Product Overview
The LJZN1(2)-10 Current Transformer is an SGCC-standard, fully enclosed, post-type cast-resin current transformer designed for indoor 10 kV AC power systems with a maximum system voltage of 12 kV.
Developed and manufactured in accordance with the technical specifications of the State Grid Corporation of China (SGCC), the transformer uses an epoxy resin vacuum-casting process. It features a busbar-type primary winding and multiple secondary windings for metering and protection circuits.
The product meets SGCC requirements for metering accuracy, protection performance, short-time thermal current, dynamic current withstand capability, and standardized mounting dimensions. It is widely used in SGCC-standard indoor medium-voltage switchgear, box-type substations, distribution stations, and switching stations.
The transformer provides high-accuracy current measurement, energy metering, relay protection, and current signal acquisition for standardized 10 kV distribution systems.
Product Features
SGCC-Standard Electrical Performance
- High-accuracy metering winding:
The metering winding provides stable and precise error characteristics and complies with Class 0.2S and Class 0.5 energy-metering requirements. It supports accurate and reliable energy measurement in SGCC-standard metering systems. - Reliable protection characteristics:
The protection winding provides sufficient accuracy limit factors, including 5P20 and 10P20, to ensure reliable relay protection operation during system short-circuit faults. It helps prevent incorrect operation and failure to trip. - High short-time thermal and dynamic current withstand capability:
The short-time thermal current and dynamic current parameters are designed in accordance with SGCC requirements. The transformer can withstand current stresses caused by system short-circuit faults and is suitable for distribution systems with high short-circuit capacity. - Low partial discharge:
The advanced casting process limits partial discharge to no more than 10 pC. This meets SGCC insulation-performance requirements and helps reduce long-term insulation ageing.
Insulation and Structural Features
- Epoxy resin cast insulation:
The transformer is vacuum-cast using high-quality epoxy resin. The solid insulation contains no internal air gaps and provides excellent dielectric performance. - Suitable for 12 kV systems:
The transformer can withstand the operating voltage, power-frequency withstand voltage, and lightning impulse withstand voltage requirements of 10 kV systems with a maximum system voltage of 12 kV. - Fully enclosed post-type structure:
The primary and secondary windings are enclosed within the integrated cast-resin body, with no exposed internal live components. - IP20 protection rating:
The product provides an IP20 protection rating and is suitable for installation inside indoor switchgear, helping reduce the ingress of dust and moisture. - SGCC-standard mounting dimensions:
The compact structure and mounting dimensions are compatible with SGCC-standard switchgear, including SGCC versions of KYN28 metal-clad switchgear. - Convenient installation and replacement:
Standardized dimensions support batch installation, direct replacement, equipment acceptance, and routine maintenance. - Standardized secondary terminals:
The secondary terminals are protected by a transparent cover and clearly marked in accordance with SGCC secondary-circuit wiring requirements. - Reduced wiring risk:
The terminal arrangement helps prevent incorrect connection and short circuits while reducing the risk of accidental secondary-circuit opening.
Operation and Maintenance Features
- Low-maintenance operation:
The epoxy resin body provides high mechanical strength, impact resistance, and ageing resistance. Its oil-free structure eliminates leakage and routine insulating-oil maintenance. - Wide operating temperature range:
The transformer can operate at ambient temperatures from -30°C to +70°C. The epoxy resin maintains stable insulation and mechanical properties without becoming brittle or deformed. - Suitable for different regional environments:
The wide temperature range meets SGCC environmental adaptability requirements for equipment used in different climatic regions. - Traceable quality control:
Production, testing, and factory inspection are carried out under standardized quality-control procedures. - Complete quality documentation:
Product certificates, factory test reports, and SGCC grid-entry inspection documentation can be provided for equipment acceptance and asset management.
Technical Specifications
Electrical Parameters
| Parameter | Specification |
|---|---|
| Applicable System Voltage | 10 kV AC, Um = 12 kV |
| Rated Frequency | 50 Hz |
| Rated Primary Current | 10–2,000 A, SGCC-standard ratings |
| Rated Secondary Current | 5 A or 1 A, SGCC-standard options |
| Metering Accuracy Class | 0.2S / 0.5 |
| Protection Accuracy Class | 5P10 / 10P10 / 5P20 / 10P20 |
| Power-Frequency Withstand Voltage | 42 kV for 1 minute, phase-to-earth and phase-to-phase, without breakdown |
| Lightning Impulse Withstand Voltage | 75 kV peak, without breakdown |
| Partial Discharge | ≤10 pC |
| Short-Time Thermal Current (Ith) | 20 times the rated current for 1 second |
| Dynamic Current (Idyn) | 2.5 times Ith |
Structural and Material Parameters
| Parameter | Specification |
|---|---|
| Insulating Medium | Cast epoxy resin |
| Protection Rating | IP20 |
| Installation Type | Indoor post-type bolt mounting with SGCC-standard dimensions |
| Thermal Class | Class B, 130°C |
Environmental Parameters
| Parameter | Specification |
|---|---|
| Installation Altitude | ≤2,000 m; high-altitude versions available |
| Operating Temperature | -30°C to +70°C |
| Storage Temperature | -40°C to +85°C |
| Relative Humidity | ≤95%, non-condensing |
Applicable Standards
| Category | Standard |
|---|---|
| National Standards | GB 1208, Current Transformers |
| National Standards | GB/T 20840.1, Instrument Transformers—Part 1: General Requirements |
| SGCC Requirements | State Grid Corporation of China technical specifications for current transformers |
| SGCC Requirements | SGCC grid-entry inspection and acceptance specifications |
Applications
Applicable Voltage Level
The LJZN1(2)-10 Current Transformer is suitable for indoor 10 kV AC power systems with a maximum system voltage of 12 kV.
Applicable Systems
The product is designed for standardized 10 kV distribution systems operated or specified according to State Grid Corporation of China requirements.
Typical Applications
- Current measurement, energy metering, and relay protection in SGCC-standard KYN28 indoor medium-voltage switchgear
- SGCC-standard box-type substations
- Distribution stations and switching stations
- Standardized 10 kV distribution systems in industrial and mining enterprises
- Commercial buildings and industrial parks
- Current monitoring and control in power automation systems
- Applications requiring compatibility with SGCC automation interfaces
- Incoming, outgoing, metering, and protection panels in standardized medium-voltage switchgear
Main Functions
The current transformer converts the high primary current in the power system into a standardized secondary current of 5 A or 1 A at a specified ratio.
It supplies current signals to:
- Energy meters
- Measuring instruments
- Relay protection devices
- Monitoring equipment
- Control systems
- Power automation equipment
The transformer also provides electrical isolation between the primary power circuit and the secondary metering and protection circuits, helping protect connected equipment and operating personnel.
Its standardized electrical and mechanical design supports the operating, acceptance, and maintenance requirements of SGCC-standard distribution systems.
Operating Conditions
Normal Operating Conditions
- Installation altitude: no more than 2,000 m
- Ambient temperature: -30°C to +70°C
- Severe or sudden temperature changes should be avoided
- Relative humidity: no more than 95%, non-condensing
- The environment should be free from corrosive gases
- Flammable or explosive substances are not permitted
- Severe vibration and mechanical impact should be avoided
- Significant dust and salt-spray contamination should be avoided
- Indoor post-type installation
- Direct sunlight, rain, and condensation should be avoided
- Installation must comply with SGCC requirements for equipment inside medium-voltage switchgear
Special Operating Conditions
Customized products are required for:
- Installation altitudes above 2,000 m
- Ambient temperatures outside the range of -30°C to +70°C
- Severe pollution or salt-spray environments
- Chemically corrosive environments
- Applications involving strong vibration or mechanical impact
- Non-standard current ratios
- Special accuracy classes
- Non-standard mounting dimensions
Installation and Maintenance
Installation Requirements
- Pre-installation inspection:
Inspect the current transformer and confirm that the epoxy resin body is free from cracks, bubbles, mechanical damage, and other visible defects. Check that all terminal markings are clear and that the supplied accessories are complete. Verify that the model, specifications, current ratio, and accuracy classes comply with the system design and applicable SGCC requirements. Confirm that the required SGCC grid-entry inspection report and supporting quality documents are available. - Mounting:
Position the transformer at the specified location inside the switchgear and secure it with bolts through the mounting holes in the base. Ensure that the transformer is firmly installed without looseness or displacement. The mounting surface should be level to prevent uneven mechanical stress. Installation must comply with SGCC requirements for equipment positioning and mounting inside switchgear. - Primary-side connection:
Connect the primary busbar according to the system design. Ensure close contact between the busbar and the transformer primary terminals. Tighten all bolts securely to prevent overheating caused by poor electrical contact. The primary connection must comply with the applicable SGCC primary-circuit wiring requirements. - Secondary-side connection:
Connect the secondary terminals according to their markings. Metering and protection windings must be wired separately and correctly in accordance with the SGCC secondary-circuit wiring requirements. The secondary circuits must never be left open while the primary circuit is energized. One point of each required secondary circuit must be reliably earthed to prevent hazardous overvoltage. - Insulation inspection:
After installation, measure the insulation resistance between:- Primary winding and earth
- Secondary windings and earth
- Primary winding and secondary windings
Maintenance Requirements
- Regularly inspect the epoxy resin body for cracks, mechanical damage, discharge marks, and contamination.
- Check the terminals for looseness, oxidation, and abnormal heating.
- Carry out routine inspections in accordance with the applicable SGCC equipment inspection requirements.
- Regularly inspect the primary busbar and secondary wiring to ensure that all connections remain secure.
- Check for overheating, discoloration, unintended open circuits, and short-circuit risks.
- Confirm that the secondary-circuit earthing remains reliable.
- Periodically test the insulation resistance and current-ratio error.
- Verify that the metering and protection accuracy remains within the specified limits.
- Carry out metering and protection verification according to the applicable SGCC inspection requirements.
- Clean dust and contamination from the transformer surface.
- Prevent oil and corrosive substances from contacting the epoxy resin body.
- Keep the equipment clean and dry.
- If cracking, electrical discharge, overheating, or excessive measurement error is detected, immediately de-energize and inspect the equipment.
- Replace defective equipment where necessary in accordance with the applicable equipment-defect management procedures.
Precautions
- The secondary windings must never be left open while the primary circuit is energized. An open secondary circuit may generate a hazardous overvoltage of several thousand volts, creating a serious risk to equipment and personnel.
- During maintenance, the secondary windings must be securely short-circuited and earthed before disconnection in accordance with the applicable secondary-circuit safety procedures.
- Avoid impact or collision with the epoxy resin body during transportation and installation. Mechanical damage may crack the insulation and affect equipment acceptance.
- The equipment must be reliably earthed. The grounding terminal on the metal base must be securely connected to the switchgear grounding busbar.
- Store the product in a dry, ventilated, and shaded environment. Avoid direct sunlight, high temperatures, moisture, compression, and mechanical impact.
- Installation, commissioning, and maintenance must be carried out by qualified electrical personnel in accordance with applicable electrical safety procedures and SGCC operation and maintenance requirements.
Standard Supply List
| No. | Item | Function |
|---|---|---|
| 1 | LJZN1(2)-10 SGCC-Standard Current Transformer | Main device for current transformation and electrical isolation, designed to SGCC requirements |
| 2 | Mounting Bolts and Washers | Used to secure the transformer and match SGCC-standard mounting dimensions |
| 3 | Transparent Secondary Terminal Cover | Protects the secondary terminals against incorrect connection and short circuits and supports standardized secondary-circuit protection |
| 4 | Product Instruction Manual | Provides installation, operation, maintenance, and SGCC-standard mounting guidance |
| 5 | Product Certificate, Factory Test Report, and SGCC Grid-Entry Inspection Report | Provide product quality and performance documentation for SGCC equipment acceptance |
Applicable Standards and Certification
The product complies with the following standards and technical requirements:
- GB 1208, Current Transformers
- GB/T 20840.1, Instrument Transformers—Part 1: General Requirements
- State Grid Corporation of China technical specifications for current transformers
- SGCC grid-entry inspection and equipment acceptance requirements
The product has passed the applicable type tests and SGCC grid-entry inspections. Its performance meets the operating requirements of SGCC-standardized 10 kV distribution systems.
