GE 869 Instruction Manual page 260

PROTECTION
4–128
RTD BIAS MINIMUM
Range: 0 to 250°C in steps of 1
Default: 40°C
RTD BIAS CENTER
Range: 0 to 250°C in steps of 1
Default: 130°C
RTD BIAS MAXIMUM
Range: 0 to 250°C in steps of 1
Default: 155°C
The RTD bias feature is a two-part curve (RTD Bias Thermal Capacity Used) constructed
from three points: minimum, center and maximum. If the maximum stator RTD
temperature is below the RTD Bias Minimum setting (typically 40°C), no biasing occurs. If
the maximum stator RTD temperature is above the RTD Bias Maximum setting (typically
at the stator insulation rating or slightly higher), then the thermal memory is fully biased
and RTD bias thermal capacity used is forced to 100%. At values in between, the present
RTD bias thermal capacity used created by other features of the thermal model is
compared to the RTD bias thermal capacity used. If the value of the RTD bias thermal
capacity used is higher, then this value is used from that point onward. The RTD Bias
Center setting must be set to the rated running temperature of the motor. The relay
automatically determines the RTD bias thermal capacity used value for the center point
using the Hot/Cold Safe Stall Ratio setting.
At < RTD_Bias_Center temperature
At > RTD_Bias_Center temperature,
where:
• RTD_Bias_TCU = thermal capacity used due to hottest stator RTD
• Temp = current temperature of the hottest stator RTD
actual
• Temp = RTD Bias minimum setting
min
• Temp = RTD Bias center setting
center
• Temp = RTD Bias maximum setting
max
• TCU at RTD_Bias_Center = thermal capacity used defined by the Hot/Cold Safe Stall
Ratio setting
869 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 4: SETPOINTS
Eq. 20
Eq. 21
Eq. 22