Calculating "theta" Using Step Up Transformer

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SUMMARY

The discussion centers on calculating the angle theta in a step-up transformer scenario using the formula VI = P cos(theta). The user provided a primary voltage of 7.42V, a primary current of 0.41A, and a primary power of 3.2W, leading to confusion as the calculated apparent power (3.042 VA) is less than the actual power measured. Participants emphasized that the real power (P) must be less than or equal to the apparent power (VA), highlighting the importance of accurate power measurement methods in transformer applications.

PREREQUISITES
  • Understanding of electrical power formulas, specifically VI = P cos(theta)
  • Knowledge of step-up transformer operation and characteristics
  • Familiarity with measuring voltage, current, and power in AC circuits
  • Basic grasp of trigonometric functions related to power factor calculations
NEXT STEPS
  • Research methods for accurately measuring power in AC circuits
  • Learn about power factor and its implications in transformer efficiency
  • Study the principles of step-up transformers and their applications
  • Explore the use of phasor diagrams in analyzing AC circuits
USEFUL FOR

Electrical engineers, students studying power systems, and professionals working with transformers and AC circuits will benefit from this discussion.

Carolyn
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Hi, so I know that VI = P cos (theta), but during an experiment using a step up transformer,

I got the primary voltage 7.42V, primary current 0.41A, and primary power 3.2W. How then should I calculate the angle theta. I can't use arcosine, 'cause that will give me undefined.

Thanks a lot.
 
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Doesn't sound right. You have Power in Watts (3.2) higher than the VA figure (3.042)

And P = VI x Cos phi
 
How are you measuring the power? And the voltage and current, for that matter?

As Pumblechook said, P should be less than or equal to V*I=3.04 VA
 

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