Solution to bypass the ATV61

If you need variable speed only for starting and stopping, using ATS48 should save money compared to the ATV solution. It has to be checked.

It's clearly not possible to apply the mains supply voltage to the motor connections of the ATV.

It's mandatory to insulate the output of the ATV (downstream contactor) before closing the DOL contactor also named in this case "bypass contactor".

Remark: The bypass function is not included in the ATV61.

To bypass a drive the power sequence must be the following:

Set OPL=OAC or

OPL=no and select a freewheel stop.

To start:

- close the drive downstream contactor

- start the motor with the drive

- open the downstream contactor (drive isolation)

- wait the time necessary to demagnetize the motor

- close the bypass contactor.

- stop the drive

Tostop:

- open the bypass contactor.

- wait the time necessary to demagnetize the motor

- close the drive downstream contactor

- start the drive (it will catch on fly the motor)

- stop the drive for decelerating.

The drive output must never be connected to the main (risk of big damage)

Before bypassing you must respect a time in freewheel to wait the motor demagnetization (Tm) otherwise there would be an inrush current peak and a violent motor braking at bypass on the main.

Tm is equal to around 6 times the motor rotoric constant.

The rotoric constant is given by the formula:

- Tr = 1/(2*PI*Fs) * CosPhi / SinPhi

Where Fs is the slipping frequency in Hz

But if the application has a high inertia, the speed of the motor will not decrease to much between the time when the downstream contactor is opened and when the bypass contactor is closed. That should limit the motor overcurrent when the motor is connected directly to the line via the bypass contactor.

Tests are necessary to define the good value of the temporisation.

There are other problems:

- When the motor is demagnetized, at switching on the main it will absorb the starting current (4 to 6In). The duration of this current depends on the load

If the application has a strong resistant torque, during the demagnetizing delay, the speed decrease strongly and when you close the bypass there is long starting current necessary to reach the nominal speed again.

For upstream short circuit protection you must choose a breaker with a motor curve as for a direct starting on the main.

In some cases it could be necessary to add a tripping delay (depending on the inrush current value and shape).

I.e. add to a NS breaker an option STR53UE which allows to set the tripping current (up to 10In) and a delay up to 300mS.