72.5kV Capacitor Voltage Transformer (CVT), also known as a Capacitive Voltage Transformer (CVT) or Capacitor Potential Transformer (CPT), is a high-voltage instrument transformer designed to reduce transmission system voltages up to 72.5 kV to standardized low-voltage signals for metering, protection, control, and power system automation.
A CVT combines a capacitive voltage divider with an electromagnetic transformer unit to provide accurate voltage transformation while maintaining electrical isolation between the high-voltage system and secondary equipment.
Working Principle
A 72.5kV CVT consists of a capacitor divider and an intermediate transformer.
1. Capacitive Voltage Divider
Two capacitor sections divide the high voltage:
·C1 – High-voltage capacitor section
·C2 – Low-voltage capacitor section
2. Intermediate Transformer
·The intermediate transformer converts the reduced voltage into standard secondary outputs.
Main Components
·High-voltage capacitor stack
·Capacitive voltage divider
·Intermediate transformer
·Compensation reactor
·Ferroresonance suppression circuit
·Damping resistor network
·Insulating oil system
·Porcelain or composite insulator housing
·Primary terminal
·Secondary terminal box
·Grounding terminal
·Mounting frame
Typical Technical Specifications
·Highest System Voltage: 72.5 kV
·Rated Primary Voltage: 66 kV or 69 kV
·Rated Secondary Voltage: 100 V, 110 V, 100/√3 V, 110/√3 V
·Frequency: 50 Hz / 60 Hz
·Accuracy Class: 0.2, 0.5, 1.0, 3P, 6P
·Rated Burden: 25–200 VA
·Voltage Factor: 1.2 continuous, 1.5 short time
·Insulation Level: 140/325 kV (Typical)
·Installation: Outdoor
·Insulation Type: Oil-paper / composite insulation
Applications
A 72.5kV CVT is commonly used in:
·Transmission substations
·Utility switching stations
·Industrial high-voltage systems
·Renewable energy substations
·Wind farm grid connections
·Solar power plants
·Railway electrification systems
Main Functions
Voltage Measurement
Provides accurate voltage signals for:
·Energy meters
·Digital measuring devices
·Power quality analyzers
Protection
Provides voltage inputs for:
·Overvoltage protection
·Undervoltage protection
·Distance protection
·Synchronizing protection
·Auto-reclosing systems
System Automation
Used for:
·SCADA monitoring
·RTU systems
·Substation automation
·Fault recording
Advantages
·Compact design compared with traditional inductive VT at higher voltages
·Reliable voltage transformation
·Excellent insulation performance
·Good transient response
·Suitable for outdoor transmission applications
·Reduced size and weight
·Long service life
·Low maintenance requirements
Typical Secondary Outputs
Common outputs include:
·100 V
·110 V
·100/√3 V
·110/√3 V
Connected equipment:
·Protection relays
·Metering systems
·Synchronizing relays
·SCADA systems
·Digital fault recorders
·Automation controllers
Common Standards
A 72.5kV capacitor voltage transformer is designed according to:
·IEC 61869-5 – Additional requirements for Capacitor Voltage Transformers
·IEC 61869-1 – General requirements for instrument transformers
·IEEE C57.13 – Instrument Transformer Standards
Typical Applications in a 72.5kV Substation
·Busbar voltage measurement
·Transmission line monitoring
·Protection relay voltage input
·Synchronizing circuits
·SCADA voltage acquisition
·Power system automation
·Fault and disturbance recording
A 72.5kV Capacitor Voltage Transformer (CVT) is an important component in high-voltage substations, providing accurate voltage measurement, electrical isolation, and reliable protection signals for modern transmission and distribution networks. Its compact structure and excellent performance make it widely used in 66kV-class and 72.5kV-class power systems.