Switchgear protections

Have low contact resistance

Be clean and smooth

Be of sufficient size and proper shape

Have all above properties

zero current

maximum current

minimum voltage

maximum voltage

1.5 sec

5 to 10 sec

5 to 20 sec

20 to 30 sec E. none of the above

Air blast circuit breakers

Circuit breaker with SF6 gas

Vacuum circuit breakers

Oil circuit breakers

transposing transmission as well as communication lines

increasing the height of the trans-mission line tower

increasing the distance between the two lines

all of the above

low currents circuits

low voltages circuits

high voltages and large currents circuits

all circuits

Lightning arresters

Relays

Step-down transformer

Switchgear

11 kV

33 kV

60 kV

110 kV

good selectivity and reliability

economy and simplicity

high speed and selectivity

all of the above

Photoelectric effect

Electrostatic effect

Heating effect

Magnetic effect