24kV Voltage Transformer (Indoor type)

24kV Voltage Transformer

24kV Indoor Voltage Transformer (VT), also known as an Indoor Potential Transformer (PT), is an instrument transformer designed to step down medium-voltage system voltages up to 24 kV into standardized low voltages for metering, protection, monitoring, and control. These transformers are commonly installed in indoor metal-clad switchgear, Ring Main Units (RMUs), and medium-voltage substations.

Main Functions
Voltage Measurement: Converts primary voltage to standardized secondary voltages (typically 100 V or 110 V) for measuring instruments.
Protection: Supplies accurate voltage signals to protection relays for overvoltage, undervoltage, directional, synchronization, and distance protection.
Electrical Isolation: Safely isolates low-voltage measuring and protection equipment from the medium-voltage network.

Typical Applications
·Indoor medium-voltage switchgear
·Ring Main Units (RMUs)
·Utility distribution substations
·Industrial power systems
·Commercial buildings
·Renewable energy plants (solar and wind)
·Mining, oil & gas, and manufacturing facilities

Typical Technical Specifications
·Rated Voltage: 24 kV
·Highest System Voltage: 24 kV or 25.8 kV
·Rated Frequency: 50 Hz / 60 Hz
·Rated Primary Voltage: 22 kV, 24 kV, or 22/√3 kV
·Rated Secondary Voltage: 100 V, 110 V, 100/√3 V, 110/√3 V
·Accuracy Class: 0.1, 0.2, 0.5, 1.0, 3P, 6P
·Rated Burden: 10 VA, 15 VA, 30 VA, 50 VA, 100 VA
·Insulation Type: Epoxy resin cast
·Cooling Method: Natural Air (AN)
·Installation: Indoor

Construction
A typical 24kV indoor voltage transformer includes:
·High-voltage primary winding
·One or more secondary windings
·Laminated silicon steel magnetic core
·Vacuum-cast epoxy resin insulation
·Primary terminal
·Secondary terminal box
·Mounting base
·Earthing terminal

The epoxy resin casting provides:
·Excellent dielectric insulation
·High mechanical strength
·Moisture and pollution resistance
·Low partial discharge
·Maintenance-free operation

Common Types
·Single-phase inductive voltage transformer
·Two-pole insulated voltage transformer
·Three-pole insulated voltage transformer
·Withdrawable (plug-in) voltage transformer
·Fuse-protected voltage transformer
·Dual-secondary voltage transformer for metering and protection

Advantages
·High measurement accuracy
·Reliable insulation performance
·Compact design for switchgear installation
·Maintenance-free service
·Long operational life
·High resistance to humidity and contaminants
·Excellent thermal and mechanical performance
·Suitable for continuous indoor operation

Applicable Standards
·IEC 61869-1 – Instrument Transformers – General Requirements
·IEC 61869-3 – Additional Requirements for Inductive Voltage Transformers
·IEEE C57.13 – IEEE Standard Requirements for Instrument Transformers

Typical Wiring
Primary Side
·Connected phase-to-phase or phase-to-earth on the 24 kV network.

Secondary Side
·Energy meters
·Voltmeters
·Protection relays
·Power quality analyzers
·SCADA and automation systems

Typical Applications by Industry
·Utility Distribution: Revenue metering and feeder protection
·Industrial Plants: Motor, transformer, and feeder protection
·Commercial Buildings: Medium-voltage distribution monitoring
·Wind Farms: Collector circuit voltage measurement
·Solar Power Plants: Inverter and feeder monitoring
·Mining: Underground and surface switchgear
·Oil & Gas: Process power distribution systems

Key Features
·Rated system voltage up to 24 kV
·Indoor epoxy resin cast construction
·High insulation reliability
·Precise voltage transformation for metering and protection
·Multiple secondary winding configurations
·Low partial discharge and high dielectric strength
·Compact, lightweight, and maintenance-free
·Compliant with IEC 61869 and IEEE C57.13 standards