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VFDs 2
- Thread starter Ripcord13
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Here is a little on the subject if there is still a question:
VFDs are not designed to supply the inrush current that occurs when a motor is energized by connection to a power source by connecting to a power source by energizing a starter or closing a disconnect switch. Most VFDs are designed to protect themselves and safely trip if this is done, but some manufacturer's still tend to recommend an interlock to prevent the VFD from starting until any motor contactor or disconnect switch has been closed.
Disconnect switches are often installed between VFDs and motors for use as safety lockout switches. Contactors may occasionally be used for a similar purpose. These devices would be intended to prevent starting and for emergency shutdown and would normally be closed before starting the VFD.
There may be some (very few) VFDs that can be damaged if the load is disconnected during operation and many will not operate properly without a load. Many VFDs will trip if the load is disconnected during operation and manufacturers tend to recommend against it.
It would require a very much oversized VFD to accommodate starting the VFD first and then starting a motor by connecting it to the VFD by closing a switch or contactor. As far as I know, there is no possible advantage to operating that way and it is never done. There are reasons for connecting many small motors to a large VFD and starting them one-at-a-time with motor starters. VFDs can be sized and configured to accommodate that type of operation.
VFDs are not designed to supply the inrush current that occurs when a motor is energized by connection to a power source by connecting to a power source by energizing a starter or closing a disconnect switch. Most VFDs are designed to protect themselves and safely trip if this is done, but some manufacturer's still tend to recommend an interlock to prevent the VFD from starting until any motor contactor or disconnect switch has been closed.
Disconnect switches are often installed between VFDs and motors for use as safety lockout switches. Contactors may occasionally be used for a similar purpose. These devices would be intended to prevent starting and for emergency shutdown and would normally be closed before starting the VFD.
There may be some (very few) VFDs that can be damaged if the load is disconnected during operation and many will not operate properly without a load. Many VFDs will trip if the load is disconnected during operation and manufacturers tend to recommend against it.
It would require a very much oversized VFD to accommodate starting the VFD first and then starting a motor by connecting it to the VFD by closing a switch or contactor. As far as I know, there is no possible advantage to operating that way and it is never done. There are reasons for connecting many small motors to a large VFD and starting them one-at-a-time with motor starters. VFDs can be sized and configured to accommodate that type of operation.
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- #5
LionelHutz
Electrical
You can install it between the VFD and the motor but interlock it so the VFD won't run with the contactor open. Most VFD's have a interlock circuit which cuts-off output power as soon as the circuit opens.
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