Electro-magnetic interference (EMI) and leakage currents
PRECAUTIONS FOR USE OF THE INVERTER
75
3
3.1.2
Precautions against inverter-generated EMI
Some electromagnetic noises enter the inverter or the converter unit to cause its malfunction, and others are radiated by the
inverter or the converter unit to cause the peripheral devices to malfunction. Though the inverter or the converter unit is
designed to have high immunity performance, it handles low-level signals, so it requires the following basic techniques. Also,
since the inverter chops outputs at high carrier frequency, that could generate electromagnetic noises. For prevention of
malfunction of peripheral devices caused by electromagnetic noises EMI precautions should be taken to suppress noises.
These techniques differ slightly depending on EMI paths.
• Basic techniques
- Do not run the power cables (I/O cables) and signal cables of the inverter or the converter unit in parallel with each other
and do not bundle them.
- Use shielded twisted pair cables for the detector connecting and control signal cables and connect the sheathes of the
shielded cables to terminal SD.
- Ground (Earth) the inverter or the converter unit, motor, etc. at one point.
• Techniques to reduce electromagnetic noises that enter and cause a malfunction of the inverter or the converter unit (EMI
countermeasures)
When devices that generate many electromagnetic noises (which use magnetic contactors, electromagnetic brakes, many
relays, for example) are installed near the inverter or the converter unit and it may malfunction due to electromagnetic
noises, the following countermeasures must be taken:
- Provide surge suppressors for devices that generate many electromagnetic noises to suppress electromagnetic noises.
- Install data line filters (
) to signal cables.
- Ground (Earth) the shields of the detector connection and control signal cables with cable clamp metal.
• Techniques to reduce electromagnetic noises that are radiated by the inverter or converter unit to cause the peripheral
devices to malfunction (EMI countermeasures)
Noises generated from the inverter or the converter unit are largely classified into those radiated by the cables connected to
the inverter or the converter unit and its 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.
Noise directly radiated
from the inverter or the
converter unit
Inverter generated
electromagnetic
noise
Air propagated
noise
Electrical path
propagated noise
Electromagnetic
induction noise
Electrostatic
induction noise
Path (c)
Path (b)
Path (a)
Path (h)
Path (g)
Path (d), (e)
Path (f)
Noise propagated through
power supply cable
Noise radiated from
power supply cable
Noise radiated from
motor connection cable
Noise from earthing
(grounding) cable due to
leakage current
M
(a)
(b)
(c)
(c)
(h)
(g)
(e)
(g)
(d)
(f)
Converter
unit
Inverter
(a)
Motor
Telephone
Sensor
Instrument
Receiver
Sensor
power supply
Summary of Contents for FR-A842-07700
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