06-02-2013, 03:32 PM
Construction of Circle Diagram
1Construction of Circle .pdf (Size: 207.82 KB / Downloads: 238)
Conduct No load test and blocked rotor test
on the induction motor and find out the per phase
values of no load current I0, short circuit current ISC
and the corresponding phase angles Φ0 and ΦSC.
Also find short circuit current ISN corresponding to
normal supply voltage. With this data, the circle
diagram can be drawn as follows.
1. With suitable scale, raw vector OA with
length corresponding to I0 at an angle Φ0 from
the vertical axis. Draw a horizontal line AB.
2. Draw OS equal to ISN at an angle ΦSC and join
AS.
3. Draw the perpendicular bisector to AS to meet
the horizontal line AB at C.
4. With C as centre, draw a portion of circle
passing through A and S. This forms the circle
diagram which is the locus of the input
current.
5. From point S, draw a vertical line SL to meet
the line AB.
6. Divide SL at point K so that SK : KL = rotor
resistance : stator resistance.
7. For a given operating point P, draw a vertical
line PEFGD as shown.
Efficiency line
1. The output line AS is extended backwards to
meet the X-axis at O′.
2. From any convenient point on the extended
output line, draw a horizontal line QT so as to
meet the vertical from O′. Divide the line QT
into 100 equal parts.
3. To find the efficiency corresponding to any
operating point P, draw a line from O′ to the
efficiency line through P to meet the
efficiency line at T1. Now QT1 is the
efficiency.
Slip Line
1. Draw line QR parallel to the torque line,
meeting the vertical through A at R. Divide
RQ into 100 equal parts.
2. To find the slip corresponding to any
operating point P, draw a line from A to the
slip line through P to meet the slip line at R1.
Now RR1 is the slip
Power Factor Curve
1. Draw a quadrant of a circle with O as centre
and any convenient radius. Divide OCm into
100 equal parts.
2. To find power factor corresponding to P,
extend the line OP to meet the power factor
curve at C′. Draw a horizontal line C′C1 to
meet the vertical axis at C1. Now OC1
represents power factor.