Definition of Power Factor

Power factor is a measure of the efficiency with which electrical power is consumed in an alternating current (AC) circuit. It represents the ratio of real power (also known as active power) to apparent power in the circuit.

Real power is the actual power that performs useful work, such as lighting bulbs or driving electric motors. It is measured in watts (W). Apparent power, on the other hand, is the product of voltage and current in the circuit, measured in volt-amperes (VA).

The formula for power factor is:

$\text{Power Factor}=\frac{\text{Real Power}}{\text{Apparent Power}}$

A power factor of 1.0 indicates a purely resistive load where real power and apparent power are equal, meaning all the electrical power is being used to do useful work. However, in many practical AC circuits, especially those involving inductive or capacitive elements, the power factor is less than 1.0 due to the presence of reactive power.

Inductive loads, such as electric motors and transformers, cause the current to lag behind the voltage, leading to a lagging power factor (usually denoted as "PF"). Capacitive loads, on the other hand, cause the current to lead the voltage, resulting in a leading power factor.

Utilities and industries often aim to improve power factor to reduce energy losses, improve system efficiency, and avoid penalties imposed by utilities for poor power factor. This is typically achieved by installing power factor correction capacitors or other devices to offset the effects of inductive loads and bring the power factor closer to unity (1.0).

Parallel operation of transformers

• Parallel operation of transformers involves connecting two or more transformers to a common electrical system so that they share the load. This arrangement offers several benefits, including increased system reliability, load flexibility, and efficiency. Here's how parallel operation of transformers works:

  1. Similar Characteristics: Before connecting transformers in parallel, it's crucial to ensure that they have similar voltage ratios, phase shifts, impedance values, and other characteristics. Transformers with significantly different characteristics can cause circulating currents and uneven distribution of the load.

  2. Parallel Connection: Transformers are connected in parallel by connecting their primary windings to a common supply source and their secondary windings to a common load. The connections must be made so that the polarities of the windings are aligned correctly.

  3. Load Sharing: Once connected in parallel, the transformers share the total load in proportion to their respective ratings and impedance characteristics. Transformers with lower impedance or higher ratings will carry a larger portion of the load.

  4. Load Distribution: In ideal conditions, the load is distributed evenly among the parallel transformers. However, slight differences in transformer characteristics or unequal loading can lead to unequal load distribution. Transformers with higher impedance may experience higher voltage drops and carry less load.

  5. Circulating Currents: If transformers connected in parallel have slightly different voltage ratios or phase shifts, circulating currents may flow between them. These circulating currents can lead to increased losses, reduced efficiency, and overheating of the transformers. To mitigate circulating currents, transformers can be equipped with phase-shifting devices or parallel reactors.

  6. Control and Protection: Parallel operation of transformers requires proper control and protection measures to ensure safe and reliable operation. This includes synchronizing the transformers' voltages and frequencies, monitoring load sharing, and implementing protective devices such as fuses, circuit breakers, and relays.

  7. Maintenance: Regular maintenance and inspection of parallel transformers are essential to identify and address any issues that may arise, such as imbalances in load sharing, insulation degradation, or mechanical failures.

  Overall, parallel operation of transformers offers advantages such as increased system reliability, load flexibility, and efficiency. However, it requires careful planning, installation, and maintenance to ensure safe and reliable operation. Proper control, protection, and monitoring are essential to prevent issues such as circulating currents, unequal load distribution, and transformer overheating.