Overview
The LZZB9-20, LZZB9-24/220b/4S is an indoor epoxy cast-resin current transformer designed for 20kV, 22kV, and 24kV medium-voltage switchgear systems. It features a fully enclosed epoxy resin casting with a ribbed external insulation structure, providing enhanced dielectric strength and mechanical stability for indoor applications.
This CT supports standard secondary currents of 5A or 1A and complies with IEC 61869-1 and IEC 61869-2 standards. It is engineered for accurate current measurement, energy metering, feeder monitoring, and relay protection in 50Hz or 60Hz AC power systems, commonly deployed in utility substations, industrial distribution rooms, and indoor switchgear panels.
Key Ratings Snapshot
| Parameter | Rating |
|---|---|
| Voltage Class | 20kV / 22kV / 24kV |
| Rated Insulation Level | 24/65/125kV |
| Rated Primary Current | 20A – 3150A |
| Rated Secondary Current | 5A or 1A |
| Secondary Configuration | 4S (four independent windings) |
| Frequency | 50Hz or 60Hz |
| Application | Metering, measurement, protection |
| Protection Class | 5P10, 5P20 (as configured) |
| Indoor/Outdoor | Indoor only |
| Insulation Material | Epoxy cast-resin |
| Standards | IEC 61869-1, IEC 61869-2 |
| Operation Environment | Switchgear cabinets, substations |
Construction
The LZZB9-24/220b/4S features a fully enclosed epoxy cast-resin body, molded under vacuum to eliminate voids and ensure uniform dielectric properties. The external surface incorporates longitudinal ribs to extend the creepage distance, enhancing insulation performance in indoor medium-voltage environments. All magnetic cores and secondary windings are permanently encapsulated within the resin matrix, providing excellent moisture resistance, thermal stability, and mechanical robustness. A dedicated lower terminal box houses the four secondary winding outputs, allowing organized and secure wiring for metering, measurement, protection, and backup circuits. This construction meets the demands of high-reliability indoor switchgear installations without requiring outdoor-rated sealing or UV resistance.
Technical Parameters
Service Conditions
- Installation site: indoor medium-voltage switchgear
- Rated voltage: 20kV, 22kV and 24kV class systems
- Rated frequency: 50Hz or 60Hz
- Ambient temperature: maximum +40°C, minimum -5°C, daily average not exceeding +30°C
- Atmospheric conditions: no severe pollution, conductive dust, corrosive gas or abnormal condensation
- Altitude, humidity, pollution level and seismic requirements: should be confirmed according to project specification.
Technical Parameters
The LZZB9-24/220b/4S is an indoor epoxy cast-resin current transformer designed for 20kV, 22kV, and 24kV class systems. It operates within an ambient temperature range of -5°C to +40°C, complies with IEC 61869-1/-2 and GB/T 20840.1/.2 standards, and supports primary current ratings from 20A to 3150A.
| Rated Primary Current (A) |
Accuracy Classes Combination |
Rated Output (VA) | Rated Short-Time Thermal Current (kA/1s) |
Rated Dynamic Current (kA) |
|||
|---|---|---|---|---|---|---|---|
| 0.2(S) | 0.5(S) | 5(10)P10 | 5(10)P20 | ||||
| 20–200 | 0.2(S)/0.2(S)/5(10)P 0.2(S)/0.5(S)/5(10)P 0.2(S)/5(10)P/5(10)P 0.2(S)/5(10)P/5(10)P |
15 | 15 | 20 | 20 | 150 I1n | 375 I1n |
| 300 | 31.5 | 80 | |||||
| 400–500 | 45 | 110 | |||||
| 600–800 | 63 | 130 | |||||
| 1000–3150 | 20 | 30 | 100 | 160 | |||
Windings & Terminal Marking
| Terminal | Function | Application Note |
|---|---|---|
| P1 / P2 | Primary terminals | Used for primary current direction and polarity reference. |
| 1S1 / 1S2 | First secondary winding | Usually assigned to metering or high-accuracy measurement. |
| 2S1 / 2S2 | Second secondary winding | Usually assigned to measurement or energy metering. |
| 3S1 / 3S2 | Third secondary winding | Usually assigned to relay protection. |
| 4S1 / 4S2 | Fourth secondary winding | Used for backup protection, independent relay circuit or project-specific monitoring. |
| Grounding point | Protective grounding | One point of the secondary circuit should be grounded according to project practice. |
Installation & Wiring
Installation Diagram
The LZZB9-24/220b/4S current transformer is designed for indoor installation within 24kV switchgear. It is mounted using the base mounting holes as shown in the installation diagram. Ensure proper alignment with the primary busbar and verify clearance for secondary wiring access through the lower side terminal box. Confirm primary terminal orientation and hole pattern based on the selected current range (20–1250A or 1500–3000A) before final assembly.
Selection & FAQs
Selection Guide
- Select for indoor use only—this cast-resin current transformer is not rated for outdoor environments.
- Confirm system voltage compatibility: designed for 20kV, 22kV, and 24kV indoor systems with insulation level 24/65/125kV.
- Specify the required current ratio and secondary output (5A or 1A) based on metering and protection needs.
- Choose accuracy classes per winding function—common combinations include 0.2S, 0.5S, 5P10, and 5P20.
- Verify mechanical and electrical interface details: primary terminal layout, mounting dimensions, secondary terminal box orientation, and busbar clearance.
Frequently Asked Questions
Q1: What voltage systems is this epoxy cast-resin current transformer designed for?
It is designed for 20kV, 22kV, and 24kV class indoor medium-voltage switchgear. Ensure your system voltage matches these ratings before ordering. Contact us to verify specific project requirements.
Q2: Which accuracy classes are available for metering and protection functions?
The LZZB9-24 offers 0.2S and 0.5S classes for metering, plus 5P and 10P classes for protection. Select the combination based on your relay and meter specifications. Factory calibration is available upon request.
Q3: Can this indoor current transformer operate in extreme cold environments?
The minimum ambient temperature rating is -5°C, with a maximum of +40°C. It requires an indoor environment free from severe pollution and corrosive gases. Confirm altitude and humidity limits with our engineering team.
Q4: How does this CT handle high short-circuit fault currents?
It features high rated short-time thermal and dynamic current capacities to withstand fault conditions. The exact kA ratings depend on your chosen primary current rating from 20A to 3150A. Request the detailed datasheet for specific thermal limits.
Q5: What international standards does this 24kV current transformer comply with?
The transformer fully complies with IEC 61869-1/-2 and GB/T 20840.1/.2 standards. All units undergo rigorous factory testing prior to shipment. Please specify your required certification documents during the inquiry.
Q6: Can the primary current rating be customized for specific load requirements?
Yes, primary current ratings are customizable from 20A up to 3150A. Specify your exact rated primary current and accuracy class combination in your RFQ. Our sales team will confirm technical feasibility and lead time.
Q7: Is this manufacturer capable of supplying medium-voltage switchgear components globally?
Yes, we specialize in manufacturing indoor epoxy cast-resin current transformers for global medium-voltage applications. Our products are engineered for international switchgear integration. Contact our export department for shipping and packaging details.