123kV Capacitor Voltage Transformer

123kV CVT

123kV Capacitor Voltage Transformer (CVT), also called a Capacitive Voltage Transformer or Capacitor Potential Transformer (CPT), is a high-voltage instrument transformer used in 110kV-class transmission systems to reduce high system voltages to standardized low-voltage outputs for metering, protection, control, synchronization, and automation applications.

A CVT uses a capacitive voltage divider combined with an electromagnetic transformer unit to provide accurate voltage measurement and electrical isolation between the transmission system and secondary equipment.

Working Principle
A 123kV CVT operates through two main stages:

1. Capacitive Voltage Divider
The high voltage is divided by a series capacitor arrangement:
·C1: High-voltage capacitor element
·C2: Low-voltage capacitor element

2. Intermediate Transformer
·The intermediate transformer further reduces the voltage to a standard secondary output suitable for measuring and protection equipment.

Main Components
·High-voltage capacitor stack
·Capacitive voltage divider
·Intermediate transformer
·Compensation reactor
·Ferroresonance suppression circuit
·Damping circuit
·Oil-paper insulation system
·Porcelain or composite insulator housing
·Primary high-voltage terminal
·Secondary terminal box
·Grounding terminal
·Mounting frame

Typical Technical Specifications
·Highest System Voltage: 123 kV
·Rated Primary Voltage: 110 kV or 115 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: 230/550 kV (Typical)
·Installation: Outdoor
·Insulation Type: Oil-paper / composite insulation

Applications
A 123kV CVT is commonly installed in:
·110kV transmission substations
·Utility switching stations
·Power generation plants
·Renewable energy grid connection substations
·Industrial high-voltage substations
·Railway traction substations

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

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

Automation and Communication
Used in:
·SCADA systems
·Substation automation
·Remote monitoring
·Fault recording systems

Advantages
·Compact design compared with conventional inductive VT
·High insulation capability
·Reliable operation in outdoor environments
·Good transient voltage response
·Lower weight for transmission applications
·Suitable for protection and metering
·Long service life with minimal maintenance

Typical Secondary Outputs
Standard outputs include:
·100 V
·110 V
·100/√3 V
·110/√3 V

Connected equipment:
·Protection relays
·Energy meters
·Synchronizing devices
·SCADA/RTU systems
·Digital fault recorders
·Automation controllers

Common Standards
A 123kV 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 123kV Substation
·Busbar voltage measurement
·Transmission line voltage monitoring
·Protection relay voltage input
·Synchronizing circuits
·SCADA voltage acquisition
·Power system automation
·Fault and disturbance recording
·Energy metering

Key Features
·Designed for 123kV transmission systems
·High dielectric strength and insulation reliability
·Multiple secondary windings available
·Suitable for outdoor installation
·Stable voltage transformation performance
·Supports protection, control, and measurement functions

A 123kV Capacitor Voltage Transformer (CVT) is a critical component in modern transmission substations, providing accurate and isolated voltage signals for protection relays, metering equipment, and automation systems. Its compact structure and reliable performance make it widely used in 110kV-class power networks worldwide.