Simplify the following text for a Grade 9 native English-speaking person.
Original: Centralised power generation became possible when it was recognized that alternating current power lines can transport electricity at very low costs across great distances by taking advantage of the ability to raise and lower the voltage using power transformers .
Simplified: Making electricity in one central place became possible with the use of power transformers which could change voltage . Electricity could be sent as alternating current along electric power lines for great distances cheaply .