Ch 3 Equipment Description
A. G
enerAl
The Power/Vac
®
Electrical Ground and Test
Device uses sealed vacuum ground switches
to make or break contact between the primary
stud and the equipment ground. Primary
connections to the associated metal-clad
switchgear are made by horizontal bars
and disconnect fingers, electrically and
mechanically connected to the vacuum
interrupters. Molded interrupter supports,
one per phase on a three phase ground and
test device, provide mountings for the primary
bars, interrupters, current transfer fingers,
and heat dissipation fins (where used). The
operating mechanism provides vertical motion
at each phase location in order to move the
lower contact of the vacuum interrupters from
an open position to a spring loaded closed
position and then back to the open position on
command.
The ML-17 mechanism is of the stored energy
type and uses a gear motor to charge a closing
spring. During a closing operation, the energy
stored in the closing spring is used to close the
vacuum interrupter contacts, compress the
wipe springs which load the contacts, charge
the opening springs, and overcome bearing
and other friction forces. The energy then
stored in the wipe springs and opening springs
will open the contacts during an opening
operation.
Closing and opening operations are controlled
electrically by a remote control cable attached
to the front of the ground and test device. For
maintenance and checkout, the closing spring
may be manually charged, and a method for
slow-closing the ground switch is available.
B. Ml-17H G
enerAl
d
eScrIptIon
(63
k
A o
nly
)
The ML-17H mechanism is a very high energy
unit used in 63kA applications. It has much
stiffer wipe springs to achieve the required
high closing and latching forces. It also has
a double close spring to overcome the forces
of the opening and wipe springs. Special
runbacks and primary fingers are incorporated
to withstand higher peak currents. The use of
#271 Loctite
®
and jam nuts on many bolts and
hardware make a more durable mechanism.
Also, note that wipe and gap measurements
are different for ML-17H ground and test
devices than for standard ML-17 ground and
test devices. Refer to
for wipe and gap parameters.
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6
Equipment Description
Power/Vac® Electrical Ground and Test Devices
Equipped with ML-17 Mechansim
01.4IB.50100
