Acoustic Noise; Du/Dt Conditions - GE AF-650 GP Design Manual

4.8.1 Acoustic Noise

The acoustic noise from the frequency converter comes from three sources:
1. DC intermediate circuit coils.
2. Integral fan.
3. RFI filter choke.
The typical values measured at a distance of 1 m from the unit:
Unit Size
12
13
15
21
22
31
32
41+43
42+44
51/52 *
51/52 **
* 250 kW, 380-480 VAC and 355-400 kW, 525-690 VAC only
** Remaining 51+52 power sizes.
*** For 4 and 5 sizes, reduced fan speed is at 87%.

4.9.1 du/dt Conditions

NB!
380-690V
To avoid premature ageing of motors (without phase insulation paper or other insulation reinforcement) not designed for frequency converter operation, GE
strongly recommend to fit a du/dt filter or a Sine-Wave filter on the output of the frequency converter.
When a transistor in the inverter bridge switches, the voltage across the motor increases by a du/dt ratio depending on:
- the motor cable (type, cross-section, length screened or unscreened)
- inductance
The natural induction causes an overshoot U
rise time and the peak voltage U affect the service life of the motor. If the peak voltage is too high, especially motors without phase coil insulation are affected.
PEAK
If the motor cable is short (a few metres), the rise time and peak voltage are lower.
If the motor cable is long (100 m), the rise time and peak voltage are higher.
Peak voltage on the motor terminals is caused by the switching of the IGBTs. The AF-650 GP complies with the demands of IEC 60034-25 regarding motors
designed to be controlled by frequency converters. The AF-650 GP also complies with IEC 60034-17 regarding Norm motors controlled by frequency converters
Measured values from lab tests:
AF-650 GP 230V 7.5 HP
Cable Mains
length [m] voltage [V]
5 240
50 240
100 240
150 240
AF-650 GP 230V 10 HP
Cable Mains
length [m] voltage [V]
36 240
136 240
150 240
At reduced fan speed (50%) [dBA] ***
51
51
54
61
58
52
55
74
73
73
82
78
in the motor voltage before it stabilises itself at a level depending on the voltage in the intermediate circuit. The
PEAK
Rise time
[μsec]
0.13
0.23
0.54
0.66
Rise time [μsec]
0.264
0.536
0.568
Full fan speed [dBA]
du/dt
Upeak
[kV] [kV/μsec]
0.510 3.090
2.034
0.580 0.865
0.560 0.674
Upeak
[kV] du/dt [kV/μsec]
0.624 1.890
0.596 0.889
0.568 0.800
AF-650 GP Design Guide
60
4
60
63
67
70
62
65
76
74
74
83
80
77