Current Transformer

The core conversion function from high voltage to low voltage

In high-voltage power systems, directly measuring large currents is not only dangerous but also difficult to achieve. This Current Transformer serves as the core conversion component, undertaking the crucial task of converting the large current on the high-voltage side into a standard low-voltage small current for use by instruments and protection devices.

Standardized signal output: It can precisely convert currents of several hundred amperes or even higher from the high voltage side into a standard 5A small current, for use by meters and protection devices.

Dual functions of measurement and protection: It provides precise measurement signals for metering instruments and action signals for relay protection devices, ensuring that the circuit can be quickly disconnected in case of a fault.

System complementarity: It complements the function of voltage transformers and together forms the standard configuration of the high-voltage distribution system, serving as the cornerstone for ensuring the safe operation of the power grid.

Product Parameter

High-precision measurement and metering performance

For power metering and protection, data accuracy is of utmost importance. This Current Transformer achieves industry-leading precision control and can meet stringent metering requirements.

Extremely low measurement error: We offer two high-precision grades, 0.2 class and 0.5 class, which can accurately capture current changes and ensure the authenticity and reliability of metering data.

Wide adaptability: Whether for power energy metering in trade settlement or current measurement for system monitoring, it can provide stable and consistent high-precision data.

Suitable for harsh environments: In those scenarios where measurement accuracy is extremely critical, such as precise metering and critical node protection.

Sturdy and durable fully-sealed protection design

Considering that high-voltage equipment often needs to operate in complex outdoor or industrial environments, we have adopted a fully-sealed structural design to ensure the long-term stability of the equipment under harsh conditions.

High insulation performance: The Current Transformer uses specialized high-voltage insulation protection materials, ensuring reliable insulation performance and effectively preventing the risk of high-voltage breakdown, thereby safeguarding the safety of personnel and equipment.

Waterproof and dustproof capability: The fully-sealed structure gives it excellent waterproof and dustproof capabilities, fully adapting to outdoor environments and eliminating the concern of erosion by rain or accumulation of dust causing malfunctions.

Low failure rate operation: The sturdy sealing design significantly reduces the equipment failure rate, decreases maintenance costs, and ensures the long-term stable operation of the power system.

Flexible and adaptable engineering installation solution

To meet the installation requirements of various power engineering projects, this Current Transformer has been designed with full consideration of the convenience and universality of installation.

Standardized installation interface: The product design complies with industry standards and can be directly installed in switchgear such as high-voltage cabinets and ring-main units, without the need to modify the cabinet structure.

Widely applicable voltage levels: It supports rated voltages of 10KV and 35KV, and the rated current ratio covers a wide range from 5/5 to 2500/5, capable of adapting to various high-voltage distribution scenarios.

Customized services: We offer customization for current ratio and accuracy. Based on your specific high-voltage requirements, we can create an exclusive current transformer solution.

Application Scenarios and Application Domains

High-voltage power distribution system: Used for current measurement and monitoring in high-voltage distribution cabinets to ensure power distribution safety.

Substation project: Undertakes current measurement and relay protection tasks in substations, safeguarding the power grid hub.

Photovoltaic power generation system: Used for high-voltage current measurement and protection in photovoltaic booster stations, facilitating the grid connection of clean energy.

High-voltage engineering project: Current measurement and monitoring in various high-voltage projects, providing precise data support.

Quality Commitment and Service of the Source Factory

As a professional power equipment manufacturer in China, Junray Electrical strictly follows the national standards for current transformers in its production, and is committed to providing customers with high-quality Current Transformers.

Strict factory tests: Every transformer must undergo strict accuracy tests, withstand voltage tests and insulation tests before leaving the factory to ensure stable and safe operation.

Strong manufacturing capabilities: Relying on our own factories and mature production processes, we can guarantee the consistency and reliability of the products, meeting the needs of large-scale engineering procurement.

Professional technical support: We provide comprehensive after-sales service and technical support, answering your questions at any time and safeguarding your power projects.

Frequently Asked Questions

1. Is this Current Transformer suitable for outdoor installation?

Absolutely. The product adopts a fully sealed structure and has excellent waterproof and dustproof performance, which enables it to adapt to various harsh outdoor environments. There is no need to worry about water or dust entering and affecting the operation.

2. What are the differences between precision grades 0.2 and 0.5?

The measurement error of grade 0.2 is smaller and the accuracy is higher. It is usually used in trade settlement scenarios with extremely high measurement requirements. Grade 0.5 has slightly lower accuracy and is suitable for general industrial measurements and protection circuits. You can choose based on your actual needs.

3. Do you offer non-standard customization?

Junray Electrical has a professional technical team that supports customization of parameters such as current ratio and accuracy level. We can create exclusive products based on your specific high-voltage requirements, ensuring perfect compatibility with special scenarios.

Retrofit Case Study

I. Project Overview

This project involves the remediation and retrofit of equipment at a 110kV urban core substation. The existing cast-resin current transformers (CTs) in the 10kV feeder bays had been in service for over 12 years, enduring long-term load fluctuations, grid harmonics, and cyclic temperature and humidity changes. During operation, issues such as sampling data drift, abnormal protection sampling, and overheating (detected via infrared thermography) occurred frequently. These problems caused imbalances in monitored current and power data and posed significant safety risks—including protection failure to operate, maloperation, and high-voltage generation due to secondary circuit open-circuits—thereby severely compromising regional power supply reliability.

To thoroughly eliminate risks associated with aging equipment and to enhance metering accuracy and protection reliability, all substandard and aging CTs across the substation were replaced with high-precision, high-insulation, and aging-resistant units. Concurrently, secondary circuit rectification, polarity verification, primary current injection testing, and protection setting verification were performed to ensure the safe and stable operation of the power grid.

II. Issues Prior to Retrofit

Internal insulation aging and severe partial discharge: Long-term operation of the old CTs led to coil insulation embrittlement and moisture ingress; internal partial discharge occurred, and test results for gas content and insulation resistance failed to meet standards.

Sampling accuracy drift and three-phase data imbalance: Magnetic performance of the iron cores degraded, resulting in errors exceeding limits under both light and heavy load conditions; metering was inaccurate, and significant current fluctuations were observed in the monitoring system.

Significant secondary circuit risks: Non-standard wiring at old terminal blocks and failure to short-circuit/ground spare windings created major risks of high-voltage generation and terminal ablation caused by arcing during secondary open-circuit conditions.

Poor protection reliability: Inter-turn insulation defects in the CTs caused sampling distortion, leading to maloperation or failure to operate of line protection systems, thereby threatening the safety of line equipment.

Inability to fundamentally resolve O&M risks: Equipment had exceeded its service life and exhibited multiple hotspots during infrared thermography; routine maintenance and testing could not thoroughly eliminate the risks posed by internal aging. III. Equipment Configuration Plan

Based on the substation's primary equipment parameters, protection and metering requirements, and State Grid equipment standardization specifications, all 10kV medium-voltage current transformers (CTs) will be replaced. The configuration features independent windings for protection and metering, a high-precision and low-magnetic-saturation structure, and strict adherence to standardized secondary circuit installation practices.

Core Equipment Parameters

Model: LZZBJ9-10 Indoor Medium-Voltage Current Transformer

Rated Voltage: 10kV (compatible with the substation's 10kV distribution system)

Transformation Ratio: 600/5A (matched to feeder load)

Accuracy Class: Metering Class 0.2S; Protection Class 5P20 (meeting dual requirements for high-precision metering and accurate protection)

Structural Characteristics: Fully cast insulation, aging-resistant, low magnetic saturation, and resistant to harmonic interference

Secondary Circuit Specifications: All spare windings are reliably short-circuited and grounded to eliminate the risk of high voltage caused by secondary open circuits

Test Items: Post-replacement polarity check, transformation ratio test, insulation test, primary current injection test, and protection relay operation test

Functions/Applications: Line current sampling, energy metering, overload/short-circuit protection, and backend data monitoring

IV. Construction and Application Highlights

Independent dual-winding design with clear functional separation: The metering winding ensures precise, error-free energy measurement, while the protection winding ensures reliable operation during faults; the two operate independently without mutual interference, ensuring high safety.

Low magnetic saturation and stable sampling: High-quality core materials provide resistance to harmonics and overload surges, ensuring excellent sampling linearity across light-load, heavy-load, and fault conditions.

Complete elimination of secondary open-circuit hazards: Strict adherence to short-circuiting and grounding protocols for secondary windings and the rectification of outdated, non-compliant wiring eliminate the root causes of arcing, insulation breakdown, and high-voltage injury risks.

Excellent insulation performance suitable for long-term operation: A new epoxy resin cast structure offers moisture, dust, and aging resistance, effectively preventing partial discharge and inter-turn short-circuit risks.

Comprehensive testing and compliant acceptance: A full suite of post-replacement electrical tests and operation checks confirms compliance; data aligns precisely with backend systems, fully meeting State Grid acceptance standards. V. Operational Performance After Retrofitting

Precise and stable metering data: Three-phase currents are balanced, and data remains free from drift or fluctuation; metering errors are kept within standard limits, ensuring accurate and reliable line loss statistics.

Sensitive and reliable protection: Fault sampling for short-circuits and overloads is accurate and authentic; the protection system operates correctly without false trips or failures to trip, significantly enhancing the safety and protection capabilities of line equipment.

Elimination of major safety hazards: High-risk defects—such as insulation aging, partial discharge, secondary circuit open-circuits, and terminal arcing—have been completely eradicated, and equipment temperature rise during operation remains within normal limits.

Accurate and valid backend monitoring data: Telemetry and telesignaling data are transmitted in real-time with high precision, enabling O&M personnel to accurately assess load conditions and fault statuses.

Upgraded equipment service capabilities: The new equipment offers superior resistance to aging, interference, and mechanical shock, meeting the requirements for long-term, safe, and stable substation operation.

VI. Case Summary

Medium-voltage current transformers (CTs) are core sensing components in substations, medium-voltage switchgear, line protection systems, and energy metering setups, playing a dual role in data acquisition and protection triggering. Aging CTs are prone to issues such as insulation degradation, magnetic saturation, and secondary circuit defects, which can lead to metering inaccuracies, protection malfunctions, and high-voltage safety incidents. This retrofit project—involving the installation of new, high-precision CTs, standardized secondary circuit workmanship, and comprehensive testing and calibration—has effectively improved grid metering accuracy and protection reliability, serving as a model standardized project for hazard remediation and quality/efficiency enhancement in substation equipment.