help needed to solve two problems in electrical engineering!!!

- S
- Sadsack William
  
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posted
19 years ago

Sun, Sep 19, 2004 8:11 AM

hi,

I am an undergraduate student of engineering technology. I need help to solve the following

2 questions for an electrical engineering assignment. I am studying through correspondence while holding a full time job and don't have access to a library. The prescribed text does not help much. I did some research on the Internet and was able to solve two other questions relating to power factor correction but not these.

Can somebody help me to answer these questions?

Q1. Show with a the aid of a phasor diagram that for both star and delta connected loads the active power is (root 3 VI Cos phi) where V and I are line quantities.

Q2. A 200 KVA transformer has 800 turns on the primary and 160 turns on the secondary. the primary and secondary resistances are 0.3 ohms and 0.02 ohms, the corresponding leakage reactance are 1.1 ohm and 0.07 ohm respectively. If supply voltage is 2200V, calculate equivalent impedence referred to secondary and voltage regulation at

3/4 full load having a p.f of i) 0.85 lag and ii) 0.6 lead

Also, Are there other resources on the net to help people like me studying on their own? (in general, not limited to electrical engineering alone)

I will be very grateful to all who can help.

Thanks in advance,

Regards, Sadsack William

- B
- B J Conner
  
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Vote on answer
posted
19 years ago

Mon, Sep 20, 2004 12:50 AM

- D
- Don Kelly
  
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posted
19 years ago

Fri, Sep 24, 2004 4:21 AM

------------ For each - draw the phasor diagrams as suggested. Assume some phi between Vphase and I phase. draw and find Vline and Iline (how big are they compared to Vphase and Iphase)and determine the magnitude of their product (do for both Y and delta) with respect to the product of the phase values.

Note- avoid the error of assuming phi is the angle between line current and voltage. It is a phase quantity (and you don't actually need it to solve this problem)

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----------- You know the turns ratio: what is the impedance ratio in terms of the turns ratio? Use it to transfer primary Z to secondary or vice versa. For voltage regulation determine the magnitudes of the primary voltage and secondary voltage at the desired loads- Have you covered AC circuits -namely calculation of V1=V2+IZ ?.

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------------------ Lots of resources, and lots of texts off line. Try Schaum's Outline on Electric circuits What is your math background.? Try to tackle these problems yourself and I am willing to look at what you have done and provide help but I will not solve the problems for you -contact me directly if you wish.