Overview
The LJK-φ100~φ240 series are split-core zero-sequence current transformers designed for ground fault detection in 6 kV to 35 kV AC power systems. They feature an epoxy resin fully-sealed magnetic core enclosed in ABS engineering plastic, ensuring high insulation performance and environmental resistance for indoor applications.
Available in accuracy classes 0.2, 0.5, 1.0, and 3.0, these transformers support residual current monitoring, earth leakage protection, and cable insulation assessment. They comply with standard requirements for medium-voltage protective relaying and are rated for 50 Hz/60 Hz operation with IP54 protection.
Key Ratings Snapshot
| Parameter | Rating |
|---|---|
| Voltage range | 6 kV ~ 35 kV |
| Frequency | 50 Hz / 60 Hz |
| Accuracy class | 0.2, 0.5, 1.0, 3.0 |
| Rated burden | 5 VA, 10 VA, 15 VA |
| Secondary terminals | K1, K2 |
| Insulation level | 0.72/3 kV |
| Protection rating | IP54 |
| Application | Ground fault protection, residual current detection |
Model Designation
- L: Current transformer (CT)
- J: Ground (earth) protection application
- K: Split-core (openable) structure
- φ100~φ240: Inner aperture diameter in millimeters
Construction
The transformer employs a ring-type split-core configuration with a high-permeability magnetic core fully sealed in epoxy resin, housed within an ABS engineering plastic enclosure. This construction delivers excellent moisture resistance, corrosion protection, and long-term insulation stability. The openable design enables installation around existing cables without disconnecting primary conductors, ideal for retrofit projects. Secondary terminals K1 and K2 are clearly marked in accordance with standard CT polarity conventions. Anti-rust treatment and robust thermal management ensure reliable operation in demanding indoor environments.
Technical Parameters
Service Conditions
- Installation environment: Indoor installation only
- Altitude: Not exceeding 2000 m above sea level (higher altitude requires specification at ordering)
- Ambient temperature: −25 °C to +40 °C
- Relative humidity: ≤ 95% (no condensation)
- Environmental conditions: Free from conductive dust, metallic particles, corrosive gases, or mold; no severe vibration or mechanical shock
Technical Parameters
The LJK-φ100~φ240 series are cast-resin insulated zero-sequence current transformers designed for indoor use in AC power distribution systems up to 0.66 kV. They operate within an ambient temperature range of −25 °C to +40 °C and at altitudes not exceeding 2000 m, complying with relevant IEC standards for accuracy and insulation performance. The primary current range accommodates typical cable bundle or busbar configurations with aperture diameters from φ100 mm to φ240 mm.
Technical Specifications
| Type | Classes | Rated Output (VA) |
|---|---|---|
| LJK-φ100 | 10P5~10P10 | 5~2.5 |
| LJK-φ120 | 10P5~10P10 | 5~2.5 |
| LJK-φ140 | 10P5~10P20 | 10~2.5 |
| LJK-φ160 | 10P5~10P20 | 10~2.5 |
| LJK-φ180 | 10P5~10P20 | 10~5 |
| LJK-φ200 | 10P5~10P20 | 15~5 |
| LJK-φ240 | 10P5~10P20 | 15~5 |
Note: If user’s data go beyond the above-mentioned scopes, they may be subject to an agreement between manufacturer and purchaser.
Selection Note: Aperture diameter shall be selected based on cable bundle size or busbar dimensions with adequate clearance. Accuracy class and rated burden shall be coordinated with connected protective relays or monitoring instruments.
Installation & Wiring
Installation Diagram
The LJK series zero-sequence current transformers are available in split-core design for easy retrofit installation on existing cables or busbars. The outline dimensions shown correspond to the dimensional specifications provided in the table above. Ensure proper alignment of the core halves and maintain adequate clearance around the unit for safety, heat dissipation, and future maintenance access.
Selection & FAQs
Selection Guide
- Confirm the residual-current measurement range, relay input, protection pickup, and required accuracy class.
- Measure the complete cable group and select a 100mm–240mm aperture with adequate installation clearance.
- Choose the 1A or 5A secondary and 50A–1000A ratio that match the relay or monitoring device.
- Calculate connected-device and cable-loop burden and select 2.5VA, 5VA, 10VA, or 15VA output.
- Verify same-direction conductor routing, clean split faces, full core closure, K1/K2 polarity, grounding, and IP54 conditions.
Frequently Asked Questions
Q1: What is the LJK-φ100~φ240 used for?
It is a split-core residual-current CT for earth-fault protection, leakage monitoring, and cable-insulation supervision.
Q2: Which aperture sizes are available?
The series provides 100mm, 120mm, 140mm, 160mm, 180mm, 200mm, 220mm, and 240mm windows.
Q3: What current ratios can be specified?
Published options extend from 50/1A or 50/5A to 1000/1A or 1000/5A.
Q4: Which accuracy classes are offered?
Model configurations include class 1 or 3 for measurement and 5P or 10P for protection.
Q5: Can it monitor 6kV–35kV cables?
It can surround properly insulated medium-voltage cables, while the CT secondary insulation itself is rated 0.72/3kV.
Q6: What is the benefit of the split-core design?
It installs around existing cable groups without disconnecting or re-terminating the primary conductors.
Q7: What causes inaccurate residual-current measurement?
Incomplete core closure, dirty mating faces, incorrect conductor routing, or excessive secondary burden can reduce accuracy.