145kV Capacitor Voltage Transformer

145kV CVT

145kV Capacitor Voltage Transformer (CVT), also known as a Capacitive Voltage Transformer or Capacitor Potential Transformer (CPT), is an extra-high-voltage instrument transformer used in 132kV/145kV-class transmission systems to reduce high system voltage to standardized low-voltage outputs for metering, protection, control, synchronization, and automation systems.

A CVT combines a capacitive voltage divider and an electromagnetic transformer unit to provide accurate voltage transformation and electrical isolation between the high-voltage network and secondary equipment.

Working Principle
A 145kV CVT works through two conversion stages:
1. Capacitive Voltage Divider
The capacitor divider reduces the high voltage through capacitive division:
·C1 – High-voltage capacitor section
·C2 – Low-voltage capacitor section

2. Intermediate Transformer
·The intermediate transformer converts the reduced voltage into standard secondary outputs required by protection and measurement devices.

Main Components
·High-voltage capacitor stack
·Capacitive voltage divider
·Intermediate transformer
·Compensation reactor
·Ferroresonance suppression circuit
·Damping resistor circuit
·Oil-paper insulation system
·Porcelain or composite silicone rubber insulator
·High-voltage terminal
·Secondary terminal box
·Grounding terminal
·Expansion chamber (oil-filled type)
·Steel mounting structure

Typical Technical Specifications
·Highest System Voltage: 145 kV
·Rated Primary Voltage: 132 kV or 138 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: 25–300 VA
·Voltage Factor: 1.2 continuous, 1.5 short time
·Insulation Level: 275/650 kV (Typical)
·Installation: Outdoor
·Insulation Type: Oil-paper / composite insulation

Applications
A 145kV CVT is widely used in:
·132kV transmission substations
·Utility switchyards
·Power generation plants
·Renewable energy grid connection stations
·Industrial EHV substations
·Railway traction substations
·Grid monitoring systems

Main Functions
1. Voltage Measurement
Provides accurate voltage signals for:
·Revenue metering
·Energy management systems
·Digital meters
·Power quality monitoring equipment

2. Protection Applications
Provides voltage inputs for:
·Distance protection
·Overvoltage protection
·Undervoltage protection
·Synchronizing protection
·Auto-reclosing systems
·Fault recording

3. Automation and Monitoring
Used in:
·SCADA systems
·Substation automation systems
·RTU equipment
·Digital protection systems

Advantages
·Compact design compared with traditional inductive VT
·High insulation capability for transmission systems
·Reliable outdoor operation
·Good transient response performance
·Suitable for protection and measurement
·Long service life
·Low maintenance requirements
·Stable voltage transformation characteristics

Typical Secondary Outputs
Common secondary voltages:
·100 V
·110 V
·100/√3 V
·110/√3 V

Secondary circuits supply:
·Protection relays
·Energy meters
·Synchronizing devices
·SCADA systems
·Digital fault recorders
·Automation controllers

Common Standards
A 145kV capacitor voltage transformer is manufactured and tested 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 145kV Substation
·Busbar voltage measurement
·Transmission line voltage monitoring
·Protection relay voltage input
·Synchronization circuits
·SCADA voltage acquisition
·Power system automation
·Energy metering
·Fault and disturbance recording

Key Features
·Designed for 145kV transmission networks
·High dielectric strength and mechanical reliability
·Multiple secondary windings available
·Suitable for harsh outdoor environments
·Supports metering, protection, and automation
·Compatible with modern digital substations

A 145kV Capacitor Voltage Transformer (CVT) is an essential component in high-voltage transmission substations, providing accurate voltage measurement and reliable protection signals. Its compact structure, insulation performance, and ability to support advanced power system monitoring make it widely used in 132kV/145kV-class transmission networks.