How does a Capacitive Voltage Transformer (CVT) measure high-voltage in AC systems?
1 Answer
A Capacitive Voltage Transformer (CVT) is a type of instrument transformer used to measure high voltages in AC systems. It is also known as a Capacitor Voltage Transformer or a Capacitor Coupled Voltage Transformer. The CVT operates based on the principle of capacitive voltage division, and it is commonly used for voltage measurement in high-voltage power systems such as substations.
Here's how a Capacitive Voltage Transformer works to measure high voltages in AC systems:
Basic Components: A CVT consists of a capacitance voltage divider, a core with primary and secondary windings, and a burden resistor. The core is generally made of high-grade insulation materials to withstand high voltage levels.
Capacitive Voltage Divider: The primary winding is connected across the high-voltage supply that needs to be measured. The primary winding of the CVT is capacitive, consisting of a series of high-voltage capacitor units. These capacitors have high capacitance values and are designed to handle the high voltage without breakdown.
Step-Down Ratio: The secondary winding is connected to a burden resistor and the measuring instruments (voltmeters or relays). The secondary winding is connected to the primary winding through the insulation, and there is no direct electrical connection between the primary and secondary circuits.
Capacitive Voltage Division: When the high-voltage AC is applied to the primary winding, it creates an electric field across the capacitive elements of the primary. This electric field generates an induced voltage in the secondary winding through the principle of capacitive voltage division. The secondary voltage is proportional to the primary voltage but at a much lower level due to the capacitive voltage divider.
Step-Down Voltage Output: The secondary voltage of the CVT is reduced compared to the primary voltage according to the capacitive voltage division formula. The step-down ratio is determined by the capacitance values of the capacitors in the primary winding. Typical step-down ratios are around 1000:1 or higher.
Burden Resistor: The secondary winding is connected to a burden resistor, which converts the secondary current into a measurable voltage. The voltage across the burden resistor is then measured by voltmeters or used for protective relaying purposes.
Isolation and Safety: Since there is no electrical connection between the primary and secondary circuits, the CVT provides isolation and safety in high-voltage measurement applications. The insulation between primary and secondary windings ensures that the high voltage on the primary side does not affect the secondary circuit.
Accuracy and Calibration: CVTs are designed to have high accuracy, and their performance can be calibrated to meet specific accuracy requirements in power system applications.
By utilizing the principle of capacitive voltage division and isolation between primary and secondary circuits, the Capacitive Voltage Transformer provides an accurate and safe means of measuring high voltages in AC systems, making it an essential component in high-voltage power systems for monitoring, control, and protection purposes.
Here's how a Capacitive Voltage Transformer works to measure high voltages in AC systems:
Basic Components: A CVT consists of a capacitance voltage divider, a core with primary and secondary windings, and a burden resistor. The core is generally made of high-grade insulation materials to withstand high voltage levels.
Capacitive Voltage Divider: The primary winding is connected across the high-voltage supply that needs to be measured. The primary winding of the CVT is capacitive, consisting of a series of high-voltage capacitor units. These capacitors have high capacitance values and are designed to handle the high voltage without breakdown.
Step-Down Ratio: The secondary winding is connected to a burden resistor and the measuring instruments (voltmeters or relays). The secondary winding is connected to the primary winding through the insulation, and there is no direct electrical connection between the primary and secondary circuits.
Capacitive Voltage Division: When the high-voltage AC is applied to the primary winding, it creates an electric field across the capacitive elements of the primary. This electric field generates an induced voltage in the secondary winding through the principle of capacitive voltage division. The secondary voltage is proportional to the primary voltage but at a much lower level due to the capacitive voltage divider.
Step-Down Voltage Output: The secondary voltage of the CVT is reduced compared to the primary voltage according to the capacitive voltage division formula. The step-down ratio is determined by the capacitance values of the capacitors in the primary winding. Typical step-down ratios are around 1000:1 or higher.
Burden Resistor: The secondary winding is connected to a burden resistor, which converts the secondary current into a measurable voltage. The voltage across the burden resistor is then measured by voltmeters or used for protective relaying purposes.
Isolation and Safety: Since there is no electrical connection between the primary and secondary circuits, the CVT provides isolation and safety in high-voltage measurement applications. The insulation between primary and secondary windings ensures that the high voltage on the primary side does not affect the secondary circuit.
Accuracy and Calibration: CVTs are designed to have high accuracy, and their performance can be calibrated to meet specific accuracy requirements in power system applications.
By utilizing the principle of capacitive voltage division and isolation between primary and secondary circuits, the Capacitive Voltage Transformer provides an accurate and safe means of measuring high voltages in AC systems, making it an essential component in high-voltage power systems for monitoring, control, and protection purposes.