BASIC OF TRANSMISSION AND DISTRUBUTION SYSTEM

WHAT IS MEAN BY CORONA?

•         Corona is a self-electrical discharge of atmosphere air
•         If the operating voltage of the transmission line is more than dielectric strength        of atmosphere air then the air molecules are ionized conducting path is created        between the conductors, ozone gas is released if corona occurs.
•     And also produce some violet glow 

SKIN EFFECT

Accumulation of current on the surface of conductor is called skin effect due to skin effect effective area of current flowing path is reduced which causes Rac>Rdc

SKIN EFFECT DEPENDS ON :-

•         Frequency

•         Conductivity

•         Relative permeability

•         Size of the conductor

•         Skin depth 

PROXIMITY EFFECT

•         It occurs due to current flowing in mutual conductor reduces non uniform flux linkages so that effect area of current flowing path is reduced which causes Rac>Rdc.
•         Proximity effect depend on frequency, conductivity, permeability and distance between the conductors.
•         In case of power cable distance between the conductors is smaller so that proximity effect is higher in case of overhead distance is lager so that proximity effect is negligible.

FERRANTI EFFECT

•         In electrical engineering the Ferranti effect is an increase in voltage occurring at the receiving end of the transmission line above the voltage at the sending end.

•         this occurs when the line is energized but there is a very light load or the load is disconnected.

•          the capacitor line charging current produced a voltage drop across the line inductance that is in phase with the sending end voltage.

•         assuming negligible line resistance.

•         Therefore, both line inductance and capacitance are responsible for this phenomenon.

LIGHTNING ARRESTER

•         It is the electrical equipment which protect the system like transmission, distribution and substation transient of voltage and current which produce due to the lightning stroke.

•         Lighting arrester made of metal oxides like zine oxide, silicon carb

•         It provides high resistance for normal voltage and low resistance for lightening surge.

•         It has impulse ratio of unity.

 WHAT IS RING MAIN UNIT?

•         In an electrical power distribution system, RMU is a switchgear unit, RMU used at the load connection points of ring-type distribution network.

•         It includes in one unit two switches that can connect the load to either or both main conductors, and a circuit breaker that feed a distribution transformer.

•         We can connect two or more supply to load with the help of RMU.

•         it installs at load or section point.

•         In RMU one supply is at standby mode and other supply the load.

There are two type of RMU: -

1.     Indoor RMU

2.     Outdoor RMU

3.     way type RMU: -

a.     3way RMU: -

In this type of RMU, it contains two isolator and one circuit breaker.

b.     4way RMU: -

In this type of RMU, it contains two isolator and two circuit breakers.

 working of RMU :-

in above fig.a  we can see that 3way RMU .where supply is coming from two cable .but both connection are isolated . now we connect the one supply to transformer through isolator and circuit breaker and other connected to standby ,which is shown in fig.b

if any fault occurs in cable no 2 then we disconnect  it and connect supply to the load with cable no 1.in this way can maintain the re-ability system with help of RMU system. 

WHAT IS MEAN BY VOLLAGE GRADIENT/POTENTIAL GRADIENT AND ALSO TOUCH POTENTIAL ,STEP POTENTIAL

POTENTIAL GRADIENT/VOLTAGE GRADIENT:-

Change in voltage/ potential with respect to the distance under line to ground fault  called as voltage /potential gradient.

STEP POTENTIAL:-

Under the line to ground fault condition if any person come in that area then the current flow from his step or legs then it is called as step potential

TOUCH POTENIAL:-

Under the  same condition mention in above topic if the wire touch to pole and then some one touch that pole then current flow from his /her  hand to ground then its called as touch potential.

FUNCTION OF CHOKE AND STARTER IN FLUORESCENT TUBE

 WHAT IS THE FUNCTION OF CHOKE IN TUBE LIGHT?

The choke has two main function:-

• It causes tube to ignite by using the back EMF to create a plasma in the tube and it control the current through the tube when it is ignite.

• It also provide the high voltage pulse necessary to strike the lamp and when lamp is running it limits  the running current to a safe value to prevent the heaters blowing out of lamp.

• It may the 40 watt tube it will trigger 500v not measurable time fraction of seconds and  it will drop nearly 110-120 volt across the choke , remaining the tube. 

WHAT IS THE FUNCTION OF STARTER  IN TUBE LIGHT?

• fluorescent tube light convert an electrical discharge in the mercury vapour present in the tube light at the phosphor coating inside the tube .

• But this discharge can not take place of its own when normal supply voltage is applied , because this voltage is not sufficient to cause ionization of the gas in the tube.

• The common fluorescent  tube starter it self glow tube  but filled with the mixture of gas that can ignite at supply voltage .it incorporates space between its contacts.

• When power is switch on to the tube light circuit ,a glow discharge takes place in starter which heat the bimetallic strip.

• The strip bends and closed the contact of the switch.

• When the contacts of the starter close a glow is not possible  ,once glow extinguishes ,there is no longer any heating of the bimetal.

BASIC OF ELECTRICAL

 why single phase induction motor are not self start?

  for rotation of motor required following things required:-

• phase difference
• rotating magnetic field
• torque

but in single phase induction motor :-

• phase difference - zero
• rotating magnetic field - alternating magnetic field
• torque - zero