GE VALUTROL MAIN CONTROL MODULE Instructions Manual page 17

SEQUENCE OF OPERATION
POWER APPLIED
The control transformer (CPT) is energized through its
primary fuses. The fans (if supplied) will come on.
The power supply card is energized and the DC output ( ±20
volt) are applied through their fuses to the rest of the cards.
All readings carry a tolerance of ±10%.
The motor field supply is energized. Refer to the motor field
supply instructions for details.
If no faults have been detected by the monitor section of
the interface card, the fault relay FLT will close, and the
"Ready to Run" indicator on the main control card will
illuminate. Table II tabulates the fault conditions which
are monitored.
The oscillator will start, and the synchronizing signals SA,
SB, SC will measure 8.5 volts RMS, (±1O%). See Figure
17.
SWITCH LOGIC
RUN or JOG will be switched from +30V
to
-30 volts.
(under purchaser control).
The control line MAC from the main control card to the
interface will be pulled down to -20 volts.
The interface card checks that no faults exist and that
"control on" is connected to -30 volts before applying
power to the coil of the pilot relay MAX.
MAX picks up, releasing the preconditioning signal PRE
from common and applies power to the coil of the M relay
which picks up the contactor.
When PRE is released from common, it switches to -4
volts which will release the main control card
preconditioning after approximately 80 milliseconds.
Releasing preconditioning allows the drive to send firing
pulses to the gates of the SCR's in the conversion module,
and allows the normal signal flow to occur.
SIGNAL FLOW
If RUN is switched, the reference at SR is applied to the
linear time section. The timed reference output TR will
ramp to a voltage proportional to SR. The
REF SCALE
GEK-24994
adjustment is used to set TR to 10.0 volts when the input at
SR is set for top speed. The time for TR to ramp from 0 to
10 volts is adjustable from .3 to 60 seconds with the
LIN TIME
adjustment. See jumper table on system elementary.
(Ranges: .3 to 10 sec. or 2 to 60 sec.)
The speed (or CEMF) feedback from the motor tachometer
is scaled with a selectable resistor network on the interface
card, and rectified (if required) on the main control card.
The output of the speed feedback section is SFB, and will be
10 volts at top speed.
MAK SPEED
is adjusted to make the
actual top speed correspond to desired top speed. See
Figures 18 and 2l.
The timed reference TR, the JOG reference JOGR, and the
speed feedback SFB are summed by the regulator error
amplifier. The error amplifier output EAO will be a low
voltage (nearly zero) when the drive is regulating speed.
EAO will not be low when the drive is in current limit or
CEMF limit. The gain of the error amplifier is set with the
GAIN
adjustment. The
GAIN
adjustment is used primarily to
improve the response of the drive in the constant
horsepower region when the motor field supply is a motor
field control MFC.
To maintain good load regulation, the error amplifier is fed
into the regulator integrator. The output of the integrator
is the reference, DR, to the driver. The response of the
control below base speed is set WIth the
RESPONSE
adjustment.
There is a limit, however, to how responsive a drive may be
set. Stability of the drive is decreased as its response is
increased. If motor field supply is the motor field control
(MFC) , the
RESPONSE
adjustment is desensitized when the
drive is operating in the constant horsepower region of the
torque speed curve.
To protect the system, three limit sections are provided;
counter-EMF (CEMF) limit and two current limits. The
output of the CEMF limit and the primary current limit
drive the regulator integrator and will override the error
amplifier, if requlred. The primary current limit is set with
the
CUR £/",IT
adjustment and the counter EMF limit with
the
CEMF LIMIT
adjustment. Typically, the primary or
regulator current limit is set at
150%
of the motor
nameplate current of 3.75 volts ( ±1O%) of current
feedback, CFB. The counter EMF is normally limited to
250
armature volts at no load, or
5.75
volts ( ±1O%) of
CEMF for drives rated 240 volts DC. For drives rated 500
volts DC the CEMF limit is normally 510 volts at no load or
5.60 volts ( ±1O%) at CEMF. The secondary or driver
current limit is in the drIver section and will be described
later. The primary current limit, if used, should not be set
higher than the driver current limit. The driver current
limit may be inhibited or adjusted.
17