12kV Indoor Voltage Transformer (VT), also known as a Potential Transformer (PT), is an instrument transformer designed to accurately step down medium-voltage system voltages (up to 12 kV) to standardized low voltages (typically 100 V, 110 V, or √3-based values) for metering, protection, and monitoring in indoor switchgear.
Main Functions
Voltage Measurement: Supplies accurate voltage signals to energy meters and measuring instruments.
Protection: Provides voltage inputs to protection relays for overvoltage, undervoltage, directional, synchronization, and distance protection.
Electrical Isolation: Electrically isolates secondary equipment from the high-voltage network, improving personnel and equipment safety.
Typical Applications
·Medium-voltage switchgear
·Ring Main Units (RMUs)
·Industrial substations
·Commercial buildings
·Renewable energy plants
·Power distribution networks
·Mining and manufacturing facilities
Typical Technical Specifications
·Rated Voltage: 12 kV
·Highest System Voltage: 12 kV or 17.5 kV
·Rated Frequency: 50 Hz / 60 Hz
·Rated Primary Voltage: 11 kV, 12 kV, or 11/√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 Level: According to IEC/IEEE standards
·Cooling: Natural Air (AN)
·Installation: Indoor
Construction
A typical indoor 12 kV voltage transformer consists of:
·Primary winding
·Secondary winding(s)
·Laminated silicon steel core
·Epoxy resin cast insulation
·High-voltage terminal
·Secondary terminal box
·Mounting base
·Earthing terminal
The transformer is usually vacuum-cast in epoxy resin, providing excellent dielectric strength, moisture resistance, mechanical robustness, and minimal maintenance.
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
Advantages
·High measurement accuracy
·Excellent insulation performance
·Compact and lightweight
·Maintenance-free operation
·Long service life
·High mechanical strength
·Flame-retardant epoxy resin insulation
·Suitable for harsh industrial environments
Applicable Standards
·IEC 61869-1 – General requirements for instrument transformers
·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-ground on the 12 kV network.
Secondary Side
Connected to:
·Energy meters
·Voltmeters
·Protection relays
·Power quality analyzers
·SCADA and automation systems
Typical Applications by Industry
·Utility Substations: Revenue metering and protection
·Manufacturing Plants: Motor and feeder protection
·Commercial Buildings: Distribution monitoring
·Wind Farms: Collector system measurement
·Solar Power Plants: Inverter and feeder protection
·Mining: Distribution switchgear
·Oil & Gas: Process power distribution
Key Features
·Rated system voltage up to 12 kV
·Indoor epoxy resin cast construction
·High insulation reliability
·Accurate voltage transformation
·Multiple secondary winding options
·Suitable for metering and protection
·Low partial discharge
·Maintenance-free throughout its service life