Advanced Power technologies TTC-1000 Instruction & Operation Manual page 90

NOTE: The LTCDIFF and LTCDIFF1 & 2 temperature displayed is the
±20°C
calculated differential up to a maximum of . The corresponding
analog output tracks this differential temperature only if the probe or
probes used are named LTCDIFF or LTCDIFF1 or LTCDIFF2.
All LTCDIFF temperature set points are designed to read negative as well as
positive because sometimes the LTC tank runs cooler than the top oil
temperature. It is recommended that you monitor the LTCDIFF temperature for a
period of time to determine the normal operating differential for the transformer. A
good rule of thumb is to set the LTCDIFF pickup temperature from 3 to 7 degrees
higher than the observed operating differential. The security of this setting can be
improved through the use of the LTC pickup timers (LTCPUTMR1 & 2) settings.
The recommended setting for the LTCPUTMR is between 360 to 480 minutes (6
to 8 hours) to ignore the affects of daylight heating on a lightly load transformer.
The LTCPUTMR can be set up to 999 minutes (16 hours 39 minutes).
To use this feature you must first make sure one of the probes has been named
LTCDIFF, LTCDIFF1, LTCDIFF2, LTCTANK, DIVTANK or SELTANK. Next,
program the LTCDIFF(1 or 2) PU (pickup) and LTCDIFF(1 or 2) DO (drop out)
temperatures. As mentioned earlier, it is a recommended that the LTCDIFF
temperature be monitored to determine the transformer's normal operating point.
For LTCDIFF(1 or 2), the appropriate LTCPUTMR can be set once the
transformers normal operating condition is determined. Setting the LTCPUTMR
to zero permits the associated LTCDIFF set point to pickup as soon as the
LTCDIFF PU temperature is reached (essentially the same function as
LTCDIFF). Setting the LTCPUTMR(1 or 2) to some time other than zero will
delay the pickup of the LTCDIFF(1 or 2) set point as long as the LTCDIFF1 or 2
temperature is equal to or above the LTCDIFF(1 or 2) PU temperature.
NOTE: The LTCPUTMR will not change while in progress. New settings will
take effect after the set point drops out or if the LTCDIFF temperature were
to drop below the LTCDIFF PU temperature while the timer is in progress.
Once you have established the pickup and drop out settings you are ready to
assign the LTC set point to a specific output. This set point will not pickup an
output until you assign it to OUT1, OUT2, OUT3, OUT4, OUT5, or OUT6.
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