Overview
The LFS-10, LFSB-10, LFS-10Q, LFSB-10Q, LZZB-10, and LZZBJ-10 are indoor single-phase current transformers designed for 10kV, 11kV, and 12kV medium-voltage systems. These units feature a fully enclosed post-type structure with epoxy resin cast insulation, encapsulating the primary winding, secondary winding, and magnetic core to ensure high dielectric strength, moisture resistance, and pollution immunity.
They support both measurement (0.2 or 0.5 class) and protection (10P) applications, making them suitable for energy metering, feeder monitoring, and relay protection in metal-clad and handcart-type switchgear. The devices comply with IEC 61869-1 and IEC 61869-2 standards and operate at 50Hz or 60Hz frequencies with secondary outputs of 1A or 5A.
Key Ratings Snapshot
| Parameter | Rating |
|---|---|
| Voltage class | 10kV / 11kV / 12kV |
| Rated insulation level | 12/42/75kV |
| Rated frequency | 50Hz / 60Hz |
| Primary current | As per design (project-specific) |
| Secondary current | 1A or 5A |
| Measurement accuracy | 0.2, 0.5 |
| Protection accuracy | 10P10 |
| Typical combinations | 0.2/0.2, 0.5/0.5, 0.2/0.5, 0.2/10P10, 0.5/10P10 |
| Application | Metering, protection, monitoring |
| Installation | Indoor switchgear |
| Insulation material | Epoxy resin cast |
| Standards | IEC 61869-1, IEC 61869-2 |
Model Designation
- L: Current transformer
- F: Enclosed type
- S: For handcart-type switchgear application
- B: Protection configuration
- 10: Voltage grade (10kV class, compatible with 12kV insulation coordination)
- Q: Reinforced insulation configuration
Construction
The transformer features a compact post-type design with all active components—primary winding, secondary winding, and magnetic core—fully encapsulated in a solid epoxy resin cast body. This construction provides excellent electrical insulation, mechanical strength, and environmental resistance against moisture and contaminants. The resin casting ensures stable performance under continuous operation and transient overvoltage conditions typical in 10kV–12kV indoor switchgear environments. The unit is lightweight and allows flexible mounting orientation to accommodate various busbar layouts and cabinet configurations.
Technical Parameters
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
- Vibration resistance: suitable for switchgear applications according to project test requirements
- Installation environment: should be free from severe pollution, corrosive gas, explosive medium, abnormal condensation, and heavy conductive dust
Technical Parameters
The LFSB-10, LFSB-10Q, and LZZB(J)-10 are epoxy resin cast current transformers designed for 10kV–12kV indoor switchgear applications. They feature a rated primary current range of 5A to 1000A (with custom ratios available), operate within an ambient temperature of -5°C to +40°C at altitudes up to 1000m, and comply with IEC 61869-1/-2 standards.
| Type | Rated primary current (A) |
Accuracy classes combination |
Rated output (VA) |
1s thermal stability current (kA) |
Dynamic stability current (kA) |
||
|---|---|---|---|---|---|---|---|
| 0.2 | 0.5 | 10P | |||||
| LFS-10 | 5~200 | 0.2/10P 0.5/10P |
10 | 10 | 15 | 80×I1n | 200×I1n |
| 300~1000 | 10 | 10 | 15 | ||||
| LFSB-10 | 5~200 | 0.2/10P 0.5/10P |
10 | 10 | 50 | 80×I1n | 200×I1n |
| 300~1000 | 10 | 10 | 50 | ||||
Installation & Wiring
Installation Diagram
The LFS(B)-10 series current transformers are designed for installation in indoor handcart or metal-clad switchgear. Mounting is achieved via the base plate with pre-defined holes as per the approved outline drawing. Primary terminals (P1/P2) and secondary terminals (1S1/1S2, optionally 2S1/2S2) must align with the switchgear layout and wiring diagram. Ensure proper phase clearance, grounding, and maintenance access during installation.
Selection & FAQs
Selection Guide
- Choose the model family by secondary duty. Use LFS/LZZB for 0.2/0.2, 0.5/0.5, 0.2/0.5 or selected 15VA protection combinations; choose LFSB/LZZBJ where a 20VA 10P10 protection core is required.
- Treat Q as a structural option requiring a drawing. LFS-10Q and LFSB-10Q are described as reinforced versions, but the page does not quantify their dimensional or dielectric differences; obtain the exact approved outline.
- Select the ratio from the verified schedule. Detailed data covers 5A–1000A with ratio-specific thermal and dynamic withstand. A 1500A reference appears only in a curve group and needs separate technical confirmation.
- Choose 1A or 5A secondary with a burden calculation. The detailed table is primarily expressed for 5A; any 1A version requires confirmation of accuracy, output, protection factor and terminal arrangement.
- Complete switchgear and test requirements. Confirm 12/42/75kV insulation, partial-discharge limit, pollution conditions, base mounting, primary-terminal spacing, terminal-cover access and the certified fault-current duration.
Frequently Asked Questions
Q1: Can these epoxy resin current transformers be installed outdoors?
No, they are strictly designed for indoor medium-voltage switchgear. The installation environment must be free from severe pollution, corrosive gases, and heavy conductive dust. Contact us for outdoor alternatives.
Q2: Which accuracy class combinations are available for these models?
Multiple accuracy class combinations are available depending on your specific application needs. Refer to the technical parameters table for standard options. Custom accuracy requirements are subject to factory confirmation.
Q3: How do I select the correct thermal stability current?
The 1-second thermal stability current is specified in the technical parameters table based on your rated primary current. Ensure the selected CT meets your specific switchgear fault level requirements.
Q4: What is the rated insulation level for 12kV systems?
The rated insulation level is 12/42/75kV, making it fully suitable for 10kV, 11kV, and 12kV class systems. Verify specific altitude and temperature conditions with our engineering team.
Q5: Can we order custom primary current ratios above 1000A?
Standard models cover a rated primary current range of 5A to 1000A. Custom ratios beyond this range are available subject to technical evaluation. Please contact our sales team for details.
Q6: What factory tests are performed before shipment?
All units undergo routine testing to ensure compliance with IEC 61869-1 and IEC 61869-2 standards. Specific type test reports and factory acceptance test certificates are subject to confirmation.
Q7: What applications are these current transformers primarily designed for?
These epoxy resin cast current transformers are primarily used in indoor medium-voltage switchgear for 10kV to 12kV power distribution systems. They operate at 50Hz or 60Hz rated frequencies.
Q8: Which international standards do these LFSB and LZZB models meet?
The LFSB-10, LFSB-10Q, and LZZB(J)-10 models fully comply with IEC 61869-1 and IEC 61869-2 international standards. Request specific compliance documentation from your regional distributor.