GE MULTILIN 269 MOTOR MANAGEMENT RELAY Series Instruction Manual page 109

The INITIALIZE module is performed whenever the
relay is powered on to ensure that the system comes
up in a known state. Parts of this module are executed
whenever the relay is reset as well. The SYSTEM
EXECUTIVE then causes execution to loop through a
series of modules which perform most of the relay
functions.
The O/L module uses the positive to negative sequence
current ratio calculated by the U/B module and the
RMS phase currents to fill a thermal memory register.
The O/L module discharges this register at either a
learned or preset cooling rate when no overload is pre-
sent. The average stator RTD temperature calculated
in the RTD module is used to bias the thermal memory.
This module also compares the RMS phase current
values to the Undercurrent and Rapid Trip/Mechanical
Jam trip and alarm levels, and starts appropriate timers
if the current levels are out of range.
The U/B module computes the phase current ratios
Ib/Ia and Ic/Ia, and uses them in conjunction with a
look-up table to determine the negative to positive se-
quence current unbalance ratio In/Ip.
compared to the Unbalance trip and alarm levels and
appropriate timers are initiated if trip/alarm conditions
are met.
The RTD module uses the RTD voltage reading from
each of the 8 RTD inputs and computes the average
stator RTD temperature. This is then used to bias the
thermal memory. The RTD readings are compared to
the trip and alarm levels and relay activation is initiated
if conditions are met. Each RTD is read 128 times over
a one second scan interval.
5-3
The KEYSERVICE/EXTERNAL SWITCH module takes
in all of the data associated with the keypad and exe-
cutes the function of each key. Timers for the closure
times of the VALUE UP/DOWN, PAGE UP/DOWN, and
LINE UP/DOWN keys are initiated and the display is
updated accordingly.
Emergency Restart and External Reset inputs and initi-
ates appropriate action.
The MESSAGE module handles all of the message
look-up functions and sends the message data to the
display. The displayed messages are made up of indi-
vidual messages, common message strings, and vari-
able data. Non-displayed control bytes are used to
indicate the message type, variable data type, decimal
point placement, and other control information.
The D/A module gives the DAC the current digital value
for the selected option output for conversion to an
analog value. This analog voltage is then fed to a volt-
age-to-current converter circuit.
The SELF-TEST module causes the 80C32 to send out
This value is regular voltage signals to indicate to the power supply
watchdog circuit that the system is operating properly.
This module also performs all of the self-test features
outlined in section 3.23.
The TRIP/ALARM module is executed when any relay
trip or alarm setpoint has been exceeded. This module
handles output relay activation and TRIP/ALARM mes-
sage output.
Statistical data is updated whenever a statistical value
changes.
5 THEORY OF OPERATION
This module also reads the