## Questions and Answers

What is the purpose of increasing the field current in steps until the armature current exceeds the rated value by 25%?

To determine the open-circuit characteristics of the alternator

What is the significance of plotting the open-circuit, short-circuit, and zero-power factor characteristics on the same graph?

To compare the three characteristics and understand their relationships

What is the purpose of drawing the Potier-triangle?

To estimate the value of armature leakage reactance

What is the significance of determining the saturated and unsaturated values of the synchronous reactance at rated voltage?

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What is the purpose of increasing the inductance in steps and recording the corresponding values of field current and armature voltage?

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What is the significance of converting all measured quantities to per unit values?

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What is the assumption while calculating the unsaturated synchronous reactance?

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What is the purpose of increasing the field current in steps during the open-circuit test?

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What is the unit of unsaturated synchronous reactance Xs(ag) when calculated as Vt/Ia?

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What is the characteristic of the synchronous reactance Xs(sat)?

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What is the condition for the short-circuit current Ia on the S.C.C curve?

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What is the purpose of the short-circuit test as shown in Fig.2 (b)?

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What is the main objective of performing open-circuit, short-circuit, and zero power factor tests on an alternator?

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What is plotted in the open-circuit characteristic curve of an alternator?

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What is the base value used to plot the short-circuit characteristic curve of an alternator?

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What is the condition under which the zero power factor characteristic curve of an alternator is obtained?

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Which of the following can be determined from the open-circuit and short-circuit characteristics of an alternator?

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What is the significance of the synchronous speed in the open-circuit, short-circuit, and zero power factor tests on an alternator?

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## Study Notes

### Experiment Objectives

- To perform open-circuit, short-circuit, and zero power factor tests on an alternator (synchronous generator)
- To determine the various parameters of the alternator from the test results

### Experiment Procedure

- Increase field current in steps until armature current exceeds rated value by 25%, recording armature current and field current values at each step
- Connect circuit as shown in Fig.2(c) with armature winding connected to a variable inductance
- Adjust inductance to minimum value and increase field current until armature current reaches recommended value (5A), recording field current and armature voltage values
- Increase inductance value in steps, repeating field current increase and measurement
- Measure resistance of one phase of armature winding using a digital ohmmeter

### Result and Conclusion

- Convert measured quantities to per unit values and plot open-circuit, short-circuit, and zero-power factor characteristics on the same graph
- Determine saturated and unsaturated values of synchronous reactance at rated voltage from O.C.C and S.C.C
- Draw the Potier-triangle and estimate armature leakage reactance for two types of synchronous machines
- Comment on curve shapes and values obtained for all parameters

### Synchronous Reactance

- Unsaturated synchronous reactance (Xs(ag)) found from air-gap line of O.C.C and S.C.C, neglecting saturation
- Saturated synchronous reactance (Xs(sat)) found from O.C.C and S.C.C, taking into account saturation effects

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## Description

This quiz is based on an experiment to study the characteristics of a DC machine. It involves measuring armature current and field current, and adjusting inductance to achieve recommended values. Understand the principles and relationships between these electrical parameters.