Product Overview
The LZZBJ9-10C Current Transformer is a fully enclosed, post-type current transformer designed for indoor 10 kV AC power systems with a maximum system voltage of 12 kV.
Manufactured using an epoxy resin vacuum-casting process, the product is available with a busbar-type or through-type primary winding, while the secondary windings are wound with enamelled copper wire. It features multiple secondary winding outputs, high short-time thermal and dynamic current withstand capability, and stable accuracy characteristics.
The current transformer can simultaneously meet the requirements of current measurement, energy metering, and multi-circuit relay protection. It is widely used in indoor medium-voltage switchgear, box-type substations, distribution stations, and other power distribution equipment.
Product Features
Insulation and Electrical Performance
- Epoxy resin cast insulation: Manufactured through vacuum casting using high-quality epoxy resin. The solid insulating body contains no internal air gaps and provides excellent dielectric performance. It can withstand the operating voltage, power-frequency withstand voltage, and lightning impulse withstand voltage requirements of 12 kV systems. The cast structure provides a long insulation service life without oil leakage.
- Multiple secondary winding outputs: Supports multiple secondary windings, such as one metering winding combined with one or more protection windings. It can simultaneously provide current signals to metering instruments, protection devices, and control equipment, meeting multi-circuit protection requirements.
- Wide range of current ratios: Multiple primary-to-secondary current ratios are available, including 10/5 A, 20/5 A, 30/5 A, and ratios up to 2,000/5 A. Accuracy classes such as 0.2S, 0.5, 5P, and 10P can be customized according to metering and protection requirements.
- High short-time thermal and dynamic withstand capability: The product can withstand the specified short-time thermal current and dynamic current generated during system short-circuit faults. It is suitable for high-current and high-short-circuit-capacity applications.
- Low partial discharge: The advanced casting process limits partial discharge to no more than 10 pC, helping reduce insulation ageing and improve long-term operating reliability.
Structural and Installation Features
- Fully enclosed post-type structure: The one-piece cast structure contains no exposed live parts and provides an IP20 protection rating. It is suitable for indoor switchgear installation and helps reduce the ingress of dust and moisture.
- Compact modular design: The compact structure occupies minimal installation space and is compatible with standard 10 kV switchgear, including KYN28 series equipment. It supports convenient multi-circuit arrangements inside the cabinet.
- Multiple secondary terminals: The secondary terminals are protected by a transparent cover and clearly marked for convenient wiring. Multiple terminal outputs can provide current signals to several protection devices while reducing the risk of incorrect connection and short circuits.
- Flexible installation: The metal mounting base includes fixing holes for secure bolt installation. The transformer can be installed horizontally or vertically inside indoor switchgear and provides reliable vibration resistance.
Operation and Maintenance Features
- Low-maintenance operation: The epoxy resin cast body provides high mechanical strength, impact resistance, and ageing resistance. It contains no insulating oil and therefore presents no leakage risk, helping reduce routine maintenance requirements.
- 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 performance without becoming brittle or deformed.
- Stable low-error characteristics: Metering windings provide low and stable measurement errors and can meet Class 0.2S high-accuracy energy metering requirements. Protection windings provide sufficient accuracy limit factors to support reliable relay protection operation and reduce the risk of incorrect or failed tripping.
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, customizable |
| Rated Secondary Current | 5 A or 1 A |
| Metering Accuracy Class | 0.2S / 0.2 / 0.5 |
| Protection Accuracy Class | 5P10 / 10P10 / 5P20 / 10P20; multiple protection windings available |
| 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, customizable |
| Dynamic Current (Idyn) | 2.5 times Ith, customizable |
Structural and Material Parameters
| Parameter | Specification |
|---|---|
| Insulating Medium | Cast epoxy resin |
| Protection Rating | IP20 |
| Installation Type | Indoor post-type bolt mounting |
| 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
| Standard | Description |
|---|---|
| GB 1208 | Current Transformers |
| GB/T 20840.1 | Instrument Transformers—Part 1: General Requirements |
Applications
Applicable Voltage Level
Suitable for indoor 10 kV AC power systems with a maximum system voltage of 12 kV.
Typical Applications
- Current measurement, energy metering, and multi-circuit relay protection in indoor medium-voltage switchgear, including KYN28 and XGN series equipment
- Multi-circuit current signal acquisition in box-type substations, distribution stations, and switching stations
- 10 kV power distribution systems in industrial and mining enterprises
- Commercial buildings and industrial parks
- Multi-circuit current monitoring and control in power automation systems
- Main incoming cabinets, bus-section cabinets, and other applications requiring multiple protection circuits and high short-time thermal and dynamic current withstand capability
Main Functions
The current transformer converts high primary current into standardized secondary currents of 5 A or 1 A at a specified ratio.
Multiple secondary windings can simultaneously provide current signals to:
- Energy meters
- Measuring instruments
- Relay protection devices
- Monitoring equipment
- Control systems
It also provides electrical isolation between the primary and secondary systems, helping protect connected equipment and operating personnel.
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
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 impact
- Non-standard current ratios
- Special multi-winding configurations
- Special accuracy classes
- Non-standard mounting dimensions
Installation and Maintenance
Installation Requirements
- Pre-installation inspection:
Inspect the current transformer and confirm that the cast body is free from cracks, bubbles, mechanical damage, and other defects. Check that all terminal markings are clear and that the supplied accessories are complete. Verify that the model, specifications, current ratio, accuracy class, and winding configuration match the design requirements. - Mounting:
Position the current 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 avoid uneven mechanical stress. - Primary-side connection:
Connect the primary busbar according to the electrical design. Ensure close contact between the busbar and the primary terminals and tighten all bolts securely to prevent overheating caused by poor contact. - Secondary-side connection:
Connect each secondary winding according to the terminal markings. Metering and protection windings must be wired separately and correctly. All secondary circuits must remain closed while the primary circuit is energized. Each required secondary circuit must be reliably grounded at one point to prevent hazardous overvoltage. - Insulation inspection:
After installation, measure the insulation resistance between:- Primary and earth
- Secondary and earth
- Primary and secondary
- Individual 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 overheating.
- Regularly inspect the primary busbar and all secondary wiring to ensure that connections remain secure and free from overheating or discoloration.
- Ensure that none of the secondary circuits are accidentally open-circuited or incorrectly short-circuited.
- Periodically test the insulation resistance and current-ratio error of each winding to confirm that metering and protection accuracy remain within the specified limits.
- Clean dust, oil, and contamination from the current transformer surface and keep the equipment clean and dry.
- If cracking, discharge, overheating, or excessive measurement error is detected, immediately de-energize and inspect the equipment. Replace the current transformer where necessary.
Precautions
- All 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, all unused or disconnected secondary windings must be securely short-circuited and grounded.
- Avoid impact or collision with the cast body during transportation and installation. Mechanical damage may crack the epoxy resin and reduce insulation performance.
- The equipment must be reliably grounded. The grounding terminal on the 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.
Standard Supply List
| No. | Item | Function |
|---|---|---|
| 1 | LZZBJ9-10C Current Transformer | Main device for current transformation and electrical isolation, supporting multiple secondary winding outputs |
| 2 | Mounting Bolts and Washers | Used to secure the current transformer during installation |
| 3 | Transparent Secondary Terminal Cover | Protects the secondary terminals and helps prevent incorrect connection or short circuits |
| 4 | Product Instruction Manual | Provides installation, operating, maintenance, and multi-winding wiring guidance |
| 5 | Product Certificate and Factory Test Report | Provides evidence of product quality and performance, including accuracy test data for each winding |
Applicable Standards and Certification
The product complies with the following standards:
- GB 1208, Current Transformers
- GB/T 20840.1, Instrument Transformers—Part 1: General Requirements
- GB/T 20840.2, Instrument Transformers—Part 2: Additional Requirements for Current Transformers
The product has passed the applicable type tests, and its performance meets the operating requirements of power distribution systems.
