The regulation state that the voltage must recover within 1.5 seconds. However an acceptable recovery time would be 0.5 seconds for a brushless and 0.2 seconds or less for a compounded machine.

(ii) Effect on small power installation:

When a large load is suddenly applied, the electrical system experiences a significant voltage dip. Initially, there is a sharp drop in voltage due to the high inrush current drawn by the load. This is followed by a slower decrease as the alternator's reactance and power factor affect the voltage. During this period, the alternator’s excitation system, AVR (Automatic Voltage Regulator), and prime mover governor work to restore the voltage.

The sudden load causes a drop in power factor, increasing the reactive power demand on the system. If the voltage dip is significant and prolonged, sensitive equipment may malfunction, and other connected loads might experience disruptions. The system's ability to recover depends on the alternator's capacity, excitation response, and governor speed control.

In this method, the output voltage of the bus bar is continuously measured and compared to the normal rated voltage. Any deviation from the desired voltage generates an error signal, which is sent to the excitation system. This error signal adjusts the excitation to regulate the output voltage. For instance, if the voltage drops, the excitation current is increased, and if the voltage rises, the excitation is reduced.

Examples of error-operated voltage control include brushless alternators with an Automatic Voltage Regulator (AVR) and alternators using a carbon pile AVR and DC exciter.

(ii) Functional Voltage Control:

This type of voltage control is directly based on the instantaneous value of the voltage. If the voltage falls, the excitation is increased proportionally to the amount of voltage drop, and vice versa. Since the excitation is a direct function of the voltage, it is referred to as functional voltage control.

Static excitation systems are an example of functional voltage control. These systems offer faster response times compared to error-operated methods, making them suitable for applications requiring precise and rapid voltage regulation.