help3

Question

Answer 1

Step 1:

(3.1)

The open-circuit characteristics of a seperately-excited DC generator are given in a table.

Plot the open-circuit characteristics with the values in the table.

Graph:

Draw the coordinate plane.

Plot the points from the table.

Connect the points to a smooth curve.

The graph shows the open-circuit characteristics of a seperately-excited DC generator.

Step 2 :

(3.1.1)

Find the open-circuit voltage for a shunt-excited DC generator if the field circuit resistance is 8 ohms.

Draw a 8 ohms resistance line on open-circuit characteristics curve.

Consider the points (0, 0) and (1, 8) with a slope of 8.

Now draw a line connecting (0, 0) and (1, 8) on open-circuit characteristics curve.

Observe the graph:

The 8 ohm resistance line intersects the open-circuit characteristics curve at (2, 16).

Therefore the open-circuit voltage when the field circuit resistance 8 ohms is 16 V.

Step 3 :

(3.1.2)

Find the open-circuit voltage if the field circuit resistance is 8 ohms.

Draw a resistance line on open-circuit characteristics curve such that it is tangent line to the curve at origin.

Observe the graph:

The line resistance represents critical resistance line.

Critical resistance is the slope of the tangent line.

Slope of the tangent line is .

Therefore the critical resistance is 24 ohms.

Solution :

(3.1.1) The open-circuit voltage when the field circuit resistance 8 ohms is 16 V.

(3.1.2) The critical resistance is 24 ohms.

Answer 2

Step 1 :

The short-shunt compound generator supplies a load current of 50 A.

Shunt field resistance is 11 .

Armature resistance is 0.1 .

Field resistance is 0.2 .

Terminal voltage is 100 v.

Construct a circuit daigram of short-shunt compound generator with specifications.

EMF generated by the DC generator is , where .

Step 2 :

Calculate .

Armature current .

EMF generated by the DC generator is .

.

EMF generated by the DC generator is .

Solution :

EMF generated by the DC generator is .