Product Overview
The LB7-35W outdoor oil-immersed current transformer is a high-voltage instrument transformer for 35kV / 40.5kV outdoor power systems. It is used for current sampling, energy metering, power monitoring and relay protection in high-voltage transmission and distribution lines. The product uses an oil-immersed insulation system, high-quality magnetic core material and precision winding technology to provide stable secondary current signals for meters, relays and grid automation equipment.
This model should be positioned as a 35kV outdoor oil-immersed iron-tank current transformer. Compared with outdoor epoxy cast-resin CTs, the LB7-35W uses transformer oil and a sealed metal tank to improve internal insulation, heat dissipation and long-term outdoor dielectric stability. It is suitable for 35kV substations, feeder bays, industrial and mining power systems, and utility distribution networks where high insulation strength, metering accuracy and strong anti-breakdown capability are required.
Product Type
| Item | Specification |
|---|---|
| Product name | Outdoor Oil-Immersed Current Transformer |
| Model | LB7-35W |
| Installation condition | Outdoor |
| Insulation type | Oil-immersed insulation with sealed iron tank |
| Application | Current sampling, energy metering, power monitoring and relay protection |
| Voltage class | 35kV / 40.5kV class high-voltage power system |
| Rated insulation level | 40.5/95/185kV |
| Rated frequency | 50Hz or 60Hz |
| Rated secondary current | 5A or 1A |
| Structure focus | Outdoor porcelain / bushing insulation with iron oil-tank base |
Model Explanation
- 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.
- 5A or 1A: Rated secondary current option.
- Accuracy class: Metering classes such as 0.2S / 0.5S and protection classes such as 5P or 10P according to project requirements.
Product Positioning
The LB7-35W is best written as a high-voltage outdoor oil-immersed CT for 35kV grid metering and protection. Its main value is not compactness, but reliable insulation coordination, iron-tank durability, high impulse withstand capability and stable metering / protection output in outdoor high-voltage applications.
| Positioning Point | Technical Meaning | Website Expression |
|---|---|---|
| Oil-immersed structure | Transformer oil improves insulation and heat dissipation | Designed for 35kV outdoor grid service and dielectric reliability |
| Iron tank base | Sealed metal oil tank provides mechanical strength | Durable iron-tank structure for outdoor substation installation |
| 40.5/95/185kV insulation | Power-frequency and impulse withstand platform | Suitable for IEC-style 35kV / 40.5kV insulation coordination |
| Metering + protection | Current sampling for meters and fault signals for relays | Supports energy metering, grid monitoring and relay protection |
| Multiple wiring schemes | Single ratio, tapped ratio and two-secondary-winding options | Flexible secondary terminal arrangement for utility projects |
Applications
- 35kV outdoor substations and high-voltage feeder bays
- 35kV transmission and distribution line current sampling
- Revenue metering and utility energy measurement systems
- Relay protection for feeders, transformers and grid equipment
- Industrial and mining enterprise 35kV power systems
- Outdoor switching stations and grid connection points
- Projects requiring oil-immersed insulation and iron-tank outdoor construction
Features
- Oil-immersed insulation system: Transformer oil improves dielectric strength and heat dissipation for outdoor high-voltage operation.
- Sealed iron-tank structure: Robust metal tank construction supports long-term outdoor service and mechanical durability.
- 35kV / 40.5kV insulation platform: 40.5/95/185kV insulation level supports 35kV high-voltage grid requirements.
- Accurate metering performance: 0.2S / 0.5S class options can be selected for energy measurement and grid metering.
- Protection-class output: 5P or 10P secondary windings support relay protection and fault-current detection.
- Outdoor adaptability: Suitable for rain, humidity, temperature variation and outdoor substation environments when installed according to the approved drawing.
- Convenient installation: Metal tank base, secondary terminal box and grounding point support field installation and maintenance.
Operating Principle
The LB7-35W converts the high primary current of a 35kV line into a standardized low secondary current signal, normally 5A or 1A. The secondary signal is used by metering instruments, protection relays, monitoring devices and automation systems. The oil-immersed insulation system isolates the high-voltage primary circuit from the low-voltage secondary circuit while supporting dielectric strength and thermal stability.
For energy metering, the CT must maintain ratio accuracy and phase displacement within the selected metering class and rated burden. For relay protection, the protection winding must reproduce fault-current information within the designed accuracy limit. Current ratio, accuracy class, rated output, short-time thermal current, dynamic current and secondary wiring scheme should be selected together as a complete engineering set.
Technical Data
| Parameter | Specification |
|---|---|
| Model | LB7-35W |
| Product type | Outdoor oil-immersed current transformer |
| Rated voltage class | 35kV / 40.5kV class |
| Rated insulation level | 40.5/95/185kV |
| Rated frequency | 50Hz or 60Hz |
| Rated secondary current | 5A or 1A |
| Rated primary current | 5A to 1200A reference range according to supplied catalogue data |
| Accuracy class | 0.2S / 0.5S for metering; 5P or 10P protection class by project requirement |
| Rated output | 10VA, 15VA, 20VA, 30VA or 40VA depending on ratio and winding function |
| Ambient temperature | -25°C to +55°C reference from supplied catalogue data |
| Insulation medium | Transformer oil |
| Tank structure | Sealed iron tank / metal tank base |
| Applicable standards | IEC 61869-1, IEC 61869-2, GB/T 20840.1, GB/T 20840.2; legacy GB/T 1208 or IEC 60044-1 references by agreement |
Selection Table
The following table is reorganized from the supplied catalogue data and optimized for website display. Long headings are split into multiple lines to avoid overflow on product pages.
| Rated
Primary |
Accuracy Class Rated Output |
Short-Time Thermal Current |
Rated
Dynamic |
|---|---|---|---|
| 5–300 | 0.2S: 10VA 0.5S: 15VA 5P30: 15VA |
80 × I1n | 200 × I1n |
| 400 | 0.2S: 20VA 0.5S: 30VA 5P30: 20VA |
31.5kA | 100kA |
| 500 | 0.2S: 20VA 0.5S: 30VA 5P30: 20VA |
45kA | 112.5kA |
| 600 | 0.2S: 20VA 0.5S: 30VA 5P30: 20VA |
63kA | 160kA |
| 750–800 | 0.2S: 30VA 0.5S: 40VA 5P30: 20VA |
80kA | 200kA |
| 1000–1200 | 0.2S: 30VA 0.5S: 40VA 5P30: 20VA |
100kA | 250kA |
Note: This table is for preliminary selection. Final current ratio, winding number, accuracy class, burden, short-time thermal current, dynamic current and terminal arrangement shall be confirmed according to the nameplate, approved drawing and factory test report.
Normal Operating Conditions
| Parameter | Value |
|---|---|
| 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 |
Installation and Dimensions
The LB7-35W should be installed vertically on a stable outdoor foundation, steel structure or substation support. The metal tank base must be fixed securely before conductor connection. Oil sealing condition, primary terminal direction, secondary terminal box and grounding point should be checked before energizing.
| Dimension / Installation Item | Reference Value / Recommended Check Point |
|---|---|
| Overall height | Approx. 1299 ± 5mm reference from drawing |
| Tank height reference | Approx. 470mm lower tank section reference |
| Front base width | Approx. 376mm reference |
| Side base width | Approx. 345mm reference |
| Top tank / head | Oil conservator / top metal head structure with primary terminals |
| Primary terminals | Top P1 / P2 terminal arrangement |
| Secondary terminal box | Lower metal tank side terminal box for secondary wiring |
| Grounding point | M10 grounding point reference from drawing |
| Mounting check | Confirm foundation strength, base hole layout, outdoor clearance, oil sealing, grounding and cable outlet before installation. |
Windings & Terminal Marking
The LB7-35W platform can be supplied with single ratio, tapped ratio and two-secondary-winding configurations. Final terminal marking must follow the approved wiring diagram and nameplate.
| Terminal Marking | Function | Application Note |
|---|---|---|
| P1 / P2 | Primary terminals | Used for primary current direction and polarity reference. |
| S1 / S3 | Single-ratio secondary winding reference | Used where one secondary output is required. |
| S1 / S2 / S3 | Tapped secondary winding | Used for multiple transformation ratios or tapped output configuration. |
| 1S1 / 1S2 | First secondary winding | Usually assigned to metering or current measurement. |
| 2S1 / 2S2 | Second secondary winding | Usually assigned to relay protection or backup protection. |
| Grounding point | Secondary / tank grounding reference | One point of the secondary circuit and the metal tank should be grounded according to project practice. |
Standards and Compliance
For current international documentation, the LB7-35W should be specified according to IEC 61869-1 and IEC 61869-2. For GB-based projects, GB/T 20840.1 and GB/T 20840.2 can be used. Older tender documents may refer to GB/T 1208 or IEC 60044-1. Final standard scope should be confirmed in the technical agreement, routine test plan and order documents.
Safety Notes
- Confirm the 35kV / 40.5kV voltage class, rated insulation level, current ratio, secondary current, accuracy class and rated burden before installation.
- Check oil sealing condition, tank appearance, primary terminal direction and secondary terminal box before lifting and installation.
- Confirm outdoor electrical clearance, support strength, conductor mechanical load and foundation stability before energizing.
- Ground the metal tank and one point of the secondary circuit according to the substation grounding design.
- The CT secondary circuit must not be open-circuited while primary current is flowing.
- Before disconnecting meters, relays or test equipment, short-circuit the secondary circuit with an approved shorting device.
- Keep the transformer upright during transport, storage and installation to protect the oil-immersed insulation structure.
- Installation and commissioning shall be performed by qualified high-voltage electrical personnel.