3.1 Define the following terms: 3.1.1 Reactive power 3.1.2 Efficiency 3.2 Calculate the value of the phase voltage in a star-connected three-phase system if the line voltage is 380 V - NSC Electrical Technology Power Systems - Question 3 - 2020 - Paper 1

Efficiency is the percentage ratio of the output power to the input power in a system. It can be calculated using the formula:

For a star-connected system, the relationship between line voltage ($V_L$) and phase voltage ($V_{PH}$) is given by:

A low power factor can lead to several negative effects on an electrical system, including:

1. Increased losses: Low power factor results in higher current, which increases resistive losses in conductors, leading to overheating.
2. Reduced capacity: Low power factor reduces the overall capacity of the electrical system, requiring larger equipment and conductors.
3. Voltage drop: Higher currents cause more significant voltage drops along transmission lines, leading to poor voltage quality at the load.
4. Increased demand charges from utility providers.

Methods to improve power factor include:

1. Using power factor correction capacitors: By adding capacitors in parallel with the load, the reactive power is counteracted, thereby improving the power factor.
2. Utilizing synchronous motors: These can be operated at leading power factors to compensate for lagging loads.
3. Employing variable speed drives: These devices can help manage load conditions more effectively and improve the overall power factor.

The instrument used to measure electrical power over a specific period of time is the Kilowatt-hour meter (KWh meter) or Energy meter.

The line current ($I_{L}$) delivered by a delta-connected generator is calculated as follows:

The phase voltage ($V_{PH}$) for a star-connected load is equal to the line voltage:

Active power ($P$) generated by the generator can be calculated using the formula:

In this case:

The total input power measured by the wattmeters is the sum of the individual readings:

A wattmeter can be used to measure the input power/output power in an AC system, providing essential information for monitoring and managing energy consumption.