24kV Current Transformer (Outdoor type)

24kV Current Transformer

24 kV Current Transformer (Outdoor Type) is a medium-voltage instrument transformer designed for 24 kV power systems, typically used on 22 kV distribution networks. It is installed in outdoor substations, pole-mounted structures, and open-air switchyards to measure high primary current and convert it into a standardized secondary current (usually 1 A or 5 A) for metering, protection, and control systems.

It is specifically engineered to withstand harsh environmental conditions such as rain, UV radiation, pollution, wind load, and lightning impulses, making it suitable for utility and industrial outdoor applications.

Main Functions
·Measures line current in outdoor MV networks
·Supplies current signals to protection relays
·Supports energy metering and load monitoring
·Provides electrical isolation between HV and LV systems
·Detects overloads, short circuits, and earth faults

Construction
A typical 24 kV outdoor current transformer consists of:

Primary Conductor
-Busbar or line conductor passing through the CT core
-Bar-type or wound-type primary design
Magnetic Core
-High-permeability silicon steel or nanocrystalline core
-Ensures accurate measurement and low losses
Secondary Windings
-Metering core for accuracy
-Protection core for fault detection
-Multiple cores possible in one unit
Insulation System
-Porcelain insulator (traditional) or silicone rubber composite (modern)
-Designed for high pollution and outdoor durability
Insulating Medium
-Oil-immersed or epoxy resin insulated designs depending on manufacturer
Metal Base Structure
-Galvanized steel base for pole or ground mounting
-Designed for mechanical strength and stability
Secondary Terminal Box
-Weatherproof enclosure for secondary wiring
-Includes grounding and short-circuit links

Typical Technical Specifications
·Parameter: Typical Value
·Rated Voltage: 24 kV
·Highest System Voltage: 24 kV
·System Voltage: 22 kV
·Frequency: 50/60 Hz
·Primary Current: 5–3000 A
·Secondary Current: 1 A or 5 A
·Accuracy Class: 0.2, 0.5, 1.0, 5P10, 5P20, PX
·Rated Burden: 5–20 VA
·Short-Time Thermal Current: Up to 31.5 kA (1 s)
·Dynamic Current : Up to 80 kA peak
·Insulation Type: Porcelain / Composite / Oil-filled
·Installation: Outdoor (pole or substation mounted)

Working Principle
·The primary conductor carries load current through the CT core
·The current generates magnetic flux in the core
·The flux induces a proportional secondary current
·The secondary output (1 A or 5 A) is sent to meters and relays
·Electrical isolation ensures safe operation of protection systems

Advantages
·Designed for harsh outdoor environments
·High resistance to pollution, UV, and moisture
·Reliable metering and protection performance
·Long service life (typically 25–30+ years)
·Suitable for pole-mounted and substation use
·Multiple insulation options (porcelain or composite)
·Low maintenance requirements

Typical Applications
·22 kV distribution networks
·Outdoor distribution substations
·Pole-mounted transformer protection
·Utility feeder protection systems
·Industrial outdoor switchyards
·Renewable energy (solar/wind) collection systems
·Rural electrification projects

Applicable Standards
·IEC 61869-1 – Instrument Transformers General Requirements
·IEC 61869-2 – Current Transformers
·IEEE C57.13 – Instrument Transformers
·IEC 60044-1 – Legacy standard

Typical Core Configurations
·Metering Core Revenue energy measurement
·Protection Core Overcurrent / earth fault protection
·Backup Core (optional) Redundant protection schemes

Key Features
·Weatherproof design for outdoor installation
·High mechanical strength for wind and seismic loads
·Available in porcelain or composite insulators
·Supports multiple secondary cores
·Suitable for pole-mounted and ground-mounted substations
·High reliability in polluted or coastal environments

A 24 kV Outdoor Current Transformer is a rugged and reliable instrument transformer used in 22 kV distribution systems, designed to operate in harsh outdoor environments while delivering accurate current measurement and dependable protection performance for utility and industrial power networks.