Product Overview

The COL-24 / COL-36 outdoor oil-immersed current transformer is a medium-voltage instrument transformer designed for outdoor distribution systems, pole-mounted metering points, substations, feeder measurement and relay protection. The product uses an oil-immersed insulation system with an outdoor porcelain / composite insulating body and a sealed metal base, providing reliable dielectric performance for exposed service conditions such as humidity, rain, dust and tropical environments.

This product should be positioned differently from indoor epoxy cast-resin CTs. Its core value is outdoor oil-immersed insulation, long creepage distance, high impulse withstand capability and utility-side metering reliability. The COL-24 version is suitable for 24kV class systems, while the COL-36 version can be used for 36kV class distribution projects. Standard secondary output is normally 5A, with 1A available according to project requirements.

Product Type

COL-24, COL-36 Outdoor Oil-Immersed Current Transformer Product Display

Item	Specification
Product name	Outdoor Oil-Immersed Current Transformer
Model	COL-24 / COL-36
Application	Current measurement, energy metering and relay protection
Installation condition	Outdoor
Insulation type	Oil-immersed insulation system
Product structure	Outdoor upright CT with sealed base and primary terminal connectors
Voltage class	24kV and 36kV medium-voltage systems
Rated secondary current	5A standard; 1A available by project confirmation
Ratio type	Single-ratio reference configuration
Typical accuracy	0.2S / 0.2 / 0.5S / 0.5 for metering; protection class by agreement

Product Positioning

The COL series is best described as an outdoor oil-immersed metering CT for 24kV and 36kV distribution networks. Compared with dry-type indoor CTs, it is not optimized for compact switchgear installation; it is optimized for outdoor insulation coordination, weather resistance, terminal connection reliability and utility metering service.

Positioning Point	Technical Meaning	Website Expression
Outdoor oil-immersed design	Transformer oil improves internal insulation and heat dissipation	Designed for exposed outdoor feeder and metering applications
24kV / 36kV platform	Suitable for medium-voltage distribution networks	COL-24 for 24kV systems and COL-36 for 36kV systems
Metering accuracy	Supports 0.2S / 0.2 / 0.5S / 0.5 classes	Suitable for revenue metering and distribution measurement
High impulse withstand	125kV BIL reference for COL-24	Designed for outdoor insulation coordination and lightning impulse stress
NEMA pad / compression terminal	Outdoor primary connection arrangement	Supports field connection to overhead or substation conductors

Applications

24kV and 36kV outdoor distribution feeders
Outdoor utility metering points and revenue metering systems
Pole-mounted metering units and outdoor substation yards
Medium-voltage distribution line current measurement
Feeder monitoring, protection relay input and SCADA signal circuits
Industrial outdoor substations and grid connection points
Tropical, humid or exposed service environments requiring oil-immersed insulation

Features

Outdoor oil-immersed insulation: Transformer oil and sealed construction support stable insulation performance and heat dissipation in outdoor service.
High metering accuracy: 0.2S, 0.2, 0.5S and 0.5 accuracy options support utility metering and distribution measurement.
24kV / 36kV coverage: COL-24 and COL-36 variants cover common medium-voltage distribution voltage levels.
High impulse withstand capability: COL-24 reference insulation data includes 125kV impulse withstand voltage and 65kV power-frequency withstand level.
Outdoor terminal connection: NEMA pad or compression-type primary connector can be specified according to the project.
Field-oriented base design: Four-hole mounting layout and grounding clamp support outdoor installation and maintenance.

Operating Principle

The COL outdoor current transformer converts the primary line current of a medium-voltage circuit into a standardized low secondary current signal, normally 5A. The primary current flows through the outdoor primary terminal path, while the secondary winding provides an isolated proportional output for meters, relays or monitoring devices.

The oil-immersed insulation system improves internal dielectric strength and supports heat dissipation under outdoor operating conditions. For metering use, the CT must maintain accuracy within the specified burden. For protection use, the CT must provide sufficient output under fault-current conditions according to the required protection class and accuracy limit factor.

Model Designation

Code	Meaning
COL	Outdoor oil-immersed current transformer series
24	24kV highest system voltage class
36	36kV highest system voltage class
Single ratio	One rated primary current / one rated secondary current combination
5A / 1A	Rated secondary current option

Technical Data

Item	COL-24 Reference	COL-36 Reference
Product type	Outdoor oil-immersed current transformer	Outdoor oil-immersed current transformer
Highest system voltage	24kV	36kV
Rated insulation level	24/65/125kV	Project-specific 36kV insulation level by confirmation
Rated frequency	50Hz or 60Hz	50Hz or 60Hz
Rated secondary current	5A standard; 1A available	5A standard; 1A available
Primary current range	5A to 400A according to catalogue reference; 20–600A market reference	20A to 600A market reference
Rated output	30VA or 40VA according to accuracy class and ratio	10VA to 30VA reference by project specification
Accuracy class	0.2S / 0.2 / 0.5S / 0.5	0.2 / 0.5 / protection class by agreement
Ambient temperature	-25°C to +55°C	-25°C to +55°C reference
Creepage distance	Minimum 600mm reference	According to insulation level and pollution requirement
Approximate mass	35kg reference	Project-specific
Applicable standards	IEC 61869-1, IEC 61869-2, GB/T 20840.1, GB/T 20840.2; legacy IEC 60044-1 / GB20840 references by agreement	IEC 61869-1, IEC 61869-2 and project-specific requirements

Selection Table

The following table is reorganized for website display. Long table headings are split into multiple lines to improve responsive layout.

Model	Highest System Voltage	Rated Primary Current (A)	Rated Secondary Current	Accuracy Class/ Rated Output	Short-Time Thermal Current	Rated Dynamic Current
COL-24	24kV	5–300	5A or 1A	0.2S: 30VA 0.2: 30VA 0.5S: 30VA 0.5: 40VA	80 × I1n	200 × I1n
COL-24	24kV	400	5A or 1A	0.2S: 30VA 0.2: 30VA 0.5S: 30VA 0.5: 40VA	31.5kA	100kA
COL-24	24kV	20–200	5A	10VA market reference	Project-specific confirmation
COL-24	24kV	250–600	5A	10VA market reference	Project-specific confirmation
COL-36	36kV	20–200	5A	10VA market reference	Project-specific confirmation
COL-36	36kV	250–600	5A	10VA market reference	Project-specific confirmation

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.

Outdoor Construction

Construction Item	Technical Description
Insulation body	Outdoor oil-immersed insulation structure with ribbed external insulation path
Tank / base	Sealed metal base suitable for outdoor mounting
Primary terminal	NEMA pad or compression-type connector by project requirement
Secondary terminal	Brass stud M6 reference
Grounding clamp	Suitable for 50–95mm² grounding conductor reference
Mounting	Four mounting holes, 230 × 130mm layout with 15mm hole diameter reference
Creepage distance	Minimum 600mm reference for COL-24

Windings & Terminal Marking

COL-24, COL-36 Outdoor Oil-Immersed Current Transformer Terminal Marking

The COL outdoor oil-immersed CT is normally supplied with primary terminals marked P1 and P2. The secondary terminal group is normally marked S1 and S2. Polarity and grounding must follow the approved wiring diagram and project standard.

Terminal	Function	Application Note
P1 / P2	Primary terminals	Primary current direction and polarity reference.
S1 / S2	Secondary winding terminals	Output to meter, relay or monitoring device.
Grounding terminal	Secondary / base grounding reference	One point of the secondary circuit and the equipment base should be grounded according to project practice.

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 should avoid long-term immersion, abnormal mechanical impact and corrosive chemical atmosphere beyond project design limits.

Standards and Compliance

For new international documentation, the COL-24 / COL-36 current transformer should be specified according to IEC 61869-1 and IEC 61869-2. Older project documents may still refer to IEC 60044-1. The supplied product information also references GB20840.1-2010 and GB20840.2-2014. Final applicable standards should be confirmed in the technical agreement and routine test plan.

Installation and Dimensions

Dimensions

Dimension Item	COL-24 Reference Value / Note
Overall front width	Approx. 330mm reference
Base width	Approx. 320–360mm reference from drawing views
Base depth	Approx. 320mm reference
Terminal top diameter	Approx. Ø200mm reference
Mounting layout	Four-hole base mounting; 230 × 130mm reference from technical table
Secondary terminal location	Lower side terminal box / secondary outlet position
Grounding point	Base grounding clamp

The transformer should be installed vertically on a stable outdoor steel support, concrete foundation, pole-mounted bracket or substation structure. Before installation, confirm the primary terminal type, conductor direction, base mounting hole pattern, grounding conductor size, secondary cable route and minimum electrical clearance. Secondary cable entries should be sealed to prevent moisture ingress into the terminal box.

Safety Notes

Confirm voltage class, current ratio, secondary current, accuracy class, burden and insulation level before installation.
Check primary connector type, mounting holes, grounding clamp and secondary terminal location before field assembly.
Keep the oil-immersed body upright and avoid mechanical impact during transport and installation.
The CT secondary circuit must not be open-circuited while primary current is flowing.
Before disconnecting meters or relays, short-circuit the secondary circuit with an approved shorting device.
Ground the CT base and one point of the secondary circuit according to local electrical safety regulations.
Outdoor installation and commissioning shall be performed by qualified medium-voltage electrical personnel.

Selection Guide

Confirm voltage platform: Use COL-24 for 24kV systems and COL-36 for 36kV systems.
Confirm outdoor insulation: Select oil-immersed outdoor CTs when the installation is exposed to rain, humidity, dust and outdoor temperature variation.
Select current ratio: Choose the primary current according to feeder load, utility metering range and protection requirement.
Define accuracy class: Use 0.2S or 0.2 for high-accuracy metering, and 0.5 or 0.5S for general metering / measurement.
Confirm rated burden: Calculate the total burden of meters, relays, terminal blocks and secondary cables.
Check outdoor connectors: Confirm NEMA pad or compression connector according to the conductor and site installation method.
Approve drawings: Confirm base mounting layout, grounding point, terminal position and secondary outlet before production.

FAQs

It is an outdoor oil-immersed current transformer for medium-voltage distribution metering, current measurement and relay protection. COL-24 is used for 24kV systems, while COL-36 is used for 36kV systems.

Indoor cast-resin CTs are designed mainly for switchgear installation. COL outdoor CTs use an oil-immersed insulation system and outdoor terminal structure, making them more suitable for exposed feeder, pole-mounted and substation applications.

The standard secondary current is normally 5A. A 1A secondary output can be supplied when the project requires lower secondary cable burden or specific relay / metering compatibility.

Typical metering accuracy classes include 0.2S, 0.2, 0.5S and 0.5. The final class should be selected according to the utility metering requirement, rated burden and current ratio.

Check the base mounting holes, primary connector type, grounding clamp, secondary terminal box, cable sealing method, creepage distance, pollution level and minimum phase-to-ground clearance.

When primary current is flowing, an open secondary circuit may generate dangerous high voltage across the secondary terminals. This can damage insulation and create serious safety risks. The secondary circuit must be shorted before meter or relay disconnection.

Please provide model, voltage class, insulation level, current ratio, secondary current, accuracy class, burden, terminal connector type, mounting drawing, creepage distance, environmental conditions, test report and certificate requirements.

COL-24, COL-36 Outdoor Oil-Immersed Current Transformer