pf (lagging) Efficiency (%) 110 100 90 80 70 60 50 40 30 20 10 0 0 10 20 30 40 50 60 70 80 90 100 110 Motor Loading (%) The relationship between % of full load for each motor and power factor (they are all the same) is given by the graph below: 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0 20 40 60 80 100 120 Motor Loading (%) и 27.9 kVRMS 400 VRMS M M M Motor 1 80 hp Motor 2 80 hp Motor 3 80 hp

Electricity for Refrigeration, Heating, and Air Conditioning (MindTap Course List)
10th Edition
ISBN:9781337399128
Author:Russell E. Smith
Publisher:Russell E. Smith
Chapter7: Alternating Current, Power Distribution, And Voltage Systems
Section: Chapter Questions
Problem 12RQ
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Question

Each motor is rated at 80 hp but is only loaded mechanically as follows: 
Motor # % Loading 
1               40 
2               50 
3               70 

The relationship between % of full load for each motor and efficiency (they are all 
the same) is given by the graph below: 

a) What is the minimum required transformer rating in kVA? 
b) By what percentage could the required transformer rating be reduced if a 
capacitor bank were installed in parallel with the motors, improving the power 
factor of the loadcentre to unity?

pf (lagging)
Efficiency (%)
110
100
90
80
70
60
50
40
30
20
10
0
0 10 20 30
40 50 60 70 80 90 100 110
Motor Loading (%)
The relationship between % of full load for each motor and power factor (they are
all the same) is given by the graph below:
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
20
40
60
80
100
120
Motor Loading (%)
Transcribed Image Text:pf (lagging) Efficiency (%) 110 100 90 80 70 60 50 40 30 20 10 0 0 10 20 30 40 50 60 70 80 90 100 110 Motor Loading (%) The relationship between % of full load for each motor and power factor (they are all the same) is given by the graph below: 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0 20 40 60 80 100 120 Motor Loading (%)
и
27.9 kVRMS
400 VRMS
M
M
M
Motor 1
80 hp
Motor 2
80 hp
Motor 3
80 hp
Transcribed Image Text:и 27.9 kVRMS 400 VRMS M M M Motor 1 80 hp Motor 2 80 hp Motor 3 80 hp
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