4.5.1 Protect the VFD and input power cable in short-circuit
Protect the VFD and input power cable during short-circuit to avoid thermal overload.
Carry out protective measures according to the following requirements.
Figure 4–16 Fuse configuration
Note: Select the fuse according to operation manual. During short-circuit, the fuse will protect input power cables to avoid damage to the VFD; when internal short-circuit occurred to the VFD, it can protect neighboring equipment from being damaged.
4.5.2 Protect the motor and motor cable in short circuit
If the motor cable is selected based on rated VFD current, the VFD will be able to protect the motor cable and motor during short circuit without other protective devices.
| If the VFD is connected to multiple motors, it is a must to use a separated thermal overload switch or breaker to protect the cable and motor, which may require the fuse to cut off the short circuit current. |
4.5.3 Protect motor and prevent thermal overload
According to the requirements, the motor must be protected to prevent thermal overload. Once overload is detected, users must cut off the current. The VFD is equipped with motor thermal overload protection function, which will block output and cut off the current (if necessary) to protect the motor.
4.5.4 Bypass connection
In some critical occasions, industrial frequency conversion circuit is necessary to ensure proper operation of the system when VFD fault occurs.
In some special cases, eg, only soft startup is needed, it will converts to power-frequency operation directly after soft startup, corresponding bypass link is also needed.
| Do not connect any power source to VFD output terminals U, V and W. The voltage applied to motor cable may cause permanent damage to the VFD. |
If frequent switch-over is needed, users can use the switch which carries mechanical interlock or a contactor to ensure motor terminals will not be connected to input power cables and VFD output ends simultaneously.