First PMA With Lackluster Results

[joestue]

I thought she was referencing the 2 phase proposal.

well the 2 phase proposal as drawn is one phase.

real 2 phase which is a 90 degree phase shift (per pole, so you divide by the number of poles to get physical degrees)

so anyhow any number of phases more than 1 is constant power unless you have an asymetrical phase shift. 2 phase motors and distribution systems did exist in the 1920's problem being you need 4 wires to distribute it. 3 wires and phases is easier.

[Adriaan Kragten]

I thought she was referencing the 2 phase proposal.

2-phase rectification for a normal 2-phase winding (so with 90° phase difference in between the phases) is explained in chapter 6 of report KD 340. The fluctuation of the current is given in figure 9 of KD 340. The fluctuation is much stronger than for 3-phase rectification. There are two highest values and two lowest values within 360° phase angle. So the frequency of the fluctuation is double the phase frequency. A 2-phase winding with 180° phase angle in between the phases gives the same fluctuation of the DC current as for a 1-phase current and this therefore gives a very much higher torque fluctuation than for a normal 2-phase winding.

There is a difference in between a 2-phase asynchronous motor used on a 2-phase grid and a normal 2-phase generator which is rectified. A 2-phase grid creates a rotating magnetic field with a constant strength in the stator and therefore there is no fluctuation of the torque. This is because both phases are used all the time. But for a 2-phase generator which is rectified, the diodes of the rectifier make that a current is flowing in one phase only during 75 % of the time. This sudden change of the current in the coils causes torque fluctuations.