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3.2.3 Total Tap Change Count Relay
The 1250-LTC can count the number of tap position changes and turn on a relay and
LED when a programmed limit (10 to 999,990 counts) is reached. The alarm code “ttCLt”
will also be displayed momentarily. The counter can be pre-set to any number. A date can be
entered for reference purposes when the count is preset. (This date is stored in memory for
reference only, it will not increment as time passes. It can be read through the Front Panel or
the serial port.) The user can program which relay will assert when the Total Tap Change
Count limit is reached. Please note that the counter limit and pre-set values are set in
THOUSANDS of tap changes. For example, if an alarm is required at 125,000 operations,
set the alarm limit to “0125.0”. If it is known that the LTC already has 2,300 operations, pre-
set the counter to “0002.3”.
Use the OP 55, ttCLt, TTCLMT command to set the Total Tap Change Count Limit.
Use the OP 56, ttrLY, TTCRLY command to select which relay (OFF, LO or HI) asserts
when the Total Tap Change Count Limit is reached. When this value is set to “OFF” this
function is disabled. Use the OP 57, ttPrE, TTCPRE command to pre-set the Total Tap
Change Counter value. If the alarm relay is asserted, it will be cleared when the counter is
preset to a value lower than the alarm limit. Use the OP 58, ttPdt, TTCDATE command to
enter a reference date. To do this using the programming menu: Select OP 58, ttPdt and
press the ENTER key. First, set the Day of the month value and press the ENTER key. Next,
set the Month value and press the ENTER key. Finally, set the Year value and press the
ENTER key. Use the OP 59, ttCdS, DUMP command to display the present counter value
and the reference date. The counter value will be displayed for 2 seconds, and then the date
will scroll across the display. This will repeat until the ENTER key is pressed, which will exit
the command.
3.2.4 On-Tap Alarm Relay
The 1250-LTC has the accuracy and resolution to monitor minute differences in LTC
tap position. Ideally, the LTC should always stop in the exact center of each tap position. A
properly functioning LTC should consistently stop within a tolerable band of degrees, with
every tap change. As the mechanism wears or if something breaks, the LTC may begin to
stop in positions further from the center of the tap position, on one or more taps.
The 1250-LTC can be programmed to give an alarm when it detects that the LTC has
stopped in a position that is outside the tolerable band of degrees. The width of this band of
tolerable error is programmable in degrees, with 0.1 degree resolution.
A three second time window is given for the LTC to be outside of the acceptable
Guard Band area. After three seconds, if the LTC is found in the “Error Zone”, the On-Tap
Alarm Relay will assert.
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