4.5.1 Protecting the VFD and input power cable in short circuit
The VFD and input power cable can be protected during short-circuit to avoid thermal overload.
Carry out protective measures according to the following requirements.
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 Protecting the motor and motor cable in short circuit
If the motor cable is selected according to the VFD rated current, the VFD can perform short-circuit protection for the motor and motor cable, without the use of other protective devices.
| ² If the VFD is connected to multiple motors, an additional thermal overload switch or breaker must be used to protect the motor and motor cable. Such a device may use the fuse to cut off the short-circuit current. |
4.5.3 Protecting the motor from thermal overload
According to the requirements, the motor must be protected to prevent thermal overload. Once overload is detected, you 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 critical occasions, power-variable frequency conversion circuit is necessary to ensure proper operation of the system when VFD fault occurs. In some special cases, for example, only soft startup is needed, it will convert to power-frequency operation directly after soft startup, corresponding bypass link is also needed.
| ² Do not connect the power supply to the VFD output terminals U, V and W. The voltage applied to the motor cable may cause permanent damage to the VFD. |
If frequent switchover is needed, you can use the switch/contactor which carries mechanical interlock to ensure motor terminals are not connected to input power cables and VFD output ends simultaneously.