12/24kV Dual-Voltage Platform with 1250A High-Current Option
The switch covers two standard medium-voltage tiers: 12kV for urban and industrial distribution, and 24kV for higher-voltage distribution feeders and rural networks. Within each voltage tier, rated current options of 400A, 630A and 1250A allow the same frame and mounting pattern to serve secondary substation transformers, high-current busbar sections and capacitor-bank feeders. The 1250A version uses reinforced blade-type contacts and wider pole spacing to handle continuous currents up to 1250A without excessive temperature rise, making it suitable for large transformer feeders or main incomer switches in compact substations.
Puffer-Type Dual Arc-Extinguishing System
The arc-extinguishing system uses a puffer principle with two sequential air blasts. As the moving contact withdraws, a piston compresses air in the extinction chamber. A current-independent blast starts automatically at the correct point in the opening stroke, cooling and stretching the arc column. When the arc intensifies, a current-dependent gas blast is generated as the hot arc erodes the arcing nozzle walls. The combined action interrupts load currents up to 1250A, capacitive currents up to 150A at 12kV, and earth-fault currents up to 150A at 12kV. Because the system uses ambient air rather than sealed vacuum or SF6, the arc chutes and nozzles are field-replaceable after long service periods.
Modular Configuration and Optional Functions
The basic unit consists of a frame, insulators and current-carrying parts. Factory-fitted or field-installed modules expand the function without changing the mounting footprint. Fuse bases mount current-limiting fuses above the switch body for transformer protection; a mechanical fuse tripping link drives all three phases open when any fuse blows. An earthing switch closes a grounded blade on the load side after the main contacts open. Auxiliary switches, shunt trip devices and motor operators bolt onto the standard mechanism housing. Mechanical door interlocks and key interlocks prevent access to live compartments or unsafe operating sequences. This modularity lets switchgear builders stock one frame and configure variants to order.
Dual Operating Mechanism Types
Type K is a snap-action mechanism that releases stored energy instantaneously for rapid contact separation. It is used where fast opening is required for motor switching or capacitor-bank control. Type A is a stored spring-energy mechanism that charges a spring through the manual handle or motor drive, then releases it to drive the contact system. Type A provides a consistent operating force regardless of operator strength, with a closing torque of 115–120Nm and an opening torque of only 3Nm. Both mechanisms rotate the operating shaft through 130 degrees and achieve an opening time of 40–60ms. Motor operators for AC/DC 110V or 220V mount directly on either mechanism type without panel modifications.
Extended Switching Capabilities Beyond Active Load
In addition to standard active load breaking at full rated current, the switch is tested for capacitive current switching (150A at 12kV, 80A at 24kV), inductive load switching at low power factor (16A at cosφ=0.15), and earth-fault interruption (150A at 12kV, 75A at 24kV). These ratings allow the switch to control capacitor banks, unloaded cables and small motors without requiring separate dedicated contactors or circuit breakers. The capacitive earth-fault breaking ratings (90A at 12kV, 31.5A at 24kV) cover resonant-grounded network conditions where earth-fault currents have a significant capacitive component.
Application Scope
This load switch is intended for indoor metal-enclosed switchgear, pad-mounted transformers, ring main units, cable distribution boxes and compact substations. The 12kV version serves urban distribution networks, industrial plants and commercial building substations. The 24kV version extends coverage to higher-voltage rural distribution and utility secondary substations. The 1250A rating suits main incoming feeders and large transformer protection, while the 400A and 630A fuse-combination versions protect distribution transformers up to about 12.5MVA at 12kV and 10MVA at 24kV depending on fuse selection.
