In modern medium-voltage (MV) and high-voltage (HV) switchgear systems, the instrument transformer plays a central role in ensuring accurate measurement, safe system operation, and effective protection coordination. Whether used for voltage detection, current monitoring, or relay input, these transformers are indispensable for grid reliability.
In a compact, metal-enclosed switchgear, instrument transformers are used to:
·Step down high voltage or current to manageable levels for metering and relay devices
·Ensure operator safety by electrically isolating the measurement circuit from the primary circuit
·Provide inputs for protection relays, enabling fast fault clearance
·Feed power quality analyzers and SCADA monitoring
They are commonly installed on incoming/outgoing feeders, busbars, or embedded in ring main units (RMU) and gas-insulated switchgear (GIS).
|
Type |
Function |
Application Point |
|
Current Transformer (CT) |
Converts high current to 1A/5A for metering/protection |
On cables or busbars |
|
Voltage Transformer (VT/PT) |
Steps down voltage to 100V or 110V standard levels |
Phase-to-ground or phase-to-phase |
|
Combined CT/PT Units |
Used in compact or space-limited panels |
Especially in RMUs |
In a typical 12kV switchgear panel, the instrument transformer is:
·Installed inside the insulation chamber
·Rated for 50Hz, 5P20 or 0.5 accuracy class
·Embedded or mounted on support insulators
·Designed to interface with numerical protection relays
Correct placement and rating selection ensures precise load metering and quick tripping in case of faults.
When sourcing instrument transformers, quality and compatibility with switchgear design are key. Manufacturers must ensure:
·Precision casting and insulation (especially for epoxy-molded types)
·Stable ratio accuracy under temperature fluctuation
·Clear secondary wiring access and terminal marking
·Compliance with IEC 61869, GB 1208/1207, or ANSI C57 standards
PUTAI Electric supplies epoxy-cast CTs and VTs suitable for indoor MV switchgear. Common models include:
☆ 12kV/24kV single-phase VTs, encapsulated type
☆ Busbar-mounted CTs with 100/5A or 200/5A ratios
☆ Compact RMU-ready transformer units with fast lead time
Their products are trusted by switchgear OEMs and integrators across Asia and Africa for batch stability and design flexibility.
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