Siemens Midimaster Eco Reference Manual page 109

ECO REFERENCE MANUAL
Parameter
2
The I t Motor Overload
•
Protection function protects
the motor against
overheating by monitoring
the motor's current and its
speed (heat is dissipated
from the motor by the
motor's internal cooling fan)
and calculating an estimate
of the motor's temperature.
2
This I t Motor Overload
Protection (P074) function
acts independently of the
Current Limit (P086)
function. The Current Limit
function acts quickly to
reduce the speed and
voltage (in order to try to
reduce the inverter load
current) in the event of a
current overload it will
generally act much faster
than the Motor I
Protection.
The Current Limit function
(P086) may reduce the
motor speed and current in
an attempt to prevent
inverter nuisance trips.
This may therefore prevent
or extend the time that it
takes to trip the inverter on
2
I t Motor Overload
Protection (even if P074=4,
5, 6 or 7).
Function Range
[default]
0 - 7
[1]
2
t
Description / Notes
Selects the most appropriate curve for the
motor de-rating at low frequencies due to
the reduced cooling effect of the shaft
mounted cooling fan.
CURRENT
P074 = P074 = P074 =
0/4 1/5 3/7
100%
50%
I
50% 100%
F F
I = Nominal motor current (P083)
N
F = Nominal motor frequency (P081)
N
I = Nominal motor current (P083)
N
F = Nominal motor frequency (P081)
N
0 = No de-rating. Suitable for motors with
separately powered cooling or no fan
cooling which dissipate the same
amount of heat regardless of speed.
1 = For 2 or 4-pole motors which generally
have better cooling due to their higher
speeds. The inverter assumes that the
motor can dissipate full power at • 50%
nominal frequency.
2 = Suitable for special motors not
continuously rated at nominal current at
nominal frequency..
3 = For 6 or 8-pole motors. The inverter
assumes that the motor can dissipate
full power at • nominal frequency.
4 = As P074 = 0 but the inverter trips
(F074) instead of reducing the motor
torque / speed.
5 = As P074 = 1 but the inverter trips
(F074) instead of reducing the motor
torque / speed.
6 = As P074 = 2 but the inverter trips
(F074) instead of reducing the motor
torque / speed.
7 = As P074 = 3 but the inverter trips
(F074) instead of reducing the motor
torque / speed.
P074 =
2/6
150% SPEED
F
13-19