Section 4: Description And Operation - Eaton FP-25-LV-VSR Instruction Book

FP-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 arc boxes are required, because any arc formed
between opening contacts in a vacuum has no ionized 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" . A three-pole contactor has three
vacuum bottles. A metal bellows (like a small, circular accordion)
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.
Figure 4.1. V201 Non-Reversing Contactor.
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.
10 Instruction Book IB019008EN October 2016 www.eaton.com
Contact Force and Altitude
A vacuum contactor is affected by atmospheric pressure on the
bellows of the vacuum bottles. Up to an altitude of 3,300 ft (1005.8
m), the contactor is designed to tolerate normal variations in
barometric pressure. If the contactor is to be operated over 3,300 ft
(1005.8 m) 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 over-travel, or wear allowance. When the contactor
is fully closed, there is a gap underneath the lower bottle nut and
the pivot plate (see section 6.3.2 – Contact Wear Allowance). As
the contacts wear, this gap decreases. When any gap goes below
.020 in., the unit should be replaced. Use the fork-shaped over-travel
gauge (Part No.7874A59H01) supplied for this measurement.
WARNING
DO NOT RE-ADJUST THE BOTTLE NUTS TO RESET OVER-TRAVEL. ONCE
PLACED INTO SERVICE, OVER-TRAVEL 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 at their common point. Both coils
are encapsulated in one environment-immune coil shell, which
also contains a full-wave bridge rectifier. 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 primarily 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 200 kA available symmetrical fault
at 600 Vac.