Contacts
Several connection conditions are satisfied by the variety
of contact structures. They are divided into arcing and
non-arcing.
The non-arcing contacts consist of front and rear slip rings,
which serve as the connection point for opposite ends of
the reactor windings and one end of the two main movable
contacts. All contact surfaces are Electrical Tough Pitch
(ETP) copper and all joints are riveted, bolted, or brazed
to maintain a high-conductivity current path. Contact pres-
sure between moving points is maintained by opposing
steel compression springs.
There are several types of arcing contacts on a regulator
tap-changer. They can be divided into two categories:
main and reversing.
•
The main stationary contacts are connected to the
series-winding taps. The main movable contacts con-
nect the slip rings to the main stationary contacts.
•
The reversing stationary contacts are connected to
opposite ends of the series winding. The reversing
movable contacts connect the neutral stationary con-
tacts to the reversing stationary contacts.
All stationary contact bodies are made of ETP copper.
Copper-tungsten inserts are brazed to the edges of the
stationary contacts since those contacts are subject to
damage from impact or arcing duty. The main movable
contacts are constructed of a copper-tungsten. The mov-
able contacts are split to make connection on both sides of
the stationary contacts. This split resists separation in the
event of high-current surges.
The tap-changer stationary contact body is copper. The
reversing movable contacts are the same construction as
the main movable contact.
Contact erosion is a function of many variables such as
system parameters, regulated and unregulated voltages,
line currents, power factor, voltage and current harmonics,
and reactor and main core and coil designs.
Stationary contacts should be replaced before the arcing
inserts erode to the point where there may be burning on
the copper. Movable contacts should be replaced when
approximately 1/8 inch of smooth surface remains.
2
S225-10-30
!
SAFETY
FOR LIFE
Figure 19 .
QD-5 Quik-Drive tap-changer .
Figure 20 .
QD-8 Quik-Drive tap-changer .
