Type 50-DH-50 Air Circuit Breaker
Contacts
The contacts should be inspected periodically
for wear and for evidence of undue burning. Under
normal conditions the contacts should be usable for
a large number of operations within the rated
rupturing capacity of the breaker. On the earlier
models cup washers, held in compression by bolts
and castle nuts, were used to obtain contact pres
sure on both the lower hinge contacts, and the
upper contacts. On later models the cup washers
were replaced by conical compression springs. The
conical spring assembly is interchangeable with
the cup washer assembly and should the customer
at any time require those replacement parts it will
be to his advantage if he ordered the later assembly.
The contact pressure adjustments are made with
the breaker in the closed position. Correct pressure
for all models at the lower, hinge, contact is secured
by turning the nut two-thirds of a turn past the
point where it becomes snug. Correct pressure at
the upper contacts for the earlier models is secured
by turning the castle nuts five-sixths of a turn after
they have been made snug. In the later models the
compression of the conical spring is limited by a
spacer; in this case the nut is turned up tight on
the bolt and cottered in that position. When cor
rectly adjusted the moving contact blades will sep
arate approximately
-h
inch when the arcing con
tacts engage. There will also be a slight clearance
between the arcing contacts when the blades are in
the fully closed position, this separation is desirable
to assure full pressure on the main contacts.
Any excessive roughness on the arcing contact
surfaces may be removed with a fine file or sand
paper, dust from emery cloth is conducting so should
be removed before putting breaker in service.
Check the tightness of the screws by which the sta
tionary arcing contact is bolted to the upper stud.
The breaker should be opened slowly by hand to
determine that the two contact surfaces part in
proper sequence which should be as follows:
(1)
the main contacts part, (2) the arcing contacts part.
When the contacts become worn to the point of
changing this sequence of parting they should be
replaced. This condition should not appear until
the breaker has had a large number of operations.
In operating the contacts by hand there should
be no binding or excessive friction. When opening
the contacts slowly by hand, see that the contact
arm passes to the full-open position so that the
mechanism breaker lever engages the bumper.
Electrical Operating Mechanism
A type SAF-2 electrical mechanism, Figure
7,
Page
9,
slightly modified to best suit the particular
operating conditions, is used to operate the Type
50-DH-5e Breaker. The mechanism is the direct
current solenoid type which operates on standard
direct-current control voltages or, when equipped
with a Rectox unit, on alternating-current. It is a
mechanically full automatic mechanism and is trip
free in all positions. An electrical closing operation
10
is secured by energizing the closing coil. A magnetic
flux generated by the closing coil forces the moving
core and attached push rod upwards against the
push rod roller (located at the junction of the
breaker lever links and the mechanism links.) By
referring to Figure
7
it will be seen that this up
ward force straightens the toggle formed by the
mechanism links and the breaker lever links causing
the breaker lever to rotate counter-clockwise, as
the trigger roller (which is fastened to the mecha
nism links) is held stationary by the trigger. Just
before the moving core strikes the top plate, the
main latch is forced under the push rod roller by
the main latch spring, thus locking the mechanism
in the closed position. The toggle formed by the
breaker lever and the mechanism links is prevented
from going over center by an adjustable stop on the
breaker operating shaft. This stop is arranged to
strike the back plate of the breaker.
Energizing the trip coil rotates the tripping lever
counter-clockwise to break the tripping toggle,
and pull the trigger out of engagement with the
trigger roller.
This permits the entire linkage,
(mechanism links, breaker lever links and breaker
lever) to move horizontally to the right and off
the main latch, thus permitting the mechanism to
move to the open position. As the push rod roller
slides off the main latch, the retrieving springs pull
the push rod roller downwards to reset the mecha
nism.
On truck mounted breakerl5
an
interlocking ar
rangement is connected to the SAF-2 mechanism
in such a manner as to make it impossible to close
the . breaker if the arms of the racking-in device
are mother than the "operating" or "test" position,
also, this interlock prevents the rotation of the
racking-in device arms when the breaker contacts
are closed.
By adjusting the compressed length of the trip
ping lever bumper spring the toggle joint between
the trigger and the tripping lever should be set
either on toggle or slightly over toggle to prevent
unlatching when closing the breaker on maximum
voltage.
Single and Four Coil Tripping Attachments
The four coil attachment, Figure
8,
Page
11,
bolts to the mechanism frame in place of the single
coil trip attachment. In bolting either attachment
in position it is only necessary to observe that the
coil plungers push the tripping lever upwards suf
ficiently to trip the mechanism. A tripping lever
having suitable extensions must be used with the
four coil attachment. The four coil attachment is
designed to accommodate four tripping assemblies
which may be equipped with either shunt or over
current coils and instantaneous or inverse time
limit assemblies.
Overload Release
The overload release, Figure
9,
Page
11,
consists
of the parts shown in the reference figure. The
moving core is magnetically drawn against the trip
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