S225-10-5
2-10
Motor Circuit
The motor circuit power is brought from the 6-ampfuse, through a
set of back-to-back diodes (for current division), to the AUTO/
OFF/MANUAL selector switch. When this switch is set for auto-
matic operation, motor power is applied to the relays. An appro-
priate relay closure then applies this power to the tap changer
motor, after first passing through the limit switch contacts in the
position indicator. When the switch is set for manual operation,
the power is transferred to the momentary toggle switch labeled
RAISE/LOWER. By actuating this switch in one direction or the
other, power is applied through the limit switch contacts, directly
to the tap changer motor, completely bypassing the circuit board.
Also included as a part of the motor circuit is an “alternate
feed” to the motor called the “holding switch circuit.” Located on
the tap changer is a single-pole, double-throw switch, which is
driven by a cam operated off of the tap changing mechanism.
Motor rotation closes this switch (one direction or the other), and
establishes a complete circuit for motor current until the rotation
is complete and the cam drops out. During the time the holding
switch is closed, motor current is drawn through an input on the
circuit board which permits the control to detect that a tap change
is in progress. The microprocessor uses this information in its
decision making process, as described in the following section.
Two other unassociated circuits which share the 6 amp motor
source are the drag hand reset and neutral light circuits. The
drag hand reset function is accomplished simply by operating a
momentary toggle switch which applies power to the reset
solenoid in the position indicator. The neutral light is similarly
actuated for test purposes and it is also energized from a neutral
light switch (located on the tap changer) when in the neutral tap
position.
AUTOMATIC/MANUAL OPERATION
Automatic
In the automatic mode of operation, the power switch will be set
on INTERNAL and the AUTO/OFF/MANUAL switch will be
placed on AUTO. The regulator is assumed energized from the
primary circuit. If the sequential control response is selected (the
standard mode), the control response is as follows:
1. As the primary voltage moves to a level which represents an
out-of-band condition, the sensing voltage will corresponding-
ly reflect the same results on the 120V base. Assuming the
voltage dropped low, a lower than nominal signal will appear
at the printed circuit board input, terminals 10 and 11.
2. The signal is rectified and harmonic filtered before passing
into a differential amplifier for comparison with a reference
signal. The resulting amplifier output is fed into an analog-to
digital converter on the microprocessor chip.
3. The microprocessor, recognizing the voltage condition as
low and out-of-band, issues an output which lights the
“LOW” band edge LED, and starts an internal timer which is
equivalent to the time delay setting.
4. During the time out period, the voltage is continually sensed
and sampled. Should the voltage momentarily move into
band, the timer is reset.
5. At the end of the time delay period, the microprocessor
issues an output which causes the “RAISE” relay coil to be
energized. An internal 4-second timer is also started.
6. The tap changer motor begins to turn as a result of the relay
closure, and a cam on the tap changer closes the “RAISE”
holding switch. This now provides an alternate source for
the motor current, which passes through the “current sense”
inputs on the circuit board, terminals 1 and 2.
7. The microprocessor now recognizes that current is flowing in
the holding switch circuit, and performs three actions: (1 ) an
output is issued which partially increments the operations
counter, (2) the RAISE relay is deenergized, thus opening its
contacts, and (3) the four second timer is reset.
8. As a result of the relay contact opening, the motor current is
now carried solely by the holding switch circuit. When the
motor rotation is complete, the holding switch opens as a
result of the cam action, and the motor stops.
9. The microprocessor recognizes that the tap change is now
complete and issues an output action which completes the
incrementing of the operations counter. A two second pause
then occurs, allowing the sensing voltage to stabilize from
the motor operation. At the end of this pause, the voltage is
monitored.
10. If out-of-band conditions still exists, another output is issued
to close the RAISE relay, thus starting another tap change
sequence (step 5). If the voltage is in-band, the LOW LED is
turned off, and the time delay timer is reset. The micropro-
cessor continues to sample the input voltage for a change of
positions.
This sequence is altered slightly if the voltage averaging or
time integrating mode of operation is selected. These character-
istics are described in Section 3 under Control operating Modes.
The CL-2A regulator control also includes a feature called
relay retry. If motor current is not detected within four seconds
after the relay closes (step 5), the processor opens the relay con-
tacts, and idles for 30 seconds before trying again. This feature
is intended to prevent the control from becoming “locked up” in
the unlikely event a good electrical contact is not made when the
relay contacts close. The control will also enter this retry mode
when the limit switches prevent additional tap changes from
occurring or if the AUTO/OFF/MANUAL switch is in a position
other than automatic.
Manual
In the manual mode of operation, the power switch can be set
on either INTERNAL or EXTERNAL, and the AUTO/OFF/MANU-
AL switch will be placed on MANUAL. If the EXTERNAL position
is chosen, an external source must be applied through the termi-
nals on the front panel.
Operation of the momentary toggle switch RAISE/LOWER
applies power through the limit switch contacts, directly to the tap
changer motor. The printed circuit board still functions as if it
were issuing the commands; however, the motor power is now
not connected to the relays, so any relay closure has no effect on
the tap changer motor. As the tap changer rotates, the holding
switch is closed, as described in the preceding section, step 6.
Again, this holding switch current is sensed by the circuit board,
and the operations counter is appropriately incremented.
Tap changes will continue to occur as long as the RAISE/
LOWER switch is closed and the limit switch is not opened.
SUPERVISORY CONTROL AND DATA
AQUISITION (SCADA)
SCADA is a supervisory system used by some utilities for remote
control of their system. SCADA may take on many forms: from
the single retrieval of a few analog values (such as voltage, cur-
rent, power factor, etc.) to remote control of the tap change
(raise, lower, inhibit), to complete remote control which allows
everything to be performed remotely that could be performed at
the regulator front panel. Complete remote control can only be
accomplished through a digital communications link with the CL-
4C Control.
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