Understanding Electrical Disconnectors: Types, Standards, and Applications Summary

1. Definition and Standards

An electrical disconnector (or isolator switch) is an electromechanical device with visible contacts used exclusively to isolate circuits by creating a clearly observable open gap, ensuring complete de-energization before maintenance.
They are off-load switches lacking arc-quenching mechanisms and must only be operated after upstream interruption by a breaker or load switch.
Internationally, disconnectors are standardized under IEC 62271-102, which sets requirements for AC disconnectors and earthing switches rated above 1 kV in indoor or outdoor installations.

2. Mechanical Configurations

Disconnectors are chosen based on substation layout and space:

• Centre-break: Two arms hinge at the center, opening in one location.

• Double-break: Provides two separations for enhanced dielectric performance.

• Pantograph: Folding-arm design for limited vertical clearance.

• Horizontal-break (knee): Hinged horizontally, ideal for bus-bar sections.

• Vertical-break: Contacts separate vertically, common on line sections.

• Coaxial: Compact, inline design with contacts on a single axis.

2.1 Switch-Disconnectors

A switch-disconnector merges visible isolation with limited load-making/breaking capability, enabling safe operation under nominal currents but still requiring upstream arc interruption.

2.2 Integrated Disconnecting Circuit Breakers

Some modern breakers integrate disconnectors within the same housing (“disconnecting circuit breakers”), reducing separate components but necessitating mandatory earthing switches due to non-visible gaps.

3. Operation and Safety Features

Disconnectors can be manual (via geared handwheels or detachable handles) or motor-operated (remote control).
Key safety provisions include:

• Visible Contacts: Clear indication of open/closed state.

• Lockout-Tagout (LOTO): Padlockable handles or trapped-key interlocks prevent inadvertent closing.

• Earthing Blades: Optional ground blades to safely discharge isolated sections.
  Typical operation sequence: open upstream breaker, release interlocks, operate disconnector, engage earthing, then apply padlock.

4. Maintenance Intervals

Open-air disconnectors generally require preventive maintenance every 5 years (or 2 years in heavily polluted environments), whereas modern circuit breakers can extend maintenance cycles to 15 years.

5. Applications

1. High-Voltage Substations: Isolate transformers, breakers, and lines for safe service.

2. Industrial Power Distribution: De-energize motors and switchgear during repairs.

3. Renewable Energy Installations: Safely isolate inverters and turbine transformers for maintenance.

4. Emergency Isolation: Rapid manual shutdown in fault or hazard conditions.

6. Selection Considerations

When specifying a disconnector, evaluate:

• Rated Voltage (Ue): Match to system voltage (e.g., 11 kV, 33 kV, 132 kV).

• Rated Current (Ie): Ensure nominal current-carrying capacity aligns with load.

• Pole Configuration: Single-pole for DC systems; three-pole for three-phase AC.

• Environmental Conditions: Pollution degree and altitude affect required clearances.

• Mounting Style: Outdoor substation versus indoor switchgear enclosure.

• Interlocks & Earthing Requirements: Ensure compliance with LOTO and grounding sequences.