Sel 751A, Instruction Manual

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4.28
SEL-751A Relay Instruction Manual Date Code 20100129
Protection and Logic Functions
RTD-Based Protection
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-751A provides temperature warnings and trips through use of the
RTD temperature measurements and the warning and trip temperature settings
in
Table 4.15 .
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.
Figure 4.16 lists the RTD resistance versus temperature for the four supported
RTD types.
Table 4.16 RTD Resistance versus Temperature (Sheet 1 of 2)
Temp
(°F)
Temp
(°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