Product Overview
Functional Definition
The LFS-10 epoxy resin current transformer 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 with fully-enclosed epoxy resin construction to provide galvanically isolated secondary current signals proportional to primary current in 10kV distribution systems.
Key Ratings
| Item | Specification (per order / nameplate) |
|---|---|
| System voltage class | 10 kV class (indoor switchgear and distribution applications) |
| Rated frequency | 50 Hz / 60 Hz |
| Rated primary current | 5A to 1000A (standard ratios available) |
| Rated secondary current | 1 A or 5 A |
| Accuracy classes | Metering: 0.2S, 0.2, 0.5 / Protection: 10P10, 10P15 |
| Rated burden | 10VA, 15VA, 20VA (per core/winding as specified) |
| Burden power factor | cosφ = 0.8 (lagging) unless otherwise specified by project standard |
| FS / ALF (where specified) | Metering security factor (FS) and protection accuracy limit factor (ALF) per ordered specification |
| Short-circuit withstand | Ith up to 63kA (1 s) and Idyn up to 130kA (peak) as specified |
| Insulation level | 12kV BIL, 28kV power frequency withstand (1 min) |
| Applicable standards | IEC 61869-1 / IEC 61869-2; GB/T 20840.1 / 20840.2; IEEE C57.13 |
| Environmental rating | Indoor use: -5°C to +40°C, ≤1000m altitude |
Product Show
Working Principle
Operating on Faraday’s law of electromagnetic induction, the LFS-10 transformer features a toroidal magnetic core with primary conductor passing through the central 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 ensures superior electrical insulation and environmental protection.
System Application Position
- Medium Voltage Distribution: 6-10kV indoor switchgear and distribution panels
- Energy Metering: Revenue-grade electricity measurement systems (Class 0.2S/0.2)
- Protection Circuits: Overcurrent, differential, and distance protection schemes (Class 10P10/10P15)
- 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 compact design provides reliable operation in constrained switchgear environments while maintaining excellent electrical clearance and creepage distances per IEC 61869 requirements.
Model Designation
Code Explanation
- L — Current transformer (CT)
- F — Fully-enclosed structure
- S — Solid insulation (epoxy resin cast)
- 10 — Voltage class (kV)
Configuration Examples
| Model Code | Primary Current | Secondary Current | Accuracy Classes |
|---|---|---|---|
| LFS-10-100/5-A | 100A | 5A | 0.2S + 10P10 |
| LFS-10-300/1-B | 300A | 1A | 0.5 + 10P15 |
| LFS-10-600/5-C | 600A | 5A | 0.2 + 0.2 + 10P10 |
Service Conditions
The LFS-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 requires derating)
- 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
Construction
Construction Design
- Structure: Fully-enclosed epoxy resin cast design for indoor use
- Insulation: Solid epoxy resin insulation system with integrated primary and secondary insulation
- Core: High-permeability silicon steel ring-type magnetic core
- Primary: Single-turn primary (busbar through-type) or multi-turn wound primary
- Housing: Flame-retardant epoxy resin with UV-resistant properties
The epoxy resin casting provides stable insulation properties and resistance to moisture, contamination, and aging for long-term indoor service with minimal maintenance requirements.
Windings & Terminal Marking
- Primary terminals: P1 / P2 (or through-hole for busbar mounting)
- Secondary terminals (Group 1): 1S1 / 1S2
- Secondary terminals (Group 2): 2S1 / 2S2 (when multi-core configuration)
- Secondary terminals (Group 3): 3S1 / 3S2 (when applicable)
Terminal markings follow IEC 61869 and IEEE C57.13 standard CT polarity conventions. Under normal operating conditions, the reference current direction is defined from P1 to P2. Correct terminal identification shall be observed to ensure proper metering and protection performance.
Technical Data
This section provides selection-oriented technical data for the LFS-10 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 (1 s). Idyn is the rated dynamic current (peak).
Notation: Ith/Idyn values are based on standard configurations. Custom short-circuit ratings available upon request. Acceptance shall be based on nameplate values and factory test report.
Data Reference
| Rated Primary Current (A) |
Accuracy Class Combinations |
Rated Output (VA) |
Short-time Thermal Current (Ith) – kA/1s |
Rated Dynamic Current (Idyn) – kA peak |
|---|---|---|---|---|
| 5–50 | 0.2S / 10P10 0.2 / 10P10 0.5 / 10P15 |
10 / 15 10 / 15 10 / 20 |
2.5 | 6.25 |
| 75–100 | 0.2S / 10P10 0.2 / 0.2 / 10P10 0.5 / 10P15 |
10 / 15 10 / 10 / 15 10 / 20 |
5.0 | 12.5 |
| 150 | 0.2S / 10P10 0.2 / 10P15 0.5 / 10P10 |
10 / 15 10 / 20 15 / 15 |
13.5 | 34 |
| 200 | 0.2S / 10P10 0.2 / 10P15 0.5 / 10P10 |
10 / 15 15 / 20 15 / 15 |
18 | 45 |
| 300 | 0.2S / 10P10 0.2 / 10P15 0.5 / 10P10 |
15 / 15 15 / 20 15 / 15 |
27 | 67.5 |
| 400 | 0.2 / 10P10 0.5 / 10P10 0.5 / 10P15 |
15 / 15 15 / 15 15 / 20 |
36 | 90 |
| 500 | 0.2 / 10P10 0.5 / 10P10 0.5 / 10P15 |
15 / 15 15 / 15 15 / 20 |
45 | 112.5 |
| 600 | 0.2 / 10P10 0.5 / 10P10 0.5 / 10P15 |
15 / 15 15 / 15 20 / 20 |
54 | 135 |
| 750 | 0.5 / 10P10 0.5 / 10P15 10P10 / 10P10 |
15 / 15 20 / 20 15 / 15 |
63 | 130 |
| 800–1000 | 0.5 / 10P10 0.5 / 10P15 10P10 / 10P10 |
20 / 15 20 / 20 15 / 15 |
63 | 130 |
Standards & Normative References
| Standard | Title | Application |
|---|---|---|
| IEC 61869-1 | Instrument Transformers – Part 1: General Requirements | General requirements |
| IEC 61869-2 | Instrument Transformers – Part 2: Additional Requirements for Current Transformers | CT-specific requirements |
| 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) |
| IEEE C57.13 | Standard Requirements for Instrument Transformers | North America project reference |
| GB 1208-1997 | Current Transformers | National CT standard where specified by project |
| IEC 60085 | Electrical Insulation – Thermal Evaluation | Insulation thermal evaluation reference |
Factory Test Compliance
- Routine tests per applicable IEC/GB requirements (polarity/marking, ratio verification, accuracy verification per specified class and burden)
- Dielectric tests per insulation coordination requirements and applicable standard
- Partial discharge test where specified by project requirement (≤10pC at 1.2Um/√3)
- Visual and dimensional inspection including marking and workmanship conformity
- Type and special tests as required by project specification
Installation & Dimensions
Outline
- Outline dimensions and mounting details are provided in certified drawings supplied with order acknowledgment
- The transformer shall be securely mounted using the designated fixing holes with appropriate torque specifications
- Primary conductor connection via busbar through-hole or bolted terminals, depending on configuration
- Adequate clearance shall be maintained for insulation, heat dissipation, and maintenance access per local codes
- Secondary wiring shall use appropriate cable size for burden and distance requirements
Installation Requirements
| Parameter | Requirement | Notes |
|---|---|---|
| Mounting orientation | Vertical preferred, horizontal acceptable | Consult drawings for specific orientation requirements |
| Clearance distances | Per IEC 61936-1 / IEEE 80 | Minimum 150mm all directions for maintenance access |
| Primary connection torque | As specified in installation manual | Use calibrated torque wrench, apply anti-seize compound |
| Secondary grounding | One point solidly grounded | Per local electrical safety regulations |
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
- Use appropriate PPE and follow lockout/tagout procedures during installation and maintenance
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)
- Environmental conditions (if different from standard)
- Mounting and terminal arrangement
- Applicable standards (IEC, IEEE, GB, etc.)
Selection Guide
Step 1: Determine rated primary current (Ip) based on feeder/load rating and expected operating range.
Step 2: Select metering and/or protection accuracy requirements (e.g., 0.2S / 0.5 for metering; 10P10 for protection).
Step 3: Confirm rated burden (VA) for each secondary circuit based on connected meters/relays and wiring losses.
Step 4: Verify short-circuit withstand capability (Ith/Idyn) against the switchgear fault level.
Step 5: Specify mounting configuration and terminal arrangement requirements.
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