The correct answer is A) increase or decrease circuit voltage as required. A potential transformer is a device used in electrical circuits to convert a higher voltage to a lower voltage. This is done to allow electrical instruments and meters to safely measure and monitor higher voltages without being damaged. The potential transformer steps down the voltage to a level that can be handled by the measuring equipment, while maintaining the proportional relationship between the input and output voltages. The other answer choices are incorrect because: B) a potential transformer does not transform electrical energy into mechanical energy, C) it does not convert AC to DC, and D) it does not generate its own electrical power - it simply steps down the voltage from the circuit.