Product Overview
The JSZW12-10 Voltage Transformer is a three-phase integrated, epoxy resin cast voltage transformer designed for indoor 10 kV AC power systems with a maximum system voltage of 12 kV.
Featuring a three-phase five-limb magnetic core, the transformer provides three-phase voltage measurement, energy metering, relay protection, and insulation monitoring within a single unit.
It is widely used in 10 kV indoor medium-voltage switchgear, ring main units, box-type substations, switching stations, and other distribution systems. The product is particularly suitable for insulation monitoring in systems with non-effectively earthed neutrals.
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 operating voltage, power-frequency withstand voltage, 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. It is suitable for modern indoor oil-free distribution systems. - Three-phase five-limb core design:
The transformer uses a three-phase five-limb magnetic core and can provide both metering or protection secondary windings and a residual voltage winding. - Integrated insulation monitoring:
The residual voltage winding supplies a signal for earth-fault detection and insulation monitoring without requiring additional auxiliary voltage transformers. It is also suitable for signal acquisition by low-current earth-fault line-selection devices. - Multiple voltage ratios:
Standard three-phase voltage ratios such as 10/0.1/0.1/3 kV are available. - Multiple accuracy classes:
Metering accuracy classes up to Class 0.2 are available, while protection accuracy classes such as 3P and 6P can be customized for different metering, protection, and insulation-monitoring requirements. - 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 three-phase dry-type structure:
The three-phase windings are integrally cast into a single enclosed body with no exposed internal live components. - IP20 protection rating:
The product provides an IP20 protection rating and is designed for installation inside indoor electrical equipment. - Compact, space-saving construction:
Compared with three separate single-phase voltage transformers, the integrated structure can reduce switchgear installation space by approximately 30%. - Three plug-in high-voltage bushing interfaces:
The high-voltage side features three tubular plug-in bushing interfaces. These interfaces are suitable for direct connection to three-position switches or compatible cable connectors inside the switchgear. - Simplified primary-circuit installation:
The plug-in connection design reduces additional primary wiring, simplifies installation, and minimizes the number of potential connection points. - Clearly identified secondary terminals:
The three-phase secondary terminals and residual voltage winding terminals are grouped and clearly marked. Metering, protection, and insulation-monitoring circuits can be connected separately. - Secure mounting and lifting arrangement:
The metal base includes mounting holes and lifting eyes. It supports horizontal bolt installation inside indoor switchgear and facilitates safe lifting and positioning.
Operation and Maintenance Features
- Low-maintenance operation:
The dry-type, oil-free construction eliminates leakage and oil-related fire risks. 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 without becoming brittle or deformed. - High-reliability construction:
The magnetic core is made from high-quality laminated silicon steel sheets, while the windings are wound with enamelled copper wire. - Low operating losses:
The optimized magnetic core and winding design provides low losses, limited temperature rise, and stable measurement accuracy. - Overvoltage withstand capability:
The transformer can withstand switching and lightning overvoltages within its specified insulation level, supporting reliable metering, protection, and insulation-monitoring functions.
Technical Specifications
Electrical Parameters
| Parameter | Specification |
|---|---|
| Applicable System Voltage | 10 kV AC, Um = 12 kV |
| Rated Frequency | 50 Hz |
| Rated Primary Voltage | 10 kV, three-phase |
| Rated Secondary Voltage | 100 V for three-phase metering and protection; 100/3 V for residual voltage and insulation monitoring |
| Metering Accuracy Class | Class 0.2 / 0.5 / 1 |
| Protection Accuracy Class | 3P / 6P |
| Power-Frequency Withstand Voltage | 42 kV for 1 minute at the high-voltage terminal, without breakdown |
| Lightning Impulse Withstand Voltage | 75 kV peak, without breakdown |
| Partial Discharge | ≤10 pC |
| Insulation Resistance | ≥1,000 MΩ between high voltage, low voltage, and earth |
Structural and Material Parameters
| Parameter | Specification |
|---|---|
| Insulating Medium | Fully cast epoxy resin with integrated three-phase construction |
| 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 1207 | Voltage Transformers |
| GB/T 20840 Series | Instrument Transformers |
Applications
Applicable Voltage Level
The JSZW12-10 Voltage Transformer is suitable for indoor 10 kV AC power systems with a maximum system voltage of 12 kV.
Typical Applications
- Three-phase voltage measurement in KYN28 series indoor medium-voltage switchgear
- Ring main units
- Energy metering and relay protection in box-type substations
- Voltage monitoring in distribution and switching stations
- 10 kV distribution systems in industrial and mining enterprises
- Commercial buildings and industrial parks
- Insulation monitoring in systems with non-effectively earthed neutrals
- Low-current earth-fault line-selection systems
- Compact switchgear using three-position switches or direct cable plug-in connections
- Applications requiring integrated three-phase voltage measurement and residual voltage monitoring
Main Functions
The transformer converts the three-phase system voltage into a standardized secondary voltage, normally 100 V, at a specified ratio.
It supplies three-phase voltage signals to:
- Energy meters
- Measuring instruments
- Relay protection devices
- Monitoring equipment
- Control systems
- Insulation monitoring devices
- Earth-fault line-selection equipment
The transformer also provides electrical isolation between the primary and secondary systems, helping protect connected equipment and operating personnel.
The residual voltage winding provides a signal for detecting system earth faults and monitoring the insulation condition of systems with non-effectively earthed neutrals.
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 mechanical impact
- Non-standard voltage ratios
- Special accuracy classes
- Non-standard mounting dimensions
Installation and Maintenance
Installation Requirements
- Pre-installation inspection:
Inspect the voltage 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, and voltage ratio match the system design requirements. - 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. Use the lifting eyes on the base when lifting the transformer. Avoid impact or collision during handling and positioning. - High-voltage plug-in connection:
Insert the compatible three-position switch connectors or cable connectors into the three high-voltage bushing interfaces. Confirm that each connector is fully inserted, correctly positioned, and securely engaged. The contact surfaces must provide reliable electrical contact without looseness or displacement. Maintain adequate electrical clearance between the high-voltage components, earthed parts, and other live components. - Secondary-side connection:
Connect the three-phase secondary terminals and residual voltage winding terminals according to their markings. Metering, protection, and insulation-monitoring circuits must be wired separately and correctly. The voltage transformer secondary circuits must never be short-circuited. One point of the required secondary circuit must be reliably earthed in accordance with the system design and applicable electrical safety requirements. - Insulation inspection:
After installation, measure the insulation resistance between:- High voltage and low voltage
- High voltage and earth
- Low voltage and earth
Maintenance Requirements
- Regularly inspect the epoxy resin body for cracks, mechanical damage, discharge marks, and contamination.
- Check the high-voltage bushing interfaces for looseness, oxidation, contamination, or abnormal heating.
- Ensure that the surfaces of the three high-voltage bushing interfaces remain clean.
- Regularly inspect the contact condition between the plug-in connectors and high-voltage bushing interfaces.
- Confirm that all connectors remain fully inserted and securely engaged.
- Check for overheating, discoloration, oxidation, or poor electrical contact at the plug-in interfaces.
- Regularly inspect the secondary wiring to ensure that all connections remain secure and free from overheating or discoloration.
- Confirm that the secondary-circuit earthing remains reliable.
- Periodically test the insulation resistance and three-phase voltage ratio.
- Verify that the metering and protection accuracy remains within the specified limits.
- Check the residual voltage circuit and insulation-monitoring function regularly.
- Clean dust and contamination from the transformer surface.
- Keep the plug-in contact surfaces free from oxidation and contamination.
- Prevent oil and corrosive substances from contacting the epoxy resin body.
- If cracking, electrical discharge, overheating, excessive voltage-ratio error, or functional failure is detected, immediately de-energise and inspect the equipment. Replace the transformer where necessary.
Precautions
- The voltage transformer secondary windings must never be short-circuited while the primary system is energised. A secondary short circuit may produce excessive current and create a serious risk to equipment and personnel.
- During maintenance, the transformer must be de-energised, and the secondary circuits must be safely isolated and earthed in accordance with applicable procedures.
- Avoid impact or collision with the epoxy resin body and the three high-voltage bushing interfaces during transportation and installation. Mechanical damage may reduce insulation performance and plug-in connection reliability.
- Confirm that the high-voltage connectors are fully compatible with the three bushing interfaces before installation.
- Do not force incompatible or misaligned connectors into the high-voltage interfaces, as this may damage the transformer or connector insulation.
- Keep the plug-in contact surfaces clean and free from oxidation or contamination. Poor contact may cause overheating and electrical failure.
- 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.
Standard Supply List
| No. | Item | Function |
|---|---|---|
| 1 | JSZW12-10 Three-Phase Five-Limb Voltage Transformer | Main device for three-phase voltage transformation, electrical isolation, and insulation monitoring |
| 2 | Mounting Bolts and Washers | Used to secure the voltage 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 wiring guidance |
| 5 | Product Certificate and Factory Test Report | Provides product quality and performance documentation, including voltage-ratio and accuracy test data |
Applicable Standards and Certification
The product complies with the following standards:
- GB 1207, Voltage Transformers
- GB/T 20840.1, Instrument Transformers—Part 1: General Requirements
- GB/T 20840.3, Instrument Transformers—Part 3: Additional Requirements for Inductive Voltage Transformers
The product has passed the applicable type tests, and its performance meets the operating requirements of indoor 10 kV power systems.
