Product Overview
Functional Definition
The LZJC-10Q and LZJC-10G series current transformers are precision electromagnetic instruments designed for accurate current measurement, energy metering, and relay protection applications in medium-voltage AC power systems. These transformers utilize electromagnetic induction principles to provide galvanically isolated secondary current signals proportional to primary current in 10 kV indoor electrical installations.
Key Ratings
| Item | Specification (per order / nameplate) |
|---|---|
| System voltage class | 10 kV class (indoor switchgear and distribution applications) |
| Rated frequency | 50 Hz / 60 Hz (dual frequency capability) |
| Primary current range | 5 A to 1000 A (selectable ratios) |
| Rated secondary current | 1 A or 5 A |
| Accuracy classes | Metering: 0.2S, 0.2, 0.5 / Protection: 10P10, 10P15 |
| Rated burden | Up to 20 VA per core/winding as specified |
| Burden power factor | cosφ = 0.8 (lagging) unless otherwise specified |
| Short-circuit withstand | Ith up to 63 kA (1 s) / Idyn up to 130 kA (peak) |
| Insulation level | 10 kV class per IEC 61869-2 and GB 1208 |
| Applicable standards | IEC 61869-1 / IEC 61869-2; GB 1208-2006; GB/T 20840.1 / 20840.2 |
| Model variants | LZJC-10Q / LZJC-10G (different mounting configurations) |
Product Shows
Working Principle
Operating on Faraday’s law of electromagnetic induction, the transformer features a toroidal magnetic core with primary conductor passing through the aperture and secondary windings wound around the core. The magnetic flux generated by primary current induces proportional voltage in the secondary winding, delivering standardized output current through connected burden. The fully-enclosed epoxy resin construction provides superior insulation performance while maintaining precise magnetic coupling.
System Application Position
- Medium Voltage Distribution: 6-10kV switchgear and distribution panels
- Energy Metering: Revenue-grade electricity measurement systems with Class 0.2S accuracy
- Protection Circuits: Overcurrent, differential, and distance protection schemes
- SCADA Integration: Supervisory control and data acquisition systems
- Power Quality Monitoring: Harmonic analysis and power factor measurement
Structural Overview
Epoxy resin cast construction with fully-enclosed design ensures superior insulation performance, moisture resistance, and mechanical strength. The post-type mounting configuration provides compact installation in constrained switchgear environments while maintaining excellent electrical clearance and creepage distances. The design incorporates high-grade silicon steel core materials for optimal magnetic performance and minimal losses.
Model Designation
Model Code Explanation
LZJC-10Q / LZJC-10G Structure:
- L — Current transformer (CT)
- Z — Indoor support (pillar) type
- J — Reinforced design for enhanced performance
- C — Cast-resin (epoxy) insulated, fully enclosed structure
- 10 — Voltage class (kV)
- Q / G — Model variant code (installation/structure differences)
Variant Differences
LZJC-10Q and LZJC-10G are electrically equivalent when specified with the same ratio, accuracy classes, burdens, and Ith/Idyn. The differences between Q/G variants are primarily mechanical and installation-related to match different switchgear layouts and mounting constraints:
- LZJC-10Q: Standard post-type mounting with traditional terminal arrangement
- LZJC-10G: Enhanced mounting design for specific switchgear integration requirements
Service Conditions
The LZJC-10 series current transformers are designed for indoor operation under normal service conditions in medium-voltage power systems.
- Installation environment: Indoor installation only
- 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
- Atmospheric pressure: 80 kPa to 110 kPa
- Pollution degree: Class 2 per IEC 61869-1
Construction
Construction Design
- Structure: Support (post) type for indoor switchgear
- Insulation: Fully enclosed epoxy resin cast insulation system
- Core: Ring-type magnetic core with grain-oriented silicon steel
- System: Integrated primary and secondary insulation coordination
- Materials: UV-resistant epoxy resin formulation for long-term stability
The epoxy resin casting provides stable insulation properties and resistance to moisture, contamination, and aging for long-term indoor service. The design offers exceptional resistance to electrical stress, environmental aging, and mechanical shock.
Windings & Terminal Marking
- Primary terminals: P1 / P2 (top-mounted bus bars with polarity marking)
- Secondary terminals (Group 1): 1S1 / 1S2 (metering applications)
- Secondary terminals (Group 2): 2S1 / 2S2 (protection applications, where applicable)
- Terminal material: Tin-plated copper for corrosion resistance
Terminal markings follow standard CT polarity conventions per IEC 61869-2. Under normal operating conditions, the reference current direction is defined from P1 to P2. Correct terminal identification shall be observed to ensure metering and protection performance.
Technical Data
This section provides selection-oriented technical data for the LZJC-10Q/LZJC-10G series indoor, cast-resin current transformer used in 10 kV class AC systems (50/60 Hz). Data shown below is intended for preliminary selection of accuracy class combinations, rated burdens, and short-circuit withstand capability.
Definitions: Accuracy class combination indicates available metering/protection cores in one CT (multi-core configuration may apply). Rated output (VA) is specified per secondary core. Ith is the rated short-time thermal current (typically 1 s). Idyn is the rated dynamic current (peak).
Notation: Ith/Idyn may be expressed as kA or as multiples of rated primary current (×In) depending on configuration; acceptance shall be based on nameplate values and the factory test report.
Data Reference
| Rated Primary Current (A) |
Accuracy Class |
Rated Output (VA) |
Short-time Thermal Current (Ith) |
Rated Dynamic Current (Idyn) |
|---|---|---|---|---|
| 5–100 | 0.2S / 10P10 | 10 / 15 | 100 × In | 250 × In |
| 5–100 | 0.2 / 10P15 | 10 / 15 | 100 × In | 250 × In |
| 5–100 | 0.5 / 10P10 | 10 / 20 | 100 × In | 250 × In |
| 150 | 0.2S / 10P10 | 15 / 15 | 13.5 kA | 34 kA |
| 200 | 0.2 / 10P15 | 15 / 15 | 18 kA | 45 kA |
| 300 | 0.5 / 10P10 | 15 / 20 | 27 kA | 67.5 kA |
| 400 | 0.2S / 10P15 | 15 / 15 | 36 kA | 90 kA |
| 500 | 0.2 / 10P10 | 20 / 20 | 45 kA | 112.5 kA |
| 600 | 0.5 / 10P15 | 15 / 20 | 54 kA | 135 kA |
| 750 | 0.2S / 10P10 | 20 / 20 | 63 kA | 130 kA |
| 800–1000 | 0.5 / 10P15 | 20 / 20 | 63 kA | 130 kA |
Standards & Normative References
| Standard | Title | Application |
|---|---|---|
| IEC 61869-1 | Instrument Transformers – Part 1: General Requirements | General requirements and testing procedures |
| IEC 61869-2 | Instrument Transformers – Part 2: Additional Requirements for Current Transformers | CT-specific requirements and performance criteria |
| GB/T 20840.1 | Instrument Transformers – Part 1: General Requirements | National standard (aligned with IEC 61869 framework) |
| GB/T 20840.2 | Instrument Transformers – Part 2: Current Transformers | National CT requirements (aligned with IEC 61869-2) |
| GB 1208-2006 | Current Transformers | National CT standard for legacy applications |
| IEEE C57.13 | Standard Requirements for Instrument Transformers | Optional (North America project reference) |
| IEC 60068-2-17 | Environmental Testing – Salt Mist | Optional (project-specific environmental validation) |
| IEC 60085 | Electrical Insulation – Thermal Evaluation | Optional (insulation thermal evaluation reference) |
Factory Test Compliance
- Routine tests per applicable IEC/GB requirements (including polarity/marking, ratio verification, and accuracy verification per specified class and burden)
- Dielectric tests per insulation coordination requirements and applicable standard
- Partial discharge test where specified by the project requirement
- Visual and dimensional inspection including marking and workmanship conformity
- Type and special tests as required by the project specification
- Short-circuit withstand tests for Ith and Idyn verification
Installation & Dimensions
- Outline dimensions and mounting details are provided in the dimensional drawings.
- The transformer shall be securely mounted using the designated fixing holes with appropriate torque specifications.
- Primary conductor connection may be made via busbar or bolted terminals, depending on the variant.
- Adequate clearance shall be maintained for insulation, heat dissipation, and maintenance access.
- Installation orientation: Flexible mounting in any direction (specify orientation at ordering)
Outlines
Safety Notes
- Secondary circuit must never be left open when the transformer is energized, as dangerous high voltage may appear across the secondary terminals.
- During inspection or maintenance, the secondary circuit shall be short-circuited before disconnecting any instruments.
- One point of the secondary circuit should be reliably grounded in accordance with applicable standards.
- All installation and maintenance work shall comply with local electrical safety regulations and company safety procedures.
- Verify proper phase sequence and polarity before energization.
Ordering Information
When placing an order, the required configuration shall be specified according to the local grid requirements, applicable standards, and project technical specification. The following parameters shall be clearly stated for technical confirmation and production release:
- Rated primary current / transformation ratio
- Rated secondary current (1 A or 5 A)
- Application and accuracy requirements (metering and/or protection accuracy class combination)
- Rated burden (VA) for each secondary core/winding
- Short-circuit withstand requirements: Ith (1 s) and Idyn (peak)
- Model variant: LZJC-10Q or LZJC-10G
- Frequency: 50 Hz or 60 Hz
- Special requirements: Environmental conditions, certificates, documentation language
How to Select
- Determine rated primary current (Ip) based on feeder/load rating and expected operating range (typically 80-120% of normal load current).
- Select metering and/or protection accuracy requirements (e.g., 0.2S / 0.5 for metering; 10P10 for protection).
- Confirm rated burden (VA) for each secondary circuit based on connected meters/relays and wiring losses.
- Verify short-circuit withstand capability (Ith/Idyn) against the switchgear fault level and protection coordination.
- Select appropriate model variant (Q or G) based on installation requirements and switchgear design.
If local utility or project requirements apply (e.g., insulation level, partial discharge limit, terminal arrangement, mounting constraints, documentation language, or required certificates), specify them at the ordering stage. Special configurations shall be confirmed by technical agreement and final data sheet prior to production.
FAQs