3
Instructional Leaflet
IB48041
Effective December 2009
Instructions for AMPGARD 400A
medium voltage starter
eaton corporatIon
www.eaton.com
Description
Controller
The AMPGARD 400A, 7.2 kV controller consists of a non-loadbreak
isolation switch, medium voltage current-limiting fuses, one or
more Type SL vacuum-break contactors, a set of current transform-
ers, plus control and protection devices. The isolating switch has a
limited make and break rating, suitable only for closing and opening
limited transformer magnetizing currents. The controller is designed
to start, stop, and protect a three-phase medium voltage motor
within the ratings shown in
Table 1
. The controller may also be used
to switch transformer windings or capacitor loads as shown. For
applications other than those indicated, consult the factory. Each
AMPGARD controller occupies all or a portion of a steel structure
that may also enclose a horizontal bus system to distribute power to
two or more sections and a vertical bus system to connect individual
starters to the horizontal bus. The controllers are configured for full-
voltage or reduced-voltage starting, reversing or non-reversing, in
single-speed or two-speed applications.
Starters are available with bolt-in or clip-in main fuses. Contactors
may have bolted connections or stab-in connections to the
starter cell.
The flow of current through a starter with bolted fuses and a
stab-in contactor can be described as follows: The line finger
assembly mounted at the back of the enclosure serves to connect
the isolation switch moving stabs to the controller line terminals
when the switch is closed. Power flows from the switch moving
stabs through a flexible shunt to the upper fuse mountings. The
fuses are connected to the lower fuse mountings that contain the
line-side stab connections to the line finger assemblies for the main
contactor. With the main contactor energized, power flows through
the contactor’s vacuum interrupters to the contactor load fingers,
which are engaged on to the contactor load-side stabs. Medium
voltage cables connect the load-side stabs to the motor load
connections. The contactor is held in place by a set of rails
mounted in the lower part of the cell. Current transformers are
typically mounted immediately behind the main contactor, under the
load-side stabs. The motor load connections are mounted to the left
of the main fuses in the rear of the compartment, facing forward.
Figure 2. Medium Voltage Compartment
Low voltage components
The low voltage components consisting of a protective relay,
interposing relay, test power circuit, terminal blocks, and optional
equipment are mounted in the low voltage control compartment
located on the front of the controller medium voltage door. The low
voltage compartment is fabricated from steel sheets to provide iso-
lation from the medium voltage components mounted behind the
low voltage compartment. A window is provided in the low voltage
compartment to allow the user to view the position of the isolation
switch before entering the medium voltage compartment. See the
“Isolation Switch” section for further details.
Figure 3. Low Voltage Compartment
Isolation switch
The controller isolation switch is a non-loadbreak device.
Mechanical and electrical interlocks are provided to ensure that
the main contactor is de-energized before the switch can be
operated. In the open position, the switch isolates medium voltage
from the main controller compartment, allowing access to the
controller for inspection and maintenance. For standard applications,
the isolation switch includes ground fingers that ground the line side
of the power fuses when the switch is in the open position. The
isolation switch has a mechanical endurance rating of 10,000
operations. Isolation switches in starters with double-barrel fuses
are supplied with additional phase barriers that must be installed to
maintain the proper dielectric rating of the starter.
Danger
ampgarD controllers are sometimes energizeD by a back-feD
conDition that allows the meDium voltage compartment to be
energizeD with the isolation switch in the open position. stuDy
the plant single line Diagrams to make certain that no back-
feeD situation exists before entering the meDium voltage
compartment.
All power sources must be isolated and locked out before
servicing the equipment.
For applications where the controller is back fed, the grounding
fingers should be removed from the isolation switch.
The switch consists of a fixed rear portion and a removable front
portion. Refer to
Figures 5
and
6
. The fixed portion includes the
controller line fingers and a moveable shutter that isolates the line
fingers when the switch is in the open position. The removable
portion is operated by a handle mechanism that extends through the
controller medium voltage door. With the handle in the up position,
the switch is closed and medium voltage is available for connection
to the controller load. With the handle in the down position, the
switch is open and medium voltage is isolated from the controller
and the controller load.
An isolation switch viewing window is provided in the upper rear
corner of the low voltage control compartment. After opening the
isolation switch and before opening the medium voltage door, the
switch should be visually examined through the viewing window to
verify that it is in the open position. Three green and white “barber
poles” will be visible when the switch is in the open position and
the shutter assembly is in the isolating position. See
Figure 4
for
location of barber poles. The use of a flashlight will help in verifying
the position of the barber poles.
Isolation Switch
Position View
Window
