Product Overview
The LSY-10 Three-Phase Current Transformer is an integrated epoxy resin cast current transformer designed specifically for indoor 10 kV ring main units with a maximum system voltage of 12 kV.
The product incorporates the current-sensing functions of phases A, B, and C within a single cast body. It is mainly used for current measurement, energy metering, relay protection, and overcurrent monitoring in ring main units and box-type substations.
Its compact, integrated structure is suitable for 10 kV distribution systems, switching stations, industrial and mining enterprises, commercial buildings, and other applications requiring space-efficient ring main unit designs.
Product Features
Insulation and Electrical Performance
- Three-phase integrated cast insulation:
The three-phase windings are enclosed within a single body manufactured using an epoxy resin vacuum-casting process. The solid insulation contains no internal air gaps and provides excellent dielectric performance. - Suitable for 12 kV systems:
The transformer can withstand the specified power-frequency and lightning impulse withstand voltage requirements of 10 kV systems with a maximum system voltage of 12 kV. - Oil-free dry-type construction:
The product contains no insulating oil, eliminating the risks of oil leakage, oil contamination, and oil-related fire hazards. - Wide range of current ratios:
Standard current ratios from 50/5 A to 2,000/5 A are available. Other current ratios can be customized according to the system design. - High-accuracy metering:
Metering accuracy classes of 0.2S, 0.5S, and 0.5 are available for high-accuracy energy measurement. - Reliable protection performance:
Protection accuracy classes such as 5P and 10P can be configured for overcurrent protection, short-circuit protection, and relay protection applications. - High short-time thermal and dynamic current withstand capability:
The transformer uses high-quality silicon steel cores and high-strength winding materials. It can withstand the thermal and electrodynamic effects generated by system short-circuit currents. - 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
- Integrated three-phase dry-type structure:
The three-phase sensing units are cast into a single fully enclosed body with an IP20 protection rating. - Space-saving design:
Compared with three separate single-phase current transformers, the integrated structure can reduce the required switchgear installation space by approximately 40%. - Designed for compact ring main units:
The compact dimensions are suitable for space-limited ring main unit compartments and integrated distribution equipment. - Three-phase through-aperture design:
The A-, B-, and C-phase busbars pass directly through their respective apertures, enabling current detection without additional primary winding connections. - Simplified primary circuit:
The through-type structure simplifies the primary circuit layout, reduces installation procedures, and minimizes the number of potential connection points. - Clearly marked phase apertures:
The three apertures are clearly identified as phases A, B, and C to facilitate correct busbar installation. - Clearly identified secondary terminals:
The secondary terminals are grouped and clearly marked for convenient connection to energy meters, protection relays, monitoring devices, and control equipment. - Secure bolt mounting:
The integrated body is installed using standard mounting holes and bolts, providing reliable mechanical stability and vibration resistance.
Operation and Maintenance Features
- Low-maintenance operation:
The dry-type, oil-free construction eliminates oil leakage and oil replacement requirements. The epoxy resin body provides high mechanical strength, impact resistance, and ageing resistance. - 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 under both high- and low-temperature conditions. - Stable accuracy:
High-quality laminated silicon steel cores and enamelled copper windings provide low operating losses, limited temperature rise, and stable metering accuracy. - Reliable protection operation:
The transformer can withstand switching overvoltage and short-circuit current effects within its specified ratings, supporting dependable overcurrent and short-circuit protection.
Technical Specifications
Electrical Parameters
| Parameter | Specification |
|---|---|
| Applicable System Voltage | 10 kV AC, Um = 12 kV |
| Rated Frequency | 50 Hz |
| Rated Primary Current | 50–2,000 A, customizable |
| Rated Secondary Current | 5 A standard; 1 A available |
| Metering Accuracy Class | 0.2S / 0.5S / 0.5 |
| Protection Accuracy Class | 5P10 / 10P10, customizable |
| Power-Frequency Withstand Voltage | 42 kV for 1 minute, without breakdown |
| Lightning Impulse Withstand Voltage | 75 kV peak, without breakdown |
| Partial Discharge | ≤10 pC |
| Insulation Resistance | ≥1,000 MΩ between the primary conductors, secondary circuits, and earth |
| Short-Time Thermal and Dynamic Current | Customized according to the system short-circuit rating, such as 20 kA for 2 seconds or 31.5 kA for 2 seconds |
Structural and Material Parameters
| Parameter | Specification |
|---|---|
| Insulating Medium | Fully cast epoxy resin with integrated three-phase construction |
| Protection Rating | IP20 |
| Installation Type | Indoor bolt-mounted installation |
| 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 Series | Instrument Transformers |
Applications
Applicable Voltage Level
The LSY-10 Three-Phase Current Transformer is suitable for indoor 10 kV AC power systems with a maximum system voltage of 12 kV.
Typical Applications
- Three-phase current measurement in indoor ring main units
- Energy metering and relay protection in box-type substations
- Overcurrent and short-circuit protection
- 10 kV distribution systems in switching and distribution stations
- Industrial and mining enterprises
- Commercial buildings and industrial parks
- Three-phase current monitoring and control in power automation systems
- Compact ring main units requiring fewer components and a simplified primary circuit
Main Functions
The LSY-10 converts the three-phase primary currents into standardized secondary currents, normally 5 A, at specified ratios.
It supplies three-phase current signals to:
- Energy meters
- Measuring instruments
- Relay protection devices
- Overcurrent protection devices
- Monitoring equipment
- Control systems
The transformer also provides electrical isolation between the primary power circuit and secondary measurement and protection circuits.
It can be used for:
- Energy metering
- Load monitoring
- Overcurrent protection
- Short-circuit protection
- Current signal acquisition
- Power automation control
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 fixed 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 accuracy classes
- Special short-time thermal or dynamic current withstand requirements
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 and phase markings are clear and that the supplied accessories are complete. Verify that the model, current ratio, accuracy class, and short-time thermal and dynamic current ratings meet the system design requirements. - Mounting:
Position the transformer at the specified location inside the ring main unit and secure it using bolts through the mounting holes. Ensure that the transformer is firmly installed without looseness or displacement. The mounting surface should be level to avoid uneven mechanical stress. - Primary busbar installation:
Pass the three high-voltage busbars through the corresponding apertures marked A, B, and C. Ensure that each busbar is centred within its aperture and does not contact the aperture wall. Avoid scratching or damaging the insulating surface inside the aperture. - Secondary-side connection:
Connect the three-phase secondary terminals to the energy meter, relay protection device, or monitoring equipment according to the terminal markings. The secondary circuits must never be left open while the primary circuits are energized. One point of each required secondary circuit must be reliably earthed. - Insulation inspection:
After installation, measure the insulation resistance between:- Primary conductors and secondary circuits
- Primary conductors and earth
- Secondary circuits and earth
Maintenance Requirements
- Regularly inspect the epoxy resin body for cracks, mechanical damage, discharge marks, and contamination.
- Check each busbar aperture for foreign objects, wear, or insulation damage.
- Inspect the secondary terminals for looseness, oxidation, or abnormal heating.
- Check that the busbars do not contact or rub against the aperture walls.
- Confirm that the secondary wiring remains secure and free from overheating or discoloration.
- Ensure that all secondary circuits remain closed and reliably earthed.
- Periodically test the insulation resistance and current ratio.
- Verify that the metering and protection accuracy remains within the specified limits.
- Check the correct operation of the connected protection and monitoring devices.
- Clean dust and contamination from the transformer surface.
- Keep all busbar apertures free from foreign materials.
- Prevent oil and corrosive substances from contacting the epoxy resin body.
- If cracking, electrical discharge, overheating, excessive current-ratio error, or an open secondary circuit is detected, immediately de-energize and inspect the equipment. Replace the transformer where necessary.
Precautions
- The secondary windings must never be left open while the primary circuits are 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 circuits must be securely short-circuited and earthed before disconnection.
- Avoid impact or collision with the epoxy resin body and busbar apertures during transportation and installation.
- Do not scratch the insulating surfaces inside the apertures when installing the high-voltage busbars.
- Install the A-, B-, and C-phase busbars through their corresponding marked apertures.
- Each busbar should be positioned concentrically within its aperture and must not contact the aperture wall.
- Prevent busbar movement or vibration from causing repeated contact with the aperture wall, as this may damage the insulation and create a risk of electrical discharge or short circuit.
- The equipment must be reliably earthed. The grounding terminal must be securely connected to the ring main unit 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 | LSY-10 Three-Phase Current Transformer | Main device for three-phase current transformation, electrical isolation, and signal acquisition |
| 2 | Mounting Bolts and Washers | Used to secure the current transformer during installation |
| 3 | Secondary Terminal Cover | Protects the low-voltage 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 | Provides product quality and performance documentation, including current-ratio, accuracy, and short-time thermal and dynamic current 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 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 indoor 10 kV ring main unit power systems.
