etetool.gif (3468 bytes)"Power Factor Improvement:"

 

When using power factor correction capacitors, the total KVAR on the load side of the motor controller should not exceed the value required to raise the no-load power factor to unity. Over correctiveness of this value may cause high transient voltages, currents, and torques that can increase safety hazards to personnel and possibly damage motor driven equipment.

Never connect power factor correction capacitors at motor terminals on elevator motors, plugging or jogging applications, multi-speed motors or open transition, wye-delta, auto-transformer starting and some part-winding start motors.

If possible, capacitors should be located at position 2 (see diagram). This does not change the current flowing through motor overload protectors. Connection of capacitors at position 3 requires a change of overload protectors. Capacitors should be located at position 1 for applications listed in paragraph 2 above. Be sure bus power factor is not increased above 95% under all loading conditions to avoid over excitation.

Diagram

pfdiagrm.jpg (22487 bytes)

Original
Power
Factor
Percent
Desired Power Factor Percent
100% 95% 90% 85% 80%
60% 1.333 1.004 0.849 0.713 0.583
62% 1.266 0.937 0.782 0.646 0.516
64% 1.201 0.872 0.717 0.581 0.451
66% 1.138 0.809 0.654 0.518 0.388
68% 1.078 0.749 0.594 0.458 0.328
70% 1.020 0.691 0.536 0.400 0.270
72% 0.964 0.635 0.480 0.344 0.214
74% 0.909 0.580 0.425 0.289 0.159
76% 0.855 0.526 0.371 0.235 0.105
78% 0.802 0.473 0.318 0.182 0.052
79% 0.776 0.447 0.292 0.156 0.026
80% 0.750 0.421 0.266 0.130  
81% 0.724 0.395 0.240 0.104  
82% 0.698 0.369 0.214 0.078  
83% 0.672 0.343 0.188 0.052  
84% 0.646 0.317 0.162 0.206  
85% 0.620 0.291 0.136    
86% 0.593 0.264 0.109    
87% 0.567 0.238 0.083    
89% 0.512 0.183 0.028    
90% 0.484 0.155      
91% 0.456 0.127      
92% 0.426 0.097      
93% 0.395 0.066      
94% 0.363 0.034      
95% 0.329   Assume Total plant load is 100 KW at 60% power factor. Capacitor KVAR rating necessary to improve power factor to 80% is found by multiplying KW (100) by the multiplier in table (0.583) which gives KVAR (58.3), nearest standard rating (60 KVAR) should be used.
96% 0.292  
97% 0.251  
99% 0.143  

If there is anything you would like to add or if you have any comments please feel free to email E.T.E. at http://www.elec-toolbox.com/email.htm.

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