In
electrical engineering
Electrical engineering is an engineering discipline concerned with the study, design, and application of equipment, devices, and systems that use electricity, electronics, and electromagnetism. It emerged as an identifiable occupation in the l ...
, a disconnector, disconnect switch or isolator switch is a type of
switching device with visible
contacts, used to ensure that an electrical circuit is completely de-energized for service or maintenance. They are often found in
electrical distribution and industrial applications, where machinery must have its source of driving power removed for adjustment or repair. Disconnectors can be operated manually or by a motor, and may be paired with an earthing switch to ground the portion that has been isolated from the system for ensuring the safety of equipment and the personnel working on it.
High-voltage disconnectors are used in
electrical substations to allow isolation of apparatus such as
circuit breakers,
transformers, and transmission lines, for maintenance. The disconnector is usually not intended for normal control of the circuit, but only for safety isolation. Unlike
load switches and
circuit breakers, disconnectors lack a mechanism for
suppression of
electric arc
An electric arc (or arc discharge) is an electrical breakdown of a gas that produces a prolonged electrical discharge. The electric current, current through a normally Electrical conductance, nonconductive medium such as air produces a plasma ( ...
s which occur when conductors carrying high currents are mechanically interrupted. Thus, they are off-load devices, with very low
breaking capacity, intended to be opened only after the current has been interrupted by some other control device. Safety regulations of the utility must prevent any attempt to open the disconnector while it supplies a circuit. Standards in some countries for safety may require either local motor isolators or lockable handles (which can be
padlock
Padlocks are portable Lock (security device), locks with a shackle that may be passed through an opening (such as a chain, chain link, or hasp staple) to prevent wikt:use, use, theft, vandalism or harm.
Naming and etymology
The term '':wikt: ...
ed).
IEC standard 62271-102 defines the functionality and features of a disconnector.
Disconnectors have provisions for a
lockout-tagout so that inadvertent operation is not possible. In high-voltage or complex systems, these locks may be part of a
trapped-key interlock system to ensure proper sequence of operation. In some designs, the disconnector has the additional ability to
earth
Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...
the isolated circuit thereby providing additional safety. Such an arrangement would apply to circuits that inter-connect power distribution systems where both ends of the circuit need to be isolated.
Types of disconnectors
Pantograph disconnectors for 220kV. Yellow painting allows recognition of their state
Disconnectors can be classified into various types based upon their constructional features and mounting arrangement. The major types of disconnectors are:
* Centre-break disconnectors
* Double-break disconnectors
* Pantograph disconnectors
* Horizontal break knee disconnectors
* Vertical break disconnectors
* Coaxial disconnectors
These are selected based upon the sub-station layout, clearances available and space constraints.
Switch disconnector
A switch disconnector combines the properties of a disconnector and a load switch, so it provides the safety isolation function while being able to make and break nominal currents.
Integrated disconnecting switch
In a
disconnecting circuit breaker the disconnectors are integrated in the breaking chamber, which eliminates the need for separate disconnectors. The intention of this combined device is to decrease maintenance and increase
availability and
reliability. The usage of this device instead of a disconnector is limited due to the fact that the open gap is not clearly visible and many doubts in term of safety arise during maintenance activities. Where it is adopted the earthing switch must be used and the performance must be increased by the typical value.
The open-air disconnecting switches typically need maintenance every five years (every two years under very polluted conditions), while circuit breakers have maintenance intervals of 15 years.
See also
*
Circuit breaker
*
Kill switch
*
True DC
References
*
External links
{{commonscat, Disconnecting switch
115 kV disconnector opened "hot" (video)
Electric power systems components
Safety switches