Installation And Selection Of Moulded Case Circuit Breaker; Handling Of Primary Side Magnetic Contactor; Handling Of The Secondary Side Magnetic Contactor; Thermal Relay Installation - Mitsubishi Electric FR-A700 Manual

Precautions for Peripheral Device Selection
Installation and selection of moulded
case circuit breaker
Install a moulded case circuit breaker (MCCB) on the power
receiving side to protect the wiring of the inverter input side. For
MCCB selection, refer to page 87 since it depends on the inverter
power supply side power factor (which changes depending on the
power supply voltage, output frequency and load). Especially for a
completely electromagnetic MCCB, one of a slightly large capacity
must be selected since its operation characteristic varies with
harmonic currents. (Check it in the data of the corresponding
breaker.) As an earth leakage current breaker, use the Mitsubishi
earth leakage current breaker designed for harmonics and surge
sppression. (Refer to page 88.)
When installing a moulded case circuit breaker on the output side of the
inverter, contact each manufacturer for selection of the moulded case
circuit breaker.
Handling of primary side magnetic
contactor
For operation via external terminal (terminal STF or STR used),
provide an input side MC to prevent an accident caused by a natural
restart at power recovery after a power failure, such as an
instantaneous power failure, and to ensure safety for maintenance
work. Do not use this magnetic contactor to make frequent starts and
stops. (The switching life of the inverter input circuit is about
1,000,000 times. ) For parameter unit operation, an automatic restart
after power failure is not made and the MC cannot be used to make a
start. Note that the primary side MC may be used to make a stop but
the regenerative brake specific to the inverter does not operate and
the motor is coasted to a stop.
Handling of the secondary side
magnetic contactor
Switch the magnetic contactor between the inverter and motor only
when both the inverter and motor are at a stop. When the magnetic
contactor is turned on while the inverter is operating, overcurrent
protection of the inverter and such will activate. When an MC is
provided to switch to a commercial power supply, for example, it is
recommended to use commercial power supply-inverter switchover
operation Pr.135 to Pr.139.

Thermal relay installation

The inverter has an electronic thermal relay function to protect the
motor from overheating. However, when running multiple motors
with one inverter or operating a multi-pole motor, provide a thermal
relay (OCR) between the inverter and motor. In this case, set the
electronic thermal relay function of the inverter to 0A. And for the
setting of the thermal relay, add the line-to line leakage current
(refer to page 92) to the current value on the motor rating plate.
For low-speed operation where the cooling capability of the motor
reduces, it is recommended to use a thermal protector or
thermistor-incorporated motor.
Measuring instrument on the output side
When the inverter-to-motor wiring length is large, especially in the
400V class, small-capacity models, the meters and CTs may
generate heat due to line-to-line leakage current.
choose the equipment which has enough allowance for the current
rating.
To measure and display the output voltage and output current of the
inverter, it is recommended to use the terminal AM-5 output
function of the inverter.
Disuse of power factor improving capacitor
(power capacitor)
The power factor improving capacitor and surge suppressor on the
inverter output side may be overheated or damaged by the
harmonic components of the inverter output. Also, since an
excessive current flows in the inverter to activate overcurrent
protection, do not install a capacitor or surge suppressor. For power
factor improvement, use a power factor improving DC reactor (see
page 80).
91
Wire thickness and wiring distance
When the wiring length between the inverter and motor is long, use
thick wires so that the voltage drop of the main circuit cable is 2% or
less especially at low frequency output. (A selection example for
the wiring distance of 20m is shown on page 87)
Especially at a long wiring distance, the maximum wiring length
should be within the length in the table below since the overcurrent
protection function may be misactivated by the influence of a
charging current due to the stray capacitances of the wiring.
(The overall wiring length for connection of multiple motors should
be within the value in the table below.)
Pr.72 PWM frequency selection
setting (carrier frequency)
2 or less
3 to 15
Use the recommended connection cable when installing the
operation panel away from the inverter unit or when connecting the
parameter unit.
For remote operation via analog signal, wire the control cable
between the operation box or operation signal and inverter within
30m and away from the power circuits (main circuit and relay
sequence circuit) to prevent induction from other devices.
When using the external potentiometer instead of the parameter
unit to set the frequency, use a shielded or twisted cable, and do
not earth (ground) the shield, but connect it to terminal 5 as shown
below.
(3)
(2)
(1)
Frequency setting
potentiometer
Earth (Ground)
When the inverter is run in the low acoustic noise mode, more
leakage currents occur than in the non-low acoustic noise mode
due to high-speed switching operation. Be sure to use the inverter
and motor after grounding (earthing) them. In addition, always use
the earth (ground) terminal of the inverter to earth (ground) the
inverter. (Do not use the case and chassis)
Noise
When performing low-noise operation at higher carrier frequency,
electromagnetic noise tends to increase. Therefore, refer to the
following measure example and consider taking the measures.
Depending on the installation condition, the inverter may be
affected by noise in a non-low noise (initial) status.
The noise level can be reduced by decreasing the carrier frequency
(Pr.72).
As measures against AM radio broadcasting noise and sensor
malfunction, turning on the built-in EMC filter produces an effect.
(For the switching method, refer to the instruction manual.)
As measures against induction noise from the power cable of the
inverter, providing a distance of 30cm (at least 10cm) or more and
using a twisted pair shielded cable as a signal cable produces an
effect. Do not earth (ground) shield but connect it to signal common
cable.
Therefore,
Example of noise reduction techniques
Inverter
power
supply
Separate inverter and
power line by more than
30cm (at least 10cm)
from sensor circuit.
Control
power
supply
Do not earth (ground)
enclosure directly.
Do not earth (ground) control cable.
0.4K 0.75K
300m 500m
200m 300m
Shielded cable
(3)
10 (10E)
(2)
2
(1)
5
Twisted cable
Frequency setting
potentiometer
Enclosure Decrease carrier frequency
FR-
EMC
Inverter
BLF
filter
Use 4-core cable for motor
power cable and use one cable
as earth (ground) cable.
Use a twisted pair shielded cable
Power
supply for
sensor
Do not earth (ground) shield but
connect it to signal common cable.
1.5K or
more
500m
500m
10 (10E)
2
5
Install filter (FR-BLF,
FR-BSF01) on
inverter output side.
Motor
IM
Sensor