Inverter-Generated Noises And Their Reduction Techniques - Mitsubishi Electric FR-D720S SC EC Instruction Manual

Electromagnetic compatibility (EMC)
3.7.2

Inverter-generated noises and their reduction techniques

Some noises enter the inverter to malfunction it and others are radiated by the inverter to mal-
function peripheral devices. Though the inverter is designed to be insusceptible to noises, it han-
dles low-level signals, so it requires the following basic techniques. Also, since the inverter
chops outputs at high carrier frequency, that could generate noises. If these noises cause pe-
ripheral devices to malfunction, measures should be taken to suppress noises.
These techniques differ slightly depending on noise propagation paths.
● Basic techniques
– Do not run the power cables (I/O cables) and signal cables of the inverter in parallel with
each other and do not bundle them.
– Use twisted pair shielded cables for the detector connection and control signal cables.
Earth the shield.
– Earth the inverter, motor, etc. at one point.
● Techniques to reduce noises that enter and malfunction the inverter
When devices that generate many noises (which use magnetic contactors, magnetic brakes,
many relays, for example) are installed near the inverter and the inverter may be malfunc-
tioned by noises, the following measures must be taken:
– Provide surge suppressors for devices that generate many noises to suppress noises.
– Fit data line filters to signal cables.
– Earth the shields of the detector connection and control signal cables with cable clamp
metal.
● Techniques to reduce noises that are radiated by the inverter to malfunction peripheral
devices
Inverter-generated noises are largely classified into:
– those radiated by the cables connected to the inverter and inverter main circuits (I/O),
– those electromagnetically and electrostatically induced to the signal cables of the
peripheral devices close to the main circuit power supply,
– and those transmitted through the power supply cables.
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