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5. SYSTEM PARAMETERS
Parameter
Function
P074 • • • •
I
t motor protection
2
P076 • • • •
Pulse frequency
© Siemens plc 1999
Range
Description / Notes
[Default]
0 - 7
Selects the most appropriate curve for the motor derating at low
[1]
frequencies due to the reduced cooling effect of the shaft mounted
cooling fan.
P074 =
0/4
100% I
N
50% I
N
0 = No derating. 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 50% 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.
Note: I
t motor protection is not recommended where the motor is less
2
than half the power rating of the inverter.
WARNING: Where motor thermal protection is required, an external
PTC must be used.
0 - 7
Sets the pulse frequency (from 2 to 16 kHz) and the PWM mode. If
[0 or 4]
silent operation is not absolutely necessary, the losses in the inverter
as well as the RFI emissions can be reduced by selecting lower pulse
frequencies.
0/1 = 16 kHz (230 V default)
2/3 = 8 kHz
4/5 = 4 kHz (400 V default)
6/7 = 2 kHz
Note:
When P076 = 0/1, the display of the current at frequencies
below 10 Hz is less accurate.
400V inverters require the continuous current rating reduced for
operation below 5Hz, when operating at switching frequencies greater
than 4kHz and with boost values greater than 100% (P078 + P079).
These are typically as follows:
33
P074 =
P074 =
1/5
3/7
50% F
100% F
N
N
I
= Nominal motor current (P083)
N
F
= Nominal motor frequency (P081)
N
English
P074 =
2/6
150% F
N
G85139-H1750-U049-C1
19/08/99
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