1 2 3 5 5 6 7 8 9 10 61 3. PRECAUTIONS FOR USE OF THE INVERTER 3.6 Checklist before starting operation Checkpoint Countermeasure Refer to page Check by user When using the electronic bypass operation, electrical and mechanical interlocks are provided between the electronic bypass contactors MC1 and MC2. When using a switching circuit as shown below, chattering due to misconfigured sequence or arc generated at switching may allow undesirable current to flow in and damage the inverter. Miswiring may also damage the inverter.
MC1 Interlock Power R/L1 U supply IM S/L2 V MC2 T/L3 W Undesirable current Inverter If switching to the commercial power supply operation while a failure such as an output short circuit has occurred between the magnetic contactor MC2 and the motor, the damage may further spread. If a failure has occurred between the MC2 and the motor, a protection circuit such as using the OH signal input must be provided. — A countermeasure is provided for power restoration after a power failure. If the machine must not be restarted when power is restored after a power failure, provide an MC in the inverter's input side and also make up a sequence which will not switch ON the start signal.
If the start signal (start switch) remains ON after a power failure, the inverter will automatically restart as soon as the power is restored. — A magnetic contactor (MC) is installed on the inverter's input side. On the inverter's input side, connect an MC for the following purposes: • To disconnect the inverter from the power supply at activation of a protective function or at malfunctioning of the driving system (emergency stop, etc.). • To prevent any accident due to an automatic restart at power restoration after an inverter stop made by a power failure. • To separate the inverter from the power supply to ensure safe maintenance and inspection work.
To use an MC to perform an emergency stop during operation, select the MC by applying the inverter's input-side current to the rated current specified in the JEM 1038-AC-3 class. 58 The magnetic contactor on the inverter's output side is properly handled. Switch the magnetic contactor between the inverter and motor only when both the inverter and motor are at a stop. 58 An EMI countermeasure is provided for the frequency setting signals. If electromagnetic noise generated from the inverter causes the frequency setting signal to fluctuate and the motor rotation speed to be unstable when changing the motor speed with analog signals, the following countermeasures are effective:
• Do not run the signal cables and power cables (inverter I/O cables) in parallel with each other and do not bundle them. • Run the signal cables as far away as possible from the power cables (inverter I/O cables). • Use shielded cables. • Install a data line filter to signal cable (example: ZCAT3035-1330 by TDK). 50 A countermeasure is provided for an overload operation. When performing frequent starts/stops by the inverter, rise/fall in the temperature of the transistor element of the inverter will repeat due to a repeated flow of large current, shortening the life from thermal fatigue.
Since thermal fatigue is related to the amount of current, the life can be increased by reducing current at locked condition, starting current, etc. Reducing current may extend the service life but may also cause torque shortage, which leads to a start failure. Adding a margin to the current can eliminate such a condition. For an induction motor, use an inverter of a higher capacity (up to two ranks). — The specifications and rating match the system requirements. Make sure that the specifications and rating match the system requirements. 238 Countermeasures are taken against electrical corrosion on the motor bearing.
When a motor is driven by the inverter, axial voltage is generated on the motor shaft, which may cause electrical corrosion of the bearing in rare cases depending on the wiring, load, operating conditions of the motor or specific inverter settings (high carrier frequency, use of a capacitive filter*1). The following shows examples of countermeasures for the inverter. • Decrease the carrier frequency. • Remove the capacitive filter. • Provide a common mode choke*2 on the output side of the inverter. (This is effective regardless of the use of the capacitive filter.) *1 Mitsubishi Electric capacitive filter: FR-BIF, SF[], FR-E5NF-[], FR- S5NFSA[] *2 Recommended common mode choke:
FT-3KM F series FINEMET® common mode choke cores manufactured by Hitachi Metals, Ltd. FINEMET is a registered trademark of Hitachi Metals, Ltd. —