Phenomenon of Corona

Phenomenon of Corona:-Electrical Transmission overhead line provides one of the most important property, which is a specific line voltage reveres occur. Transmission efficiency and therefore provides a degree of power in the Loss decreased. Moreover, because the line to get his prey  life span can be much reduced. And bodies created  by the induced current harmonics  line charging current increases and the nearest line of the unwanted noise is telecommunication . Also If the line is dirty or rough weather - rainy when the bodies of thousands of adverse effects. in line due to the need to design the appropriate safety  system, which provides line protection from the harmful effects can be.
What is the Corona of overhead transmission line: - two conductor (whose spacing is more than the diameter) of the AC supply to fill Ararat will gradually increase to a level that, when the voltage exceeds a certain limit. It's Critical disruptive voltage. The air around conductors ionized and Conductors  hissing noise  around a dim to be seen violet Glow Discharge. Discharge of the bodies. or (the phenomenon of violet glow, hissing noise and production of ozone gas in an overhead transmission line is known as corona.)
the makes a bodies due to bad weight gases (ozone), the Los Angeles and the origin of the radio interference .
They are less than the amount of voltage increase. The applied voltage can be increased if the

.          break-down an upgrade, then air insulation, the break in the hot blazing Conductors occurred over the Flash.
Effects of Corona: -
i. Conductor all side  Purple - Glow (violet glow) is observed.
ii. This hissing sound (hissing noise) generated by.
iii. Provides a certain amount of power is wasted. Which can be measured using  meters. The transmission efficiency decreases.
iv. Provides for the weight of the gas line to the wire with the chemical reaction. The loss is received.
v. Max is rough and dirty conductors glow.
Factors affecting corona: -
i. Atmosphere.
ii. Conductor size.
iii. Spacing between conductors.
iv. Line Voltage.
Advantages and Disadvantages of corona: -
Benefit
. The Flash - over the possibility of reduced and system performance is improved.
. This and other reasons caused lightning  reduce transient effect. It provides safety for the surgeon as the bulb .
Difficulty
. Provides the energy dissipation, or power loss, which affects the Transmission skills.
. Provides for the weight of gas (O3) is created. The loss of the metal parts.
. Bus bar   particularly damaging for the bodies. The general decrease in the discharge because switchgear  bus bar area.

. Disruptive of the relation for Disruptive critical voltage, Visual critical Voltage and Power loss due to corona: -
. Disruptive critical voltage: - Minimum phase - to – neutral voltage  bodies occur in the critical voltage Vc is the DISRUPTIVE.
Vc = mo go δ r loge D ÷ r kv / phase.
mo = irregularity factor
     = 1 for polished conductors
     = 0.98 to 0.92 for dirty conductors.
     = 0.87 to 0.8 for standard conductors.
 D = conductor spacing

  r = conductor radius
              go = wind dies - electric strength
                = 30 kv / cm (max) = 21.21 kv / cm (r.m.s.)
             δ = Air density factor = 3.92 b ÷ 273 + t
                = 1 standard condition
Corona power loss: - bodies that occur when light, heat, sound, and through chemical reactions are always some energy loss. It provides the power loss.
P = {242.2 (f +25 ÷ δ) √ r ÷ √ D (V-Vc) ² × 10 ¯ 5} kw / km / ph
Where

           p = bodies found in Los Angeles
           f = supply frequency in (Hz)
          V = face to neutral voltage (r.m.s.)
DISRUPTIVE Vc = voltage / phase (r.m.s.)
Good weather is a 132 kv line corona loss 0.6 kw / km / ph. But the weather - rain, when it increased to 5/6 times it is. The 400 kv double circuit line, almost double the loss of 10/12 times.
Methods for minimizing corona: - 66 kv or big voltage provides the intense effect. Of the hands for protection from sub-stations of 66 kv high voltage equipment and bus-bar  rating is determined. Ways provides the following effects can be reduced: -
1. By increasing conductor Size: - overhead line ACSR of using a relatively coarse.
2. By increasing conductor spacing: - If the conductor spacing provides increased voltage increases. It provides reduced effect. However, the conductor spacing should be increased to not more so. So that the support structure, such as - Cross - arm, support, and cost increases.
Solved problems on power loss due to corona:
1. 3-φ line 132 kv, 50Hz transmission line conductors 3 meter interval between  is 2.5km, but standard conductors per km of line in determining the tax bodies in corona Loss.
Answer: - 3-φ line 132 kv standard conductors
r = 2.5 cm, D = 3 cm, t = 60 º, b = 90cm
corona loss P =?
We know,
  P = {242.2 (f +25 ÷ δ) √ r ÷ √ D (V-Vc) ² × 10 ¯ 5} kw / km / ph
Here
             δ = Air density factor = 3.92 b ÷ 273 + t
                                 = 3.92 × 90 ÷ 273 + 60
                                                  = 1.06
go = wind dies - and the electric strength irregularity factor, respectively
    go = 21.21 kv / cm (r.m.s.)
    mo = 0.85 standard conductors
DISRUPTIVE critical voltage / phase, Vc = mo go δ r loge D ÷ r kv
                                     = 0.85 × 21.2 × 1.06 × 2.5 loge (300 ÷ 2.5)
Supply voltage / phase V = 132 ÷ √ 3 = 76.21 kv
Power loss  
  P = {242.2 (f +25 ÷ δ) √ r ÷ √ D (V-Vc) ² × 10 ¯ 5}
 P = 242.2 (50 +25 ÷ 1.06) √ 2.5 ÷ √ 300 (76.21-228.61) ² × 10 ¯ 5
  = 363.33 kw / km / phase
Per km line total 3-φ corona loss
= 3 × 363.33
= 1090 kw (Ans.)

             

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