Schweitzer Engineering Laboratories SEL-701-1, Инструкция по эксплуатации

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Date Code 20011009
SEL-701-1 Monitor
Settings Calculation
RTD-Based Protection
3.35
The monitor calculates RTD % Thermal Capacity using Equation 3.4 :
Equation 3.4
As ambient temperature rises, the motor’s ability to shed heat to the surroundings
is reduced and internal temperatures rise. To preserve insulation life, NEMA standards
suggest a 1°C reduction in RTD trip temperature for each 1°C rise in ambient
temperature over 40°C. When you enable RTD biasing, the SEL-701-1 Monitor
automatically reduces the RTD trip temperatures for all winding RTDs when ambient
temperature is above 40°C. The monitor reduces the trip temperatures by 1°C for each
degree rise in ambient temperature over 40°C.
Finally, when you enable RTD biasing, the monitor provides an RTD Bias Alarm
when the RTD % Thermal Capacity exceeds the thermal element % Thermal Capacity
by more than 10 percentage points while the winding temperature rise is higher than
60°C over ambient. This alarm can be a useful indicator that the motor has lost coolant
flow or that the winding RTD trip temperature is conservatively low.
For all the RTD thermal capacity and bias calculations described above, the
monitor uses the winding RTD whose measured temperature is closest to its trip value.
Table 3.26 lists the RTD resistance versus temperature for the four supported RTD
types.
RTD%
Thermal Capacity
Winding RTD
Temperature
Ambient
Temperature
è ø
æ ö
–
Winding RTD Trip
Temperature
Ambient
Temperature
è ø
æ ö
–
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