Overview
The COL-24 and COL-36 are outdoor oil-immersed current transformers designed for 24kV and 36kV medium-voltage distribution systems. They feature an oil-immersed insulation system with a sealed metal base and an outdoor-rated porcelain or composite insulating body, ensuring reliable performance in exposed environments including humidity, rain, dust, and tropical conditions.
These transformers support metering accuracy classes of 0.2S, 0.2, 0.5S, and 0.5, making them suitable for revenue metering, feeder monitoring, and relay protection applications. Standard secondary output is 5A, with 1A available upon request. They comply with standard requirements for outdoor insulation coordination, including high impulse withstand capability (e.g., 125kV BIL for COL-24), and are commonly deployed at pole-mounted metering points, outdoor substations, and industrial grid connections.
Key Ratings Snapshot
| Parameter | Rating |
|---|---|
| Voltage Class | 24kV / 36kV |
| Insulation Type | Oil-immersed |
| Rated Secondary Current | 5A (standard), 1A (optional) |
| Metering Accuracy Classes | 0.2S, 0.2, 0.5S, 0.5 |
| Protection Class | As per agreement |
| Ratio Configuration | Single-ratio |
| Impulse Withstand Voltage (COL-24) | 125kV (BIL) |
| Power-Frequency Withstand (COL-24) | 65kV |
| Installation Environment | Outdoor |
| Primary Connection | NEMA pad or compression terminal |
Construction
The COL-24 and COL-36 feature an upright outdoor design with a sealed metal base and robust primary terminal connectors. The main insulating body is constructed from either porcelain or composite material, selected for long-term outdoor service. Internally, the transformer uses an oil-immersed insulation system that enhances dielectric strength and provides effective heat dissipation under continuous outdoor operating conditions. The unit includes a four-hole mounting pattern and a grounding clamp to facilitate secure field installation on poles or substation structures. Primary terminals are configured as NEMA pads or compression-type connectors, compatible with overhead conductors or substation buswork. The entire assembly is hermetically sealed to prevent moisture ingress and maintain insulation integrity over time.
Technical Parameters
Service Conditions
- Installation location: outdoor
- Ambient temperature: -25°C to +55°C reference for COL-24
- Rated frequency: 50Hz or 60Hz
- Relative humidity: up to 100% reference in outdoor service table
- Installation altitude: up to 1000m under standard service conditions; higher altitude requires insulation coordination confirmation
- Environment: suitable for outdoor exposed conditions; severe coastal, industrial pollution or high-altitude applications should be confirmed separately
- Installation restrictions: should avoid long-term immersion, abnormal mechanical impact and corrosive chemical atmosphere beyond project design limits.
Technical Parameters
The COL-24 and COL-36 are outdoor oil-immersed current transformers designed for systems up to 24kV and 36kV respectively. They operate within an ambient temperature range of -25°C to +55°C at altitudes up to 1000m, comply with IEC 61869 and GB/T 20840 standards, and support primary current ranges from 5A to 600A depending on model and application.
| Single Current Ratio | ||||||
|---|---|---|---|---|---|---|
| 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 | 30 | 30 | 30 | 40 | 80 × I1n (A) | 200 × I1n (A) |
| 400 | 30 | 30 | 30 | 40 | 31.5 | 100 |
Note:
If user’s data go beyond the above-mentioned scopes, they may be subject to an agreement between manufacturer and purchaser.
Note: The table is for preliminary selection. Final current ratio, burden, accuracy class, protection class, insulation level, terminal connector and test requirements shall be confirmed according to the nameplate, approved drawing and factory test report.
Installation & Wiring
Installation Diagram
The COL-24 and COL-36 outdoor oil-immersed current transformers are designed for vertical mounting on stable outdoor supports such as steel structures, concrete foundations, pole-mounted brackets, or substation frames. The unit features a four-hole base mounting pattern (230 × 130mm reference) and includes a base grounding clamp. Ensure the installation surface is level and secure to maintain proper alignment and mechanical stability.
Wiring Diagram
Secondary terminals are located in a lower-side terminal box. Terminal markings typically follow standard CT notation (e.g., K1, K2 or S1, S2), with polarity clearly indicated. Connect secondary wiring to compatible metering or protection devices according to the specified current ratio and accuracy class. Seal all cable entries into the terminal box to prevent moisture ingress, which could compromise insulation integrity and long-term reliability.
Selection & FAQs
Selection Guide
- Select COL-24 for 24kV systems and COL-36 for 36kV systems based on your system voltage.
- Choose between 5A (standard) or 1A secondary current depending on relay/metering compatibility and cable burden requirements.
- Pick metering accuracy classes such as 0.2S, 0.2, 0.5S, or 0.5 according to utility specifications and rated burden.
- Verify outdoor-specific features like oil-immersed insulation, outdoor terminal design, and adequate creepage distance for exposed installations.
- Confirm mounting details including base hole pattern, primary connector type, grounding clamp, and phase-to-ground clearance before ordering.
Frequently Asked Questions
Q1: Can the COL-24 be installed on a 36kV power system?
No, the COL-24 is strictly rated for systems up to 24kV. For 36kV applications, you must select the COL-36 model. Contact us to verify your specific system voltage requirements.
Q2: When is factory confirmation required for high-altitude installation?
Standard installation altitude is up to 1000m with an ambient temperature range of -25°C to +55°C. Higher altitudes or extreme temperatures require insulation coordination confirmation. Please provide your exact site conditions for factory evaluation.
Q3: Which short-time thermal current rating is available for these models?
Short-time thermal current ratings depend on the specific primary current ratio selected, ranging across standard fault levels. Refer to the technical parameter table for exact kA/1s values. Custom ratios are subject to factory confirmation.
Q4: Are these oil-immersed current transformers compliant with international standards?
Yes, both COL-24 and COL-36 models comply with IEC 61869 and GB/T 20840 standards. Standard compliance certificates are provided with shipment. Contact our sales team if you need specific regional certifications.
Q5: How are the transformers tested before factory delivery?
Each unit undergoes routine tests according to IEC 61869 standards before dispatch. Special tests can be arranged subject to prior agreement. Request the detailed test report package during the procurement process.
Q6: Where are these COL series outdoor transformers typically applied?
These oil-immersed current transformers are designed for outdoor exposed conditions in medium voltage networks up to 36kV. They are suitable for standard environments but avoid severe coastal or industrial pollution. Severe environment suitability is subject to separate engineering evaluation.
Q7: Which accuracy classes are supported for measurement and protection?
The COL series supports multiple accuracy classes and rated outputs depending on your application needs. Primary currents range from 5A to 600A. Specify your required accuracy class and burden when requesting a quotation.