GE 469 Instruction Manual page 202

5–58
at a level that is below the
will rise or fall to a value based on the average phase current and the
settings. The
STALL RATIO THERMAL CAPACITY USED
minute or fall as dictated by the running cool time constant.
TC
used_end
where: TC =
THERMAL CAPACITY USED
used_end
I = equivalent motor heating current
eq
hot / cold =
HOT/COLD SAFE STALL RATIO
The
HOT/COLD SAFE STALL RATIO
provided or the hot and cold safe stall times. Simply divide the hot safe stall time by the
cold safe stall time. If hot and cold times are not provided, there can be no differentiation
and the
HOT/COLD SAFE STALL RATIO
RTD Bias
The 469 thermal replica operates as a complete and independent model. However, the
thermal overload curves are based solely on measured current, assuming normal 40°C
ambient and normal motor cooling. If the ambient temperature is unusually high, or motor
cooling is blocked, the motor temperature will increase. If the motor stator has embedded
RTDs, the RTD bias feature should be used to correct the thermal model.
The RTD bias feature is a two-part curve, constructed using 3 points. If the maximum stator
RTD temperature is below the
occurs. If the maximum stator RTD temperature is above the
at the stator insulation rating or slightly higher), then the thermal memory is fully biased
and
THERMAL CAPACITY USED
minimum, the
THERMAL CAPACITY USED
model is compared to the RTD Bias thermal capacity used from the RTD Bias curve. If the
RTD Bias thermal capacity used value is higher, then that value is used from that point
onward. The
RTD BIAS CENTER POINT
temperature. The 469 automatically determines the
the center point using the
TC
used at RBC
At < RTD_Bias_Center temperature,
RTD_Bias_TC
At > RTD_Bias_Center temperature,
RTD_Bias_TC
=
used
where: RTD_Bias_TC
used
T = current temperature of the hottest stator RTD
actual
T = RTD Bias minimum settings, T
min
T = RTD Bias maximum settings
max
TC = TC used defined by the
used at RBC
, the
OVERLOAD PICKUP LEVEL
will either rise at a fixed rate of 5% per
hot
 
I × 1 ×
--------- -
= –
 
eq
cold
if I
per_unit
settings
may be determined from the thermal limit curves if
should be entered as "1.00".
settings (typically 40°C), no biasing
RTD BIAS MINIMUM
is forced to "100%". At values between the maximum and
created by the overload curve and the thermal
should be set at the rated motor running
THERMAL CAPACITY USED
HOT/COLD SAFE STALL RATIO
( 1 hot cold ⁄ ) ×
= –
T T
–
actual min
× TC
------------------------------ -
=
used
T T
–
center min
T T
–
actual center
× ( 100 TC
----------------------------------- -
–
used at RBC
T T
–
max center
= TC used due to hottest stator RTD
= RTD Bias center settings
center
HOT/COLD SAFE STALL RATIO
469 MOTOR MANAGEMENT RELAY – INSTRUCTION MANUAL
CHAPTER 5: SETTINGS
THERMAL CAPACITY USED
HOT/COLD SAFE
100%
remains steady state
RTD BIAS MAXIMUM
value for
settings.
100%
used at RBC
) TC
+
used at RBC
settings
register
(EQ 5.7)
(typically
(EQ 5.8)
(EQ 5.9)
(EQ 5.10)