Capacitive Voltage Transformer (CVT)

✅ Capacitive Voltage Transformer (CVT) – Working Principle

A Capacitive Voltage Transformer (CVT) is a type of voltage transformer used to step down high transmission voltages to a lower value suitable for metering, protection, and control systems in electrical networks. It works based on capacitive voltage division and electromagnetic transformation.

➤ Main Working Principle:

Capacitive Divider:
- The CVT consists of two or more high-voltage capacitors connected in series, forming a capacitive divider.
- The high transmission voltage is applied across this capacitor arrangement.
- The voltage is proportionally divided according to the capacitance values, providing a reduced voltage at the intermediate point.
- This reduced voltage is still at high frequency and requires further processing.
Intermediate Circuit:
- The output of the capacitive divider is connected to the primary winding of a transformer.
- A compensating reactor is connected in series to counteract phase displacement and improve accuracy.
Electromagnetic Transformer:
- The transformer further steps down the voltage from the capacitive divider to a usable secondary voltage.
- The secondary output is typically 100 V or 110 V and is used for measurement, protection relays, and control circuits.
Protection Components:
- A surge arrester is used to protect the CVT from lightning surges and transient overvoltages.
- A damping resistor may be connected to reduce oscillations and prevent ferroresonance.

➤ CVT Detailed Process:

High voltage enters the CVT:
- The line voltage from the transmission system is applied to the capacitive divider.
Voltage division:
- The capacitors divide the voltage according to their capacitance values. For example, if one capacitor is twice the value of another, it will drop less voltage.
Intermediate voltage sent to transformer:
- The reduced voltage is then fed into the primary winding of the transformer, along with the compensating reactor.
Electromagnetic transformation:
- The transformer converts the intermediate voltage into a standard low voltage suitable for protective relays or meters.
Output delivered:
- The low voltage output is supplied to instruments or relay systems with electrical isolation from the high-voltage line.

➤ CVT Key Features of the Working Principle:

Capacitance-based division: Ensures the voltage is safely stepped down in a controlled manner.
Electromagnetic isolation: Provides protection to sensitive equipment from high-voltage faults.
Phase compensation: Corrects phase shift errors due to capacitive effects.
Surge protection: Safeguards the system from lightning and switching transients.
Stable operation: Ensures reliable measurements and accurate system monitoring.

➤ CVT Applications:

High-voltage transmission lines (66 kV – 765 kV)
Metering and energy monitoring
Protection relay systems
Control circuits in substations
Signal isolation in electrical networks

CVT MCQ-

✅ Q1. What is the primary function of a Capacitive Voltage Transformer (CVT)?

A) To step up voltage
B) To measure current
C) To step down high voltage for metering and protection
D) To store electrical energy

✔ Correct Answer: C) To step down high voltage for metering and protection

Explanation:
A CVT is used in high-voltage systems to step down voltage to a measurable level. It provides voltage signals for metering, protection, and control systems. It also offers isolation between the high-voltage network and the low-voltage measuring devices.

✅ Q2. What is the main component that determines the voltage ratio in a CVT?

A) The magnetic core
B) The capacitance divider
C) The rotating armature
D) The rectifier bridge

✔ Correct Answer: B) The capacitance divider

Explanation:
The voltage ratio in a CVT is determined by the capacitance divider made up of series-connected capacitors. This divider reduces the high voltage in proportion before it's further processed by the transformer.

✅ Q3. Which of the following is a major advantage of using a CVT over a conventional electromagnetic potential transformer?

A) It can handle extremely low frequencies
B) It is lighter and cheaper at very high voltages
C) It provides higher current capacity
D) It doesn’t require grounding

✔ Correct Answer: B) It is lighter and cheaper at very high voltages

Explanation:
CVTs are more cost-effective and lighter compared to electromagnetic transformers, especially for very high voltage levels (like 220 kV and above). They are easier to install and maintain in high-voltage networks.

✅ Q4. Which component in the CVT compensates for phase displacement caused by the capacitive divider?

A) Core winding
B) Secondary transformer
C) Ferroresonance circuit
D) Compensating reactor

✔ Correct Answer: D) Compensating reactor

Explanation:
The capacitive divider causes phase shift. The compensating reactor is used to correct this phase displacement to ensure accurate voltage measurement and protection relay operation.

✅ Q5. For which of the following purposes is a CVT commonly used?

A) Power factor correction
B) Voltage regulation in distribution systems
C) Providing signals for protective relays
D) Generating reactive power

✔ Correct Answer: C) Providing signals for protective relays

Explanation:
A CVT is widely used to supply accurate voltage signals for protective relays, control circuits, and metering devices in high-voltage transmission systems. It ensures proper monitoring and protection of the grid.

✅ Q6. At what voltage level are CVTs most commonly used?

A) Below 33 kV
B) 66 kV – 765 kV
C) Only at 11 kV
D) 1 kV – 10 kV

✔ Correct Answer: B) 66 kV – 765 kV

Explanation:
CVTs are preferred in extra-high voltage (EHV) and ultra-high voltage (UHV) networks, typically from 66 kV up to 765 kV, because they are more economical and manageable than electromagnetic transformers at these levels.

✅ Q7. What type of error is commonly associated with CVTs?

A) Saturation error
B) Frequency error
C) Ratio and phase angle error
D) Thermal runaway error

✔ Correct Answer: C) Ratio and phase angle error

Explanation:
CVTs introduce ratio error (difference between actual and rated voltage ratio) and phase angle error due to the capacitive divider and compensation method. These errors are minimized through proper design and compensation.

✅ Q8. Which of the following components is responsible for improving the frequency response of a CVT?

A) Surge arrester
B) Compensating reactor
C) Capacitive divider
D) Oil-filled casing

✔ Correct Answer: B) Compensating reactor

Explanation:
The compensating reactor is used to counteract the effects of capacitance and improve the frequency response of the CVT. It helps maintain accuracy across a range of frequencies.

✅ Q9. What happens if the CVT is not properly grounded?

A) It will provide better signal
B) It can cause dangerous voltages to appear on the equipment
C) It will increase power output
D) It will operate normally without any effect

✔ Correct Answer: B) It can cause dangerous voltages to appear on the equipment

Explanation:
Improper grounding can lead to dangerous voltages on the equipment and create a hazard for personnel and devices. Proper grounding ensures safety and correct operation of the CVT.

✅ Q10. What phenomenon may occur in a CVT if it is exposed to overvoltages such as lightning strikes?

A) Ferroresonance
B) Superconductivity
C) Electrical damping
D) Inductive coupling

✔ Correct Answer: A) Ferroresonance

Explanation:
Ferroresonance is a nonlinear resonance phenomenon that can occur in CVTs due to overvoltages or switching transients. It may result in excessive overvoltages and lead to equipment damage if not properly controlled.

Capacitive Voltage Transformer (CVT)