

Specifications

• Rated primary voltage

• Rated secondary voltage [110V or 110/√3]

• Rated frequency

• Rated burden /phase (VA) [ 100VA for 33kV; 300/500 VA for 132kV]

• Accuracy class; Measuring voltage transformers 0.1, 0.2, 0.5, 1 or 3 and Protection

voltage transformers 3P and 6P etc.

• Rated voltage factor: 1.2 Continuous, 1.5/1.9 for 30 sec/ 8 hours,

• Voltage error or ratio error

• Phase displacement error

• Basic Insulation Level (BIL)

Precautions.

The primary circuit of the PT is always to be protected by high voltage fuses. The secondary circuit is

always be protected by a low voltage fuse.

It is essential, as a safe measure, to earth the secondary circuit effectively at one point. The frame of

PT should also be earthed.

Proper attention should also be given to the polarity markings of the PT so that while making

connection to wattmeter, kWh meter, power factor meter or to the protective relays where both the

current and voltage signals are required for actuation.