BK Precision 4011A Instrucciones de operaciones descargar pdf (Pagina 58)

Appendix B: Equipment and Instrument Circuits

201046

The next step is to relate line currents to phase current

a ab ac

c ca cb

I I I

 

Substituting in for the currents









   

* *

Re Re

ab ab ab ac

cb ca cb cb

W V I V I

 

Summing the wattmeter readings results in

















* * * *

1 2

Re Re Re Re

ab ab ab ac cb ca cb cb

W W V I V I V I V I

    

Since

* *

ac ca

I I

 

then

















* * *

1 2

Re Re Re

ab ab ab cb ac cb cb

W W V I V V I V I

    

Finally, noting that

ab cb ac

V V V

 













* * *

1 2

Re Re Re

ab ab ac ac cb cb ab ac cb

W W V I V I V I P P P

      

results in an expression that is the sum of the real power dissipated in each phase. A similar ar-

gument can be made for a wye-connected load.

As an example, calculate the expected reading of each wattmeter if the line-to-line voltage is

208 V for a balanced load and the load impedance Z = 8.0+j6.0 Ohms. The load impedance in

polar form is:

2 2

8 6 10

36.9

  

  

The phase ab current is given by

208 0

20.8 36.9

10 36.9

I A

 

     

 

and the phase a current is given by

3 30 36.0 66.9

a ab

I I

       

with a phase c current for a balanced load of

120 36.0 53.1

c a

I I

      

1 2 ... 53 54 55 56 57 58 59 60 61 62 63 ... 72 73

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BK Precision 4011A Instrucciones de operaciones Pagina 58

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