Voltage Transformer Selection Guide for Medium and High Voltage Systems

07 15, 2025

Posted By: Peter

In modern power distribution and protection systems, the voltage transformer (VT) is an essential component for converting high voltage into standardized low voltage levels for safe metering and relay operation. It is widely used in switchgear, substations, and ring main units (RMUs) across 10kV to 40.5kV networks.

This article summarizes key VT models and compares performance parameters to help engineers and buyers choose the right solution for their system.

Common VT Models and Applications

Model Type	Rated Voltage	Construction	Typical Application
JDZX9-10	10kV	Epoxy cast, single-phase	Distribution cabinets, cable boxes
JDZ(X)11-12	12kV	Drawer or detachable type	MV switchgear, OEM panels
JDZ-35	35kV	Gas or dry type	HV substation, compact transformer stations
JDZXW-24	24kV	Anti-condensation design	High humidity/coastal areas
JDZ(X)F Series	10–40.5kV	Outdoor weatherproof	RMUs, outdoor substations

voltage-transformer-selection-guide-for-medium-and-high-voltage-systems

Key Parameters for Voltage Transformer Selection

Rated Voltage Ratio: e.g., 10kV/100V — match with system primary voltage and secondary control devices

Accuracy Class: Commonly 0.5, 1.0, or 3P — influences metering accuracy and relay sensitivity

Insulation Type: Epoxy resin casting is standard; oil-immersed or SF6 for special applications

Withstand Voltage: Including power frequency and lightning impulse — ensure IEC compliance

Thermal Class and Pollution Resistance: Critical for demanding environments

VT Application in Switchgear and Substations

Ring Main Units (RMUs): Phase voltage monitoring and fault protection

GIS Systems: Compact embedded VT designs enable high accuracy in small spaces

Transformer Secondary Circuits: Voltage protection coordination

MV/HV Metering Systems: Accurate energy billing and power quality diagnostics

PUTAI Electric – VT Manufacturer Recommendation

PUTAI Electric manufactures a full range of epoxy cast voltage transformers from 10kV to 35kV, including models like JDZX9, JDZ11, and JDZXF. These units are widely used by switchgear OEMs and contractors for their:

☆Reliable epoxy insulation, resistant to cracking and arc tracking

☆Stable accuracy (0.5/3P dual-class options available)

☆Flexible mounting (wall, base, or embedded installation)

☆Short lead times for stocked models and support for OEM batch customization

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