Isolators
An isolator (or disconnector) is a mechanical switch used in power systems to physically
separate a portion of the circuit for maintenance or inspection.
Key points:
o Operated only when the line is already de-energized (no load current).
o Provides visible isolation for safety.
o Usually installed on both sides of a circuit breaker.
2. Types Based on Contact Movement
A. Vertical Break Isolator
Working principle:
The moving contact moves in a vertical plane (up or down) to open or close.
One end is fixed, while the other end pivots upward or downward.
Construction & Operation:
Often mounted on insulators in a vertical stack.
When opened, the blade lifts away vertically from the fixed contact.
Motion is usually driven by a rotating insulator or link mechanism.
Applications:
Suitable for busbar and line isolation in substations with less space in horizontal
direction but enough height clearance.
Common in outdoor switchyards (66 kV to 400 kV).
Advantages:
Clear visual gap is seen from a distance.
Less susceptible to dust accumulation on contacts.
B. Horizontal Break Isolator
Working principle:
The moving arm/blade rotates or slides in a horizontal plane to open/close.
Usually double-arm or single-arm configuration.
Construction & Operation:
Two vertical insulators — one fixed, one rotating.
The moving contact rotates horizontally away from the fixed contact.
Needs more horizontal clearance in the switchyard.
Applications:
Used where height is limited but space is available on the ground.
Common in lower-voltage outdoor substations and also in indoor GIS bays.
Advantages:
Simpler mechanical design.
Suitable for bus section and transfer bus isolations.
C. Pantograph Type Isolator
Working principle:
Uses a pantograph mechanism (like a train’s overhead collector) to move the contact
vertically upward to engage a fixed overhead contact.
Operates in a combination of vertical and horizontal motion via linkages.
Construction & Operation:
Fixed contact is mounted above.
Moving arm (with linkages) moves up like a folding scissor to connect or disconnect.
Often motor-operated for high voltages (220 kV–765 kV).
Applications:
Used in extra high voltage (EHV) substations where space is constrained.
Allows connection to busbars at different heights without much horizontal clearance.
Advantages:
Compact footprint.
Can connect to higher bus without needing tall insulators.
Smooth operation with less phase-to-phase clearance requirement.
3. Comparison Table
Feature Vertical Break Horizontal Break Pantograph Type
Motion direction Up/down (vertical) Sideways (horizontal) Vertical with linkage action
Space More height, less Very compact in width &
More width, less height
requirement width height
Voltage range 66 kV–400 kV 11 kV–220 kV 220 kV–765 kV
Clear but more mechanical
Visual isolation Very clear Clear
parts
Outdoor/Indoor bus EHV substations, compact
Common use Outdoor switchyards
isolator yards
