Example 8.11. Each line of a 3-phase system is suspended by a string of 3 indentical insulators of self-capacitance Cfarad. The shunt capacitance of connecting metal work of each insulator is 0.2 C to earth and 0-1 C to line. Calculate the string efficiency of the system if a guard ring increases the capacitance to the line of metal work of the lowest insulator to 0.3 C.

A string of 8 suspension insulators is to be fitted with a grading ring. If the pin to earth capacitances are all equal to C, find the values of line to pin capacitances that would give a uniform voltage distribution over the string.

Does r=e14r=0.788r, which comes in calculation of inductance, play a role in capacitance computations? Yes No

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Amagnetic field is being generated by a current of 2.0A flowing through 180 turns of wire on a core having a reluctance of 210000.0 At/Wb. Determine the flux of the circuit in mWb.

4. The value of a at OdegC of a conductor is 1/236 per °C. Find the value of a at 18degC.

Three phase Bridge rectifier operated from a 380V, 50Hz source throughout three-phase Y/Y connected transformer with ration 2:1. The load current has continuous character with negligible ripples and average thyristor current of 15A. The circuit inductance per phase is 1.2mH. The rectified voltage due to overlapping angle is 90 % of that voltage when this angle is neglected. 1- How much will the voltage drop be due to circuit inductance * 2- How much will the dc average voltage Vdc(alpha) be. 3- How much will the firing angle be ? 4- The overlapping angle. 5- How much is the percentage change of the output dc power if the thyristors T2, T4 and T6 are replaced by three diodes D2, D4, D6. 6- How much will be the maximum RMS phase current for the mentioned in previous task circuit ( semi-converter). 7- If an additional of 1 mH inductances are added to the existing inductances in the phases , how much will the overlapping angle be. The dc load current is kept constant & the…

Q.4/ choose true or false: 1. The reluctance of any core is proportional directly with the length of it and inversely with both the permeability and the cross-section area of it. 2. The number of parallel paths in wave windings is equal to twice of the number of poles. 3. In dc machines with same values of Z, N, Ø, the emf for wave winding type is more than emf of lab winding type. 4. If we insert a current in such a conductor subjected to a constant magnetic field, a movement will achieved giving the principle of electric generator.