Description
24/293 Revision 11 • INSTALLATION AND OPERATING INSTRUCTIONS • NXPLUS C • 802-9081.9
9 Components
9.1 Circuit-breaker
Design The Siemens vacuum circuit-breaker (VCB) 3AH55/3AH25 is a three-pole indoor circuit-breaker
for rated voltages from 7.2 kV to 24 kV.
The circuit-breaker consists of the following components:
• Operating mechanism with stored-energy spring mechanism and control elements
• Three circuit-breaker poles with vacuum interrupters
• Partition plate
• Operating rods for contact operation, mounted in the vessel front (partition plate) in a
movable way and without seals by means of welded-in metal bellows.
The operating mechanism accommodates all electrical and mechanical components required
for closing and opening the circuit-breaker. The removable cover of the operating mechanism
contains the openings for the control elements and indicators.
The circuit-breaker is closed by pressing the ON pushbutton. After closing, the motor
recharges the closing spring. If the motor supply voltage fails, the closing spring can be
charged manually.
Vacuum interrupters The vacuum interrupter is fixed at the interrupter support. The fixed contact is directly
connected to the housing. The moving contact is firmly connected to the connection bolt and
is centrally aligned in the guide. A metal bellows forms the vacuum-tight connection to the
interrupter housing.
Fig. 22: Vacuum interrupter
Equipment The basic version of the circuit-breaker is equipped as follows:
• Electrical operating mechanism (charging motor) with mechanical and electrical anti-
pumping device (-M1)
• Closing solenoid (-Y9)
• Shunt release (-Y1)
• Low-voltage plug connector with 10-pole wiring (-Q0)
• Auxiliary switch 4NO + 4NC or 3NO + 4NC freely available (-S1)
• Position switch for "closing spring charged" indication (-S41, -S42)
• Circuit-breaker tripping signal, cutout switches (-S6, -S7)
• Operations counter
• Feeder locking device
Option • Extended auxiliary switch with 10NO + 6NC or 9NO + 6NC freely available (-S1)
• Shunt release (-Y2)
• Undervoltage release (-Y7)
• C.t.-operated release (-Y4)
• Low-energy c.t.-operated release (-Y6)
• Interlocking of feeder locking device against three-position disconnector
- Circuit-breaker only lockable in earthed position
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