Overview
The LB6-35 and LABN6-35 series are outdoor, fully-sealed oil-paper insulated current transformers designed for accurate current measurement, energy metering, and relay protection in 35 kV AC power systems. Operating at 50 Hz or 60 Hz, they deliver galvanically isolated secondary signals proportional to primary current via electromagnetic induction. The robust oil-paper insulation ensures excellent dielectric strength and long-term weather resistance for medium-voltage outdoor installations.
These post-type CTs feature toroidal magnetic cores with standardized 5 A secondary output, supporting both metering (e.g., 0.2, 0.5) and protection (e.g., 10P10, 10P20) applications in distribution substations and switchgear.
Key Ratings Snapshot
| Item | Specification |
|---|---|
| System voltage class | 35 kV (Um: 40.5 kV) |
| Rated frequency | 50 Hz or 60 Hz |
| Rated secondary current | 5 A |
| Accuracy classes | Metering: 0.2 / 0.5; Protection: 10P10 / 10P20 |
| Rated burden | 30 VA / 40 VA typical per core |
| Burden power factor | cos phi = 0.8 (lagging) |
| Insulation level | 40.5 / 95 / 185 kV (Um / LIWL / ACWL) |
| Creepage distance | Standard: >=735 mm; W2: >=1100 mm |
| Short-circuit withstand | Ith (1 s) and Idyn (peak) per primary rating |
| Applicable standards | IEC 61869-1/2; GB/T 20840.1/2 |
Model Designation
LB6-35:
- L: Current transformer (CT)
- B: Protection configuration available
- 6: Design series code
- 35: Voltage class (kV)
LABN6-35:
- L: Current transformer (CT)
- A: Outdoor installation type
- B: Protection configuration available
- N: Internal structure identifier
- 6: Design series code
- 35: Voltage class (kV)
Construction
The transformer features a post-type support structure with a fully-sealed oil tank, designed for stable outdoor mounting and compliance with 35 kV electrical clearances. The oil-paper insulation system undergoes vacuum drying and oil impregnation to eliminate moisture and air pockets, ensuring consistent dielectric performance and thermal stability over its service life.
External tank construction provides corrosion resistance and long-term weatherproofing. The toroidal magnetic core enables precise current transformation, while terminal markings (P1/P2, 1S1/1S2, etc.) follow IEC 61869-2 polarity conventions for correct metering and protection coordination.
Technical Parameters
Service Conditions
- Installation environment: Outdoor installation
- Altitude: <=1000 m above sea level
- Ambient temperature: -25°C to +40°C
- Relative humidity: Daily average <= 95%, monthly average <= 90%
- Pollution class: Grade II or Grade III
- Environmental conditions: Normal atmospheric conditions; free from corrosive gases, explosive media, or severe mechanical vibration
Technical Parameters
The LB6-35KV is an outdoor oil-immersed current transformer designed for 35kV class systems. It operates within an ambient temperature range of -25°C to +40°C at altitudes up to 1000m and complies with IEC and GB standards. The device supports primary currents from 5A to 400A with multiple accuracy class combinations.
| Rated primary current (A) |
Accuracy classed combination |
Rated Output (VA) |
10P Accuracy class limit factor |
Short-time thermal current (kA/s) |
Rated dynamic current (kA) |
|||
|---|---|---|---|---|---|---|---|---|
| 0.2 | 0.5 | 10P1 | 10P2 | |||||
| 5 | 0.5/10P1/10P2 0.2/10P1/10P2 |
30 | 40 | 40 | 30 | 20 | 0.5 | 1.28 |
| 10 | 1 | 2.55 | ||||||
| 15 | 1.5 | 3.83 | ||||||
| 20 | 2 | 5.1 | ||||||
| 30 | 3 | 7.65 | ||||||
| 40 | 4 | 10.2 | ||||||
| 50 | 5 | 12.75 | ||||||
| 75 | 7.5 | 19.13 | ||||||
| 100 | 10 | 25.5 | ||||||
| 150 | 15 | 38.3 | ||||||
| 200 | 20 | 51 | ||||||
| 300 | 30 | 76.5 | ||||||
| 400~2000 | 40 | 102 | ||||||
Installation & Wiring
Installation Diagram
The transformer must be securely mounted on a stable foundation using the designated fixing holes. Primary connection is typically made via busbar pass-through or bolted terminals. Maintain adequate clearance for insulation coordination, heat dissipation, and maintenance access per local regulations.
Outline Dimensions
| Rated Primary Current (A) |
Base Dimension B (mm) |
Height h (mm) |
Total Height H (mm) |
Oil Weight (kg) |
Total Weight (kg) |
|---|---|---|---|---|---|
| 5 â 75 | 508 | 1315 | 1475 | 25 | 160 |
| 100 â 600 | 508 | 1315 | 1475 | 25 | 160 |
| 750 â 1000 | 548 | 1315 | 1475 | 29 | 190 |
| 1200 â 1500 | 588 | 1315 | 1475 | 29 | 190 |
| 2000 | 658 | 1335 | 1495 | 32 | 205 |
Selection & FAQs
Selection Guide
- Interpret 10P1/10P2 as winding identifiers pending confirmation. They likely denote protection cores 1 and 2, while the ALF 20 column suggests a 10P20 requirement; obtain the full class per core.
- Resolve the four-output/three-function mismatch. The 30/40/40/30VA sequence has more values than listed core functions, so require an approved winding table and terminals.
- Select the 5A–2000A ratio and fault duty. Use the exact 1-second thermal/peak values and fixed 5A burden calculation; no 1A option is published.
- Confirm standard versus extended creepage. The page cites ≥735mm and W2 ≥1100mm, but the listed model lacks W2; identify the actual bushing and pollution class.
- Approve oil, weight and foundation requirements. Confirm sealed-tank design, oil quality, leakage tests, lifting, base width, 1475–1495mm height, 160–205kg weight, grounding and maintenance.
Frequently Asked Questions
Q1: What are the environmental limits for outdoor installation?
The LB6-35KV operates in ambient temperatures from -25°C to +40°C at altitudes up to 1000m. Ensure the site is free from corrosive gases and severe mechanical vibration before installation.
Q2: Which accuracy class combinations are available for this 35kV transformer?
It supports 0.5/10P1/10P2 and 0.2/10P1/10P2 combinations. Rated outputs are 30VA for 0.2 class and 40VA for 0.5/10P classes. Contact us to specify your exact metering and protection requirements.
Q3: How does it perform under short-circuit thermal conditions?
The transformer features a 10P accuracy class limit factor of 20. Specific short-time thermal and dynamic current ratings depend on the primary current selected. Please provide your system fault levels for exact sizing.
Q4: Which international standards does this oil-immersed current transformer comply with?
The LB6-35KV complies with both IEC and GB standards for 35kV class systems. Request the specific type test reports and compliance certificates during the procurement process.
Q5: Can the primary current be customized beyond the standard 400A?
Standard models support 5A to 400A primary currents. Custom ratios above 400A are subject to factory confirmation. Please provide your exact project specifications for evaluation.
Q6: What applications are suitable for the LB6-35KV current transformer?
It is designed for outdoor 35kV systems in Grade II or III pollution environments. Ideal for substation metering and protection. Contact us for specific application engineering support.
Q7: Are there specific pollution class requirements for the outdoor housing?
The outdoor oil-immersed design is rated for Grade II or Grade III pollution classes. Ensure daily average relative humidity remains below 95% to maintain optimal insulation performance.