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Grounding Design Problems

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					Problems

   1. A factory in the Philippines has the following generator sets:




 Elements      X         X'd         X"d         Xo       Voltage      MVA   Remarks
               %          %           %          %

 G1                     18.00%       10.00%      3.50%     240.00 0.300

 G2                     18.00%       10.00%      3.50%     240.00 0.300

 G3                     25.00%       14.00%      5.80%     240.00 0.625




Design and/or specify the grounding reactor for each generator.

                                 Line to ground
  Gen       Voltage              voltage
                                 Computed Eq. 1-Eq.
            Ohmic Reactance      5
            Current Rating       Use Sequence Network
2.     Power Station in Riyadh

One-line Diagram




                                                                              Remark
 Elements                        X     X'd      X"d       Xo   Voltage MVA      s
                                 %      %        %        %
                                       25.40    12.70     6.50
 GT1 -GT4                                 %        %        % 13,800 29.600
                                       26.00    13.00     7.00
 GT5                                      %        %        % 13,800 10.000
 Transformers - will
 become load bus
                                                                              0.40
 SYN BUS Reactors                                               13,800        ohms
 Diesel generating sets are
 to be retired.


REQUIREMENTS:

If grounding reactors for gas turbine generators GT1 to GT5 will be used,
find the appropriate reactances. Diesel generating sets are to be retired.
3.           Following are loads of main distribution board (MDB):

                  Load                              MDB is 3-phase, 3-w +N +gnd, 220/127 v.
      Ckt.      Description
                                                           DP-1 is 3-ph;
      No.
                                                           DP-2 is connected at phase AN.
       1        DP-1: 250 KW, 0.8
                                                           DP-3 is connected at phase BN.
                p.f lag ., 3-ph., 220 v
                                                           DP-4 is connected at phase CN
       2        DP-2: 50 KW, unity
                p.f , 1-phase, 127 v
                                                           Capacitor is 3-ph
                DP-3: 250 KW,                              DP-5 is connected at phase BN
       3        0.85                                       DP-6 is 3-ph
                p.f lag , 1-phase,
                127 v
                DP-4: 200 KW,
       4        0.80
                p.f lag , 1-phase,
                127 v
                Capacitor: 3-ph, 220
       5        v
                Max KVAR:        125.00
                DP-5: 225 KW,
       6        0.80
                p.f lag , 3-phase,
                220 v


             Draw the vector diagram showing ,phase voltage & phase currents.
             Compute line currents, phase current, ground current.
             Specify the circuit breakers.


 4.          Describe and evaluate the existing grounding system in your work site.


5.           Discuss LVCB which have several function, including those with ground fault
             protection.

				
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