Xd and Xq of Alternator | Slip Test

X_d AND X_q OF A SALIENT POLE SYNCHRONOUS MACHINE.

AIM: To find X_d and X_q of a salient pole synchronous machine by slip test.

APPARATUS: 3 F Auto transformer 1 No.

                                    Ammeter (0-10A) MI. 1 No.

                                    Voltmeter (0-300V) MI. 1No.

                                    rheostats (296 ohm/ 2.8A), (45 ohm/ 5A)

PROCEDURE:

1. Connections are made as per Circuit diagram.
2. Switch on DC supply and run the DC motor at a speed below t he synchronous speed of alternator.
3. Switch on AC supply and increase auto transformer out put to a suitable value note the variation in voltmeter and ammeter.
4. For another speed take the similar readings.
5. Adjust speed to get maximum oscillations in the ammeter and voltmeter.
6. Note maximum and minimum readings of voltmeter and ammeter.
7. Adjust the auto transformer output for a different value and take readings.
8. Vary the speed to a value greater than synchronous speed and repeat the Experiment.

Observations:

N(rpm)	Imin(amps	Imax(amps)	Vmax(volts)	Vmin(volts)	Xd(ohms)	Xq(ohms)	Xd/Xq

Precautions: Slip should be always be +/- 5%

Result:

THEORY (Determination of Xd & Xq – slip test)

            Direct  and quadrature axis reactances of a silent pole synchronous machine can be estimated by means of the test. The machine armature is connected to a 3-phase supply whose voltage is much less than the rated voltage of the machine. While the rotor is run at spee close to synchronous with the field winding fell open circuited. Since the excitation emf is zero, heavy current would be drawn by the armature, if connected to the r ated voltage supply.

            The currents drawn by armature set up an mmf wave rotating an synchronous speed. Since the rotor being run at a speed close to synchronous, the stator mmf moves slowly past the field poles at slip speed (Ns – N). When the stator mmf is alighned with the d-axis (field poles), flux f_j / pole is setup. So that effective reactance offered by the machine is Xd. Similarly when the stator mmf aligns with the q=axis, the flux set up is f_q/pole and the machine reactance is Xq. The current drawn by the armature therefore, varles cyclically at twice the slip frequency. The rmscurrent is minimum when machine reactance is Xd and is maximum when it is Xq. Because of cycle current variations and consequent voltage drop in the impedance of supply lines, the voltge at machine terminds also varies cyclically and has a mimimum value at maximum current and maximum value at mimimum current. The machine reactance can be found as

            Xd = (VE ( a1 Ia min) / (Ö3 Ia(min)

            Xq = (VE (at Ia max) / (Ö3 Ia (max)

For: Electrical Machines Lab Experiments Click below links

https://www.electricalforu.com/search/label/Machines%20lab

Parallel Operation of Alternator https://www.electricalforu.com/2020/03/parallel-operation-of-alternators.html

Parallel operation of Transformer https://www.electricalforu.com/2020/01/electrical-machines-lab-parallel.html

https://www.electricalforu.com/2020/01/electrical-machines-lab-oc-sc-test-on.html