S225-12-1
5
!
SAFETY
FOR LIFE
Contacts
All moveable and main stationary contacts employ cop-
per-tungsten copper alloy tips at points subjected to arc-
ing duty. Contact points not subjected to arcing employ
a combination of EPT copper to provide a high conduc-
tivity current path. Moveable contacts are split to make
contact on both sides of mating parts and resist sepa-
ration during high current surges. Contact pressure is
maintained by steel compression springs.
The main stationary contact has two arcing tips, one on
each side. Each arcing tip is composed of tungsten cop-
per alloy. Tungsten is used to help reduce the erosion of
the contacts due to arcing. The main stationary contact is
used for stationary contacts tap 1 through 8.
The main moveable contact assembly consists of the main
Geneva Gear, and two sets of contacts. One contact of each
mates with the main stationary contact and a button con-
tact. This mates and has constant contact with a collector
ring.
The receiving stationary contact is used in two positions,
VL and VR, and sees less operating duty than the main
stationary contacts. The reversing stationary contacts do
not utilize tungsten alloy arcing tips. The reversing sta-
tionary contact is symmetrical and can be use for either
the VL or VR positions.
Reversing Switch
The reversing switch changes the polarity of the tapped
winding. When the QD3 Quik-Drive tap-changer is in the
neutral position; the reversing switch is open (not making
contact with either of the reversing stationary contacts).
In the open position, the reversing switch is not in the
load current circuit.
The reversing switch motion on the QD3 tap-changer
occurs as the main moveable contact enters or leaves
the neutral position. The main moveable contact assem-
bly has a pivot roller located between the two moveable
contacts. The pivot roller is engaged in a pivot slot in
the reversing switch moveable contact assembly when
the main moveable contacts are in the neutral position.
The first tap step rotates the reversing moveable contact
assembly, causing the reversing switch moveable con-
tacts to engage the reversing stationary contact. This will
be either the VL or VR reversing stationary contacts.
QD3 tap-changer reversing switches may be exposed
to arcing duty. The main Geneva/contact drive assem-
bly and the reversing switch arm provide a mechanical
stop located approximately 320 degrees on either side
of neutral.
Figure 5.
Main stationary contact.
Tungsten
Copper
Arcing Tips
Figure 6.
Main moveable contact assembly.
Moveable Contact
Button Contacts
Moveable Contacts
Actuator
Lever
Figure 7.
Reversing stationary contact.
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