GE Multilin MM300, Инструкция по эксплуатации

Страница: 146 / 198

5–36 MM300 MOTOR MANAGEMENT SYSTEM – INSTRUCTION MANUAL
PROTECTION ELEMENTS CHAPTER 5: SETPOINTS
• TCU
SS
represents the steady-state thermal capacity used expressed as a percentage.
• I
eq
represents the equivalent motor heating current in per-unit values on an FLA base.
Refer to unbalance biasing for additional details.
• HCR represents the value of the
Hot/Cold Safe Stall Ratio
setpoint expressed as a
percentage.
If a
Hot/Cold Safe Stall Ratio
value of 100% is entered, the hot/cold biasing is defeated, and
unless RTD biasing is deployed, the thermal model will operate as if the motor was cold
prior to overload.
RTD biasing
The thermal model can operate based solely on measured current and the assumption of
rated ambient and normal motor cooling, as described earlier. However, if the ambient
temperature is unusually high, or motor cooling is blocked, the motor will have a non-
modeled temperature increase. The RTD biasing feature can correct for this by forcing the
Thermal Capacity Used register up to the value appropriate to the temperature of the
hottest stator RTD. Since RTDs are relatively slow, the rest of the thermal model is still
required during starting and heavy overload conditions when motor heating is relatively
fast. Thus the RTD bias feature does not prevent the thermal capacity used value from
rising above the value appropriate to the RTD temperature.
The value of the
Thermal Capacity Used register appropriate to the RTD temperature is
determined by the straight line segmented curve shown in the following figure. This curve
is characterized by minimum, center, and maximum temperature values, and by the hot/
cold ratio value.
NOTE
NOTE:
The RTD bias feature alone cannot create a trip. If the RTD bias forces thermal capacity
used to 100%, the motor current must be above FLA before an overload trip can occur.
Figure 5-28: RTD bias curve
853730A1.CDR
100%
80%
60%
40%
20%
0%
50 0 100 150 200
Hottest stator RTD temperature (°C)
100% - Hot/Cold Ratio Appr
opriate
thermal
capacity
used
R
T
D
Bia
s
-C
e
nt
e
rT
R
T
D
Bia
s
-
M
inimum
T
R
T
D
Bia
s
-
M
aximum
T