Transformator Laboratory

1. Transformator Laboratory

2. Ideal transformer • The windingresistance 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

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.

4. Practical transformer • Leakage flux • Core losses

5. Equivalent circuit

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.

7. Different types of connections

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

9. Dz10 • Practical connection. • Phase diagram and schematic connection.