13
Instruction Book IB019009EN November 2017 www.eaton.com
AK-2-25, AK-2A-25, & AK-3A-25 LV-VSR
Breaker-To-Motor Starter Conversion
SECTION 4: DESCRIPTION AND OPERATION
Vacuum Contactor
Class V201 NEMA vacuum contactors are designed for the control
of inductive or non-inductive loads at voltages between 200 and 600
Vac. The vacuum contactor in the LV-VSR is protected against short-
circuits above its capability by current limiting fuses.
General
The V201 contactor has its main contacts sealed inside ceramic
tubes from which all air has been evacuated, i.e., the contacts
are in vacuum. No arcboxes are required, because any arc formed
between opening contacts in a vacuum has no oinized air to sustain
it. The arc simply stops when the current goes through zero as it
alternates at line frequency. The arc usually does not survive beyond
the first half cycle after the contacts begin to separate. The ceramic
tube with the moving and stationary contacts enclosed is called a
vacuum interrupter or a bottle, and there is no such bottle for each
pole of the contactor. A three-pole contactor has three vacuum
bottles. A metal bellows (like a small, circular accordian) allows
the moving contact to be closed and pulled open from the outside
without letting air into the vacuum chamber of the bottle. Both the
bellows and the metal-to-ceramic seals of modern bottles have been
improved to the point that loss of vacuum is no longer cause for
undue concern.
The moving contacts are driven by a molded plastic crossbar
supported by two pre-lubricated ball bearings that are clamped in
alignment for long life and free motion.
The contacts in an unmounted bottle (vacuum interrupter) are
normally-closed, because the outside air pressure pushes against
the flexible bellows. For contactor duty, the contacts must be
“normally-open” when the operating magnet is not energized.
Therefore, the contacts of the vacuum bottles must be held apart
mechanically against the air pressure when used in a contactor. In
the contactor, all of the bottles are held open by a single kickout
spring in the rear of the contactor. The kickout spring pulls against
the moving armature and crossbar and thereby forces the bottles
into the open position. In the open position, the crossbar is pulling
the moving contacts to hold them open.
Contact Force and Altitude
A vacuum contactor is affected by atmospheric pressure on the
bellows of the vacuum bottles. Up to an altitude of 3300 feet, the
contactor is designed to tolerate normal variations in barometric
pressure. If the contactor is to be operated over 3300 feet above
sea level, consult the factory.
Contact Wear Allowance
Contact material vaporizes from the contact faces during every
interruption and condenses inside the bottle. This is normal, and is
provided for by overtravel, or wear allowance. When the contactor is
fully closed, there is a gap underneath the lower bottle nut and the
pivot plate. See Figure 6.1. As the contacts wear, this gap decreases.
When any gap goes below .020 in., the unit should be replaced.
Use the .020 in. thick fork-shaped overtravel gauge supplied for this
measurement, Part No. 7874A59H01
WARNING
DO NOT RE-ADJUST THE BOTTLE NUTS TO RESET OVERTRAVEL AS THE
BOTTLES WEAR. ONCE PLACED INTO SERVICE, OVERTRAVEL SHOULD BE
CHECKED BUT NOT ADJUSTED. A STAR-WHEEL LOCK IS INCLUDED FOR
LOCKING THE BOTTLE NUTS OF EACH BOTTLE TO PREVENT TAMPERING.
Coil
The operating coil has a “figure-eight” shape and is really two
coils in series, with a connection to their common point. Both coils
are encapsulated in one environment-immune coil shell, which
also contains a full-wave bridge. When ac is connected directly
to terminals A and B on the coil shell, the magnet excitation is
unfiltered dc. The magnet will not chatter as ac magnets sometimes
do, but at less than rated voltage it may hum slightly. A normally-
closed Type L63 auxiliary contact, set to open slightly before the
armature fully closes, is connected to terminals C and D on the coil
shell. When adjusted correctly, this contact allows a relatively high
current through the pickup winding, and as the contactor closes,
the contact inserts the holding winding, which reduces the coil
current to a low value sufficient to hold the magnet closed without
overheating. No external resistors are required.
Overload Relay
The Overload Relay provides longtime overload protection and
single phase protection. The solid-state Overload Relay provides
high accuracy and enhanced protection through the use of micro-
electronic packaging technology. The Overload Relay comes standard
with trip class 10, 15, and 20 trip characteristics.
Current-Limiting Fuses
The current limiting fuses, class J AJT600EIB are primary used to
provide short-circuit protection to the vacuum contactor. During
High-Power testing the V201 vacuum contactor was confirmed to
properly coordinate with Ferraz Shawmut type class J AJT600EIB
current limiting fuses. The contactor successfully withstood the let-
though energy of each fuse for a 200kA available symmetrical fault
at 600Vac.
4.1 ELECTRICAL CONTROL
Specific wiring schematics and diagrams are included with each
LV-VSR. (Typical Schematic Shown in Figure 4.1.)
There may be different control voltages or more than one tripping
element, but the principle mode of operation is as follows:
If control power is present, and the LV-VSR is in either the ‘Test’ or
‘Connect’ position, then the LV-VSR may be closed.
The LV-VSR may be closed by making the control switch close (CS/C)
contact. the LV-VSR may be opened any time by making the control
switch (CS/T) contacts.
Note the position switch (PS1/DT) contact in the closing circuit. This
contact remains open while the LV-VSR is being levered between
the ‘Test’ and ‘Connect’ positions. Consequently, it prevents the
LV-VSR from closing automatically, even though the control close
contact may have been made while the LV-VSR is levered to the
‘Connect’ position. PS1 is open also while the interlock tab is
manually pressed or the cell door is open.
When the CS/C contact is made, the MR1 closes the LV-VSR. If the
CS/C contact is maintained after the LV-VSR closes, and a trip signal
is sent, the T-relay contact will close and pick up the Y-relay. The Y/a
contact will seal in the Y-relay until the CS/C contact is released.
Even though the LV-VSR would open, it could not be reclosed before
CS/C was released and remade and no trip signal was present. This
is the anti-pump function.
The LV-VSR will also open if there was a overload condition that the
OL relay sensed. The LV-VSR will not close until the OL relay is reset
after an overload condition.
The LV-VSR will also open if a fuse blows or opens. The LV-VSR will
not close until the blown or open fuses are replaced.
Trip Free Operation
The LV-VSR is in a “trip-free” condition if the unit is in between the
‘Test’ and ‘Connect’ position. Also, if the local open push button is
depressed and maintained, the LV-VSR is in a “trip-free” condition.
4.2 BUSHING & DISCONNECTING CONTACT ASSEMBLIES
The line and load bushing assemblies, which are the primary
circuit terminals of the LV-VSR, consist of six tin plated conductors.
Multiple finger type primary disconnecting contacts at the ends of
the conductors provide means for connecting and disconnecting the
LV-VSR to the bus terminals in the switchgear compartment.
