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5-3.3 UNDERVOLTAGE TRIP DEVICE
The undervoltage trip device for all circuit breakers is an
electromechanical device that operates to open the
breaker at 35% or less of the voltage rating of the trip
coil. The device does not open the breaker at values
above 70% of the voltage rating of its trip coil. It may
operate, however, to open the breaker when the voltage
across the trip coil is greater than 35%, but less than
70% of the voltage rating of its trip coil. The breaker can
be closed as long as the voltage to the trip coil is main-
tained at 85% or above the rated level. The undervolt-
age trip device is available only as an instantaneous
type with rated voltages of 48VDC, 125VDC, and
250VDC.
For a basic understanding of the operation of the under-
voltage trip device refer to Figure 5-8, the following
operation description and the specific items identified in
the Figure 5-8:
1.) With the breaker closed and sufficient voltage on the
Undervoltage Trip Device coil, the moving clapper (1) is
held to the stationary yoke (2) by the magnetic force
produced by the coil (3) against the extension springs
(4) pulling the moving clapper apart from the yoke.
2.) The moving clapper is connected to the mechanism
Trip D Shaft Lever (5) by a slotted link (6).
3.) When the voltage to the Undervoltage Trip Coil goes
down as described earlier, the extension springs force
overcomes the reduced magnetic force and pulls the
moving clapper up. The slotted link in turn upsets the
Trip D Shaft and the breaker trips open.
4.) As the breaker opens, the reset lever (8) connected
to the pole shaft lever (7) operates to reset the moving
clapper. As long as the breaker remains open, the reset
lever holds down the moving clapper to the yoke.
5.) When the breaker closes, the reset lever moves
away from moving clapper. If the Undervoltage Trip
Device coil has at least 85% of the rated voltage
applied, the moving clapper is held to the yoke by the
magnetic force,even though the reset lever has moved
up.
5-4
INTERLOCKS
NEVER DISABLE OR DEFEAT ANY INTERLOCKS.
HAZARDOUS VOLTAGES WILL CAUSE DEATH,
IB131009EN
WARNING
SEVERE PERSONAL INJURY OR PROPERTY DAM-
AGE.
All W-VAC and W-VACW breakers are equipped with
several interlocks. These interlocks permit proper and
safe breaker operation.
5-4.1 FLOOR TRIPPING, SPRING RELEASE AND
ANTI-LATCH INTERLOCKS
These interlocks are operated by the inter- action
between the floor tripper rollers on the breaker bottom
and the carriage or cradle assemblies. The functions
performed are as follows:
1. The breaker is held mechanically trip free during
racking. The latch check switch is also held open,
thus preventing any electrical close signal from clos-
ing the breaker.
2. The breaker is permitted to be with drawn in the
safe mode (breaker open, springs discharged) when
bringing the breaker to the Withdrawn position or to
the Connected position.
The outlined functions are accomplished by pushing up
the tripper rollers, which in turn rotates the Trip D Shaft
or Spring Release Latch.
5-4.2 LEVERING INTERLOCK
The purpose of this interlock is to prevent the levering
crank from being engaged when the breaker is closed.
An interference device on the cradle or carriage, which
is positioned by the breaker operating shaft, prevents
the levering crank from being inserted with the breaker
in the Closed position.
5-4.3 ANTI-CLOSE INTERLOCK
This interlock prevents releasing the closing springs
electrically or manually, if the breaker is already closed.
On a closed breaker the interlock lever moves toward
the rear. In this position the movement of the spring
release clapper does not lift the lever, thus the spring
release latch cannot be moved. This interlock applies to
the fixed W-VACR circuit breaker also.
5-4.4 EARTHING DRIVE INTERLOCK
The earthing drive mechanism operates an interference
device to prevent insertion of the breaker when the
earthing switch is closed.
Instruction Book
Page 33
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