Electrical Interview: FINDING OF TRANSMISSION LINE RATING

          When ever we see the transmission lines on road side,we will find the rating of transmission line very  easy.First we calculate how many insulators are used for that transmission lines.

                Number of insulator disks = operating voltage per phase/maximum voltage of each disk(11KV )

                      Operating voltage of line = number of insulator disks x maximum voltage of each disk(11kv)
         By using this formula we can find any transmission line rating.for example
                                 
                                                  LINE                   NUMBER OF DISKS
                                                   33   kv                          3  disks
                                                   132 kv                          8  disks
                                                   220 kv                        13  disks

Electrical Interview: RATING OF TRANSFORMER

 A typical name plate rating of a single phase electrical transformer is as follows: 20 KVA , 3300/220 V, 50 HZ. Here 20 KVA is the rated output at the secondary terminals. Note that the rated output is expressed in Kilo-volt-amperes (KVA) rather than in Kilowatts (KW). This is due to the fact that rated transformer output is limited by heating and hence by the losses in the transformer. 

                              

                                            

    

                                 The two types of losses in a transformer are core loss and ohmic losses. The core loss depends on  transformer voltage and ohmic loss on the transformer current. As these losses depend on transformer  voltage (V) and current (I) and are almost unaffected by the load power factor, the transformer rated output is expressed in VA or in KVA avd not in KW.                                                                                             

TRANSFORMER WORK AT DC VOLTAGE

                     when dc voltage is applied to the transformer a constant flux is induced in the transformer winding.that instant the secondary winding do't cut the flux at that time no induced emf in the secondary winding after some tine the transformer heated very high the transformer is damaged.

                             ANSWER: damaged