Product Overview
The LMZB3-10 (G/G2) Current Transformer is a fully enclosed, busbar-type epoxy resin cast 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 transformer features a through-type busbar structure without a built-in primary conductor. The busbar passing through the central aperture serves directly as the primary circuit, while the secondary windings are wound with enamelled copper wire.
The product provides excellent insulation performance, compact dimensions, high short-time thermal and dynamic current withstand capability, and stable accuracy characteristics. It is widely used in indoor medium-voltage switchgear, box-type substations, distribution stations, and switching stations for current measurement, energy metering, and relay protection signal acquisition.
Product Features
Insulation and Electrical Performance
- 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. - Through-type busbar structure:
The primary circuit is formed by the busbar passing through the central aperture. No separate built-in primary conductor is required, simplifying installation and supporting different busbar arrangements inside switchgear. - Wide current-ratio range:
Multiple primary-to-secondary current ratios are available, including 100/5 A, 200/5 A, and ratings up to 3,000/5 A. - Configurable accuracy classes:
Metering and protection accuracy classes such as 0.2S, 0.2, 0.5, 5P, and 10P can be supplied according to system requirements. - High short-time thermal and dynamic current withstand capability:
The transformer can withstand the specified short-time thermal and electrodynamic stresses generated by system short-circuit faults. It is suitable for high-current distribution systems with high short-circuit capacity. - Low partial discharge:
The advanced casting process limits partial discharge to no more than 10 pC, helping prevent insulation ageing caused by long-term partial discharge and improving operational reliability.
Structural and Installation Features
- Fully enclosed cast-resin structure:
The secondary windings and magnetic core are completely enclosed within the epoxy 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 medium-voltage switchgear. - Compact modular design:
Its compact structure occupies minimal installation space and is suitable for installation in the busbar compartments of standard 10 kV switchgear. - Suitable for multi-circuit switchgear layouts:
The small footprint facilitates compact arrangement of multiple current transformers and busbar circuits inside the switchgear. - Clearly identified secondary terminals:
The secondary terminals are clearly marked and protected by a terminal cover, simplifying wiring and reducing the risk of incorrect connection or short circuits. - Reduced risk of secondary-circuit opening:
The protected terminal arrangement helps prevent accidental disconnection of the secondary circuit during operation and maintenance. - Flexible mounting arrangement:
The transformer supports through-type busbar installation and can be mounted horizontally or vertically in the switchgear busbar compartment. - Reliable mechanical stability:
The mounting structure provides secure fixation and excellent resistance to operational vibration.
Operation and Maintenance Features
- Low-maintenance operation:
The epoxy resin cast body provides high mechanical strength, impact resistance, and ageing resistance. Its dry-type construction eliminates oil leakage and 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. - Stable metering accuracy:
The metering windings provide low error and stable accuracy characteristics and can meet Class 0.2S high-accuracy energy-metering requirements. - Reliable protection performance:
The protection windings provide sufficient accuracy limit factors to ensure dependable relay operation under system fault conditions. - Low operating loss:
High-quality magnetic cores and enamelled copper windings provide low losses, limited temperature rise, and stable long-term performance.
Technical Specifications
Electrical Parameters
| Parameter | Specification |
|---|---|
| Applicable System Voltage | 10 kV AC, Um = 12 kV |
| Rated Frequency | 50 Hz |
| Rated Primary Current | 100–3,000 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, without breakdown |
| Lightning Impulse Withstand Voltage | 75 kV peak, without breakdown |
| Partial Discharge | ≤10 pC |
| Short-Time Thermal Current (Ith) | 20 times the rated primary 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 | Through-type busbar installation for indoor fixed 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 |
| GB/T 20840.2 | Instrument Transformers—Part 2: Additional Requirements for Current Transformers |
Applications
Applicable Voltage Level
The LMZB3-10 (G/G2) Current Transformer is suitable for indoor 10 kV AC power systems with a maximum system voltage of 12 kV.
Typical Applications
- Current measurement, energy metering, and relay protection in the busbar compartments of KYN28 and XGN series indoor medium-voltage switchgear
- Busbar current signal acquisition in box-type substations
- Distribution stations and switching stations
- 10 kV distribution systems in industrial and mining enterprises
- Commercial buildings and industrial parks
- Current monitoring and control in power automation systems
- High-current 10 kV distribution systems using busbar-type arrangements
- Applications requiring flexible central-aperture dimensions for different busbar sizes
Main Functions
The transformer converts the high current flowing through the busbar inside the central aperture 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 busbar and secondary metering and protection circuits, 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 through-type busbar 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 mechanical impact
- Non-standard current ratios
- Special central-aperture dimensions
- 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, current ratio, accuracy class, and other specifications match the system design requirements. Confirm that the central-aperture dimensions are compatible with the busbar size. - Mounting:
Position the transformer at the specified location inside the switchgear busbar compartment. Secure it with bolts through the mounting holes and confirm that there is no looseness or displacement. The mounting surface should be level to prevent uneven mechanical stress. The transformer may be installed horizontally or vertically according to the switchgear design. - Busbar installation:
Pass the primary busbar through the central aperture. Ensure that the busbar does not strike, rub against, or contact the inner wall of the aperture during installation. Secure the busbar firmly to prevent movement or vibration during operation, as excessive movement may damage the transformer or affect its performance. - Secondary-side connection:
Connect the secondary winding terminals according to their markings. Metering and protection windings must be wired separately and correctly. The secondary circuits must never be left open while the primary busbar is energised. One point of each required secondary circuit must be reliably earthed to prevent hazardous overvoltage. - Insulation inspection:
After installation, measure the insulation resistance between:- Secondary windings and earth
- Primary busbar and secondary windings
Maintenance Requirements
- Regularly inspect the epoxy resin body for cracks, mechanical damage, discharge marks, and contamination.
- Check the secondary terminals for looseness, oxidation, or abnormal heating.
- Inspect the clearance between the busbar and the inner wall of the central aperture.
- Confirm that the busbar does not contact, strike, or rub against the transformer.
- Check that the busbar remains firmly secured without vibration or displacement.
- Ensure that the secondary circuits are free from unintended open circuits or short circuits.
- 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.
- Clean dust and contamination from the transformer surface.
- Prevent oil and corrosive substances from contacting the epoxy resin body.
- Keep the product dry and clean.
- If cracking, electrical discharge, overheating, or excessive accuracy error is detected, immediately de-energise and inspect the equipment.
- Replace the transformer where necessary. Continued operation with a known defect is prohibited.
Precautions
- The secondary windings must never be left open while the primary busbar is energised. 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.
- Avoid impact or collision with the epoxy resin body during transportation and installation. Mechanical damage may crack the cast insulation and reduce dielectric performance.
- When passing the busbar through the central aperture, ensure that sharp busbar edges do not scratch or damage the inner surface of the transformer.
- The busbar must not make electrical or mechanical contact with the inner wall of the central aperture.
- The busbar must be securely fixed to prevent vibration, movement, or repeated contact with the transformer during operation.
- The equipment must be reliably earthed. 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 | LMZB3-10 (G/G2) Current Transformer | Main device for current transformation and electrical isolation in busbar-type installations |
| 2 | Mounting Bolts and Washers | Used to secure the current transformer during installation |
| 3 | Secondary Terminal Cover | Protects the secondary terminals and helps prevent incorrect connections or short circuits |
| 4 | Product Instruction Manual | Provides installation, operation, maintenance, and busbar-routing guidance |
| 5 | Product Certificate and Factory Test Report | Provide product quality and performance documentation |
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 10 kV power systems.
