Rockwell Automation 825-P Modular Protection System for Motors User Manual - Manual (Page 86)

86 Rockwell Automation Publication 825-UM004D-EN-P - November 2012
Chapter 6 Configuring Protection & Logic Functions
• Provides an RTD Bias Alarm if the winding temperature exceeds 60°C rise
over ambient and the RTD % Thermal Capacity exceeds the thermal
element % Thermal Capacity by more than 10%.
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 825-P automatically reduces the RTD Trip
Temperatures for all winding RTDs when ambient temperature is above 40°C.
The relay reduces the trip temperatures by 1°C for each degree rise in ambient
temperature over 40°C.
Finally, when you enable Thermal Model biasing, the relay 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
relay uses the winding RTD whose measured temperature is closest to its trip
value.
Voltage-Based Protection The following information applies to relay models with voltage inputs.
Undervoltage
EXAMPLE Relay Calculation of RTD% Thermal Capacity
RTD%
Thermal
Capacity
Winding RTD
Temperature
Winding RTD Trip
Temperature
Ambient
Temperature
Ambient
Temperature
=
Table 28 - Undervoltage Settings
Setting Prompt Setting Range Factory Default
UV TRIP LEVEL Off, 0.60…1.00 xVnm Off
UV TRIP DELAY 0.0…120.0 s 0.0
UV WARN LEVEL Off, 0.60…1.00 xVnm Off
UV WARN DELAY 0.0…120.0 s 5.0