Overview
The LKZB-0.5 (LBD-LCT) is a split-core zero-sequence current transformer designed for 6–35 kV medium-voltage AC cable systems. It features cast-resin (epoxy) insulation and an electromagnetic core optimized for residual current detection without requiring primary winding connections.
Rated with 10P10 accuracy class and 1 A secondary current, it supports earth-fault protection in industrial and utility applications including power generation, mining, railways, and chemical plants. The device complies with IEC 61869-1/2, GB 1208-1997, and DL/T 856-2004 standards, ensuring reliable performance in grounded and ungrounded systems.
Key Ratings Snapshot
| Parameter | Rating |
|---|---|
| System voltage class | 6–35 kV |
| Rated frequency | 50 Hz or 60 Hz |
| Rated secondary current | 1 A |
| Accuracy class | 10P10 |
| Rated burden | 1–5 VA |
| Burden power factor | cosφ = 0.8 (lagging) |
| Secondary insulation level | 3 kV AC (1 min) |
| Installation type | Split-core with bolt fastening |
| Applicable standards | IEC 61869-1 / IEC 61869-2; GB 1208-1997; DL/T 856-2004 |
Model Designation
- L: Current transformer (CT)
- K: Protection application (zero-sequence protection)
- Z: Cast-resin (epoxy) insulated, enclosed structure
- B: Split-core (opening / clamp-on) construction
- 0.5: Insulation class designation for secondary side
- LBD-LCT: Series code indicating split-core zero-sequence protection transformer
Construction
The LKZB-0.5 series employs a split-core design with ABS engineering plastic housing and epoxy resin encapsulation of the toroidal magnetic core and secondary winding. This construction ensures high mechanical strength, stable insulation performance, and resistance to moisture and contamination. The two-piece core halves are secured by bolt fastening, enabling installation without cable disconnection—ideal for retrofitting in cable termination cabinets. Two mounting holes on the base allow secure fixation. The absence of galvanic contact between primary conductors and the transformer eliminates direct electrical connection risks while maintaining precise magnetic coupling for accurate zero-sequence current sensing.
Technical Parameters
Service Conditions
- Installation environment: Indoor installation only (cable termination cabinets, distribution switchgear)
- Altitude: Not exceeding 1000 m above sea level (higher altitude shall be specified for engineering confirmation)
- Ambient temperature: −5 °C to +40 °C
- Relative humidity: Daily average ≤ 95%, monthly average ≤ 90% (at +20 °C reference)
- Environmental conditions: Free from corrosive gases or vapors; free from explosive or flammable media; no severe vibration, mechanical shock, or impact; suitable for normal indoor cable installation environments
Technical Parameters
The LKZB-0.5 (LBD-LCT) series are indoor split-core zero-sequence current transformers for 6–35 kV AC cable systems (50/60 Hz), featuring cast-resin insulation and designed for operation within −5 °C to +40 °C ambient temperature and up to 1000 m altitude. They comply with standard protection-class requirements and support primary current ratings from 50 A to 600 A with a fixed 1 A secondary output.
| Rated Current Ratio (A) | Accuracy Class | Rated Output (VA) |
|---|---|---|
| 50/1 | 10P10 | 1 |
| 75/1 | 10P10 | 1.6 |
| 100/1 | 10P10 | 2.5 |
| 150/1 | 10P10 | 5 |
| 200/1 | 10P10 | 5 |
| 300/1 | 10P10 | 5 |
| 400/1 | 10P10 | 5 |
| 600/1 | 10P10 | 5 |
Installation & Wiring
Installation Diagram
The LKZB-0.5 (LBD-LCT) split-core zero-sequence current transformers are designed for easy retrofit installation on live three-phase cable systems without disconnecting conductors. Open the split-core halves, position them around the cable bundle ensuring all three-phase conductors pass through the central aperture, then securely fasten the halves using the supplied bolts tightened to the specified torque. Mount the unit firmly using the two fixing holes to prevent movement or vibration during operation.
Selection & FAQs
Selection Guide
- Confirm the grounding system, expected earth-fault current, relay pickup, and required 10P10 protection performance.
- Select the 50A–600A primary rating and 60mm–180mm aperture from the cable bundle and protection study.
- Verify the relay accepts the fixed 1A secondary and calculate relay plus cable-loop burden.
- Confirm the selected ratio provides sufficient 1VA–5VA output for the connected secondary circuit.
- Verify all phase cables pass together, core faces align, bolts are tightened, mounting is rigid, and K1/K2 are correctly wired.
Frequently Asked Questions
Q1: What is the LKZB-0.5 used for?
It is a split-core residual-current CT for earth-fault protection on indoor 6kV–35kV cable feeders.
Q2: What primary-current range is available?
Standard ratings are 50A, 75A, 100A, 150A, 200A, 300A, 400A, and 600A with 1A secondary.
Q3: Which aperture sizes are offered?
Available inner diameters are 60mm, 80mm, 100mm, 150mm, and 180mm.
Q4: What protection accuracy does it provide?
All listed configurations use class 10P10 for relay-protection duty.
Q5: How does rated output vary by ratio?
Output rises from 1VA at 50A to 5VA from 150A upward, with 1.6VA at 75A and 2.5VA at 100A.
Q6: Can it be installed without removing the cables?
Yes. The two halves open around the complete phase-cable group and are secured with bolts.
Q7: What can cause loss of earth-fault sensitivity?
Misaligned core faces, loose bolts, incorrect conductor routing, excessive burden, or an open secondary can impair protection.