Overview
The LZZBJ9-12/175b/2S (also designated AS12/175b/2S) is an indoor epoxy cast-resin current transformer designed for 10kV, 11kV, and 12kV medium-voltage power systems. It features a fully enclosed post-type structure with epoxy resin insulation that provides high dielectric strength, mechanical robustness, and environmental protection against humidity and dust in switchgear environments.
This CT supports dual secondary outputs (2S configuration), enabling simultaneous use for accurate energy metering and reliable relay protection. It complies with standard insulation coordination levels of 12/42/75kV and operates at 50Hz or 60Hz. The design meets typical requirements for indoor switchgear applications where stable performance under thermal cycling and long-term operation is essential.
Key Ratings Snapshot
| Parameter | Rating |
|---|---|
| Voltage class | 10kV / 11kV / 12kV |
| Rated insulation level | 12/42/75kV |
| Rated frequency | 50Hz / 60Hz |
| Secondary current | 5A or 1A |
| Secondary configuration | 2S (two independent secondaries) |
| Primary conductor type | Bolted connection |
| Insulation material | Epoxy cast-resin |
| Installation type | Indoor, center-mounted switchgear |
| Application functions | Measurement, metering, protection, monitoring |
| Body size code | 175b (medium-width) |
| Protection level | With defined accuracy limit factor |
| Live display support | Optional (for ≤2 secondaries) |
Model Designation
- L: Current transformer
- Z: Indoor type / post-type structure
- Z: Epoxy resin cast insulation / fully enclosed structure
- B: With protection level
- J: Strengthened design
- 9: Design serial number
- 12: Maximum operating voltage / 12kV class
- 175b: Nominal width / structure dimension code
- 2S: Secondary schematic code / two-secondary configuration
- AS12: Alternative 12kV series designation for the same indoor epoxy cast-resin CT platform
Construction
The LZZBJ9-12/175b/2S features a monolithic epoxy cast-resin body that integrates electrical insulation, mechanical support, and environmental sealing into a single solid structure. This construction eliminates air gaps and moisture ingress paths, ensuring consistent dielectric performance and long-term reliability in indoor switchgear cabinets. The primary conductor passes axially through the core and is secured by bolted terminals on both ends, providing low contact resistance and stable thermal performance. The two secondary windings are independently wound and encapsulated within the resin matrix, offering galvanic isolation from the primary circuit and from each other. The 175b body width accommodates larger terminal spacing and facilitates easier busbar integration compared to compact variants, while maintaining compatibility with standard switchgear mounting arrangements.
Technical Parameters
Service Conditions
- Installation location: indoor medium-voltage switchgear
- System voltage: 10kV, 11kV and 12kV class networks
- Rated frequency: 50Hz / 60Hz
- Ambient temperature: -5°C to +40°C
- Installation environment: should be free from severe vibration, conductive dust, corrosive gas, explosive medium, heavy pollution and abnormal condensation.
Technical Parameters
The LZZBJ9-12/175b/2S is an epoxy cast-resin current transformer designed for indoor 10kV–12kV systems. It operates within an ambient temperature range of -5°C to +40°C, 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 | ||||
| 5 | 0.2/10P10 | 10 | 20 | 1.0 | 2.5 |
| 0.5/10P10 | 10 | 20 | |||
| 0.2/10P15 | 10 | 20 | 0.2 | 1.25 | |
| 0.5/10P15 | 20 | 20 | |||
| 10 | 0.2/10P10 | 10 | 20 | 2.0 | 5.0 |
| 0.5/10P10 | 10 | 20 | |||
| 0.2/10P15 | 10 | 20 | 1.0 | 2.5 | |
| 0.5/10P15 | 20 | 20 | |||
| 20 | 0.2/10P10 | 10 | 20 | 6.0 | 15 |
| 0.5/10P10 | 10 | 20 | |||
| 0.2/10P15 | 10 | 20 | 3.0 | 7.5 | |
| 0.5/10P15 | 20 | 20 | |||
| 30 | 0.2/10P10 | 10 | 20 | 12 | 30 |
| 0.5/10P10 | 10 | 20 | |||
| 0.2/10P15 | 10 | 20 | 4.5 | 11.25 | |
| 0.5/10P15 | 20 | 20 | |||
| 40 | 0.2/10P10 | 10 | 20 | 16 | 40 |
| 0.5/10P10 | 10 | 20 | |||
| 500 | 0.2/10P10 | 10 | 30 | 63 | 130 |
| 0.5/10P10 | 20 | 30 | |||
| 0.2/10P15 | 10 | 20 | |||
| 0.5/10P15 | 20 | 20 | |||
| 600 | 0.2/10P10 | 10 | 30 | 80 | 160 |
| 0.5/10P10 | 20 | 30 | |||
| 0.2/10P15 | 10 | 20 | |||
| 0.5/10P15 | 20 | 20 | |||
| 800 | 0.2/10P10 | 15 | 30 | 80 | 160 |
| 0.5/10P10 | 30 | 30 | |||
| 0.2/10P15 | 15 | 20 | |||
| 0.5/10P15 | 30 | 20 | |||
| 1000 | 0.2/10P10 | 15 | 30 | 80 | 160 |
| 0.5/10P10 | 30 | 30 | |||
| 0.2/10P15 | 15 | 20 | |||
| 0.5/10P15 | 30 | 20 | |||
| 1200,1250 | 0.2/10P10 | 15 | 30 | 100 | 160 |
| 0.5/10P10 | 30 | 30 | |||
| 0.2/10P15 | 15 | 20 | |||
| 0.5/10P15 | 30 | 20 | |||
| 1500,2500 | 0.2/10P10 | 30 | 30 | 100 | 160 |
| 0.5/10P10 | 60 | 30 | |||
| 0.2/10P15 | 30 | 30 | |||
| 0.5/10P15 | 60 | 30 | |||
Installation & Wiring
Installation Diagram
The LZZBJ9-12/175b/2S (AS12) indoor epoxy cast-resin current transformer is installed as a support-type unit within switchgear, with primary terminals at the top and secondary terminals located in a lower terminal box or block. Mounting is performed using bolts through designated holes aligned with the switchgear structure, ensuring proper phase clearance and accessibility for secondary wiring. Primary busbar connection must match the approved outline drawing for terminal spacing and direction.
Selection & FAQs
Selection Guide
- Choose the 175b/2S platform when two independent circuits and more busbar/wiring clearance than a compact 150b body are required.
- Select a 1A–1200A primary ratio from load, metering range and fault duty; technically confirm the unusual 1A primary option.
- Assign each 1A/5A core to 0.2S/0.2/0.5 measurement, 10P protection or a second measuring circuit, with clear terminal markings.
- Calculate burden separately and select a verified 10/20, 10/30, 20/20 or 20/30VA paired output.
- Confirm P1/P2 bolted-busbar layout, thermal/dynamic duty, mounting, 12/42/75kV insulation and any optional live-display interface.
Frequently Asked Questions
Q1: Can this epoxy cast-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, heavy pollution, and abnormal condensation. Contact us for outdoor alternatives.
Q2: What is the short-time thermal current rating for 5A primary?
The rated short-time thermal current is 1.0 kA for 1 second, with a rated dynamic current of 2.5 kA. Verify exact ratings based on your specific accuracy class combination.
Q3: Which accuracy class combination is suitable for protection relays?
Select the 10P10 or 10P15 protection class for relay applications. These ensure accurate performance during fault conditions up to 20 VA. Factory calibration is available upon request.
Q4: Why must the installation environment be free from conductive dust?
The epoxy cast-resin design requires a clean environment to prevent flashovers. Ensure the switchgear room is free from conductive dust and corrosive gases. Consult our manual for ventilation requirements.
Q5: Are these current transformers compliant with international IEC standards?
Yes, they fully comply with IEC 61869-2:2012 and GB 20840.2-2014 standards. Request the specific type test report from our sales team for your project documentation.
Q6: How can we request custom accuracy class combinations?
Customization for specific rated outputs and accuracy combinations is subject to confirmation. Please provide your detailed single-line diagram to our engineering team for feasibility assessment.
Q7: What system frequencies are supported by this indoor current transformer?
It supports both 50Hz and 60Hz rated frequencies for 10kV, 11kV, and 12kV class networks. Specify your grid frequency during the inquiry to ensure correct core design.