TFS · Practice Exam 1 · Problem 38PDFSolution in PDF ↓
TFS · Practice Exam 1 · Problem 38
Problem & Solution
Video Synthesis
- Problem: A 75KVA transformer with 99% efficiency is located in an electrical room at 70 degrees.
- Approach: So if you search the reference handbook for overall heat transfer coefficient, you will find the formula that I think by this point, you're likely to have become familiar with, but...
- Key values: 99 %, 60 %, 3 ft, 2 ft
- Reference: reference handbook
- Result: That gives us 2.84, B to U per hour foot squared degree F.
- ✅ Answer: C
Office Hours
1
Student questions asked in live office hours about this problem
OH 52
Q: Can you clarify what power factor is and how it's used in transformer problems?
A: Power factor is the ratio of real power (KW) to apparent power (KVA), defined as KW/KVA, which comes from the cosine of the phase angle in the power triangle. When power factor equals 1 (unity), all the power is real power with no reactive component; in this problem, that's what allowed us to directly convert the 100 KVA rating at 60% capacity into kilowatts to calculate heat generation.