LB7-220 Series Oil-Immersed Current Transformer

Our LB7-220 oil-immersed current transformers feature U-shaped capacitive insulation for precise measurement and protection in 220kV systems.

• Primary current up to 2500A; short-time thermal current of 31.5kA/3s.

• Fully sealed with metal bellows expander for maintenance-free operation.

• Amorphous alloy metering cores achieve Class 0.2/0.2S accuracy; up to 6 secondary cores with 5P/10P classes.

• Partial discharge ≤10pC; tanδ ≤0.005 for superior insulation reliability.

• Fast delivery, reliable quality, and extensive project experience.

LB7-220 Series Oil-Immersed Current Transformer

The LB7-220 Series is an outdoor oil-immersed current transformer specifically designed for global high-voltage transmission and distribution systems. Featuring mature and reliable capacitive insulation technology in a fully sealed construction, this series ensures long-term stability under demanding environmental conditions. It provides precise current measurement, energy metering, and relay protection functions for 220kV, 50/60Hz power networks.

Technical Specifications

Item	Parameter
Rated Voltage	220kV
Rated Primary Current	Typically covers the range from 200A to 2500A
Rated Secondary Current	1A or 5A
Rated Short-Time Thermal Current	e.g., 31.5kA (3s)
Rated Dynamic Current	e.g., 120kA
Partial Discharge Level	≤ 10 pC (at specified test voltage)
Dielectric Dissipation Factor (tanδ)	≤ 0.005
Insulation Level	Rated lightning impulse withstand voltage up to 950kV, rated power frequency withstand voltage up to 395kV

Core Design and Construction

The product utilizes a classic "U"-shaped primary winding and a capacitive oil-paper insulation structure. This design ensures highly uniform electric field distribution, resulting in very low dielectric loss and partial discharge levels, which form the foundation of the device's high insulation reliability.

To ensure long-term maintenance-free operation, the transformer is fully sealed and equipped with a metal bellows expander at the top. This device not only effectively compensates for the volume changes of the transformer oil due to temperature variations but also completely isolates the internal insulation from external air and moisture. This prevents insulation aging and moisture ingress, significantly extending the product's service life. A multi-functional valve is installed at the bottom of the tank for convenient on-site oil sampling or maintenance operations.

Superior Performance and Flexible Configuration

High-Accuracy Measurement: The secondary metering core is made of high-permeability amorphous alloy, achieving measurement accuracy as high as Class 0.2 or 0.2S, meeting the stringent requirements for revenue metering.

Flexible Protection Configuration: The product typically provides 4 to 6 independent secondary cores. The accuracy classes (e.g., 5P, 10P) and accuracy limit factors (e.g., 10, 20, 30) of these cores can be arbitrarily combined according to the user's specific relay protection scheme (steady-state or transient protection), offering comprehensive protection for lines, busbars, and transformers.

Broad Adaptability: The product design fully considers diverse application scenarios. The standard LB7-220 type is suitable for areas with an altitude below 1700 meters, while the LB7-220W1/W2 types are enhanced for polluted areas with increased creepage distance, suitable for Class IV pollution severity. The equipment can operate reliably within an ambient temperature range of -30°C to +40°C.

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