Overview
The LZZBJ9-12/185b/4S (also designated AS12/185b/4S) is an indoor epoxy cast-resin current transformer designed for 10kV, 11kV and 12kV class medium-voltage AC systems. It features a fully enclosed, support-type structure with primary conductors, magnetic cores and secondary windings encapsulated in solid epoxy resin insulation, ensuring stable dielectric performance and resistance to indoor environmental conditions.
This 4S multi-secondary model supports independent circuits for metering, measurement, protection and backup protection functions. Typical accuracy classes include 0.2S, 0.5 and 10P series, meeting IEC and relevant international standards for revenue metering and relay protection applications in switchgear panels requiring high wiring density and functional separation.
Key Ratings Snapshot
| Parameter | Rating |
|---|---|
| Voltage class | 10kV / 11kV / 12kV |
| Rated insulation level | 12/42/75kV |
| Rated frequency | 50Hz / 60Hz |
| Primary current | As per standard ratios (e.g., 100–3150A) |
| Secondary current | 5A or 1A |
| Secondary configuration | 4S (four independent cores) |
| Accuracy classes (metering) | 0.2S, 0.2, 0.5 |
| Accuracy classes (protection) | 10P, 10P15, 10P20 |
| Short-time thermal current | Per IEC 61869-2 (e.g., 20–40kA/1s) |
| Dynamic withstand current | Per IEC 61869-2 (e.g., 50–100kA peak) |
| Installation type | Indoor support-type |
| Insulation material | Epoxy cast-resin |
Model Designation
- L: Current transformer
- Z: Indoor type / support structure
- Z: Epoxy resin casting insulation
- B: Protection level available
- J: Strengthened design
- 9: Design serial number
- 12: 12kV class maximum operating voltage
- 185b: Nominal width / structure dimension code
- 4S: Multi-secondary schematic code
- AS12: Alternative 12kV series designation for the same CT platform
Construction
The LZZBJ9-12/185b/4S employs a dry-type, epoxy cast-resin construction where the primary conductor, magnetic cores and secondary windings are fully encapsulated within a solid resin body. This monolithic casting provides excellent mechanical strength, uniform electric field distribution and long-term insulation stability under indoor operating conditions. The 185b support body offers increased clearance for busbar routing and terminal connections compared to smaller frame sizes. Each of the four secondary cores is physically and electrically isolated within the casting, allowing independent specification of accuracy class, burden and terminal marking per application requirement. The design complies with IEC 61869 standards for indoor current transformers used in medium-voltage switchgear environments.
Technical Parameters
Service Conditions
- Installation location: indoor medium-voltage switchgear
- System voltage: 12kV class networks
- Rated frequency: 50Hz
- Ambient temperature: -5°C to +40°C
- Installation environment: The installation environment should be free from severe vibration, conductive dust, corrosive gas, explosive medium, heavy pollution and abnormal condensation.
Technical Parameters
The LZZBJ9-12/185b/4S is an indoor epoxy cast-resin current transformer designed for 12kV class systems. It features multiple accuracy class combinations and complies with GB 20840.2-2014 and IEC 61869-2:2012 standards.
| Rated primary current (A) |
Accuracy classed combination |
Rated Output (VA) |
Short-time thermal current (kA/1s) |
Rated dynamic current (kA) |
||
|---|---|---|---|---|---|---|
| Class 1 | Class 2 | Class 3 | ||||
| 20,30,40,50,75,100 | 0.2/0.2/5P10 | 10 | 10 | 40 | 150×I1n | 375×I1n |
| 0.2/0.5/5P15 | 10 | 15 | 30 | |||
| 0.2/0.5/5P20 | 10 | 15 | 20 | |||
| 0.2/5P10/10P15 | 10 | 20 | 20 | |||
| 0.5/5P10/10P20 | 10 | 20 | 15 | |||
| 150,200 | 0.2/0.2/5P10 | 10 | 10 | 40 | 31.5 | 80 |
| 0.2/0.5/5P15 | 10 | 15 | 30 | |||
| 0.2/0.5/5P20 | 10 | 15 | 20 | |||
| 0.2/5P10/10P15 | 10 | 20 | 20 | |||
| 0.5/5P10/10P20 | 10 | 20 | 15 | |||
| 300,400 | 0.2/0.2/5P10 | 10 | 10 | 40 | 45 | 112.5 |
| 0.2/0.5/5P15 | 10 | 15 | 30 | |||
| 0.2/0.5/5P20 | 10 | 15 | 20 | |||
| 0.2/5P10/10P15 | 10 | 20 | 20 | |||
| 0.5/5P10/10P20 | 10 | 20 | 15 | |||
| 500 | 0.2/0.2/5P10 | 10 | 10 | 40 | 63 | 130 |
| 0.2/0.5/5P15 | 10 | 15 | 30 | |||
| 0.2/0.5/5P20 | 10 | 15 | 20 | |||
Installation & Wiring
Installation Diagram
The LZZBJ9-12/185b/4S and AS12/185b/4S current transformers are installed as indoor support-type units within switchgear compartments. The primary terminals are located at the top, while the secondary terminals are arranged at the bottom. Proper alignment with mounting holes and sufficient clearance for secondary wiring must be ensured during installation. Always refer to the approved outline drawing for exact dimensions and terminal positions before proceeding with switchgear assembly or replacement.
Selection & FAQs
Selection Guide
- Confirm a 10–12kV indoor system, 12/42/75kV insulation and the need for the wider 185b body and four-secondary wiring space.
- Select a 20A–3150A primary ratio from operating current, metering range, fault study and future capacity.
- Define 1S–4S individually for revenue metering, indication, main protection and backup/auxiliary protection, including 1A/5A, class and terminals.
- Verify each core’s VA allocation because some source combinations list only three burden values despite the 4S designation; obtain a complete winding schedule.
- Check ratio-specific thermal/dynamic current, top-busbar layout, mounting holes, secondary access, environment and the correct CT test standard.
Frequently Asked Questions
Q1: Can this epoxy resin current transformer be installed outdoors?
No, it is strictly designed for indoor medium-voltage switchgear. The installation environment must be free from severe vibration, conductive dust, and corrosive gases. Contact us for outdoor alternatives.
Q2: When should I select the 0.2/0.2/5P10 accuracy class?
This combination is ideal for dual-core metering and protection. It provides 10VA output for both 0.2 class cores and 40VA for the 5P10 protection core. Confirm your specific relay burden with our engineers.
Q3: Which accuracy class combinations are available for this model?
Multiple combinations are available, including 0.2/0.5/5P15, 0.2/0.5/5P20, and 0.2/5P10/10P15. Rated outputs vary by class, such as 10VA for Class 1 and up to 40VA for Class 3. Specify your exact metering and protection needs.
Q4: What international standards does this 12kV current transformer comply with?
The LZZBJ9-12/185b/4S complies with both GB 20840.2-2014 and IEC 61869-2:2012 standards. It is designed for 12kV class networks operating at a rated frequency of 50Hz. Request the specific type test reports for your project.
Q5: Can the rated primary current be customized for our switchgear?
Customization is subject to confirmation. Standard rated primary currents range from 20A to 100A. Contact our sales team if your project requires different current ratings.
Q6: How strict are the environmental installation restrictions for this CT?
Strict environmental controls apply to this indoor CT. The ambient temperature must remain between -5°C and +40°C, free from conductive dust, corrosive gases, and abnormal condensation. Contact us to verify your specific site conditions.
Q7: Are factory routine tests performed before shipment?
Yes, standard factory routine tests are conducted prior to dispatch. All units are verified for compliance with IEC 61869-2 standards. Contact our quality department for specific third-party inspection requirements.