Product Overview
The LZZBJ9-12-GY High-Altitude Current Transformer is a fully enclosed, post-type, epoxy resin cast current transformer designed for 10 kV indoor AC power systems with a maximum system voltage of 12 kV in high-altitude regions.
Developed from the standard LZZBJ9 series, this model features an optimized insulation margin and increased creepage distance to meet operating requirements at altitudes from 2,000 to 4,000 metres. It also retains the excellent short-time thermal and dynamic current withstand capabilities and stable accuracy characteristics of the standard model.
The product is widely used in indoor medium-voltage switchgear, box-type substations, distribution stations, and other power facilities in high-altitude regions. It provides current signals for current measurement, energy metering, and relay protection.
Product Features
High-Altitude Insulation Performance
- Enhanced insulation margin: The current transformer is manufactured using an epoxy resin vacuum-casting process. Its insulation structure and creepage distance are optimized for high-altitude environments. The insulation level is corrected to compensate for reduced dielectric strength under low atmospheric pressure, helping prevent insulation breakdown in 12 kV systems.
- Corona and partial-discharge resistance: The advanced casting process limits partial discharge to no more than 10 pC. Optimized electric field distribution reduces the risk of corona discharge at high altitudes and improves long-term operating reliability.
- Stable insulation over a wide temperature range: The epoxy resin body maintains stable insulation performance from -30°C to +70°C without becoming brittle or deformed, making it suitable for the significant day-to-night temperature variations found in plateau regions.
Excellent Electrical Performance
- 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 for different 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.
- 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 ensure reliable relay protection operation and reduce the risk of incorrect or failed tripping.
Structural and Installation Features
- Fully enclosed post-type structure: The one-piece epoxy resin cast structure contains no exposed live parts and provides an IP20 protection rating. It is suitable for indoor switchgear installation and helps prevent the ingress of dust and moisture. The housing design is also optimized for heat dissipation under low atmospheric pressure.
- 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.
- Clearly marked secondary terminals: The secondary terminals are protected by a transparent cover and clearly identified for convenient wiring. The cover helps prevent incorrect connections, short circuits, and accidental opening of the secondary circuit.
- 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 for transportation and installation in high-altitude regions.
Operation and Maintenance Features
- Low-maintenance operation: The epoxy resin cast body provides high mechanical strength, impact resistance, and ageing resistance. It has no leakage risk and requires minimal maintenance during long-term operation, reducing maintenance difficulty and cost in remote high-altitude regions.
- Strong environmental adaptability: The product is suitable for ambient temperatures from -30°C to +70°C and relative humidity up to 95% under non-condensing conditions. It also provides resistance to ultraviolet radiation and wind erosion, making it suitable for the environmental characteristics of plateau regions.
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 |
| Power-Frequency Withstand Voltage | 42 kV for 1 minute, phase-to-earth and phase-to-phase, corrected for high-altitude operation, without breakdown |
| Lightning Impulse Withstand Voltage | 75 kV peak, corrected for high-altitude operation, 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 |
|---|---|
| Applicable Altitude | 2,000–4,000 m; higher-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 |
| GB/T 11022 | Common Specifications for High-Voltage Switchgear and Controlgear Standards |
Applications
Applicable Voltage Level
Suitable for indoor 10 kV AC power systems with a maximum system voltage of 12 kV.
Applicable Altitude
Designed for high-altitude regions from 2,000 to 4,000 metres. Customized versions are available for higher altitudes.
Typical Applications
- Current measurement, energy metering, and relay protection in indoor medium-voltage switchgear such as KYN28 and XGN series equipment in high-altitude regions
- Current signal acquisition in box-type substations, distribution stations, and switching stations in plateau regions
- 10 kV distribution systems in high-altitude industrial and mining enterprises
- High-altitude industrial parks and infrastructure projects
- Current monitoring and control in power automation systems
- High-altitude power distribution applications requiring enhanced insulation and high short-time thermal and dynamic current withstand capability
Main Functions
The current transformer converts high primary current 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
It also provides electrical isolation between the primary and secondary systems, helping protect connected equipment and operating personnel while meeting the special environmental requirements of high-altitude regions.
Operating Conditions
Normal Operating Conditions
- Installation altitude: 2,000–4,000 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 4,000 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 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, and accuracy class match the design requirements. Confirm that the product is the correct high-altitude version. - 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 and should accommodate transportation and installation conditions in high-altitude regions. - 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 the secondary winding terminals according to their markings. Metering and protection windings must be wired separately and correctly. The secondary circuit must never be left open while the primary circuit is energized. One point of the secondary circuit must be reliably grounded to prevent hazardous overvoltage. - Insulation inspection:
After installation, measure the insulation resistance between:- Primary and earth
- Secondary and earth
- Primary and secondary
Maintenance Requirements
- Regularly inspect the epoxy resin body for cracks, mechanical damage, and discharge marks.
- Check the terminals for looseness, oxidation, and overheating.
- Pay particular attention to contamination on creepage surfaces.
- Regularly inspect the primary busbar and secondary wiring to ensure that all connections remain secure and free from overheating or discoloration.
- Ensure that the secondary circuit is not accidentally open-circuited or incorrectly short-circuited.
- Periodically test the insulation resistance and current-ratio error to confirm that metering and protection accuracy remain within the specified limits.
- Check that the partial discharge level remains normal.
- Clean dust and contamination from the current transformer surface, particularly in windy and dusty high-altitude environments.
- Prevent oil and corrosive substances from contacting the cast body.
- If cracking, discharge, overheating, or excessive measurement error is detected, immediately de-energize and inspect the equipment. Replace the current transformer where necessary.
Precautions
- The secondary winding 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 winding 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 in high-altitude environments.
- The equipment must be reliably grounded. The grounding terminal on the base must be securely connected to the switchgear grounding busbar and must meet the grounding requirements applicable to the installation location.
- Store the product in a dry, ventilated, and shaded environment. Avoid direct sunlight, high temperatures, moisture, compression, and prolonged exposure to strong ultraviolet radiation.
- Installation, commissioning, and maintenance must be carried out by qualified electrical personnel in accordance with applicable electrical safety procedures and the special working conditions of high-altitude regions.
Standard Supply List
| No. | Item | Function |
|---|---|---|
| 1 | LZZBJ9-12-GY High-Altitude Current Transformer | Main device for current transformation and electrical isolation in high-altitude applications |
| 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, and maintenance guidance, including high-altitude operating instructions |
| 5 | Product Certificate and Factory Test Report | Provides evidence of product quality and performance, including high-altitude insulation correction test data |
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 11022, Common Specifications for High-Voltage Switchgear and Controlgear Standards
The product has undergone insulation correction and type testing for high-altitude environments. Its performance meets the operating requirements of power systems in plateau regions.
