Which of the following is NOT a valid voltage level for primary distribution?

The correct answer is option 3):66 kV

Concept:

Generation:

• Electrical power is generated by 3-ϕ alternators at 6.6 or 11 kV voltage levels due to economic considerations.
• This generated output power is further stepped up to 132 kV voltage level with the help of 3-ϕ transformers.
• These transformers connect the generator output to the grid.

Primary transmission:

• The electric power at 132 kV is transmitted by a 3-phase, 3-wire overhead system to the outskirts of the city. This forms the primary transmission.

Secondary transmission:

• The primary transmission line terminates at the receiving station which usually lies on the outskirts of the city. At the receiving station, the voltage is reduced to 33kV by step-down transformers.
• From this station, electric power is transmitted at 33kV by 3-phase, 3-wire overhead system to various sub-stations (SS) located at strategic points in the city. This forms secondary transmission.

Primary distribution:

• The secondary transmission line terminates at the sub-station where voltage is reduced from 33 kV to 11 kV, 3-phase, 3-wire. The 11 kV lines run along the important roadsides of the city. This forms the primary distribution.Hence option 3): 66 kV is wrong

Secondary distribution:

• The electric power from the primary distribution line (11 kV) is delivered to distribution sub-stations (DS). These sub-stations are located near the consumers’ localities (load) and step down the voltage to 440 V, 3-phase, 4-wire for secondary distribution