04/19/23 1

Transformator Laboratory

04/19/23 2

Ideal transformer

• The winding resistance are negligibele• All fluxes are confined to the core i.e no

leakage flux• Core losses are asumed to be negligible• Permeability of the iron core is infinite

Im=0

04/19/23 3

Polarity

• The dot mark means that the currents entering these terminals produce fluxes in the same direction in the core. Common time varying flux linking both windings will induce a voltages in such a way that in any instance of time when terminal 1 is positive the terminal 3 will also be positive. Voltages e12 and e34 are in phase.

04/19/23 4

Practical transformer

• Leakage flux• Core losses

04/19/23 5

Equivalent circuit

04/19/23 6

Phase shift in a three phase transformer

• Phase shift can be achieved by connecting the secondary side in d-, y- or z connection.

• z-connection is achieved with the help of two identical windings on each leg of a transformer. One phase is achieved with the help of windings from two different legs.

• Phase shifts that can be achieved are even multiples of 30 degrees and that is why hour marks on a clock-face are used to indicate the phase shifts.

04/19/23 7

Different types of connections

04/19/23 8

Laboratory exercise

• Dy-, Yy-, Dz- and Ydy connection.• Rectified supply with a large inductance.• BH-curve shape.• Switch on of an unloaded transformer.

04/19/23 9

Dz10

• Practical connection.

• Phase diagram and schematic connection.