Overview
The LZZBJ9-10B and LZZBJ9-12B are indoor, single-phase current transformers rated for 10kV, 11kV, and 12kV medium-voltage systems. They feature a fully enclosed post-type design with electrical-grade epoxy resin casting that encapsulates the primary winding, secondary winding, and magnetic core into a compact insulated body.
These transformers support both metering (accuracy classes 0.2S, 0.5S) and protection (10P10, 10P15, 10P20) applications, making them suitable for switchgear instrumentation, energy metering, feeder monitoring, and relay protection in 50Hz or 60Hz power systems. They comply with standard requirements for indoor medium-voltage distribution equipment and offer reliable performance under normal and fault conditions.
Key Ratings Snapshot
| Parameter | Rating |
|---|---|
| Voltage class | 10kV / 11kV / 12kV |
| Rated frequency | 50Hz / 60Hz |
| Rated secondary current | 1A or 5A |
| Metering accuracy | 0.2S, 0.5S, 0.2, 0.5 |
| Protection class | 10P10, 10P15, 10P20 |
| Insulation type | Epoxy resin cast |
| Installation type | Indoor, post-type with bottom mounting inserts |
| Primary connection | Lead-out board |
| Core configuration | Metering, protection, or combined |
| Short-circuit withstand | Per ratio and system fault level |
Model Designation
- L: Current transformer
- Z: Indoor type
- Z: Cast-resin insulated / fully enclosed structure
- B: Protection configuration available for metering and relay protection applications
- J: Reinforced design / enhanced insulation structure
- 9: Design sequence / product platform
- 10 / 12: Voltage class identification for 10kV, 11kV, or 12kV project applications
- B: B-type mechanical structure with primary lead-out board and bottom mounting inserts
Construction
The LZZBJ9-10B and LZZBJ9-12B current transformers employ a monolithic epoxy resin cast construction that fully encloses the primary winding, secondary winding, and magnetic core. This cast-resin body provides high dielectric strength, excellent moisture resistance, and robust mechanical support for indoor switchgear environments. The B-type post structure includes primary lead-out boards for secure busbar or cable connections and threaded bottom inserts for direct mounting into metal-clad switchgear panels. The design ensures safe separation between the medium-voltage primary circuit and the low-voltage secondary circuit while maintaining stable thermal and electrical performance under continuous and short-circuit operating conditions.
Technical Parameters
Service Conditions
- Installation location: indoor medium-voltage switchgear
- System voltage: 10kV, 11kV and 12kV class systems
- Rated frequency: 50Hz
- Ambient temperature: -5°C to +40°C
- Installation environment: should be free from severe vibration, corrosive gas, explosive medium, conductive dust, heavy pollution and abnormal condensation.
Technical Parameters
The LZZBJ9-10B/12B is an indoor epoxy cast-resin current transformer designed for 10kV and 12kV class systems. It operates within an ambient temperature range of -5°C to +40°C and complies with IEC and GB standards. The device supports primary currents from 5A to 1500A with multiple accuracy class combinations.
| Rated primary current (A) |
Rated Output (VA) |
1s thermal stable current (kA) |
Dynamic stable current (kA) |
||
|---|---|---|---|---|---|
| 0.2 | 0.5 | 10P | |||
| 5, 10 | 10 | 10 | 15 | 150×I1n | 2.5×I1n |
| 15~50 | 10 | 10 | 15 | 400×I1n | 2.5×I1n |
| 75 | 10 | 10 | 15 | 32 | 90 |
| 100~200 | 10 | 10 | 15 | 45 | 100 |
| 300 | 10, 15* | 15 | 20 | 63 | 130 |
| 400, 500 | 10, 20* | 20 | 30 | ||
| 600, 800 | 20, 30* | 30 | 40 | ||
| 1000~1500 | 30, 40* | 40 | 40 | ||
Installation & Wiring
Installation Diagram
The LZZBJ9-10B and LZZBJ9-12B current transformers are installed inside indoor switchgear using bottom mounting inserts. The primary lead-out boards connect to the busbar system, while secondary terminals (1S1/1S2 and optional 2S1/2S2) are wired according to the project schematic. Ensure proper alignment, phase clearance, and grounding as per the approved outline drawing before assembly.
Selection & FAQs
Selection Guide
- Select the 10B or 12B model from system and interface requirements. Confirm the highest voltage, full insulation withstand, creepage, primary-board spacing and approved outline because one universal insulation level is not stated in the source table.
- Choose the ratio from the 10A–2500A reference range. Consider continuous loading, metering range and temperature rise; high-current versions require particular attention to busbar size, joint design and heat dissipation.
- Define measurement and protection cores separately. Select 0.2S, 0.5S, 0.2 or 0.5 measurement with 10P10 or 10P20 protection, and assign the listed 10VA–20VA output to each winding.
- Resolve the 10P15 documentation inconsistency. It appears in the overview but not the detailed combinations; request written confirmation if 10P15 is required rather than inferring it from the family description.
- Verify ratio-specific fault and mounting data. Obtain certified short-time RMS current with duration, peak dynamic current, primary lead-out dimensions, bottom-insert pattern, terminal layout and applicable IEC 61869 test documentation.
Frequently Asked Questions
Q1: What are the ambient temperature limits for installing this indoor current transformer?
The operating ambient temperature ranges from -5°C to +40°C. Ensure the installation environment remains free from severe vibration and corrosive gases. Contact us for extreme climate project evaluations.
Q2: How do I determine the 1s thermal stable current for this CT?
For primary currents up to 50A, it equals 400 times the rated primary current. For 75A and above, it ranges from 32kA to 150 times the rated current. Verify specific short-circuit levels with our engineering team.
Q3: Which accuracy class combinations are available for protection and measurement?
The transformer supports 0.2, 0.5, and 10P accuracy classes. Rated outputs are 10VA for 0.2 and 0.5 classes, and 15VA for the 10P protection class. Multiple core combinations can be integrated into a single unit.
Q4: What international standards does this epoxy cast-resin current transformer comply with?
The LZZBJ9 series fully complies with IEC and GB standards for medium-voltage equipment. All units undergo standard factory testing prior to shipment. Request the specific compliance certificates for your region.
Q5: Can the primary current rating be customized up to 1500A?
Yes, the standard range covers 5A to 1500A. Custom ratios and specific accuracy class combinations are subject to factory confirmation. Lead times for non-standard ratios vary based on production schedules.
Q6: Are there specific environmental restrictions for installing this single-phase current transformer?
It is strictly designed for clean indoor medium-voltage switchgear applications. The installation site must be free from conductive dust, explosive mediums, and abnormal condensation. Confirm your switchgear dimensions with our technical department.
Q7: Why is epoxy cast-resin used for this indoor current transformer?
Epoxy cast-resin provides excellent insulation and mechanical strength for indoor medium-voltage switchgear. It ensures safe operation within the -5°C to +40°C ambient temperature range. The material also prevents abnormal condensation issues in humid environments.