4.90
SEL-751 Relay Instruction Manual Date Code 20170927
Protection and Logic Functions
Group Settings (SET Command)
RTD Type
The four available RTD types for setting RTDnTY are:
➤ 100-ohm platinum (PT100)
➤ 100-ohm nickel (NI100)
➤ 120-ohm nickel (NI120)
➤ 10-ohm copper (CU10)
RTD Trip/Warning Levels
The SEL-751 provides temperature warnings and trips through use of the RTD
temperature measurements and the warning and trip temperature settings,
ALTMPn and TRTMPn, in Table 4.17.
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 tem-
perature 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 EWDGV
equals Y. Only one excessive temperature indication is necessary if the wind-
ing trip voting is not enabled. The bearing trip voting, EBRGV, 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 ambi-
ent 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 func-
tions. The relay includes specific logic to indicate if RTD leads are shorted or
open. Ta ble 4.32 lists the RTD resistance versus temperature for the four sup-
ported RTD types.
Table 4.32 RTD Resistance Versus Temperature (Sheet 1 of 2)
Tem p ( ° F ) Tem p (°C) 100 Platinum 120 Nickel 100 Nickel 10 Copper
–58 –50.00 80.31 86.17 74.30 7.10
–40 –40.00 84.27 92.76 79.10 7.49
–22 –30.00 88.22 99.41 84.20 7.88
–4 –20.00 92.16 106.15 89.30 8.26
14 –10.00 96.09 113.00 94.60 8.65
32 0.00 100.00 120.00 100.00 9.04
50 10.00 103.90 127.17 105.60 9.42
68 20.00 107.79 134.52 111.20 9.81
86 30.00 111.67 142.06 117.10 10.19
104 40.00 115.54 149.79 123.00 10.58
122 50.00 119.39 157.74 129.10 10.97
140 60.00 123.24 165.90 135.30 11.35
158 70.00 127.07 174.25 141.70 11.74
176 80.00 130.89 182.84 148.30 12.12
NOTE: To imp rove security, RTD
ALARM and TRIP are delayed by
approximately 6 seconds.
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