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251.

Corona usually occurs when the electrostatic stress in the air around the conductor exceeds

A.	32 kV (maximum values)/cm	B.	22 kV (maximum value)/cm
C.	11 kV (rms value)/cm	D.	6.6 kV (rms value)/cm

252.

Corona effect can be detected by

A.	hissing sound	B.	faint luminous glow of bluish colour
C.	presence of ozone detected by odour	D.	all of the above

253.

The current down by the transmission line due to corona losses is

A.	sinusoidal	B.	square
C.	non-sinusoidal

254.

Presence of ozone as a result of corona is harmful because

A.	it gives bad odour	B.	it corrodes the material
C.	it transfers energy to the ground	D.	it reduces power factor

255.

In the areas where snowfall is frequent, under worst conditions, the thickness of ice on a conductor is

A.	1.25 cm	B.	2.75 cm
C.	4.75 cm	D.	6.25 cm

256.

The effect of ice deposition on conductor is

A.	increased skin effect	B.	reduced corona losses
C.	increased weight	D.	reduced sag

257.

The effect of wind pressure is more predominant on

A.	transmission lines	B.	neutral wires
C.	insulators	D.	supporting towers

258.

Guard ring transmission line

A.	improves power factor	B.	reduces earth capacitance of the lowest unit
C.	reduces transmission losses	D.	improves regulation

259.

When the power is to be transmitted over a distance of 580 km, the transmission voltage should be in the range

A.	33 kV - 66 kV	B.	66 kV - 100 kV
C.	110 kV - 150 kV	D.	150 kV - 200 kV

260.

Which relay is used on transmission lines?

A.	Thermal relay	B.	Buchholz relay
C.	MHO relay	D.	Reactance relay