4.22
SEL-749M Relay Instruction Manual Date Code 20080918
Protection and Logic Functions
PTC/RTD-Based Protection
Define the RTD location settings through use of the following suggestions:
➤ If an RTD is not connected to an input or has failed in place and
will not be replaced, set the RTD location for that input equal to
OFF.
➤ For RTDs embedded in motor stator windings, set the RTD
location equal to WDG.
➤ For inputs connected to RTDs measuring bearing race
temperature, set the RTD location equal to BRG.
➤ For the input connected to an RTD measuring ambient motor
cooling air temperature, set the RTD location equal to AMB.
Only one ambient temperature RTD is allowed.
➤ For inputs connected to monitor temperatures of another
apparatus, set the RTD location equal to OTH.
The relay allows you to independently define the type of each monitored RTD
with the RTD type settings.
If an RTD location setting is equal to OFF, the relay does not request that an
RTD type setting be entered for that input.
RTD Type
The four available RTD types are:
➤ 100-ohm platinum (PT100)
➤ 100-ohm nickel (NI100)
➤ 120-ohm nickel (NI120)
➤ 10-ohm copper (CU10)
RTD Trip/Warning Levels
The SEL-749M provides temperature warnings and trips through use of the
RTD temperature measurements and the warning and trip temperature settings
in Table 4.20.
The relay issues a winding temperature warning if any of the healthy winding
RTDs (RTD location setting equals WDG) indicate a temperature greater than
the relay RTD warning temperature setting. The relay issues a winding
temperature trip if one or two of the healthy winding RTDs indicate a
temperature greater than their RTD trip temperature settings. Two winding
RTDs must indicate excessive temperature when the winding trip voting
setting equals Y. Only one excessive temperature indication is required if
winding trip voting is not enabled. Bearing trip voting works similarly.
The warning and trip temperature settings for bearing, ambient, and other
RTD types function similarly, except that trip voting is not available for
ambient and other RTDs.
To disable any of the temperature warning or trip functions, set the appropriate
temperature setting to OFF.
Only healthy RTDs can contribute temperatures to the warning and trip
functions. The relay includes specific logic to indicate if RTD leads are
shorted or open.
Courtesy of NationalSwitchgear.com
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