Design and Implementation of Microcontroller (16f887)-Based Controlling of Power Factor Using Capacitor Banks

Abstract

 Most of the domestic and industrial installation in the country has large electrical loads which are severally inductive in nature causing lagging power factor which gives heavy penalties to the consumer by the electricity board.

This situation is taken care by a Power factor correction device. Power factor correction (PFC) is a technique of counteracting the undesirable effects of electric loads that create a power factor that is less than one.

Power factor correction may be applied either by an electrical power transmission utility to improve the stability and efficiency of the transmission network or correction may be installed by individual electrical customers to reduce the costs charged to them by their electricity supplier.

Many control methods for the Power Factor Correction (PFC) have been proposed.

This work describes the design and development of a power factor corrector using a PIC (Programmable Interface Controller) microcontroller chip.

Measuring of power factor from the load is achieved by using PIC Microcontroller-based developed algorithm to determine and trigger sufficient switching of capacitors in order to compensate demand of excessive reactive power locally, thus bringing the power factor near to unity.

GENERAL INTRODUCTION 

Electrical energy is always in great demand for industrial usage and domestic installation. It is on the increase in the development of industrial applications.

One of the most economical methods to meet the electrical energy demand is to improve system efficiency by correcting the power factor.

The system efficiency is defined as the ratio of the real power to apparent power, known as the power factor.

The loads in electrical systems are generally fed by alternating currents and they are mostly motors or loads with inductive characteristic.

They draw active and reactive power from the lines.

Active power is converted into different types of energy, such as heat, mechanical energy. But, reactive power is not converted to any type of energy.

The size of transformers and transmission lines can be larger than their rated values when the reactive power is not compensated [1].

The significance of the power factor lies in the fact that utility companies supply customers with volt-amperes but bill them for watts.

Power factors below 1.0 require a utility to generate more than the minimum volt-amperes necessary to supply the real power (watts) [2]. This increases generation and transmission costs.

Alternatively, all components of the system such as generators, conductors, transformers, and switchgear would be increased in size and cost to carry the extra current.

Hence the need for correction of the low power factor [3].

Background and Context of the Study

Historically, utility companies have implemented power factor correction at their substations by installing capacitor banks.

The problem with implementing power factor correction at the substations is that the reactive power present on the distribution system, not serviced by those capacitors, is inducing thermal losses [4].

Furthermore, the distribution system with its lower voltages and higher currents already account for the majority of the losses on the system.

In addition, more thermal losses occur on the customer side of the electric meter, within the customer premises [5].

The increased low power factor due to inductive loads are always estimated based on power produced daily or monthly.

A generator, transmission line and distribution transformers may operate below their capacity due to inductive loads with a low power factor in the system.

An accurate and applicable method is needed to estimate the effect of low power factor and harmonics on the power system that leads to instability, unreliable and non – quality power, hence this project is to minimise the inductive component of the current and thereby reducing the losses in the system, minimizing wasted energy and hence improving the efficiency of a generating plant, transmission line and distribution transformers thereby reducing high tariffs [6].

Research Problem

Electrical power generators are designed to produce quality, reliable and stable power to consumers.

It came to light that most of the loads in electrical installation used are inductive loads that produce inductive reactance and if not immediately checked, contributes to low power factor thereby increasing the amount of electrical energy that flows through the electrical network from the generating station.

Example of industrial and domestic installation loads are inductive motors, cookers, arc welding machines, etc. and air conditions, washing machines, deep freezers, refrigerators heaters, etc. respectively.

Attempts are made over the years to improve the low factor close to unity using capacitors banks to generate capacitive reactance to compensate for the inductive reactance.

Switching on and off of the capacitor banks for the compensation also produces harmonics in the system.

Therefore the need for improving the power factor using a microcontroller to do the switching of the capacitor banks on/off the system and also eliminate harmonic effect in the system.

Research Hypothesis

Electrical power generators are designed to produce different types of voltages supply: three-phase voltage (three lines +Neutral) and single-phase (Line +neutral). Some industries and domestic installations are supplied in a three-phase system therefore to carry out our research the following hypothesis should be fulfilled :

• The study is implemented in a single-phase system ;
• The study is implemented with the single-phase load;
• In the case of a three-phase system the loads should be single-phase load;
• The study is carried out with the supply of 220V and a maximum voltage of 15A;
• The system corrects automatically the power factor when is below 0.93.

General Objective and Specifics Objectives of study

General Objective

 The general objective of this study is to have a good solution to reduce energy consumption by industries and domestic installation, through a sustainable development of automatic system that corrects low power factor. The advantage of correcting power factor reduced demand charges, increased load carrying capabilities in existing circuits, improved voltage and reduced power system loses.

Specifics Objective

In light of the above scope, the specific objectives of the study are as follows:

• Develop a prototype of an automatic power factor corrector with a microcontroller as the brain of the control system.
• The overall purpose is to improve low power factor, improve energy consumption by industries and domestic installations.
• The improved stability and efficiency of the transmission network.