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Chapter 2 Installation and Wiring
2 - 14
2.2.2 Wiring of the main circuit
(1) Wiring instructions
Before wiring, be sure to confirm that the Charge lamp on the inverter is off.
When the inverter power has been turned on once, a dangerous high voltage remains in the internal
capacitors for some time after power-off, regardless of whether the inverter has been operated.
When rewiring after power-off, always wait 10 minutes or more after power-off, and check with a
multimeter that the residual voltage across terminals P and N is zero to ensure safety during rewiring
work.
1) Main power input terminals (R, S, and T)
- Connect an earth-leakage breaker for circuit (wiring) protection between the power supply and
main power input terminals (R, S, and T).
- Use an earth-leakage breaker with a high rating of a high-frequency sensitive current to prevent
the breaker from malfunctioning under the influence of high frequency.
- When the protective function of the inverter operates, a fault or accident may occur in your system.
Therefore, you are recommended to connect a magnetic contactor that interrupts the power supply
to the inverter.
- Do not use the magnetic contactor connected to the power input terminal (primary side) or power
output terminal (secondary side) of the inverter to start or stop the inverter.
To start and stop inverter operation by external signals, use only the operation commands (FW and
RV signals) that are input via control circuit terminals.
- This inverter does not support a single-phase power supply but supports only a three-phase power
supply.
If you need to use a single-phase power input, contact your supplier or local Hitachi Distributor.
- Do not operate the inverter with an phase loss power input, or it may be damaged.
Since the factory setting of the inverter disables the phase loss input protection, the inverter will
revert to the following status if a phase of power supply input is interrupted:
R or T phase interrupted: The inverter does not operate.
S phase interrupted: The inverter reverts to single-phase operation, and may trip because of
insufficient voltage or overcurrent or be damaged.
Internal capacitors remain charged, even when the power input is under an phase loss condition.
Therefore, touching an internal part may result in electric shock and injury.
When rewiring the main circuit, follow the instructions given in Item (1), "Wiring instructions."
- Carefully note that the internal converter module of the inverter may be damaged if:
- the imbalance of power voltage is 3% or more,
- the power supply capacity is at least 10 times as high as the inverter capacity and 500 kVA or more,
or
- the power voltage changes rapidly.
Example: The above conditions may occur when multiple inverters are connected to each other
by a short bus line or your system includes a phase-advanced capacitor that is turned
on and off during operation.
- Do not turn the inverter power on and off more often than once every 3 minutes.
Otherwise, the inverter may be damaged.
2) Inverter output terminals (U, V, and W)
- Use a cable thicker than the specified applicable cable for the wiring of output terminals to prevent
the output voltage between the inverter and motor dropping. Especially at low frequency output, a
voltage drop due to cable will cause the motor torque to decrease.
- Do not connect a phase-advanced capacitor or surge absorber on the output side of the inverter. If
connected, the inverter may trip or the phase-advanced capacitor or surge absorber may be
damaged.
- If the cable length between the inverter and motor exceeds 20 m (especially in the case of 400 V
class models), the stray capacitance and inductance of the cable may cause a surge voltage at
motor terminals, resulting in a motor burnout.
A special filter to suppress the surge voltage is available. If you need this filter, contact your
supplier or local Hitachi Distributor.
- When connecting multiple motors to the inverter, connect a thermal relay to the inverter output
circuit for each motor.
- The RC rating of the thermal relay must be 1.1 times as high as the rated current of the motor. The
thermal relay may go off too early, depending on the cable length. If this occurs, connect an AC
reactor to the output of the inverter.