Operating instructions

IMM AGSB-60 41
Solid State Starters
Solid state starters are standard on all AGS units. A solid state starter uses a silicon-controlled
rectifier (SCR) power section to allow a motor to be brought to full speed with a reduced
initial voltage that increases to full line voltage over a given time. The McQuay motor starter,
custom designed for this specific application, is microprocessor controlled. Along with this
starting technique, the motor starter also provides protection for the motor and monitors its
load conditions.
The starter offers:
• Solid state design.
• Closed-loop motor current control.
• Programmable motor protection.
• Programmable operating parameters.
• Programmable metering options.
The three-phase starter contains a six-SCR power section with two SCRs per phase connected
in inverse parallel. This power section is capable of providing maximum torque per amp
throughout the motor’s speed-torque curve with minimal motor and starter heating. At the
same time, the starter continually monitors the amount of current being delivered to the motor,
thus helping protecting the motor from overheating or drawing excessive current. The starter
will automatically stop the motor if the line-to-line current is not within acceptable ranges, or
if the current is lost in a line. The motor current scaling is set according to the motor size and
the specific application. The starter circuitry is contained on a single printed circuit board,
which contains all the logic and SCR gate drive circuitry.
Operating messages are displayed on a three-character LED display located in each
compressor's control panel. The LED display on the control card displays:
• Operating messages that indicate the status of the motor and/or starter.
• Operating parameters that are programmed into the starter.
• Fault codes that indicate a problem with the motor application or starter.
Operating Messages
Possible operating messages are as follows:
Message Meaning
noL Line voltage is not present.
rdy Line voltage is present and starter is ready.
acc Motor is accelerating after a start command has been received.
uts The motor has achieved full speed.
run Motor is operating at full speed, and ramp time has expired.
dCL A Stop command was received and the motor is decelerating with the
set deceleration profile.