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Powerdrive F300 User Guide 87
Issue Number: 2
Table 4-17 Maximum motor cable lengths (575 V drives)
Table 4-18 Maximum motor cable lengths (690 V drives)
4.8.2 High-capacitance / reduced diameter cables
The maximum cable length is reduced from that shown in Section
4.8.1 Cable types and lengths if high capacitance or reduced diameter
motor cables are used.For further information, refer to section
4.8.2 High-capacitance / reduced diameter cables on page 87.
Most cables have an insulating jacket between the cores and the armor
or shield; these cables have a low capacitance and are recommended.
Cables that do not have an insulating jacket tend to have high
capacitance; if a cable of this type is used, the maximum cable length is
half that quoted in the tables, (Figure 4-20 shows how to identify the two
types).
Figure 4-20 Cable construction influencing the capacitance
The maximum motor cable lengths specified in Section 4.8.1 Cable
types and lengths is shielded and contains four cores. Typical
capacitance for this type of cable is 130 pF/m (i.e. from one core to all
others and the shield connected together).
4.8.3 Motor winding voltage
The PWM output voltage can adversely affect the inter-turn insulation in
the motor. This is because of the high rate of change of voltage, in
conjunction with the impedance of the motor cable and the distributed
nature of the motor winding.
For normal operation with AC supplies up to 500 Vac and a standard
motor with a good quality insulation system, there is no need for any
special precautions. In case of doubt the motor supplier should be
consulted. Special precautions are recommended under the following
conditions, but only if the motor cable length exceeds 10 m:
• AC supply voltage exceeds 500 V
• DC supply voltage exceeds 670 V
• Operation of 400 V drive with continuous or very frequent sustained
braking
• Multiple motors connected to a single drive
For multiple motors, the precautions given in section 4.8.4 Multiple
motors on page 87 should be followed.
For the other cases listed, it is recommended that an inverter-rated
motor be used taking into account the voltage rating of the inverter. This
has a reinforced insulation system intended by the manufacturer for
repetitive fast-rising pulsed voltage operation.
Users of 575 V NEMA rated motors should note that the specification for
inverter-rated motors given in NEMA MG1 section 31 is sufficient for
motoring operation but not where the motor spends significant periods
braking. In that case an insulation peak voltage rating of 2.2 kV is
recommended.
If it is not practical to use an inverter-rated motor, an output choke
(inductor) should be used. The recommended type is a simple iron-cored
component with a reactance of about 2 %. The exact value is not critical.
This operates in conjunction with the capacitance of the motor cable to
increase the rise-time of the motor terminal voltage and prevent
excessive electrical stress.
4.8.4 Multiple motors
Open-loop only
If the drive is to control more than one motor, one of the fixed V/F modes
should be selected (Pr 05.014 = Fixed or Squared). Make the motor
connections as shown in Figure 4-21 and Figure 4-22. The maximum
motor cable lengths specified in section 4.8.1 Cable types and lengths
on page 86 apply to the sum of the total cable lengths from the drive to
each motor.
It is recommended that each motor is connected through a protection relay
since the drive cannot protect each motor individually. For
connection, a
sinusoidal filter or an output inductor must be connected as shown in
Figure 4-22, even when the cable lengths are less than the maximum
permissible. For details of inductor sizes refer to the supplier of the drive.
575 V Nominal AC supply voltage
Model
Maximum permissible motor cable length for each of
the following switching frequencies
2
kHz
3
kHz
4
kHz
6
kHz
8
kHz
12
kHz
16
kHz
05500039
200 m
(660 ft)
05500061
05500100
06500120
300 m
(984 ft)
200 m
(660 ft)
150 m
(490 ft)
100 m
(330 ft)
75 m
(245 ft)
50 m
(165 ft)
06500170
06500220
06500270
06500340
06500430
07500530
200 m
(660 ft)
07500730
08500860
250 m (820 ft)
08501080
09501250
250 m (820 ft)
09501500
10502000
250 m (820 ft)
11502480
250 m (820 ft)
11502880
11503150
690 V Nominal AC supply voltage
Model
Maximum permissible motor cable length for each of
the following switching frequencies
2
kHz
3
kHz
4
kHz
6
kHz
8
kHz
12
kHz
16
kHz
07600230
250 m
(820 ft)
185 m
(607 ft)
125 m
(410 ft)
90 m
(295 ft)
07600300
07600360
07600460
07600520
07600730
08600860
250 m
(820 ft)
185 m
(607 ft)
125 m
(410 ft)
90 m
(295 ft)
08601080
09601250
250 m
(820 ft)
09601550
10601720
250 m
(820 ft)10601970
11602250
250 m
(820 ft)
11602750
11603050
Normal capacitance
Shield or armour
separated from the cores
High capacitance
Shield or armour close
to the cores
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