Overview
The LZZBJ9-24/185h/2S is an indoor, single-phase, epoxy cast-resin current transformer rated for 20kV, 22kV and 24kV medium-voltage switchgear systems. It features a fully enclosed dry-type construction with multilayer honeycomb winding and cascade magnetic circuit design, providing reliable insulation and stable performance in 50Hz or 60Hz AC networks.
This CT supports dual secondary outputs (5A or 1A) and is suitable for current measurement, energy metering, and relay protection applications. It complies with standard requirements for partial discharge, accuracy class stability, and insulation coordination in indoor MV switchgear environments, including utility substations and industrial power distribution systems.
Key Ratings Snapshot
| Parameter | Rating |
|---|---|
| System Voltage Class | 20kV / 22kV / 24kV |
| Rated Insulation Level | 24/65/125kV |
| Primary Current | As per standard ratios (e.g., 100–3000A) |
| Secondary Current | 5A or 1A |
| Secondary Windings | 2 (2S configuration) |
| Accuracy Classes | Measurement: 0.2, 0.5; Protection: 5P10, 5P15, 5P20 |
| Frequency | 50Hz or 60Hz |
| Installation Type | Busbar-type, indoor switchgear |
| Insulation Medium | Epoxy cast-resin |
| Magnetic Circuit | Cascade type |
| Winding Structure | Multilayer honeycomb |
| Phase | Single-phase |
Construction
The LZZBJ9-24/185h/2S employs a fully enclosed epoxy cast-resin insulation system, ensuring high dielectric strength, moisture resistance, and long-term operational reliability in indoor environments. Its core uses a cascade magnetic circuit structure to support independent accuracy requirements for metering and protection functions. The windings are arranged in a multilayer honeycomb pattern, optimizing space utilization while maintaining thermal and electrical stability. Primary conductors pass through top-mounted busbar terminals (P1/P2), enabling straightforward integration into compact switchgear layouts. The robust cast-resin housing provides mechanical strength, low partial discharge levels, and minimal maintenance needs over the product lifetime.
Technical Parameters
Service Conditions
- Installation: indoor
- Ambient temperature: -5°C to +40°C reference range; catalogue also provides -5°C to +40°C general technical data
- Altitude: ≤2000m; higher altitude available on special request
- Humidity: maximum relative humidity at room temperature is 95%
- Contamination severity: class II
- Atmospheric conditions: No gas, vapor, chemical deposition, explosive or corrosive media that would seriously affect insulation
Technical Parameters
The LZZBJ9-24/185h/2S 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 at altitudes up to 2000m, complies with GB/T 20840.1, GB/T 20840.2, IEC 61869-1, and IEC 61869-2 standards, and supports rated primary currents from 20A to 2500A.
| Rated Primary Current (A) |
Accuracy Classes Combination |
Rated Output (VA) | Rated Short-Time Thermal Current (kA/1s) |
Rated Dynamic Current (kA) |
|||
|---|---|---|---|---|---|---|---|
| 0.2S | 0.2 / 0.5S | 0.5 | 5P | ||||
| 20–40 | 0.2S/0.5 0.2/0.5 0.2/5P10 0.5/5P10 0.2/5P10 0.5/5P10 |
10 | 15 | 15 | 15 | 250 I1n | 625 I1n |
| 50–100 | 300 I1n | 750 I1n | |||||
| 150–250 | 40 | 100 | |||||
| 300–2500 | 15 | 20 | 63 | 160 | |||
| 10–200 | 0.2S/5P20 0.2/5P20 0.5S/5P20 0.5/5P20 0.2S/0.5/5P10 |
10 | 15 | 15 | 15 | 150 I1n | 375 I1n |
| 300–500 | 40 | 100 | |||||
| 600–1000 | 15 | 20 | 20 | 80 | 200 | ||
| 1200–2500 | 0.2S/5P20 0.2/5P20 0.5S/5P20 0.5/5P20 |
20 | 20 | 20 | 30 | 100 | 250 |
Note:
If user’s data go beyond the above-mentioned scopes, they may be subject to an agreement between manufacturer and purchaser.
Installation & Wiring
Installation Diagram
The LZZBJ9-24/185h/2S indoor epoxy cast-resin current transformer is designed for installation within 24kV switchgear using the provided base mounting holes. Prior to production, verify compatibility between the busbar-type primary terminal arrangement and the cabinet’s busbar layout. Ensure adequate space is allocated in the panel design for secondary terminal access, grounding, terminal cover opening, and wiring routing.
Selection & FAQs
Selection Guide
- Select the LZZBJ9-24/185h/2S for compact 24kV indoor switchgear applications requiring epoxy cast-resin insulation.
- Choose this model when two secondary winding groups are needed—one for metering (e.g., 0.2S or 0.5S) and one for protection (e.g., 5P10 or 5P20).
- Prefer the 185h platform over larger alternatives like 220b when space is limited in the switchgear layout.
- Verify compatibility with system voltage classes: 20kV, 22kV, or 24kV, with a rated insulation level of 24/65/125kV.
- Confirm mechanical fit by checking busbar terminal spacing, base mounting holes, CT body width, and secondary wiring access before production.
Frequently Asked Questions
Q1: Can this 24kV current transformer be used on 20kV switchgear?
Yes, it is fully compatible with 20kV, 22kV, and 24kV indoor systems. The design complies with IEC 61869-2 standards for these voltage classes. Please specify your exact system voltage during inquiry.
Q2: What are the maximum altitude and temperature limits for installation?
Yes, standard installation is limited to 2000m altitude and -5°C to +40°C. Higher altitude versions are available upon special request. Confirm your exact site conditions with our engineering team.
Q3: Which accuracy class combination is best for protection relays?
Select a 5P class combination, such as 0.2/5P10 or 0.5/5P10, for protection applications. This configuration meets standard protection relay requirements. Request specific rated output VA values from our sales team.
Q4: How is the short-time thermal current rating determined for this CT?
The rated short-time thermal and dynamic currents depend on your specific primary current selection, ranging from 20A to 2500A. Provide your primary current and fault level data for exact factory calculation.
Q5: Does this epoxy cast-resin CT comply with international IEC standards?
Yes, the LZZBJ9-24 model strictly complies with IEC 61869-1 and IEC 61869-2 standards. It also meets domestic GB/T 20840.1 and GB/T 20840.2 requirements. We can provide standard compliance certificates upon request.
Q6: What routine factory tests are performed before shipment?
Standard routine tests include ratio, polarity, and insulation resistance checks according to IEC 61869. Special tests like temperature rise or partial discharge are subject to confirmation. Specify your required test protocol in the purchase order.
Q7: Is this current transformer suitable for outdoor substation applications?
No, the LZZBJ9-24/185h/2S is strictly designed for indoor installation only. It requires environments free from explosive or corrosive media with a maximum 95% relative humidity. Contact us for outdoor-rated alternatives if needed.