ZENER 8000-V Installation Manual
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IM00165
Electromagnetic Compatibility (EMC)
Installation practices and EMC
Electromagnetic compatibility covers a wide range of phenomena including emission and immunity to
harmonics, flicker, and conducted and radiated interference. The material presented in this section relates to
the conducted and radiated interference aspects of EMC.
Technical limits for emissions and immunity to interference are specified in a number of local and
international standards of which Australian Standard AS 61800 Adjustable speed electrical power drive
systems, Part 3: EMC requirements and specific test methods is typical.
Clause 6.6 Engineering practice provides a methodology for dealing with C4 category equipment such as ZENER
8000-V systems as well useful information on problems associated with applying the more usual kind of AC line
filter employed in low voltage appliances to power systems with isolated or impedance grounded
neutrals (IT
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network).
Practical resolution of interference issues usually centres around conducted rather than radiated issues and
especially paying close attention to the path of high frequency common mode currents around the installation.
In many instances, the use of screened power cables will be of assistance.
In the case of a drive system in an “IT” supply system environment (ie a system where fitting a large capacitance
between AC input and earth is not allowed) the principle benefits of a screened motor cable are:
Substantial reduction in the capacitive leakage current between the motor cable phase conductors and
nearby conductors such as cable trays, cable support hardware and other cables.
Reduction in the high frequency voltage appearing between the ends of the motor cable earth wire by
reducing the impedance of the earth connection between the inverter and motor. This reduces the
opportunity for high frequency currents to flow in incidental paths between inverter and motor.
Incidental paths may involve cables of other circuits or perhaps metal structures in the vicinity.
Screened power cables will generally have a higher stray capacitance between the phase conductors and the
earth/screen than an unscreened cable. This difference will usually quite small compared to the total stray
capacitance of the motor and cable together. The benefits of a screened motor cable will generally outweigh
this consideration.
Please note that this situation is significantly different to the case of “TN” supplied drive systems where
substantial capacitors are fitted between the AC input and earth as part of an EMC filter. This arrangement, in
conjunction with a properly installed screened motor cable, is very effective in isolating most of the capacitive
leakage current effects from other parts of the installation.
In order to achieve the best electrical performance from a screened motor cable at high frequencies, it is
essential that the screen of the cable has a 360° connection to both the gland plate of the metallic (typically
switchboard) enclosure containing the ZENER 8000-V and the motor terminal box. The correct type of metal
cable gland to suit the screened cable should be used. The protective earth (PE) conductor should be
terminated in the usual way to meet the local wiring codes.
Isolation switches wired between the ZENER 8000-V and the motor should be in a metallic enclosure with the
power cable screen properly terminated on both sides. Failure to properly terminate the screened power cable
(or alternative metal sheath) will result in a severe degradation of the screened cables performance at high
frequencies and increase the possibility of EMC problems. The screened motor cable should only contain the
phase and earth (PE) conductors of one inverter and the associated motor. Do not include other conductors
inside the screen.
