Product Overview
The LFS-10 / LFSB-10 / LFS-10Q / LFSB-10Q current transformer, also referenced as LZZB-10 / LZZBJ-10 in some switchgear applications, is an indoor single-phase epoxy resin cast current transformer for medium-voltage power systems. It is designed for current measurement, electric energy metering, feeder monitoring, and relay protection in 10kV, 11kV, and 12kV class indoor switchgear systems with rated frequency of 50Hz or 60Hz.
The product adopts a fully enclosed post-type epoxy resin casting structure. The primary winding, secondary winding, and magnetic core are encapsulated in the resin body, providing insulation performance, moisture resistance, anti-pollution capability, and compact installation. The product is small and lightweight, and it can be installed in different mounting directions according to cabinet layout and busbar arrangement. The B version is used where protection-class performance is required, and the Q version indicates reinforced insulation configuration.
Product Type
| Item | Specification |
|---|---|
| Product name | Indoor Epoxy Resin Cast Fully Enclosed Current Transformer |
| Model series | LFS-10 / LFSB-10 / LFS-10Q / LFSB-10Q / LZZB-10 / LZZBJ-10 |
| Product structure | Indoor single-phase, enclosed-type, epoxy resin cast, post-type current transformer |
| Voltage class | 10kV, 11kV, and 12kV medium-voltage systems |
| Rated insulation level | 12/42/75kV |
| Rated frequency | 50Hz / 60Hz |
| Rated secondary current | 5A or 1A according to project requirement |
| Application type | Current measurement, energy metering, relay protection, and switchgear monitoring |
| Installation location | Indoor metal-clad switchgear, handcart switchgear, and medium-voltage distribution cabinets |
| Applicable standard | IEC 61869-1 / IEC 61869-2; IEC 60044-1 can be referenced for legacy projects |
Product Display
Main Applications
- 10kV, 11kV, and 12kV indoor medium-voltage distribution systems
- Metal-clad switchgear and handcart-type switchgear assemblies
- Current measurement and electric energy metering circuits
- Relay protection circuits requiring 10P accuracy performance
- Industrial substations, utility distribution rooms, and commercial power distribution cabinets
- Power monitoring, SCADA, and energy management systems requiring isolated CT secondary signals
Key Technical Features
- Fully enclosed epoxy casting: The primary winding, secondary winding, and core are encapsulated in epoxy resin for insulation stability, moisture resistance, and anti-pollution performance.
- Post-type compact structure: The product is small, lightweight, and suitable for flexible installation in different switchgear positions and directions.
- Protection version available: LFSB-10 / LFSB-10Q and LZZBJ-10 are used for protection-class applications where 10P performance is required.
- Reinforced insulation option: Q-type models such as LFS-10Q and LFSB-10Q are available when reinforced insulation configuration is required.
- 1A or 5A secondary output: Secondary output can be selected according to meter, relay, cable length, and burden calculation.
- Measurement and protection combinations: Typical accuracy combinations include 0.2/0.2, 0.5/0.5, 0.2/0.5, 0.2/10P10, and 0.5/10P10.
Working Principle
The LFS(B)-10 current transformer operates according to electromagnetic induction. Primary current flowing through the primary winding generates magnetic flux in the core, and the secondary winding outputs a proportional current signal to meters, relays, or monitoring devices. The epoxy resin casting body provides insulation between the medium-voltage primary circuit and the low-voltage secondary circuit.
For metering applications, the CT must maintain the required ratio accuracy and phase displacement under the rated burden. For protection applications, the 10P winding must provide a reliable secondary current signal during fault-current conditions and coordinate with relay settings, rated burden, and accuracy limit factor.
Model Designation
The model designation identifies the current transformer structure, switchgear application, protection configuration, voltage class, and reinforced insulation option.
| Code | Meaning |
|---|---|
| L | Current transformer |
| F | Enclosed type |
| S | For switch of handcart / handcart-type switchgear application |
| B | For protection configuration |
| 10 | Voltage grade, kV; applicable to 10kV systems and 12kV insulation coordination projects |
| Q | Reinforced insulation configuration |
Model coverage: This product page covers LFS-10, LFSB-10, LFS-10Q, LFSB-10Q, LZZB-10, and LZZBJ-10. The final model should be confirmed according to switchgear type, protection requirement, insulation configuration, current ratio, secondary output, and approved outline drawing.
Technical Data
| Item | Specification |
|---|---|
| Rated voltage class | 10kV / 11kV / 12kV medium-voltage systems |
| Highest voltage for equipment | 12kV class |
| Rated insulation level | 12/42/75kV |
| Rated frequency | 50Hz / 60Hz |
| Rated primary current | 5A to 1000A reference range; customized ratios available according to project requirement |
| Rated secondary current | 5A or 1A |
| Accuracy class combination | 0.2 / 0.2, 0.5 / 0.5, 0.2 / 0.5, 0.2 / 10P10, 0.5 / 10P10 |
| Rated output | 10VA / 15VA / 20VA according to model and secondary core configuration |
| Protection accuracy class | 10P10 or project-specific protection class |
| Partial discharge test | Available according to IEC 61869 project requirement |
| Pollution class | Class II reference for indoor application |
| Insulation medium | Epoxy resin casting insulation |
| Applicable standard | IEC 61869-1 / IEC 61869-2; IEC 60044-1 can be referenced for legacy specification |
Windings & Terminal Marking
The LFS(B)-10 current transformer can be supplied with metering, measurement, protection, or combined secondary winding configurations. Terminal markings should be confirmed according to the approved wiring diagram and secondary core configuration.
| Terminal Marking | Function | Application Note |
|---|---|---|
| P1 / P2 | Primary terminals | The reference primary current direction is normally defined from P1 to P2. |
| 1S1 / 1S2 | First secondary winding | Usually used for metering, measurement, or the first specified secondary core. |
| 2S1 / 2S2 | Second secondary winding | Usually used for relay protection or an additional secondary circuit when required. |
| Secondary terminal cover | Secondary wiring protection | Terminal cover supports safer wiring inspection and reduces accidental contact risk. |
Terminal markings follow standard CT polarity conventions. Correct terminal identification shall be observed to ensure metering accuracy, relay direction judgment, and protection performance. The secondary circuit must not be open-circuited when the primary circuit is energized.
Rated Current, Accuracy and Short-Circuit Withstand Reference
| Model | Rated
Primary Current (A) |
Accuracy
Class Combination |
Rated
Output 0.2 (VA) |
Rated
Output 0.5 (VA) |
Rated
Output 10P10 (VA) |
Short-Time
Thermal Current |
Rated
Dynamic Current |
|---|---|---|---|---|---|---|---|
| LFS-10 / LZZB-10 LFS-10Q |
5–200 | 0.2 / 0.2 0.5 / 0.5 0.2 / 0.5 0.2 / 10P10 0.5 / 10P10 |
10 | 10 | 15 | 80 × I1n | 200 × I1n |
| 300 | 21kA | 50kA | |||||
| 400 | 24kA | 60kA | |||||
| 600 | 30kA | 70kA | |||||
| 800 | 40kA | 75kA | |||||
| 1000 | |||||||
| LFSB-10 / LZZBJ-10 LFSB-10Q |
5–200 | 0.2 / 10P10 0.5 / 10P10 |
10 | 10 | 20 | 80 × I1n | 200 × I1n |
| 300 | 21kA | 50kA | |||||
| 400 | 24kA | 60kA | |||||
| 600 | 30kA | 70kA | |||||
| 800 | 40kA | 75kA | |||||
| 1000 |
Note: The table is for preliminary technical selection. If the secondary current is 1A, or if the requested parameters exceed the listed range, final current ratio, accuracy class, rated output, thermal current, dynamic current, terminal arrangement, and test requirements shall be confirmed by technical agreement.
10P Accuracy Limit Factor Reference
The following curve reference is used to evaluate the relationship between 10P accuracy limit factor and connected secondary burden. The actual protection performance depends on current ratio, secondary winding design, burden, relay input impedance, cable resistance, and the selected protection accuracy class.
| Curve
Group |
Applicable
Models |
Typical
Current Ratios |
Engineering
Use |
|---|---|---|---|
| LFS-10 10P curve | LFS-10 / LZZB-10 / LFS-10Q | 5–200/5, 300/5, 400/5, 600/5, 800/5, 1000/5 | Used for checking 10P accuracy limit factor under different secondary burden values. |
| LFSB-10 10P curve | LFSB-10 / LZZBJ-10 / LFSB-10Q | 75–400/5, 600/5, 800/5, 1000/5, 1500/5 reference groups | Used for protection-class CT selection where higher burden or different relay settings are required. |
Protection-class selection should not be based only on current ratio. The connected burden and relay requirement must be checked together with the 10P accuracy limit factor curve or factory technical data.
Service Conditions
- Installation location: indoor medium-voltage switchgear
- System voltage: 10kV, 11kV, or 12kV class
- Rated frequency: 50Hz / 60Hz
- Rated insulation level: 12/42/75kV
- Altitude: not over 1000m under standard service conditions
- Ambient temperature: -5°C to +40°C
- Relative humidity: less than 85% at 20°C under reference conditions
- The product has vibration resistance suitable for switchgear applications according to project test requirements.
- The installation environment should be free from severe pollution, corrosive gas, explosive medium, abnormal condensation, and heavy conductive dust.
Standards and Compliance
The LFS-10 / LFSB-10 / LFS-10Q / LFSB-10Q / LZZB-10 / LZZBJ-10 current transformer can be supplied according to IEC 61869-1 and IEC 61869-2. IEC 60044-1 may be referenced for legacy project specifications. Routine tests, dielectric tests, polarity verification, ratio test, accuracy test, partial discharge test, and insulation resistance test should be confirmed according to the final technical agreement.
Installation and Dimensions
The LFS(B)-10 series is designed for indoor handcart or metal-clad switchgear installation. The cast-resin body, primary terminals, secondary terminal cover, base mounting holes, terminal direction, and installation clearances shall be confirmed according to the approved outline drawing before switchgear design or batch production.
Structure & Dimensions
| Item | Selection Note |
|---|---|
| Mechanical variants | LFS-10 / LFSB-10 / LFS-10Q / LFSB-10Q / LZZB-10 / LZZBJ-10 |
| Switchgear application | Handcart switchgear, metal-clad switchgear, and indoor medium-voltage cabinets |
| Primary terminals | P1 / P2 terminal arrangement according to approved drawing |
| Secondary terminals | 1S1 / 1S2 and optional 2S1 / 2S2 according to secondary core configuration |
| Mounting base | Base plate and mounting holes according to outline drawing |
| Drawing confirmation | Final outline, terminal direction, and mounting dimensions shall be confirmed before switchgear production |
Installation and Safety Notes
- Confirm the model, voltage class, current ratio, secondary current, accuracy class, burden, insulation level, and short-circuit withstand requirement before installation.
- Check switchgear mounting space, primary terminal connection, phase clearance, grounding arrangement, and maintenance access against the approved drawing.
- Connect primary and secondary terminals according to the terminal markings and project wiring diagram.
- The secondary circuit of a current transformer must not be left open when the primary circuit is energized.
- During meter or relay maintenance, short-circuit the CT secondary circuit before disconnecting any secondary wiring.
- Secondary grounding shall follow the project specification and local electrical safety requirements.
- Installation and maintenance shall be performed by qualified medium-voltage electrical personnel.
Ordering Information
Please provide the following information when ordering or requesting a quotation:
- Product model: LFS-10, LFSB-10, LFS-10Q, LFSB-10Q, LZZB-10, or LZZBJ-10
- System voltage: 10kV, 11kV, or 12kV
- Rated primary current / current transformation ratio
- Rated secondary current: 1A or 5A
- Accuracy class combination and rated output for each secondary core
- Protection class and 10P accuracy limit factor requirement
- Short-circuit withstand requirement: short-time thermal current and dynamic current
- Insulation level and applicable IEC standard
- Switchgear type, handcart layout, terminal direction, and required outline drawing
- Quantity, labeling, certificates, routine test reports, and packaging requirements
- Special customized current ratio, secondary winding, burden, or terminal arrangement requirements
Selection Guidelines
- Confirm system voltage: Select this CT for indoor 10kV, 11kV, or 12kV switchgear using 12kV-class insulation coordination.
- Confirm model variant: Use LFS-10 / LZZB-10 for standard measurement and metering applications; use LFSB-10 / LZZBJ-10 where protection-class output is required; use Q-type models when reinforced insulation is specified.
- Confirm current ratio: Select the primary current according to feeder load, continuous operating current, and relay protection setting range.
- Confirm secondary current: Select 5A or 1A according to the meter, relay, cable length, and secondary burden calculation.
- Verify 10P performance: For protection circuits, check the 10P accuracy limit factor against the connected burden using the curve data or manufacturer technical data.
- Check short-circuit withstand: Ensure the short-time thermal current and rated dynamic current meet the switchgear fault-current level.
- Confirm drawings: Verify outline dimensions, terminal direction, mounting holes, and phase clearances before production.
FAQs