79
(2) Line-to-line leakage current
When the leakage current passes the distributed capacitance among output cables at the output end of the drive, its
high-order harmonics may cause misoperation of the external thermal relay. For the drive with small capacity (7.5 kW
and below) and long wires (over 50 m), the leakage current will increase, which makes misoperation more likely to
happen.
Suppression measures:
Lower the carrier frequency, but the motor noise will increase;
Install a reactor at the output end.
To reliably protect the motor, it is recommended to use a temperature sensor to monitor the motor temperature, and
use the overload protection function (electronic thermal relay) of the drive instead of the external thermal relay.
4.3.6 Proper EMC installation of drive
Partition principle
In the drive system formed by the drive and motor, the drive, control unit, and sensor are installed in the same cabinet.
The noise needs to be suppressed at the main connection points. Therefore, the radio noise filter and incoming reactor
shall be installed in the cabinet. The cabinet shall also meet the EMC requirements.
To isolate the noise source and noise receiver through physical space in the mechanical/system design stage is the most
effective but most expensive measure to reduce the interference. In the drive system formed by the drive and motor,
the noise source could be the drive, braking unit and contactor, and noise receiver could be the automation device,
encoder and sensor.
Different EMC areas are divided according to the electrical characteristics of the mechanical/system design. It is
recommended to install the device in the corresponding area as shown in Fig. 4-36.
To Next Page
Loading...
