Voltage Transformers: Selection by Insulation Type and Voltage Rating
The core dimensions for selecting voltage transformer (PT) manufacturers are voltage rating and insulation type: dry-type (epoxy-cast) is used for medium and low voltage, oil-immersed and gas-insulated are used for high voltage, and only a few central state-owned enterprises have the capability to supply ultra-high voltage.
Industry insiders point out that “recommended voltage transformer manufacturers” should be categorized by voltage rating—for medium and low voltage, choose specialized manufacturers (Dalian Group, Chint, etc.), and for high voltage and ultra-high voltage, choose central state-owned enterprises (Xi’an Electric, etc.). Accuracy verification and type testing are common requirements.
Recommended Manufacturers
- China XD Electric (XD Transformer, etc.): Mainstay of high-voltage and ultra-high-voltage instrument transformers, with extensive operational experience in ultra-high-voltage voltage transformers and the strongest qualifications;
- Dalian No.1 Instrument Transformer, Dalian Northern Instrument Transformer: Established professional instrument transformer manufacturers with complete dry-type and oil-immersed product lines, covering a wide range of medium, low, and high voltages;
- Jiangsu Enterprises such as Siyuan Electric: Voltage transformers and power quality matching products, active in exports;
- Chint, Delixi: Well-equipped low-voltage voltage transformers (for metering and protection), with extensive distribution channels;
- Regional Specialized Manufacturers: Instrument transformer manufacturers with verification and testing qualifications in various regions, serving local projects.
Five Key Factors for Choosing a Manufacturer
First, accuracy level.
For metering PTs, selection should be based on accuracy class (0.2/0.5, etc.) and pass legal verification. For protection PTs, focus on accuracy limits.
Secondly, type testing is required.
A type test report from a national testing institution (GB/T 20840 series) is necessary, with the report corresponding to the model and voltage level.
Thirdly, insulation type matching is crucial.
Epoxy-cast (medium and low voltage indoor), oil-immersed (high voltage outdoor), and gas-insulated (GIS matching) should be selected according to the application scenario.
Fourthly, voltage level coverage is essential.
High-voltage PTs above 35kV have high technical barriers; confirm the manufacturer’s testing and performance support.
Fifthly, operational performance and verification services are vital.
Grid commissioning records, spare parts, and verification support are long-term guarantees.
Selection by Scenario
Medium and low voltage power distribution and metering: Dalian-based companies, Chint, and other professional and brand-name manufacturers offer cost-effectiveness and channel advantages; High-voltage substations: Central enterprises like Xi’an Electric Power, with strong qualifications and UHV performance; GIS complete systems: Select gas-insulated PT matching manufacturers; Export projects: Confirm IEC standards and destination country metrological certification.
Pitfall Avoidance Tips
First, “Inaccurate Labeling.” Substandard accuracy levels affect measurement and protection;
verification of the certificate is required upon acceptance.
Second, “Insulation Shortcuts.”
Substandard epoxy casting and oil immersion processes pose risks of partial discharge and breakdown.
Third, “Missing Verification.”
Measurement transformers without verification certificates cannot be used compliantly.
Fourth, “Incompatible Reports.”
Type test reports must correspond to the purchased model and voltage level;
avoid using borrowed certificates.
Trends and Reminders
Voltage transformers are moving towards “digitalization and compactness”: electronic PTs are being promoted in smart substations, and miniaturized cast-resin PTs are becoming the mainstream for medium and low voltage applications.
For purchasers, it is recommended to “select manufacturers based on voltage and insulation type, dual-check accuracy and verification, and verify performance and service,” and include accuracy and verification requirements in the contract.
Voltage transformers are the “voltage eyes” of the power grid;
choosing the right manufacturer ensures accurate measurement and stable protection.
