Overview
The LB7-35W is a 35kV outdoor oil-immersed current transformer designed for high-voltage power systems rated up to 40.5kV. It features an oil-immersed insulation system with a sealed iron tank and high-quality magnetic core, ensuring reliable dielectric strength and thermal stability in outdoor environments.
This CT supports both metering (0.2S/0.5S) and protection (5P/10P) accuracy classes, making it suitable for revenue metering, relay protection, and grid monitoring in 35kV substations, industrial facilities, and utility distribution networks. It complies with standard insulation coordination levels for 35kV class systems and operates at 50Hz or 60Hz.
Key Ratings Snapshot
| Parameter | Rating |
|---|---|
| Voltage class | 35kV / 40.5kV |
| Rated insulation level | 40.5/95/185kV |
| Insulation type | Oil-immersed with sealed iron tank |
| Installation condition | Outdoor |
| Rated frequency | 50Hz or 60Hz |
| Rated secondary current | 5A or 1A |
| Metering accuracy class | 0.2S, 0.5S |
| Protection accuracy class | 5P, 10P |
| Application | Current sampling, energy metering, relay protection |
| Structure | Porcelain/bushing insulation with iron oil-tank base |
| Primary conductor | Bushing-type, integrated with tank |
| Secondary terminals | Accessible via terminal box on tank |
Model Designation
- L: Current transformer.
- B: Oil-immersed current transformer structure series reference.
- 7: Design sequence or product platform code.
- 35: 35kV rated voltage class, normally used with 40.5kV highest system voltage platforms.
- W: Outdoor type.
Construction
The LB7-35W features a robust sealed iron-tank construction filled with transformer oil, providing enhanced internal insulation, heat dissipation, and long-term dielectric stability in outdoor conditions. The primary winding is integrated into a high-voltage porcelain or composite bushing mounted atop the tank. The magnetic core, made of high-permeability grain-oriented silicon steel, ensures low excitation loss and high accuracy under both metering and protection loads. Secondary windings are precision-wound and encapsulated within the oil-filled chamber, with leads routed to a weatherproof terminal box on the tank exterior. The entire assembly includes a grounding point and is designed to withstand environmental stresses including rain, humidity, and wide temperature variations when installed per approved engineering drawings.
Technical Parameters
Service Conditions
- Installation place: Outdoor
- Rated frequency: 50Hz or 60Hz
- Ambient temperature: -25°C to +55°C reference
- Altitude: ≤ 1000m under standard service conditions; higher altitude by agreement
- Atmospheric condition: No severe pollution, corrosive gas or explosive atmosphere beyond design limits
- Outdoor exposure: Suitable for outdoor substation and high-voltage feeder environments
- Installation condition: No severe shock, abnormal vibration or mechanical stress beyond design limits
Technical Parameters
The LB7-35W is an outdoor oil-immersed current transformer rated for 35kV / 40.5kV class systems, using transformer oil as the insulation medium. It operates within an ambient temperature range of -25°C to +55°C at altitudes up to 1000m and complies with IEC 61869 and GB/T 20840 standards. The device supports primary currents from 5A to 1200A with secondary outputs of 1A or 5A.
| Rated primary current (A) |
Accuracy Classes / Rated Output (VA) |
Short-time thermal current (kA/1s) |
Rated dynamic current (kA) |
||
|---|---|---|---|---|---|
| 0.2(S) | 0.5(S) | 5(10)P30 | |||
| 5~300 | 10 | 15 | 15 | 80×I1n | 200×I1n |
| 400 | 20 | 30 | 20 | 31.5 | 100 |
| 500 | 45 | 112.5 | |||
| 600 | 63 | 160 | |||
| 750~800 | 30 | 40 | 20 | 80 | 200 |
| 1000~1200 | 100 | 250 | |||
Installation & Wiring
Installation Diagram
The LB7-35W outdoor oil-immersed current transformer is designed for pole or structure mounting in high-voltage applications. Installation must be performed by qualified personnel following local and national electrical codes. Ensure proper grounding, alignment, and secure fastening of all hardware as shown in the diagram.
Selection & FAQs
Selection Guide
- Confirm the oil-system construction. The page mentions both a sealed tank and a top conservator/head; establish whether it is hermetic, how oil level is indicated and what sampling or maintenance applies.
- Select the 5A–1200A ratio and taps. For multiple ratio, specify all S1/S2/S3 connections and guarantee accuracy, output and fault withstand at every tap.
- Use the detailed 5P30 data for protection selection. Generic 5P/10P references are not supported by a ratio-specific table; any 10P version needs separate documentation.
- Coordinate oil, dielectric and environmental tests. Specify oil quality, moisture, sealing/leak test, dielectric loss, partial discharge, bushing creepage, pollution, altitude and temperature.
- Approve transport and foundation interfaces. Confirm approximately 1299mm height, 376 × 345mm base, lifting/transport orientation, oil sealing, terminal forces, M10 ground and fault-current duration.
Frequently Asked Questions
Q1: Can the LB7-35W be installed in 40.5kV systems?
Yes, it is rated for 35kV and 40.5kV class systems. The oil-immersed design complies with IEC 61869 standards. Please provide your system voltage for factory verification.
Q2: Which accuracy class is suitable for protective relaying?
Select the 5P30 or 10P30 class for protection applications. This ensures accurate secondary output during high fault currents up to 30 times the rated value. Specify your exact burden during ordering.
Q3: What are the altitude limits for outdoor installation?
Standard service conditions support altitudes up to 1000m. For installations exceeding 1000m, derating or custom design is required. Submit your site elevation data for engineering review.
Q4: How does it handle short-circuit thermal currents?
The transformer withstands a short-time thermal current of 80kA for 1 second. It also supports a rated dynamic current of 80kA. Confirm your specific primary current rating for exact thermal parameters.
Q5: Are primary current ratings customizable above 300A?
Yes, the LB7-35W supports primary currents up to 1200A. Secondary outputs can be configured for 1A or 5A. Please specify your required primary and secondary current ratios for quotation.
Q6: Do these transformers comply with international IEC standards?
Yes, the device complies with IEC 61869 and GB/T 20840 standards. Factory routine tests are conducted strictly per these specifications. Request the detailed test certificate package prior to dispatch.
Q7: Where is this oil-immersed current transformer typically applied?
It is designed for outdoor substations and high-voltage feeder environments. The unit operates reliably in ambient temperatures from -25°C to +55°C. Ensure the site lacks severe corrosive gases or explosive atmospheres.