Question

What is a per-unit systerm? Describe the relationship between torque and electromagnetic field(s). (You may use a generator or a motor as an example.) Describe a three phase machine

Answer 1

Quiz 11.
Per unit system is ratio of the primary / actual value in any unit and the reference value in the same unit. WE can say that per unit is a scale to measure or analyze an electrical network system easily, because quantities expressed as per-unit do not change when they are referred from one side of a transformer to other.

The voltage, current, impedance and the other power analysis measurement can be transformed into per unit system.

E.g:  V_pu = (V_pri / V_base)

_Ipu = (I_pri / I_base) etc.

Quiz 9.

There are two types of torques developed in electro-mechanical devices (like generator or motors), first one is caused by the interaction of the fields produced by the currents in two windings which may move relative to each other, which is called induced torque. and the second one is called reluctance torque, caused by the current in only one winding and mostly is due to the change of flux in the winding.

Induced torque:

2. Aoas 2 aie gap To dal egyn 2. aue ap Maha 아- 2. 41 心:

12 3 乙 12.

This is the relation between torque and electromagnetic field in a electrical machine.

quiz 7.

A three phase machine is a system which has three Alternating supply voltages displaced in phase relative to each other with a phase difference of 2$\pi$/3.
In a symmetrical three phase machine the each voltage is of the same magnitude and frequency and is displaced by and equal amount which is known as phase difference.