Calculating Secondary Voltage and Current using Transformer Equation: A Science Tutorial

If a high-voltage transformer has 100 primary turns and 35,000 secondary turns, and is supplied by 220 V and 75 A, what are the secondary voltage and current? A 200 A and 77 V B 200 mA and 77 kVp C 20 A and 77 V D 20 mA and 77 kVp

The correct answer is (B). The high-voltage, or step-up, transformer functions to increase voltage to the necessary kilovoltage. It decreases the amperage to milliamperage. The amount of increase or decrease is dependent on the transformer ratio-the ratio of the number of turns in the primary coil to the number of turns in the secondary coil. The transformer law is as follows:To determine secondary V,To determine secondary I:

We can use the transformer equation to determine the secondary voltage and current:

Vp / Vs = Np / Ns

where Vp is the primary voltage, Vs is the secondary voltage, Np is the number of primary turns, and Ns is the number of secondary turns.

In this case, we are given Vp = 220 V, Np = 100, and Ns = 35,000. Solving for Vs:

220 / Vs = 100 / 35,000

Vs = 77 V

So the secondary voltage is 77 V.

To find the secondary current, we can use the power equation:

P = VI

where P is power, V is voltage, and I is current.

We know that power is conserved in a transformer (ignoring losses), so we can say that the power in the primary equals the power in the secondary:

Vp * Ip = Vs * Is

We are given Vp = 220 V and Ip = 75 A. Solving for Is:

220 * 75 = 77 * Is

Is = 20.39 A

So the secondary current is 20.39 A.

Therefore, the answer is C) 20 A and 77 V.

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