 | Switchgear - Basic Vocational Knowledge |
 |  | 2. Important components of switches |
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2.3. Switch mechanisms
They change the switching position of switches (CLOSED-OPEN). For this purpose a force is required. In accordance with the type of force generation the mechanisms are classified in:
- manually-operated mechanisms
- solenoid-operated mechanism
- motor-operated mechanism, and
- pneumatic-operated mechanism.
Manually-operated mechanism
Actuation elements are knob, pushbutton or lever. Rated currents up to approximately 100 A can be switched by means of these mechanisms. The manually-operated mechanism is the cheapest mechanism. Examples for these mechanisms are installation switches, gang switches, pushbutton switches.
Solenoid-operated mechanism
By switching on a control current an electromagnet is excited. The armature of a magnet actuates the contact members. Examples for solenoid-operated mechanisms are contactors, relays, installation remote switches.
Motor-operated mechanism
The motor either drives the interrupter shaft via a gear or the motor acts on a spring energy store. As far as the motor-operated mechanism with spring energy store is concerned, simultaneously with the closing operation a disconnection spring is tensioned and latched. When the spring is unlatched, it opens the contact members independently of the motor.
Pneumatic-operated mechanism
By means of 15 to 20 MPa compressed air the contact members are actuated via pressure piston and linkage mechanism.
This type of mechanism is mostly used for high-voltage circuit breakers.
Survey 3 Summary of the most common switch mechanisms
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S Mechanisms |
Examples of application |
Functional principle |
Advantages and disadvantages |
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Manually-operated mechanism Pushbutton and lever-operated mechanism Stirrup-operated mechanism |
Low-voltage circuit breaker Load-break switch Isolating switch Earthing switch Power circuit breaker up to 30 kV |
 The actuation element is attached directly to the interruptor shaft. The switch linkage transmits the switching force from the front side of the cell to the switch fastened on the rear. |
Favourable as to costs, no high switching frequency. At rated currents above 100 A escessive switching forces required |
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Manually operated mechanism by means of a twist knob |
Multisection cam-operated switch |
 The switch lever is arranged directly on the camshaft |
Simple design, un-objectionable switching of high currents at a speed almost independent of the operator |
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Snap-action connection (toggle latching mechanism) |
El circuit breaker |
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Unobjectionable switching of high currents at a speed independent of the operator |
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Solenoid-opera ted mechanism |
Contactors r Relays |
 1 excitation coil, 2 spacing between armature and magnet 3 lifting limits, 4 return spring. 5 armature, 6 magnet |
Relatively high power consumption by the switching magnet. A high making current can load the network., |
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Motor-operated mechanism |
El circuit breakers SCI circuit breakers |
The interruptor shaft is driven directly by a motor via a worm gearing and an excentric. When an energy store is used, the motor tensions the closing spring. By unlatching this spring the switch is closed and the opening spring is pretensioned. During the opening sequence the closing spring is preten-sioned. |
Compared with the solenoid-opera ted mechanism, the motor-operated mechanism is more economical for high rated currents |
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Pneumatic-operated mechanism and D3AF |
Isolating switches Circuit breakers of types DCI |
 1 spring, 2 piston, 3 compressed-air, 4 interruptor shaft |
Remote control possible. Simpler design compared with electric-operated mechanisms. Higher switching speed and smoother switching |
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