4.2
Bolted Pressure Isolation Switch
4.2.1 A fixed mounted, gang-operated isolation switch shall be provided with each controller to
isolate the medium voltage compartment from the power source.
4.2.2 The switch shall be directly driven by an externally operable handle mounted on the right
hand flange of the cubicle. The handle shall provide positive indication of the position of the
switch.
4.2.3 The switch mechanism shall be designed such that in the closed position it provides the
equivalent of a bolted pressure joint at both ends of the movable blades, rather than relying on
spring pressure.
4.2.4 The line side of the switch shall be bus connected to the main horizontal power bus or to
the incoming terminals of the controller. The load side of the switch shall be bus connected to
the main controller power fuses.
4.2.5 The switch blades shall automatically ground the line side of the power fuses when the
switch is opened. This allows any stored energy in the controller load circuit to be discharged by
closing the contactor using test power.
4.2.6 It shall be possible to visually confirm that the switch blades are open and grounded by
viewing the blades through the viewing window with the medium voltage door closed. Also, there
shall be a mechanical operated flag (visible through the window in the medium voltage door)
displaying the switch in the “OPEN” position with the door closed.
4.2.7 A shutter mechanism shall automatically isolate the medium voltage compartment from all
live parts when the switch is opened.
4.2.8 The external operating handle for the isolation switch shall be designed to accept up to
three external padlocks in the OFF position.
4.2.9 The switch shall be capable of interrupting the no-load current of the largest control power
transformer which can be connected to it. The interrupting capability of the switch shall be a
minimum of 0.4 amperes at 110% of rated line voltage.
4.2.10 The switch shall be rated as follows:
720 amperes @ 5.0kV
4.2.11 The mechanical life of the switch and its operating mechanism shall be 10,000 operations
minimum.
4.2.12 All switch current-carrying parts shall be silver plated. An optional tin-over-silver plated
switch shall be available for use in paper mill applications.
4.3
Vacuum Contactor
4.3.1 The Toshiba CV-6KAU vacuum contactor shall be used in these controllers.
4.3.2 The contactor shall be bolted into the medium voltage compartment. It shall be arranged
such that the power connections are front-accessible so it can be unbolted and removed if
necessary for maintenance.
