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Chapter: Transmission and Distribution : Mechanical Design of Lines and Grounding

Important Short Questions and Answers: Mechanical Design of Lines and Grounding

Transmission and Distribution - Mechanical Design of Lines and Grounding - Important Short Questions and Answers: Mechanical Design of Lines and Grounding

129. Define sag of a line.


The difference in level between the points of supports and the lowest point of the conductor is called as sag.


130.Mention the factors that affect sag in the transmission line.


Weight of the conductor, length of the span , working tensile strength and the temperature.


131. What is the reason for the sag in the transmission line?


While erecting the line , if the conductors are stretched too much between supports then there prevails an excessive tension on the line which may break the conductor. In order to have safe tension in the conductor a sag in the line is allowed.


132. How the capacitance effect is taken into account in a long line?


They have sufficient length and operate at voltage higher than 100 kv the effects of capacitance cannot be neglected. Therefore in order to obtain reasonable accuracy in long lines , the capacitance effects are taken.


137. Mention the limitations of nominal T and pi methods in the line problems.


Generally the capacitance is uniformly distributed over the entire length of the line. But for easy calculations the capacitance is concentrated at one or two points .Due to these effects there are error in the calculations.


138. What are limitations of end condenser method.


There is considerable error in calculations because the distributed capacitance has been assumed to be lumped or concentrated. This method over estimates the effects of the line capacitance.


139. What is end condenser method?


It is a method used for obtaining the performance calculations of medium lines. Here the capacitance of the line is lumped or concentrated at the receiving end.


140. What is power circle diagram?


It is a diagram drawm for the transmission lines network involving the generalized circuit constants and the sending end and receiving end voltage.


141. What are the voltage regulating equipments used in transmission system?


Synchronous motors, tap changing transformers , series and shunt capacitors booster transformers , compound generators and induction regulator.


142.Mention the methods used for voltage control of lines


Tap changing auto- transformer, booster transformer , excitation control and induction regulator.


143.What is sending end power circle diagram?


The circle drawn with sending end true and reactive power as the horizontal and vertical co-ordinates are called sending end power circle diagram.


144.What is receiving end power circle diagram?

The circle drawn with receiving end values are called receiving end power circle diagram


145.Mention 2 significance of neutral grounding


the system voltage during the earth fault depends on neutral earthing.


is provided for the protection against arcing grounds , unbalanced voltages with respect to earth, protection from lightning.


146. What is neutral grounding.


Connecting the neutral or star point of any electrical equipment(generator ,transformer etc) to earth.


147. Define resonant frequency


is a reactance earthing with selected value of reactance to match with the line to ground capacitance.


is earthing through a reactance of such a value that power frequency current in neutral to ground connection is almost opposite to the power frequency capacitive current between un faulted line to earth.


148. Mention 2 disadvantages of ungrounded neutral occurrence of insulation breakdown leading to the heavy phase to phase fault condition.


system cannot be protected from earth fault.


voltages due to lightning surges do not find path to earth.


149. Mention two advantages of neutral grounding.


arcing grounds are eliminated.


voltages of healthy phases with respect to earth do not increase to 3^0.5 times with normal values.


150.       Name the various types of grounding.

solid grounding

resistance grounding

reactance grounding

resonant grounding


151.       Define screening coefficient.


Screening coefficient for ‘n’ electrodes in parallel is = (resistance of one electrode)/(resistance of n electrodes in parallel * n) substation


152.What is a substation.


The assembly of apparatus used to change some characteristic ( eg: voltage , A.C to D.C frequency power factor etc) of electric supply is called a substation.


153.Mention any two layouts of laying out a substation.

location should be at the center of the load should provide safe and reliable arrangement .


154.How substations are classified .

-according to service requirement constructional feature.


155. State the various types of substation according to its service requirements. transformer substation

switching substation

power factor correction substation

frequency changer substation

converting substation

industrial substation


156.List the types of substations classified according to its construction.


indoor substation


outdoor substation pole mounted substation


157.Mention any two comparisons between indoor and outdoor substations.


INDOOR: -space required and clearances between the conductors are less. -time required for erection and possibility of faults are more.


OUTDOOR: -space required and clearances between conductors are more. -time required for erection and possibility of faults are less.


158.List the various substation equipments.

Transformer , busbars , insulators , isolators , circuit breaker , relays , lightening arresters.


159.Define step potential.


It is the voltage between the feet of a person standing on the floor of the substation with 0.5m spacing between two feet during the flow of earth fault current through the earthing system.


160.Define touch potential.


It is the voltage between the fingers of raised hand touching the faulted structure and the feet of the person standing on the substation floor. the person should not get shocked even if the earth structure is carrying faulted current .i.e touch potential should be very very low.

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