If after cell bypass, the drive has six cells operational in phase A, ve cells in phase B, and four
cells in phase C, then the maximum voltage that the drive can produce with neutral shift from
the above formula is 5.53 kV:
Vout_bypass = 7370 * (2 * 6 - 3) / (2 * 6) = 5.53 kV
With X = 1 + 2 = 3, because 2 cells in phase C and 1 cell in phase B are bypassed.
The ratio (Vout_bypass / Vout) is available as the maximum available drive voltage (%MAV) for
display on the keypad and for use in the comparator and analog output menus.
When a cell fails, the drive control uses this information to automatically calculate the phase
angles of cell voltages in order to maintain balanced motor voltages. During neutral shift, each
phase of the drive operates with a dierent power factor. Under lightly loaded conditions, one
or more phases may absorb real power while the other phase(s) are delivering power to the
motor.
An increase of the cell dc-voltage in the cells that are absorbing real power may cause a drive trip
condition. To prevent an increase of the cell dc-voltage in the cells, the control automatically
enables the energy saver function. Refer to Section Energy Saver for information associated with
this function.
Operating the Control
7.4 Cell Bypass
NXGPro+ Control Manual
Operating Manual, A5E50491925A 191
To Next Page
Loading...
