KSB PumpDrive 2 - Electrical Protection Device; Information on Electromagnetic Compatibility; Length of Motor Connection Cable

7 Installation at Site
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PumpDrive 2
Length of motor connection cable
If the frequency inverter is not mounted on the motor to be controlled, longer motor
connection cables may be required. The stray capacitance of the connection cables
may result in high-frequency discharge currents flowing to ground. The sum of the
discharge currents and motor current may exceed the output-side rated current of
the frequency inverter. This will activate the frequency inverter's protection
equipment and the motor will be stopped. The following motor connection cables
are recommended depending on the power range:
Table29: Length of motor connection cable
Power range
[kW]
Maximum cable length
[m]
Stray capacitance
[nF]
≤ 11 (Class B) 5 ≤ 5
≥ 15kW (class A, group 1) 50 ≤ 5
Output filter
Output filters can only be used in conjunction with an asynchronous motor.
If longer connection cables than those listed above are required or the connection
cable's stray capacitance value exceeds the above values, we recommend installing a
suitable output filter between the frequency inverter and the motor to be controlled.
These filters reduce the voltage ramp-up time of the frequency inverter output
voltages and limit their peaks.
7.4.2.2 Electrical protection device
Back-up fuses
Provide three fast-acting fuses in the mains power supply line to the frequency
inverter. The fuse size must be suitable for the nominal mains current supplied to the
frequency inverter.
Motor protection switch
Separate motor protection is not required because the frequency inverter has its own
safety devices (e.g. electronic overcurrent trip). Available motor protection switches
must be dimensioned in accordance with the nominal motor current.
Residual current device
If fixed connections and appropriate supplementary earthing are used (cf.
DINVDE0160), residual current devices (RCDs) are not mandatory for frequency
inverters.
If residual current devices are used, three-phase frequency inverters must in
accordance with DIN VDE 0160 be connected via universal AC/DC sensitive RCDs, as
potential direct-current components may cause standard AC sensitive RCDs to either
fail to respond or respond erroneously.
Table30: Residual current device to be selected
Size Rated current [mA]
A, B and C 150
D and E 300
If you use a long shielded cable for the mains/motor connection, the residual-current
monitoring device may be triggered by the discharge current that flows to earth
(triggered by the carrier frequency). Remedies: Replace the RCD (residual current
device) or lower the response limit.
7.4.2.3 Information on electromagnetic compatibility
Electromagnetic interference from other electrical devices can affect the frequency
inverter. Interference can also be emitted by the frequency inverter itself, however.
The interference emitted by the frequency inverter is generally conducted through
the motor connection cables. The following measures are proposed for RFI
suppression:
▪ Shielded motor connection cables for line lengths >70cm
(especially recommended for frequency inverters with low power ratings)
▪ Metal cable ducts made from a single piece with a minimum coverage of 80% (if
shielded connection cables cannot be used)
Installation at site/
environment
For more effective shielding, install the frequency inverter in a metal cabinet.