12kV Current Transformer (Outdoor type)

12kV Current Transformer

12 kV Current Transformer (Outdoor Type) is a medium-voltage instrument transformer designed for 12 kV power systems (commonly used on 11 kV distribution networks) and installed in outdoor substations, pole-mounted structures, and open-air switchyards. It converts high primary current into a standardized secondary current (typically 1 A or 5 A) for metering, protection, and control while providing safe electrical isolation between the high-voltage primary system and secondary devices.

Unlike indoor epoxy CTs, outdoor CTs are built to withstand rain, UV radiation, pollution, temperature variation, wind load, and lightning impulses, making them suitable for harsh environmental conditions.

Main Functions
·Measures line current in outdoor distribution systems
·Supplies current signals for protection relays
·Enables energy metering and load monitoring
·Provides isolation between HV and LV systems
·Detects overloads, short circuits, and earth faults

Construction
A typical 12 kV outdoor current transformer consists of:
Primary Conductor
-Busbar or line conductor passes through the CT core
-May be bar-type or wound-type depending on design
Magnetic Core
-High-permeability silicon steel or nanocrystalline material
-Designed for accurate measurement and low losses
Secondary Windings
-Metering core for accuracy
-Protection core for fault conditions
-Multiple cores possible
Insulation System
-Porcelain insulator (traditional) or silicone rubber composite (modern)
-Designed for high pollution and outdoor exposure
-Oil or Epoxy Insulation (depending on design)
-Oil-immersed types for higher stability
-Epoxy resin types for compact outdoor installations
Base and Mounting Structure
-Steel base for pole or ground mounting
-Designed for mechanical stability and seismic withstand
Secondary Terminal Box
-Weatherproof enclosure
-Includes grounding and short-circuit links

Typical Technical Specifications
·Parameter: Typical Value
·Rated Voltage: 12 kV
·Highest System Voltage: 12 kV
·System Voltage: 11 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 25–31.5 kA (1 s)
·Dynamic Current : Up to 63–80 kA peak
·Insulation Type: Porcelain / Composite / Oil-filled
·Installation: Outdoor (pole or substation mounted)

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

Advantages
·Designed for harsh outdoor environments
·High insulation strength against lightning and pollution
·Reliable metering and protection performance
·Long service life (typically 25–30+ years)
·Suitable for pole-mounted and substation installations
·Multiple insulation options (porcelain or composite)
·Low maintenance requirement

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

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 scheme

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

A 12 kV Outdoor Current Transformer is a rugged and reliable instrument transformer used in 11 kV distribution systems, designed to withstand environmental stresses while providing accurate current measurement and dependable protection performance in outdoor power networks.