Product Overview
The LFS-10Q / LFSB-10 / LFSZ-10 current transformer is a compact indoor epoxy cast-resin medium-voltage current transformer designed for 11kV class switchgear. It is used for current measurement, energy metering, relay protection and feeder monitoring in indoor AC power systems. For international documentation, the product can be positioned for 10kV, 11kV and 12kV class medium-voltage systems, with final selection confirmed by insulation level, system voltage and project drawings.
This series is a small-size, fully enclosed single-secondary-winding MV current transformer. Compared with larger multi-winding cast-resin CTs, the LFS series focuses on compact installation, simplified secondary wiring, and practical measurement/protection performance for indoor switchgear panels. It is especially suitable for handcart switchgear, compact distribution cabinets, metering panels and feeder protection circuits where installation space is limited.
The transformer adopts epoxy resin casting insulation with a post / pillar-type structure. The resin body provides dielectric strength, moisture resistance and anti-pollution capability. The compact body can be installed flexibly inside the cabinet, and the 5A or 1A secondary output can be selected according to the meter, relay and secondary wiring burden. Typical accuracy configurations include 0.2, 0.5 and 10P10 for metering and protection applications.
Product Type
| Item | Specification |
|---|---|
| Product name | Compact Indoor Epoxy Cast-Resin Medium-Voltage Current Transformer |
| Model series | LFS-10Q / LFSB-10 / LFSZ-10 |
| Structure | Fully enclosed post / pillar type, epoxy cast-resin insulation, compact body |
| Winding configuration | Single secondary winding, with metering or protection function according to accuracy class |
| Voltage class | 10kV, 11kV and 12kV class indoor medium-voltage systems |
| Rated insulation level | 12/42/75kV |
| Rated frequency | 50Hz; 60Hz available by project confirmation |
| Rated secondary current | 5A or 1A |
| Rated primary current | 50A, 75A, 100A, 150A, 200A, 300A, 400A, 500A, 600A, 630A |
| Typical use | Current measurement, energy metering, relay protection, feeder monitoring |
Product Display
The LFS series has a compact cast-resin body with top primary terminals, lower secondary terminals and a small base for cabinet mounting. The enclosed resin structure protects the winding and core from indoor humidity and pollution. Because the product is small and light, it can be arranged flexibly inside medium-voltage switchgear where space is limited.
Applications
- 10kV, 11kV and 12kV class indoor medium-voltage switchgear
- Handcart switchgear and compact distribution cabinets
- Current measurement and electric energy metering circuits
- Relay protection circuits using 10P10 protection class
- Feeder monitoring, incoming panels, outgoing panels and metering units
- OEM switchgear projects requiring small-size indoor cast-resin CTs
Features
- Compact MV CT design: Small post-type body for limited switchgear installation space.
- Single-winding configuration: Simple secondary wiring and clear function selection for metering or protection circuits.
- Fully enclosed epoxy casting: Cast-resin insulation supports dielectric strength, moisture resistance and anti-pollution performance.
- 11kV / 12kV class documentation: The 12/42/75kV insulation level supports international 11kV and 12kV class project wording.
- Flexible secondary output: 5A is suitable for conventional systems, while 1A can be selected to reduce secondary burden in longer wiring circuits.
- Metering and protection classes: Accuracy classes such as 0.2, 0.5 and 10P10 are available for different circuit requirements.
Principle
The LFS-10Q / LFSB-10 / LFSZ-10 current transformer operates by electromagnetic induction. The primary current flows through the primary conductor path and generates magnetic flux in the internal core. The secondary winding then outputs a proportional 5A or 1A current signal to a meter, relay or monitoring device.
For metering circuits, the selected accuracy class must maintain stable ratio and phase performance within the rated burden. For protection circuits, the 10P class must provide a reliable secondary signal under fault-current conditions. Because this product is normally specified as a single-secondary-winding CT, the required function should be confirmed clearly before ordering: metering, measurement, or protection.
Model Designation
| Code | Meaning |
|---|---|
| L | Current transformer |
| F | Enclosed type structure |
| S | Handcart switchgear / switchgear application reference |
| B | Protection function reference in LFSB-type designation |
| Z | Cast-resin insulation / epoxy casting reference in LFSZ-type designation |
| 10 | 10kV catalogue voltage class; documented for 11kV and 12kV class systems by insulation confirmation |
| Q | Reinforced insulation variant |
Technical Data
| Item | Specification |
|---|---|
| Rated voltage class | 10kV, 11kV and 12kV class indoor systems by project confirmation |
| Rated insulation level | 12/42/75kV |
| Rated frequency | 50Hz; 60Hz by agreement |
| Rated secondary current | 5A or 1A |
| Rated primary current | 50A to 630A reference range |
| Accuracy classes | 0.2, 0.5, 10P10 |
| Rated output | 0.2 class: 10VA; 0.5 class: 15VA; 10P10 class: 10VA reference |
| Rated short-time thermal current | 7.5kA to 40kA reference range depending on primary current |
| Rated dynamic current | 19kA to 100kA reference range depending on primary current |
| Partial discharge | Partial discharge test condition according to current transformer standard requirements |
| Anti-pollution class | Class II reference from catalogue description |
| Ambient temperature | -5°C to +55°C |
| Applicable standards | IEC 61869-2, GB20840.2-2014; legacy IEC 60044-1 / GB1208 references by project agreement |
Selection Table
The following table is reorganized from the catalogue information and adapted for website display. Long headers are split into multiple lines to keep the table readable on product pages.
| Rated
Primary Current (A) |
Accuracy
Class Combination |
Rated
Output (VA) |
Short-Time
Thermal Current Ith (kA) |
Dynamic
Current Idyn (kA) |
|---|---|---|---|---|
| 50 | 0.2 0.5 10P10 |
0.2: 10 0.5: 15 10P10: 10 |
7.5 | 19 |
| 75 | 11.25 | 28 | ||
| 100 | 15 | 37.5 | ||
| 150 | 22.5 | 56 | ||
| 200 | 30 | 75 | ||
| 300 | 40 | 100 | ||
| 400 | ||||
| 500 | ||||
| 600 | ||||
| 630 |
Note: The table is for preliminary selection. Final current ratio, accuracy class, rated burden, thermal current, dynamic current, insulation level and test requirements shall be confirmed according to the nameplate, approved drawing and factory test report.
Variant Selection
| Variant | Recommended Use | Technical Note |
|---|---|---|
| LFS-10Q | Reinforced insulation compact indoor CT | Recommended where the project emphasizes 12/42/75kV insulation coordination and compact installation. |
| LFSB-10 | Protection-oriented compact CT variant | Suitable when the customer model reference emphasizes relay protection use. |
| LFSZ-10 | Epoxy cast-resin compact CT variant | Suitable when the customer drawing or tender specifies the LFSZ model designation. |
Dimensions
| Item | Engineering Note |
|---|---|
| Structure | Small post-type enclosed cast-resin body for indoor switchgear installation. |
| Primary terminals | Top primary terminal arrangement; confirm busbar or cable lug connection by drawing. |
| Secondary terminals | Lower secondary terminal block; confirm wiring access and terminal cover requirement. |
| Mounting base | Bottom base plate; mounting holes and base dimensions must follow approved drawing. |
| Installation direction | Can be installed flexibly according to cabinet layout, subject to clearance and mechanical support. |
Terminals
The primary terminals are normally marked P1 and P2. Since this product is usually specified as a single-secondary-winding CT, the secondary terminals are commonly marked as 1S1 / 1S2. If a special protection or measurement terminal arrangement is required, the final terminal marking shall follow the approved wiring diagram and product nameplate.
| Terminal | Function | Application Note |
|---|---|---|
| P1 / P2 | Primary terminals | Used for primary current direction and polarity reference. |
| 1S1 / 1S2 | Secondary winding | Used for the selected metering, measurement or protection circuit. |
| Grounding point | Protective grounding | Secondary circuit grounding shall follow project electrical safety practice. |
Service Conditions
- Installation location: indoor medium-voltage switchgear
- Rated voltage: 10kV, 11kV and 12kV class systems by project confirmation
- Rated frequency: 50Hz; 60Hz by agreement
- Ambient temperature: -5°C to +55°C
- Indoor environment should be free from conductive dust, corrosive gas, explosive medium, heavy pollution and abnormal condensation.
- For high humidity, coastal, high altitude or heavy-pollution projects, insulation distance and creepage coordination should be confirmed before ordering.
Standards and Compliance
For international projects, the LFS-10Q / LFSB-10 / LFSZ-10 current transformer should be specified according to IEC 61869-2 current transformer requirements. The original catalogue may reference GB1208-2006 and IEC 60044-1:2003; for new technical documents, these can be kept as legacy references while IEC 61869-2 and GB20840.2-2014 are preferred for updated specification language.
Installation and Dimensions
The LFS series is intended for compact indoor switchgear installation. Before cabinet production, the primary terminal spacing, secondary wiring direction, base mounting holes, phase-to-ground clearance, maintenance access and installation direction should be confirmed with the approved outline drawing. Because LFS-10Q, LFSB-10 and LFSZ-10 may differ in structure details, the final drawing must match the selected model and nameplate.
Safety Notes
- Confirm voltage class, insulation level, current ratio, secondary current, accuracy class and rated burden before production.
- Check primary terminal spacing, mounting holes, secondary terminal access and grounding position before switchgear assembly.
- Connect primary and secondary terminals according to polarity marks and approved wiring diagram.
- The CT secondary circuit must not be open-circuited while primary current is flowing.
- Before disconnecting meters or relays, short-circuit the secondary circuit with an approved shorting device.
- One point of the secondary circuit should be grounded according to project electrical safety practice.
- Installation and commissioning shall be performed by qualified medium-voltage electrical personnel.
Ordering Info
- Product model: LFS-10Q / LFSB-10 / LFSZ-10
- Voltage class: 10kV, 11kV or 12kV class
- Rated primary current and rated secondary current: 5A or 1A
- Single secondary winding function: metering, measurement or protection
- Accuracy class: 0.2, 0.5 or 10P10
- Rated output / burden
- Rated short-time thermal current and dynamic current
- Mounting drawing, terminal direction and switchgear layout
- IEC standard requirement, routine test report, certificate, label language and packaging requirement
Selection Guide
- Confirm the product family: Use one website page for LFS-10Q, LFSB-10 and LFSZ-10 because they belong to the same compact indoor cast-resin CT application range.
- Confirm voltage class: Use 11kV and 12kV class wording for international projects, then verify 12/42/75kV insulation level.
- Select current ratio: Choose 50A to 630A according to feeder load, meter range and relay setting.
- Confirm secondary current: Use 5A for conventional circuits or 1A for lower burden and longer secondary wiring.
- Choose function: Use 0.2 or 0.5 for metering/measurement, and 10P10 for relay protection.
- Verify short-circuit withstand: Confirm Ith and Idyn according to switchgear fault level.
- Approve drawings: Check primary terminals, secondary terminal direction, base holes and cabinet clearance before production.