EHV POWER TRANSMISSION Unit: 1 – INTRODUCTION TWO MARKS with answer

EHV POWER TRANSMISSION

Unit: 1 – INTRODUCTION

1.    What is meant by extra high voltage?

        The voltage above 230kV is nothing but a high voltage or The voltage range between 300kV to 735 kV is known as Extra High Voltage

2.    Write the nominal system voltages in kV?

                        132,220,275,345,400,500,750

3.    Write the maximum operating voltages in kV?

                145,245,300,362,420,525,765

4.    Of the following transmission voltages (given in kV) used in the world, which ones are used in India at present: 66, 132, 169, 220, 275, 345, 400, 500–525, 735–765, 1000, 1150.

5.    Distinguish between nominal system voltages and maximum operating voltages?

Nominal system voltages in kV	maximum operating voltages in kV
132	145
220	245
275	300
345	362
400	420
500	525
750	765

6.    What are the factors on which the power that can be transmitted through an EHV line depends?

a)     The   magnitude of voltage at the ends (E_s, E_r)

b)    Phase difference  

c)    The total positive sequence reactance  X per phase

7.    Write the power transmission equation?

                                                                     

8.    What is meant by power handling capacity?

                     MW

9.    Write the current equation of the transmission power?

                          

10.                       Define %power loss?

                           The percentage power loss is

                

11.                       Calculate the %power loss of 750 kV?

The percentage power loss is

r= 0.0136

x= 0.272

                               =2.5

12.                       Calculate the PHC of 1000 kV and 800 KM distance transmission line?

L=800

X=0.231

                      

          = 3000MW

13.                       What are the transmission line equipments?

·        Transmission line

·       Switchyards

·       Shunt Reactors

·       Shunt Capacitors

·       Synchronous Condensers

14.                       State the cost of 400kV AC transformer?

   400/220 kV Autotransformers

Rs. 3.7 Lakhs/MVA for 200 MVA 3-phase unit   to

Rs. 3 Lakhs/MVA for 500 MVA 3-phase unit

400 kV/13.8 kV Generator Transformers

Rs. 2 Lakhs/MVA for 250 MVA 3-phase unit      to

Rs. 1.5 Lakh/MVA for 550 MVA 3-phase unit.

15.                       Define the cost of shunt capacitor?

                   Rs. 1 Lakh/MVA

16.                       What are the mechanical considerations of   line performance?

·       Aeolian Vibration

·       Galloping

·       Wake-Induced Oscillation

·       Dampers and Spacers

17.                       Distinguish between vibrations and oscillations?

18.                       What are the factors depends upon the vibrations?

a)    conductor tension

b)   span length

c)    conductor size

d)   type of conductor

e)    terrain of line

19.                       What are the types of vibration?

a)    Aeolian Vibration

b)   Galloping

c)    Wake-Induced Oscillations

20.                       What is meant by Aeolian Vibration?

            When a conductor is under tension and a comparatively steady wind blows across it, small vortices are formed on the leeward side called Karman Vortices (which were first observed on aircraft wings). These vortices detach themselves and when they do alternately from the top

and bottom they cause a minute vertical force on the conductor. The frequency of the forces is

given by the accepted formula

                          F = 2.065 v/d, Hz

21.                       Define Galloping

                     Galloping of a conductor is a very high amplitude, low-frequency type of conductor motion and occurs mainly in areas of relatively flat terrain under freezing rain and icing of conductors. The flat terrain provides winds that are uniform and of a low turbulence.

22.                       State Wake-Induced Oscillations

                    The wake-induced oscillation is peculiar to a bundle conductor, and similar to aeolian vibration and galloping occurring principally in flat terrain with winds of steady velocity and low turbulence. The frequency of the oscillation does not exceed 3 Hz but may be of sufficient amplitude to cause clashing of adjacent sub-conductors, which are separated by about 50 cm

23.                       What is a damper?

                      When the wind energy imparted to the conductor achieves a balance with the energy dissipated by the vibrating conductor, steady amplitudes for the oscillations occur. A damping device helps to achieve this balance at smaller amplitudes of aeolian vibrations than an undamped conductor

24.                       What is meant by spacer?

                       Most modern spacers have some flexibility built into them to allow rotation of the conductor inside them such as lining the clamps with high-strength plastic or rubber washers. Some spacers are specially designed to act as dampers and may also take the form of heavy springs. The selection of the spacers is also determined by the wind speed in the locality