@Dinesh Kumar ji: As DSP Anirudh Sir said in earlier in his blog. When the ALCO starts to chugging and when it reaches the 30kmph speed there will be switching of series-parallel combination circuit to Parallel circuit. So during that time all the traction motor current goes to zero so momentumly there will be jerking. So LP and ALP will do nothing it is automatic machine process. After switching to Parallel circuit the ALCO starts to chug again.
@DSP Anirudh sir: Am I wrong in my explanation. If wrong please correct me sir.