Product Overview
The LJZ-65/80/100/120/165 epoxy resin cast zero sequence current transformer is an indoor ring-core current transformer series designed for cable earth fault detection, residual current monitoring, and grounding protection. It is suitable for indoor power distribution systems with rated frequency of 50Hz or 60Hz and rated insulation level of 0.72/3kV. The series provides multiple inner diameter options for different three-phase cable groups.
The product adopts a fully enclosed epoxy resin casting structure. The annular iron core and secondary winding are encapsulated in resin, giving the transformer a compact structure, good insulation performance, moisture resistance, and stable indoor service characteristics. During installation, all three phase cables pass through the central opening of the transformer. When a single-phase ground fault or insulation fault occurs, the transformer detects the zero sequence current and outputs a secondary signal to the relay or protection device.
Product Type
| Item | Specification |
|---|---|
| Product name | Epoxy Resin Cast Zero Sequence Current Transformer |
| Model series | LJZ-65 / LJZ-80 / LJZ-100 / LJZ-120 / LJZ-165 |
| Product structure | Indoor fully enclosed epoxy resin cast annular zero sequence current transformer |
| Inner diameter options | φ65 mm, φ80 mm, φ100 mm, φ120 mm, φ165 mm |
| Rated insulation level | 0.72/3kV |
| Rated frequency | 50Hz / 60Hz |
| Rated secondary current | 5A or 1A |
| Protection class | 10P5, 10P10, 10P15, 10P20 according to selected model and ratio |
| Installation location | Indoor |
| Typical applications | Cable earth fault detection, residual current monitoring, zero sequence current protection, grounding fault alarm and trip circuits |
Product Display
Main Applications
- Indoor cable feeder earth fault protection
- Small-current grounding system protection
- Residual current monitoring for three-phase cable groups
- Single-phase ground fault alarm and trip circuits
- Motor feeder, generator feeder, and distribution line protection
- Medium-voltage switchgear, protection panels, and cable distribution systems
- Systems requiring relay input from a zero sequence current transformer
Key Technical Features
- Epoxy resin cast structure: The transformer adopts a fully enclosed cast-resin body for insulation, moisture resistance, and mechanical stability.
- Multiple cable window sizes: φ65, φ80, φ100, φ120, and φ165 options are available for different cable outside diameters.
- Zero sequence current detection: Detects residual current caused by single-phase grounding faults or insulation faults.
- Relay protection output: Provides a secondary current signal for earth fault relays, monitoring devices, and protection circuits.
- 5A or 1A secondary output: Compatible with common relay and monitoring system inputs.
- Indoor fixed installation: Base-mounted structure suitable for switchgear, protection cabinets, and cable rooms.
Working Principle
The LJZ zero sequence current transformer measures the vector sum of the currents flowing through the three-phase cable group. Under normal conditions, the three-phase current vector sum is close to zero, so the secondary output is very small. When a single-phase ground fault occurs, the three-phase current balance is broken and zero sequence current appears. The transformer converts the residual current into a secondary signal for relay operation, alarm, or trip protection.
For correct zero sequence protection, all three phase conductors should pass through the transformer window together in the same direction. The primary insulation is provided by the cable itself, while the transformer verifies and protects the secondary winding insulation. Typical LJZ product descriptions state that the secondary winding can withstand a 3kV power-frequency test voltage to ground.
Model Designation
| Code | Meaning |
|---|---|
| L | Current transformer |
| J | For earth protection / grounding protection |
| Z | Cast-resin insulated structure |
| 65 / 80 / 100 / 120 / 165 | Inner hole diameter / cable window size code |
Technical Data
| Item | Specification |
|---|---|
| Model series | LJZ-65/80/100/120/165 |
| Product type | Indoor epoxy resin cast zero sequence current transformer |
| Rated insulation level | 0.72/3kV |
| Rated frequency | 50Hz / 60Hz |
| Rated secondary current | 5A or 1A |
| Protection class | 10P5, 10P10, 10P15, 10P20 |
| Ambient temperature | -25°C to +40°C |
| Insulation structure | Fully enclosed epoxy resin casting |
| Secondary winding withstand voltage | 3kV power-frequency withstand voltage to ground, subject to technical agreement |
| Applicable standards | GB 20840.1-2010, GB 20840.2-2014; customer-specific requirements can be confirmed by agreement |
Inner Diameter and Dimension Reference
| Model | D (mm) | d (mm) | H (mm) | h (mm) | A1 (mm) | A2 (mm) | B1 (mm) | B2 (mm) |
|---|---|---|---|---|---|---|---|---|
| LJZ-65 | 160 | 65 | 192 | 110 | 170 | 130 | 80 | 80 |
| LJZ-80 | 170 | 80 | 180 | 95 | 160 | 130 | 64 | 64 |
| LJZ-100 | 190 | 100 | 200 | 105 | 160 | 130 | 64 | 64 |
| LJZ-120 | 238 | 122 | 264 | 145 | 200 | 165 | 80 | 69 |
| LJZ-165 | 260 | 165 | 294 | 161 | 200 | 170 | 65 | 65 |
Unit: mm. Final dimensions, mounting holes, terminal position, and base layout are subject to the approved outline drawing.
Rated Current Ratio and Output Reference
| Model | Protection
Class |
5A Secondary
Current Ratio |
Rated Output
Range for 5A Secondary (VA) |
1A Secondary
Current Ratio |
Rated Output
Range for 1A Secondary (VA) |
|---|---|---|---|---|---|
| LJZ-65 | 10P5 / 10P10 / 10P15 / 10P20 | 50/5 to 400/5 | 1 to 40 depending on ratio and class | 50/1 to 150/1 | 1 to 15 depending on ratio and class |
| LJZ-80 | 10P5 / 10P10 / 10P15 / 10P20 | 50/5 to 400/5 | 1 to 30 depending on ratio and class | 50/1 to 150/1 | 1 to 10 depending on ratio and class |
| LJZ-100 | 10P5 / 10P10 / 10P15 / 10P20 | 50/5 to 400/5 | 1 to 30 depending on ratio and class | 50/1 to 150/1 | 1 to 10 depending on ratio and class |
| LJZ-120 | 10P5 / 10P10 / 10P15 / 10P20 | 50/5 to 400/5 | 1 to 40 depending on ratio and class | 50/1 to 150/1 | 1 to 15 depending on ratio and class |
| LJZ-165 | 10P5 / 10P10 / 10P15 / 10P20 | 50/5 to 400/5 | 1 to 30 depending on ratio and class | 50/1 to 150/1 | 1 to 15 depending on ratio and class |
Note: Rated output varies according to model size, current ratio, secondary current, and protection class. Parameters beyond the catalogue table can be confirmed through technical agreement.
Service Conditions
- Installation location: indoor
- Rated insulation level: 0.72/3kV
- Rated frequency: 50Hz / 60Hz
- Ambient temperature: -25°C to +40°C
- The installation environment should be free from severe vibration, corrosive gas, conductive dust, explosive medium, heavy moisture, and serious pollution.
- All three phase conductors should pass through the transformer window together in the same direction.
- The cable should pass through the window without mechanical stress on the transformer body.
- For special cable diameter, relay type, compensation capacitor, grounding system, or sensitivity requirements, technical confirmation is recommended before ordering.
Standards and Compliance
The LJZ epoxy resin cast zero sequence current transformer series is designed for indoor earth fault detection and residual current protection applications. It can be supplied according to GB 20840.1-2010, GB 20840.2-2014, and customer-specific technical requirements. Final current ratio, rated output, protection class, routine test items, insulation test, and nameplate data should be confirmed in the technical agreement.
Installation and Dimensions
The LJZ series adopts a fully enclosed annular cast-resin structure with fixed base installation. The cable group passes through the central window of the transformer, and the secondary terminals are connected to the relay or monitoring device. The selected inner diameter should provide enough clearance for the three-phase cable group and allow proper cable bending space in the cabinet.
Connection and Wiring Notes
- All three phase conductors should pass through the transformer window together in the same direction.
- Do not pass only one phase conductor through the window when the transformer is used for zero sequence protection.
- Connect secondary terminals S1 and S2, or the corresponding terminal group, according to the wiring diagram.
- If a compensation capacitor is used, connect the corresponding terminal group according to the relay and protection scheme.
- Check the relay setting, wiring resistance, polarity, terminal tightening, and secondary circuit continuity before commissioning.
- The secondary circuit of a current transformer must not be open-circuited when the primary circuit is energized.
Installation and Safety Notes
- Confirm the model, inner diameter, cable outside diameter, current ratio, secondary current, protection class, and rated output before installation.
- Ensure that the cable group can pass through the window without forcing or damaging the transformer body.
- Install the transformer on a stable indoor base or panel according to the approved drawing.
- Keep the cable group centered as far as possible in the window to support stable residual current detection.
- Check terminal markings, mounting holes, secondary wiring, relay wiring, and grounding before energizing.
- Installation, testing, and maintenance should be performed by qualified electrical personnel.
Ordering Information
- Product model: LJZ-65, LJZ-80, LJZ-100, LJZ-120, or LJZ-165
- Maximum outside diameter of the three-phase cable group
- Rated current ratio and rated secondary current: 5A or 1A
- Required protection class: 10P5, 10P10, 10P15, or 10P20
- Rated output / burden in VA
- Relay model, protection sensitivity, and whether compensation capacitor is required
- Rated frequency and installation environment
- Quantity, drawing requirements, certificates, inspection documents, labels, or packaging requirements
Selection Guidelines
- Confirm inner diameter: Select φ65, φ80, φ100, φ120, or φ165 according to the outside diameter of the three-phase cable group.
- Confirm zero sequence protection purpose: Use this series for residual current detection, cable earth fault protection, or grounding fault alarm circuits.
- Confirm relay matching: Select the relay, coil connection, and scale setting according to the protection scheme.
- Confirm compensation requirement: Determine whether compensation capacitor connection is required for higher sensitivity or relay matching.
- Select secondary current: Choose 5A or 1A according to the connected relay or monitoring device.
- Select protection class: Choose 10P5, 10P10, 10P15, or 10P20 according to the required protection performance.
- Check installation space: Verify outline dimensions, mounting holes, cable bending radius, and cabinet clearance before batch ordering.