S225-12-1
7
!
SAFETY
FOR LIFE
QD3 Operating Sequence
When the tap-changer is in the neutral position and the
control calls for a tap change, the following events occur:
1. The motor is energized and begins to turn using
120V power supplied by the control.
2. The motor gear drives the Geneva drive gear.
3. The pin on the Geneva drive gear enters a slot on
the main Geneva/contact drive assembly and the
main Geneva/contact drive assembly begins to
index.
4. The holding switch closes to ensure the tap change
will go to completion. The control removes the ini-
tial 120V power. The motor is now energized only
through the hooding switch (also 120V).
5. The reversing switch pin on the main Geneva/con-
tact drive assembly begins to drive the reversing
switch arm.
6. One of the two main interrupting moveable contacts
slides out of engagement with the neutral station-
ary contact and interrupts the circuit through that
branch.
7. The reversing switch arm rotates, which causes
the reversing switch contacts to pivot. A bridge
between the neutral contact and a stationary con-
tact connected to one end of the series winding
is thus established. NO arcing occurs across the
reversing switch contacts. When the reversing arm
rotates, a finger on the reversing switch arm engag-
es a normally closed logic switch that determines
whether the tap-changer is raising or lowering the
voltage.
8. The main interrupting contacts slide over and onto
the number one stationary contact, making a bridg-
ing position from contact N to contact 1 through the
reactor.
9. The pin on the Geneva drive gear exits the main
Geneva/contact drive assembly slot. The Geneva/
contact drive assembly stops moving and rotation is
all locked.
10. The holding switch opens and de-energizes the
motor.
The magnetic rotor in the motor stops all motion.
11. The motor shaft has completed a 120-degree turn.
The elapsed time from step 1 to step 13 is approxi-
mately 270 ms.
12. If the control issues another signal to index in the
same direction, the same sequence is repeated
except the reversing switch is not actuated. The
reversing switch does not move until the tap-chang-
er is reversed and stepped the opposite direction
back in neutral.
13. If the tap-changer is switching from position 15
to position 16, a normally closed limit switch is
engaged that is connected in parallel with the logic
switch. With both the logic and the limit switches
activated, the control cannot provide power to the
motor to index the tap-changer past the 16 posi-
tion. The tap-changer can be indexed back to the
15 position.
The following outlines maintenance procedures relating
to the QD3 voltage regulator tap-changer and compo-
nents. Before any internal or external maintenance is per-
formed, the regulator must be removed from service.
It is necessary to open the regulator for inspection of the
tap-changer. It is also necessary and recommended to
remove the QD3 tap-changer from the regulator to per-
form inspections and repairs to moveable and stationary
contacts. This section provides procedures for removing
and replacing various components of the tap-changer
with replacement kits.
Before removing the voltage regulator from service for
maintenance, refer the Removal From Service section of
the voltage regulator manual S225-10-30.
Troubleshooting and service functions of the QD3 / T350
tap-changer are performed with the regulator un-tanked
and the tap-changer removed from the regulator.
INSTALLATION
MAINTENANCE, SERVICE, AND TROUBLESHOOTING
To Next Page
Loading...
Need help?
General
