Exam Question

### (a) Purpose of AVR in an Alternator (6 Marks)
An Automatic Voltage Regulator (AVR) is an essential electronic device in an alternator system designed to control and stabilize the output voltage. Its primary purposes are:
* **Voltage Regulation and Stability:**
* **Maintaining Constant Output Voltage:** The most critical function of an AVR is to ensure that the alternator's terminal voltage remains constant within specified limits, regardless of variations in load (both active and reactive power demand) or prime mover speed fluctuations. As the electrical load on the alternator increases, the terminal voltage naturally tends to drop due to factors such as armature reaction and internal impedance drops. The AVR senses this voltage drop and automatically increases the excitation current supplied to the main field winding, thereby strengthening the magnetic field and compensating for the voltage drop to restore it to the pre-set value. Conversely, if the load decreases, the voltage would rise, and the AVR would reduce the excitation to maintain the desired voltage.