36kV Current Transformer (Outdoor type)

36kV Current Transformer

36 kV Current Transformer (Outdoor Type) is a medium-voltage instrument transformer designed for 36 kV power systems, commonly used on 33 kV distribution and sub-transmission networks. It is installed in outdoor substations, switchyards, and pole-mounted or ground-mounted structures to convert high primary current into a standardized secondary current (typically 1 A or 5 A) for metering, protection, and control applications.

This type of CT is designed to withstand harsh environmental conditions such as rain, UV radiation, pollution, wind load, temperature variation, and lightning impulses, ensuring reliable operation in utility and industrial outdoor installations.

Main Functions
·Measures line current in outdoor 33 kV systems
·Supplies current signals to protection relays
·Supports revenue metering and energy monitoring
·Provides electrical isolation between HV and LV circuits
·Detects overloads, short circuits, and earth faults

Construction
A typical 36 kV outdoor current transformer consists of:
Primary Conductor
-Busbar or line conductor passes through the CT core
-Bar-type or wound-type primary depending on design
Magnetic Core
-High-permeability silicon steel or nanocrystalline core
-Ensures accurate measurement and low excitation current
Secondary Windings
-Metering core for revenue accuracy
-Protection core for fault detection
-Multiple cores possible in one unit
Insulation System
-Porcelain insulator (traditional design) or silicone rubber composite (modern design)
-Designed for high pollution and outdoor environments
Insulating Medium
-Oil-immersed or epoxy resin insulation depending on manufacturer design
Base Structure
-Galvanized steel mounting base for ground or pole installation
-Designed for mechanical stability and seismic withstand
Secondary Terminal Box
-Weatherproof enclosure for wiring connections
-Includes grounding and short-circuiting facilities

Typical Technical Specifications
·Rated Voltage: 36 kV
·Highest System Voltage: 40.5 kV
·System Voltage: 33 kV
·Frequency: 50/60 Hz
·Primary Current: 5–4000 A
·Secondary Current: 1 A or 5 A
·Accuracy Class: 0.2, 0.5, 1.0, 5P10, 5P20, PX
·Rated Burden: 5–30 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 (AIS / pole mounted / substation)

Working Principle
·The primary conductor carries system current through the CT core
·The current produces 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 secondary systems

Advantages
·Designed for harsh outdoor environments
·High insulation strength for 33 kV systems
·Reliable metering and protection accuracy
·Long service life (typically 25–30+ years)
·Suitable for substations and pole-mounted installations
·Available with porcelain or composite insulators
·Low maintenance requirement

Typical Applications
·33 kV distribution substations
·Utility sub-transmission networks
·Outdoor switchyards
·Industrial power distribution systems
·Renewable energy plants (solar and wind farms)
·Rural electrification projects
·Feeder protection systems

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 construction for outdoor operation
·High mechanical strength against wind and seismic loads
·Suitable for polluted and coastal environments
·Multiple secondary cores for metering and protection
·Available in porcelain or silicone rubber composite insulation
·Designed for long-term reliability and low maintenance

A 36 kV Outdoor Current Transformer is a robust and reliable instrument transformer widely used in 33 kV outdoor power systems, offering accurate current measurement, strong insulation performance, and dependable protection functionality under demanding environmental and electrical conditions.