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Wednesday, December 5, 2012

CHAPTER 9 USEFUL FORMULA




ACTIVE, REACTIVE AND APPARENT POWER

 

POWER FACTOR


If j is the phase angle between a current and the voltage causing it, then cos j is the power factor.  This, when multiplied by the product of the rms volts and amperes, gives the active power (P) in watts:


SWITCHING ON - ASYMMETRY


If an a.c. circuit is switched on at the worst possible instant so that the current is initially 100% asymmetrical, the first current peak may reach approximately 2.55 times the symmetrical rms value of the current to which it eventually settles.


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