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# DC Machine Characteristics Experiment

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### 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?

<p>To understand the behavior of the synchronous reactance under different loading conditions</p> Signup and view all the answers

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

<p>To determine the zero-power factor characteristics</p> Signup and view all the answers

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

<p>To make the results more meaningful and comparable</p> Signup and view all the answers

### What is the assumption while calculating the unsaturated synchronous reactance?

<p>Negligible armature resistance</p> Signup and view all the answers

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

<p>To increase the armature voltage by 25% above the rated value</p> Signup and view all the answers

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

<p>Ohms per phase</p> Signup and view all the answers

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

<p>It takes into account the effect of saturation</p> Signup and view all the answers

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

<p>It is equal to the corresponding excitation</p> Signup and view all the answers

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

<p>To measure the short-circuit characteristics</p> Signup and view all the answers

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

<p>To determine the various parameters of the alternator</p> Signup and view all the answers

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

<p>Terminal voltage against field excitation</p> Signup and view all the answers

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

<p>Rated armature current</p> Signup and view all the answers

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

<p>The alternator is driven at synchronous speed with a recommended value of armature current at zero power factor</p> Signup and view all the answers

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

<p>Synchronous reactance and armature leakage reactance</p> Signup and view all the answers

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

<p>It ensures the alternator operates at rated conditions</p> Signup and view all the answers

## 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.

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