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.