OVERVOLTAGE CAUSED BY WINDING TERMINAL ARRANGEMENT OF THREE PHASE TRANSFORMER

Usually both ends of a transformer winding are at the same side
of the magnetic core. With this arrangement there are automaticaly
the same number of the turns for each winding in both core windows
next to the middle leg of a three phase three leg core type transformer.
Contrary to this arrangement it is possible to put the two ends
of a winding at the different sides of the core. In this case the
same number of turns in 'the both core windows corresponding to the
windings on the middle leg does not exist. It means the amperturn of
the windings of the middle leg can not compensate each other in both
windows. If then the windings on the side legs be left free i.e. not
connected to a load or to a source, a strong magnetic flux flows
through both side legs, whichare in opposite direction to each others,
and an overvoltage would be induced in the windings on the side legs.
This can takplace during a shortcircuit, or through inrush current
or load.
In the paper above problem is discussed. The overvoltages caused
by this phenomena through a sudden one phase short circuit of a three
phase power transformer and the oscillation of the overvoltage caused
by saturation of the core are calculated and compared with the measurement.