Train Track Safety Awareness (TTSA) Practice Test

What voltage is supplied from the power grid to traction power substations?

11,000 V AC 3,300 V DC 22,000 V AC 750 V DC

Correct Answer:

22,000 V AC

Explanation:

Traction power substations are fed with AC from the electrical grid at a medium voltage, which is then transformed to the voltages used on the railway system. Twenty-two thousand volts AC is a common standard for this grid supply to substations because it allows efficient transmission with manageable transformer size and insulation, and it pairs well with the downstream equipment that steps the voltage down to the traction levels. The other voltages listed are not the grid feed to substations: the lower DC values are the voltages used on the traction network after conversion, and while some systems may use other AC voltages, 22 kV AC is the typical grid feed to traction substations.

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