Overview
The LZZBJ9-24/180b/4S is an indoor, single-phase, epoxy cast-resin current transformer designed for 20kV, 22kV, and 24kV medium-voltage switchgear systems. It features a fully enclosed epoxy resin cast body with ribbed external insulation and a busbar-type primary terminal configuration, ensuring reliable performance in indoor AC environments at 50Hz or 60Hz.
This CT supports multiple secondary applications including revenue metering, panel measurement, feeder monitoring, and both main and backup relay protection. Its 4S configuration enables up to four independent secondary windings, each assignable to dedicated functions per IEC and ANSI standards for accuracy and safety in medium-voltage installations.
Key Ratings Snapshot
| Parameter | Rating |
|---|---|
| Voltage Class | 20kV / 22kV / 24kV |
| Rated Insulation Level | 24/65/125kV |
| Rated Frequency | 50Hz or 60Hz |
| Phase | Single-phase |
| Installation Type | Busbar type |
| Secondary Configuration | 4S (four winding groups) |
| Rated Secondary Current | 5A or 1A |
| Insulation Material | Epoxy cast-resin |
| Operation Condition | Indoor |
| Application | Measurement, metering, protection |
| Structure | Fully enclosed with ribbed insulation |
| Charged Display Option | Available (≤3 secondary cores) |
Model Designation
Construction
The LZZBJ9-24/180b/4S features a robust, fully enclosed epoxy cast-resin body that provides excellent dielectric strength, moisture resistance, and mechanical durability. The external surface incorporates ribs to extend the creepage distance, enhancing indoor insulation performance under medium-voltage conditions. Primary terminals are configured in a busbar-type layout (P1/P2), allowing direct integration into switchgear bus systems without additional connectors. Internally, the core and windings are vacuum-cast within the epoxy matrix to eliminate voids and ensure long-term stability. This construction meets stringent requirements for indoor 24kV-class applications, supporting reliable operation across metering, monitoring, and protection circuits.
Technical Parameters
Service Conditions
- Installation: indoor
- Rated voltage class: 20kV, 22kV and 24kV systems
- Rated frequency: 50Hz or 60Hz
- Ambient temperature: -5°C to +40°C
- Power factor for burden reference: cosφ = 0.8 lagging
- Anti-fouling level: Grade II reference
- Altitude: ≤1000m for standard service conditions; higher altitude by project confirmation
- Installation environment: No severe pollution, conductive dust, corrosive gas, abnormal condensation or strong vibration at the installation site
Technical Parameters
The LZZBJ9-24/180b/4S is an indoor epoxy cast-resin current transformer rated for 20kV, 22kV, and 24kV systems, with a primary current range from 20A to 1250A (extendable to 3000A in high-current layouts). It operates within an ambient temperature of -5°C to +40°C, is suitable for altitudes up to 1000m, complies with GB/T 20840.1, GB/T 20840.2, IEC 61869-1, and IEC 61869-2 standards, and features a 4S multi-secondary configuration.
| Type | Rated Primary Current (A) |
Accuracy Classes Combination |
Rated Output (VA) |
Short-Time Thermal Current (kA/1s) |
Rated Dynamic Current (kA) |
|---|---|---|---|---|---|
| LZZB9-24/180b/4S | 20, 30, 40, 50, 75, 100, 150 |
0.2/0.2/0.2 0.2/0.5/0.5 0.2/10P10/10P10 0.5/10P10/10P10 0.2/10P15/10P15 0.5/10P15/10P15 |
10/10/10 10/15/15 10/15/15 10/15/15 10/10/15 10/10/15 |
150 I1n | 375 I1n |
| 200 | 31.5 | 80 | |||
| 300, 400, 500 | 45 | 112.5 | |||
| 600, 800 | 0.2/0.2/0.2 0.2/0.5/0.5 0.2/10P10/10P10 0.5/10P10/10P10 0.2/10P15/10P15 0.5/10P15/10P15 |
15/15/20 15/20/20 10/20/20 15/20/20 10/15/15 15/15/15 |
63 | 130 | |
| 1000, 1250, 1500 | 80 | 160 |
Note:If user’s data go beyond the above-mentioned scopes, they may be subject to an agreement between manufacturer and purchaser.
Note: This table is for preliminary selection. Final current ratio, rated burden, accuracy class, secondary terminal arrangement, short-time thermal current and dynamic current shall be confirmed according to the nameplate, approved drawing and factory test report.
Installation & Wiring
Installation Diagram
The LZZBJ9-24/180b/4S current transformer is designed for indoor installation within 24kV switchgear. It is mounted using the base mounting holes as shown in the installation diagrams. The primary conductor passes through the central aperture, and the unit must be securely fastened to prevent movement during operation. Ensure adequate clearance around the secondary terminal box for wiring access and maintenance. Separate mounting layouts apply depending on the primary current range (5–800A or 1000–3000A), so verify the correct layout against your switchgear busbar configuration before installation.
Selection & FAQs
Selection Guide
- Select for 20kV, 22kV, or 24kV indoor switchgear applications with a rated insulation level of 24/65/125kV.
- Choose the LZZBJ9-24/180b/4S model when four secondary windings are required for metering, measurement, main protection, and backup protection.
- Verify primary terminal spacing and busbar layout compatibility before integration into switchgear design.
- Confirm secondary terminal box access, grounding point location, and terminal cover space during panel planning.
- Specify current ratio, secondary output (1A or 5A), accuracy class combination, rated burden, and short-time thermal/dynamic withstand currents (Ith/Idyn) at ordering.
Frequently Asked Questions
Q1: Can this 24kV current transformer be used on 20kV systems?
Yes, it is rated for 20kV, 22kV, and 24kV indoor systems. Ensure the installation environment is free from severe pollution and conductive dust. Contact us for specific project verification.
Q2: What are the maximum altitude and temperature limits for installation?
Standard service conditions support altitudes up to 1000m and ambient temperatures from -5°C to +40°C. For higher altitudes or extreme temperatures, custom design is subject to factory confirmation.
Q3: How is the short-time thermal current rated for this model?
The short-time thermal and dynamic current ratings depend on the selected primary current ratio, ranging from 20A to 3000A. Please specify your exact primary current for accurate thermal rating details.
Q4: Which secondary configuration is included in the 4S multi-secondary design?
The 4S designation indicates a four-core secondary winding configuration for simultaneous metering, protection, and measurement. Confirm the specific accuracy class combinations and rated output in VA with our engineering team.
Q5: Does this epoxy cast-resin CT comply with international IEC standards?
Yes, the LZZBJ9-24 model fully complies with IEC 61869-1, IEC 61869-2, and corresponding GB/T 20840 standards. Request the official type test reports and compliance certificates during the procurement process.
Q6: What routine factory tests are performed before shipment?
Standard routine tests are performed in strict accordance with IEC 61869-2 guidelines. Specific test details, reporting formats, and witness arrangements are subject to factory confirmation upon order.
Q7: Where is this indoor current transformer typically applied?
It is primarily applied in 20kV to 24kV indoor switchgear and power distribution panels. The epoxy cast-resin insulation ensures reliable performance in standard indoor environments without severe pollution.
Q8: Can the primary current range be customized beyond 1250A?
Yes, while standard configurations cover 20A to 1250A, high-current layouts can be extended up to 3000A. Contact our sales team with your exact primary current requirements for a customized quote.