Overview
The LZZW-20 and LZZW-24 are outdoor single-phase current transformers designed for 20kV and 24kV AC power systems operating at 50/60Hz. They feature a cast-resin insulation system that provides high dielectric strength and environmental resistance, making them suitable for demanding outdoor installations.
These transformers deliver accurate current transformation for both metering and protective relay applications, supporting critical functions such as over-current, overload, and single-phase ground fault protection. Built to meet international standards for outdoor current transformers, they ensure long-term reliability in substations, renewable energy plants, and industrial power networks.
Key Ratings Snapshot
| Parameter | Rating |
|---|---|
| Rated Voltage | 20kV / 24kV |
| System Frequency | 50/60Hz |
| Insulation Type | Epoxy resin cast |
| Phase Configuration | Single-phase |
| Installation Type | Outdoor |
| Primary Current (Typical) | 10–2500A (varies by model) |
| Secondary Current | 1A or 5A |
| Accuracy Class (Metering) | 0.2, 0.5 |
| Accuracy Class (Protection) | 5P10, 10P10 |
| Short-Time Thermal Current | As per IEC 61869 |
| Impulse Withstand Voltage | 125kV (1.2/50μs) |
| Power Frequency Withstand Voltage | 42kV rms (1 min) |
Construction
The LZZW-20/24 features a robust pillar-type design with a fully encapsulated core and winding assembly embedded in high-quality epoxy resin. This cast-resin construction eliminates the risk of oil leakage or fire hazards, providing excellent mechanical strength and resistance to moisture, dust, UV radiation, and temperature extremes. The housing is engineered for direct outdoor mounting without additional enclosures, ensuring maintenance-free operation in harsh environments typical of power distribution networks.
Technical Parameters
Service Conditions
- Ambient temperature: -5°C to +40°C
- Altitude: Up to 1000 m above sea level
- Relative humidity: Up to 100% at +25°C
- Installation environment: Outdoor, pollution degree III
- Seismic intensity: Not exceeding 8 degrees
Technical Parameters
The LZZW-20/24 is a single-phase outdoor cast-resin current transformer rated for 20 kV systems, designed for operation in ambient temperatures from -40°C to +40°C and altitudes up to 1000 m. It complies with IEC 61869 standards and supports primary current ranges from 10 A to 2000 A with multiple accuracy classes for measurement and protection applications.
Single Current Ratio
| Rated Primary Current (A) |
Accuracy Classes / Rated Output (VA) |
Rated Short-Time Thermal Current (kA/1s) |
Rated Dynamic Current (kA) |
|||
|---|---|---|---|---|---|---|
| 0.2S | 0.2 | 0.5S | 0.5 | |||
| 5–300 | 20 | 30 | 30 | 40 | 80 × I1n (A) | 200 × I1n (A) |
| 400 | 20 | 30 | 30 | 40 | 31.5 | 100 |
| 500 | 30 | 40 | 50 | 50 | 45 | 112.5 |
| 600 | 50 | 50 | 60 | 60 | 63 | 160 |
| 750–800 | 50 | 50 | 60 | 60 | 80 | 200 |
| 1000–1200 | 50 | 50 | 60 | 60 | 100 | 250 |
Compound Ratio or Two Secondary Windings
| Rated Primary Current (A) |
Accuracy Classes / Rated Output (VA) |
Short-Time Thermal Current (kA/1s) |
Rated Dynamic Current (kA) |
|||
|---|---|---|---|---|---|---|
| 0.2S | 0.2 | 0.5S | 0.5 | |||
| 5–300 | 10 | 15 | 20 | 20 | 80 × I1n (A) | 200 × I1n (A) |
| 400 | 20 | 30 | 30 | 30 | 31.5 | 100 |
| 500 | 20 | 30 | 30 | 40 | 45 | 112.5 |
| 600 | 20 | 30 | 30 | 40 | 63 | 160 |
| 750–800 | 30 | 40 | 40 | 50 | 80 | 200 |
| 1000–1200 | 30 | 40 | 40 | 50 | 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
Windings
Selection & FAQs
Selection Guide
- Choose based on system voltage: LZZW-20 for 20 kV systems, LZZW-24 for 24 kV systems.
- Select secondary current output: standard 5A or optional 1A depending on metering or protection requirements.
- Ensure compliance with international and local standards: IEC 61869-1, IEC 61869-2, and GB20840.2-2014.
- Opt for this model for outdoor installations where resistance to moisture, UV radiation, and pollution is critical.
- Consider maintenance needs: these units are maintenance-free except for occasional surface cleaning.
Frequently Asked Questions
Q1: What are the ambient temperature limits for outdoor installation?
The LZZW-24 operates in ambient temperatures from -40°C to +40°C. It is designed for outdoor use with pollution degree III and altitudes up to 1000 m. Contact us for extreme climate specifications.
Q2: Which accuracy class is required for protective relaying?
The provided table lists measurement classes 0.2S, 0.2, 0.5S, and 0.5. For protection applications, specify the required 5P or 10P class and rated output during inquiry for factory confirmation.
Q3: How is the short-time thermal current rated for 400A?
For a 400 A rated primary current, the rated short-time thermal current is 31.5 kA/1s, and the dynamic current is 100 kA. Verify these ratings match your specific fault level requirements.
Q4: Are these 20kV current transformers compliant with IEC standards?
Yes, the LZZW-20/24 complies with IEC 61869 standards. It is a cast-resin single-phase unit rated for 20 kV systems. Request the specific type test certificates for your project submission.
Q5: Can the primary current be customized up to 2000A?
Yes, the transformer supports primary current ranges from 10 A to 2000 A. Provide your exact rated primary current and accuracy class requirements to receive a customized factory quotation.
Q6: Why choose cast-resin for this outdoor current transformer?
Cast-resin insulation provides superior weather resistance for harsh environments. This single-phase unit is engineered for 20 kV outdoor distribution networks. Contact us for specific pole-mounted substation designs.
Q7: When is this single-phase CT suitable for outdoor use?
This unit is suitable for outdoor installations with pollution degree III and altitudes up to 1000 m. Please provide your specific site conditions for final engineering verification.