Xd- Direct-axis Synchronous Reactance the ratio of fundamental A.C. armature Voltage to A.C. armature current produced by the direct-axis flux. Xq- Quadrature-axis Synchronous Reactance the ratio of fundamental A.C. armature Voltage to A.C. armature current produced by the quadrature-axis flux.
What is direct and quadrature axis reactance?
In a salient-pole machine, xaq, the quadrature-axis reactance is smaller than xad, the direct-axis reactance, since the flux produced by a given current component in that axis is smaller as the reluctance of the magnetic path consists mostly of the interpolar spaces.
What is the advantage of keeping the value of direct axis reactance of a synchronous machine high?
A synchronous machine with a high value of SCR had a better voltage regulation and improved steady-state stability limit, but the short circuit fault current in the armature is high. It also affects the size and cost of the machine.
Why do we find determination of direct axis and quadrature axis reactance?
where Nph is the number of turns per phase of armature winding. In case of salient pole synchronous machine, the air gap is non-uniform. Therefore, Xd > Xq. But due to uniform air gap in cylindrical pole synchronous machine, both direct and quadrature axis synchronous reactance are equal i.e. Xd = Xq.
What is Q axis current?
In simpler terms, inductance is the flux linkage per unit current. The d axis, also known as the direct axis, is the axis by which flux is produced by the field winding. The q axis, or the quadrature axis is the axis on which torque is produced.
How do you calculate XD and XQ?
The method used to determine Xq and Xd, the direct and quadrature axis reactance is called slip test. Current induced in the damper winding of alternator will produce an appreciable error. Induced voltage in the open circuit field may reach dangerous values.
What is Sliptest?
Slip test is used to find the ratio of xd/xq , (that is the ratio of direct axis reactance to quadrature axis reactance). this is practically done by rotating the rotor of the alternator by an external prime mover (generally a dc motor) while rotor windings of the alternator are kept open.
Why the synchronous motor is not self starting?
Above a certain size, synchronous motors are not self-starting motors. This property is due to the inertia of the rotor; it cannot instantly follow the rotation of the magnetic field of the stator. Once the rotor nears the synchronous speed, the field winding is excited, and the motor pulls into synchronization.
What is V curve and inverted V curve?
What is V Curve and inverted v curve? The graphical representation of armature current Ia vs field current If is called V-curve since the final view looks like English letter V. At the same time the power factor vs field current is called inverted V-curve of a synchronous motor.
Why we use V and inverted V-curves?
Excitation can be increased by increasing the field current passing through the field winding of synchronous motor. Such curves obtained by plotting p.f. against If, at various load conditions are called Inverted V-curves of synchronous motor. These curves are shown in the Fig: 2.27 (b).
What is an inverted V curve?
The Inverted V Curve is a graph showing the relation of power factor as a function of field current.
Why do we use damper winding?
Damper windings helps the synchronous motor to start on its own (self starting machine) by providing starting torque. By providing damper windings in the rotor of synchronous motor “Hunting of machine”can be suppressed.
What is a damper winding?
: a short-circuited squirrel-cage winding placed in the pole faces and around the pole shoes of synchronous machines, the currents induced in the winding by the periodic variations in synchronous speed having the effect of a damper. — called also amortisseur.
Where are damper windings located?
Position of damper winding: Damper winding is placed in the slots at the surface of pole shoes in salient pole machines and in in non-salient pole machine it is placed in the same slots with magnetizing windings.
Why DC supply is used in synchronous motor?
for a synchronous motor we give balanced 3 phase supply to the stator which produces a rotating magnetic field.in order to produce torque we need another magnetic field which has to be relatively stationary with respect to the main field. this feild is produced on rotor winding by energising it with dc.
Why is excitation always DC?
The primary reason lies in the principle of operation of Synchronous machines. The rotor acts as an electromagnet with a constant flux and gets interlocked with the rotating flux of stator to provide a constant speed rotation. The rotor needs to have a constant flux and that’s why the dc excitation is provided.
Why does DC excitation is used rather than AC excitation?
In the alternator, as the rotor conductor changes its position as the rotor rotating so constant flux is to be produced in the rotor winding and it is possible only when the DC supply is given to the rotor winding. As we need constant flux that is why DC is used instead of AC for excitation of Synchronous Alternator.
What is the working principle of synchronous motor?
The principle of operation of a synchronous motor can be understood by considering the stator windings to be connected to a three-phase alternating-current supply. The effect of the stator current is to establish a magnetic field rotating at 120 f/p revolutions per minute for a frequency of f hertz and for p poles.
