What are the effects of change in field excitation on synchronous motor?

What are the effects of change in field excitation on synchronous motor?

If the field excitation is changed, back e.m.f Eb also changes. This results in the change of phase position of Ia w.r.t. V and synchronous motor for different values of field excitation. Note that extremities of current phasor Ia lie on the straight line AB. hence the power factor cos of the motor changes.

What will happen if we cut off the field circuit of the synchronous generator?

In case the field excitation of Generator is available when the steam supply to the turbine is cut off, the Synchronous Generator will draw power from the Grid and will behave as a Synchronous Motor rotating in the same direction.

What happens to the internal voltage of a synchronous motor when the load increases explain?

If the load on the motor increases, the torque angle α also increases (i.e., rotor poles lag behind the stator poles by a greater angle) but the motor continues to run at synchronous speed. The greater phase shift of back EMF Eb with respect to supply voltage V cause increases the net voltage Er in the stator winding.

What effect does varying the DC incitation have on the stator currents of a synchronous motor?

By varying the DC voltage applied to the rotor winding, it is possible to control the reactive power consumed by the motor. It is even possible to “over-excite” the motor in this fashion, making it create reactive power (leading power factor). This is a distinct advantage in applications involving a very large load.

What are the effect of loss of excitation?

When a generator loses its excitation, the rotor current gradually decreases and the field voltage decays by the field time constant as well. In this case, the generator operates as an induction generator and draws reactive power from the power system instead of generating reactive power.

Will increase in load the speed of synchronous motor?

Thus, if the load on a synchronous motor is increased the following points are considered which are given below. The motor continues to run at synchronous speed. The torque angle δ increases. The excitation voltage Ef remains constant.

What happens when motor load increases?

Assuming it is not being controlled at a constant speed, then really the same thing happens in all three cases. As the load is increased, the motor will slow down, and the torque will increase. Current into the motor will also increase. If the load is increased above the maximum, the motor may overheat after a while.

Will a synchronous motor run if the supply is DC?

The simple answer is if we give AC supply to the field winding of the synchronous motor then the magnetic locking between the stator field and rotor field will not be created. This was the reason Why DC is used not AC for excitation of Synchronous Motor.

How does a change of excitation affect its power factor?

A change in the excitation, thus, affects only the power factor of its output. This reduces the terminal voltage slightly, so let the excitation of the first alternator be increased so as to bring the terminal voltage back to its original value.

How to find the effect of field current on a synchronous motor?

To find the effect of field current variation on synchronous motor we study given below figure. First, we suppose that the motor is connected with inductive load (lagging P.F) so if we increase the field current (I F) it effect is drawn in a given figure.

How does an alternator affect a synchronous machine?

The resultant of these two voltages, E R will cause a synchronising current I sy. Thus the power delivered by the alternator, whose input power has been increased will increase by an amount equal to EI sy cos θ 1.

How does armature resistance affect a synchronous machine?

If there were no armature resistance, the synchronising current I sy would always be at 90° with respect to E and V. Thus variation in excitation will cause a large change in the reactive current supplied by the alternator, and because of armature resistance, there will be a slight change in the power that it receives or delivers to the bus.

How is a synchronous machine similar to a DC machine?

The equivalent circuit of the synchronous machine closely resembles the dc machine model used in Experiment 1. The key difference is the absence of commutator brushes, such that the armature voltage and current are ac. Also, the field winding is normally placed on the rotor with the armature winding on the stator.