Neutral Point Shift During Bypass (U11) - Siemens SINAMICS PERFECT HARMONY GH180 Function Manual

Figure 7-2 Typical Power Cell with Bypass Contactor
Once the control detects that a cell has failed, it sends a command to close the appropriate
contactor. Closing the contactor simultaneously disconnects the cell output from the circuit and
connects the two adjacent cells together. These steps effectively take the failed cell out of the
circuit. The drive can then be restarted and operation can continue at reduced capacity.
These contactors are not rated to interrupt current. Therefore the drive remains in the idle state
after a trip, until the contactor is closed.
Activating this function
Any component failure within the cell that can be detected activates the mechanical bypass
function. Even a failure in the fiber optic link that communicates to the cell can be detected and
bypassed.
Note
Cell bypass limitations
Cell bypass is limited to allow no more than nine cells at a time to be in bypass. Attempting to
bypass more than 9 cells will result in a bypass fault.
7.4.4

Neutral Point Shift during Bypass (U11)

Neutral point shift ensures that line-to-line voltage remains the same. In a Perfect Harmony
drive, the cells in each phase are connected in series. Bypassing a failed cell has no effect on the
current capability of the drive but reduces the voltage capability.
As the required motor voltage is approximately proportional to speed, reduced voltage
capability will also reduce the required maximum speed. To ensure that the drive can fulfill the
application requirements, it is important to maximize the motor voltage available after one or
more cells have failed.
NXGPro+ Control Manual
Operating Manual, A5E50491925A
Operating the Control
7.4 Cell Bypass
185