The harmonic compensation currents proportional to the harmonic current in the primary winding, which is detected real-timely, are injected to the multiple secondary winding of the transformer.
Double step drum is an integral drum with stepwise flanges and double step sections. It allows the multiple layer rope winding in non-operating portion of luffing mechanism to make drum shorter.
Directing to the problem of ac double-drum single rope winding lifter working in multiple level without electric brake in middle level, put forward the reform plan.