1. Product Overview
The KYN28-12 Metal-Clad Withdrawable Switchgear is a state-of-the-art, air-insulated, metal-clad, withdrawable AC medium voltage switchgear designed and manufactured in accordance with IEC 62271-200 (AC metal-enclosed switchgear and controlgear for rated voltages above 1 kV and up to and including 52 kV). Its primary application is for the distribution, protection, and control of electrical power in three-phase, 50/60Hz networks with a rated voltage of 12kV (and up to 15kV for certain configurations). The defining feature of its “metal-clad” (IEC 62271-200 classification) and “withdrawable” design is the compartmentalization of major functional units (circuit breaker, busbars, cable terminations) within grounded metal enclosures, and the ability to safely isolate and physically withdraw the circuit breaker assembly for inspection, maintenance, or replacement while the busbars remain energized.
2. Main Configurations
The switchgear is strictly compartmentalized into distinct, segregated sections as per IEC 62271-200 requirements for metal-clad design:
Circuit Breaker (CB) Compartment: Houses the vacuum circuit breaker (VCB) mounted on a robust withdrawable chassis (truck). The chassis incorporates rack-in/rack-out mechanisms, position indicators (Connected, Test, Disconnected/Withdrawn), and automatic shutters. Primary contacts are typically finger cluster type.
Main Busbar Compartment: Contains the main three-phase horizontal or vertical busbars, usually made of copper with tin-plating, sized for the rated current (e.g., 1250A, 1600A, 2000A, 2500A, 3150A). This compartment is fully segregated from others.
Cable Termination (Outgoing Feeder) Compartment: Located at the rear or bottom, this compartment houses cable entry points, cable terminations (lugs, separable insulated connectors), earthing switches, and often voltage transformers (VTs) and current transformers (CTs) for metering/protection. It includes provisions for surge arresters.
Low Voltage (LV) Compartment / Relay & Control Compartment: A dedicated, easily accessible compartment housing the protective relays, metering devices, control wiring terminals, indication lamps, control switches, local/remote selector, and auxiliary power supplies. This compartment is isolated from the high-voltage sections.
Mechanical Interlocks & Operating Mechanisms: Integrated system ensuring safe operation sequences, including CB operating mechanism (spring-charged motor or manual), earthing switch operating mechanism, and the withdrawable chassis drive mechanism.
3. Main Functions
The KYN28-12 Metal-Clad Withdrawable Switchgear performs critical roles in the electrical distribution system:
Circuit Protection: The Vacuum Circuit Breaker (VCB) automatically interrupts overload currents and short-circuit currents under fault conditions to protect downstream equipment and ensure system stability.
Load Switching: Provides safe and reliable making, carrying, and breaking of normal load currents under service conditions (IEC 62271-100).
Isolation: Provides safe, visible isolation points via the disconnect position of the withdrawable breaker and the operation of earthing switches (maintenance earths). The automatic shutters provide physical isolation when the breaker is withdrawn.
Earthing (Grounding): Incorporated earthing switches allow for the safe grounding of outgoing cables or busbar sections for maintenance purposes, ensuring personnel safety (IEC 62271-102).
Measurement & Metering: Accommodates Current Transformers (CTs) and Voltage Transformers (VTs) to provide scaled-down signals for energy metering, power quality monitoring, and input to protection relays.
Control & Automation: The LV compartment facilitates local manual control and provides interfaces for remote control (SCADA/DCS) and integration with protection relays (overcurrent, earth fault, etc.) for automated system protection and operation.
4. Key Features
The KYN28-12 Metal-Clad Withdrawable Switchgear is characterized by several critical features ensuring safety, reliability, and ease of use:
Metal-Clad Construction (IEC 62271-200): Ensures strict internal arc classification (IAC AFLR – Internal Arc Classified, Arc Fault tested, Limited Risk) through robust, grounded steel enclosures, pressure relief channels (arc vents) on the top/rear, and segregation of compartments preventing fault propagation.
Withdrawable Design: Allows the Vacuum Circuit Breaker on its truck to be safely moved between Service/Connected, Test, and Disconnected/Withdrawn positions without exposure to live parts, enabling efficient maintenance and minimizing downtime.
Vacuum Interruption Technology: Utilizes vacuum interrupters within the VCB, offering high dielectric strength, minimal maintenance, long electrical life, and environmentally friendly operation (no SF6 gas).
“Five Preventations” Mechanical Interlocking: A comprehensive mechanical interlock system prevents hazardous operations, specifically:
Prevents CB closing on earth faults.
Prevents CB closing while racking.
Prevents racking while CB is closed.
Prevents access to live compartments.
Prevents earthing switch operation on live circuits.
High Performance & Reliability: Rated for high short-circuit breaking currents (typically 25kA, 31.5kA, 40kA) and short-time withstand currents (typically 3s or 4s), with excellent dielectric strength exceeding IEC requirements. Vacuum interrupters offer high electrical endurance.
Enhanced Safety: Features include automatic shutters covering primary contacts upon breaker withdrawal, IP4X degree of protection for the enclosure (IP2X for internal partitions as per IEC 62271-200), pressure relief devices, and mandatory earthing of the withdrawable chassis before withdrawal.
Modular & Flexible Design: Facilitates easy extension, retrofitting, and adaptation to various substation layouts. Standardized modules simplify installation and spare parts management.
Low Maintenance: Vacuum technology significantly reduces maintenance requirements compared to older technologies (e.g., oil, SF6 – though SF6 is used in some ring main units, not typically in the main VCB of KYN28). Robust mechanical design ensures longevity.
Flame-Retardant Components: Use of flame-retardant epoxy resin for insulation (CTs, VTs, bushings, supports) enhances fire safety.
