Overview
The LJW1-35 and LJWD1-35 series are 35 kV class oil-immersed current transformers engineered for precise current measurement, energy metering, and relay protection in AC power systems. Designed for both indoor and outdoor use, these units deliver galvanically isolated secondary signals proportional to primary current through robust electromagnetic induction principles.
Built with oil-paper insulation and a sealed steel tank, the transformers ensure high dielectric strength, thermal stability, and long-term reliability across demanding utility and industrial environments. Their standardized 5 A output integrates seamlessly with meters, relays, and SCADA systems.
Key Ratings Snapshot
| Item | Specification |
|---|---|
| System voltage class | 35 kV (27.5:40.5 kV range) |
| Rated frequency | 50 Hz (60 Hz on request) |
| Rated secondary current | 5 A |
| Accuracy classes | Metering: 0.2, 0.5, 1; Protection: 3(D) |
| Continuous thermal rating | 120% of rated primary current |
| Insulation level | 40.5/95/1200 kV (Um/Ud/Ui) |
| Creepage distance | Standard: >=735 mm; W2 type: >=1100 mm |
| Current ratio range | 5:600/5 A |
| Rated output (0.2 class) | 30:50 VA |
| Construction type | Oil-immersed, single-phase, self-cooled |
Construction
The transformer features a single-phase oil-immersed self-cooled design with a ring-type magnetic core and oil-paper insulation system enclosed in a welded steel tank. Vacuum oil filtration and impregnation processes enhance dielectric performance and thermal efficiency. The tank includes a breathing device with waterproof/snow cap and diaphragm isolation to minimize oil oxidation and moisture ingress.
This construction delivers superior short-circuit withstand capabilityâthermal stability at 75 times conventional designs and dynamic stability at 187.5 timesâensuring reliable operation during fault conditions while maintaining stable performance across ambient temperatures from -25 degC to +40 degC.
Technical Parameters
Service Conditions
- Installation environment: Indoor and outdoor
- Altitude: <= 4000 m (higher requires engineering confirmation)
- Ambient temperature: -25 degC to +40 degC
- Pollution level: Class II
- Environmental conditions: Free from corrosive gases, explosive media, severe vibration or mechanical shock
Technical Data
| Model | Voltage Class (kV) |
Current Ratio (A) |
Rated Output 0.2 Class (VA) |
|---|---|---|---|
| LJW1-35 | 35 | 5:600/5 | 30:50 |
| LJWD1-35 | 35 | 5:600/5 | 30:50 |
Installation & Wiring
Installation Diagram
Mount the transformer securely using the designated base and fixing holes. Connect primary conductors via bolted terminals with specified torque. Maintain adequate clearance for insulation, heat dissipation, and maintenance access. Verify oil level regularly per maintenance schedule.
Selection & FAQs
Selection Guide
- Treat this as a legacy replacement project. Confirm the exact LJW1 or dual-winding LJWD1 nameplate, ratio, winding functions, dimensions and protection relay requirements.
- Correct the ambiguous current and output notation. Verify “5:600/5” as the intended 5A–600A/5A range and “30:50VA” as the exact per-winding output.
- Do not use the published 1200kV impulse value. The 40.5/95/1200kV sequence is implausible and must be replaced by certified power-frequency and lightning-impulse data.
- Translate legacy 3(D) protection requirements. Obtain excitation curve, knee point or limiting data, winding resistance and burden to match a modern relay; do not assume equivalence to 5P/10P/PX.
- Confirm oil-system and installation details. Resolve sealed tank versus breathing device, then verify diaphragm, oil level, bushing creepage, base, lifting, grounding, fault-current duration and maintenance.
Frequently Asked Questions
Q1: Is the LJWD1-35 suitable for outdoor installation?
Yes, it supports both indoor and outdoor environments. It operates in Class II pollution levels without corrosive gases. Confirm specific site conditions with our engineering team.
Q2: Which rated output applies to the 0.2 accuracy class?
The 0.2 class provides a rated output range of 30 to 50 VA. This ensures precise measurement for 35kV systems. Contact technical support for detailed burden calculations.
Q3: How does high altitude affect the 35kV current transformer?
Standard models are rated for altitudes up to 4000 meters. Installations exceeding this limit require specific engineering confirmation. Please provide your exact site altitude during inquiry.
Q4: Can the current ratio be customized for specific projects?
Standard models feature a 5:600/5A current ratio. Custom ratios are subject to engineering evaluation and factory confirmation. Submit your project specifications for a tailored assessment.
Q5: What routine tests are conducted prior to dispatch?
Routine testing parameters and certification details are subject to confirmation based on your order. Please contact our technical support for specific factory test documentation.
Q6: Where is this oil-immersed current transformer typically applied?
This 35kV steel tank transformer is ideal for power measurement and protection in substations. It integrates seamlessly into 35kV switchgear systems. Request application engineering support for integration guidance.
Q7: Why are environmental conditions critical for this equipment?
The unit requires an ambient temperature between -25°C and +40°C. It must be free from explosive media and severe mechanical shock. Verify your installation environment meets these operational limits.