Investigating the effects of reactive power control on the characteristics of induction motors by considering different events in a sample network

Dissertation for Master's Degree

Trend: Power Electricity

Abstract

Increase in the presence of non-linear power electronic loads in distribution networks on the one hand and the ongoing changes in distribution networks such as the presence of scattered production sources and the possibility of forming power microgrids [1], require new studies in It has increased distribution networks. The mentioned changes can increase or decrease the power quality in the power network. On the other hand, the injection of network reactive power can be affected. Therefore, the need to study elements related to reactive power in the network has become more important. Because the compensation of reactive power is not only to increase the quality of network voltage and power quality, but more importantly, it is to prevent the occurrence of voltage instability in the network. Therefore, this research can be considered both the study of the effect of voltage instabilities and the study of bad voltage quality on the performance of induction machines. This research, while reviewing the topics of reactive power, types of compensators and topics of voltage stability, induction machines as a set of industrial reactive loads, has studied the sensitivity of performance against the supply or non-supply of reactive power. For this purpose, studies based on the design of different scenarios have been carried out. The results indicate the importance of supplying the required reactive power and increasing the voltage quality locally so that the induction machines can work at a high power factor and with high efficiency and not stop.

Key words: reactive power, distribution networks, induction machines, reactive power compensation, power quality

Chapter One: General Research

1-1 Introduction

According to the progress made in the electronic discussion The use of non-linear loads has increased both in the domestic and industrial sectors, and this has caused various power quality phenomena such as flickers, harmonics and voltage fluctuations in the distribution network. On the other hand, the sensitivity of industrial loads to power quality causes the need for network power quality compensators and controllers to increase day by day. One of the most common controllers in distribution and transmission networks are reactive power compensators. Considering that a huge part of the consumption of factories is dedicated to electric motors and among electric motors, the frequency of induction motors is more than other types of motors, therefore the researcher in this thesis tries to investigate the effect of reactive power control on the performance characteristics of the induction motor in a sample network as a part of the distribution network in the industrial sector.  In this regard, events will be considered. For example, this study is checked for when various errors occur in the network. The practical purpose of this research is to investigate the effect of reactive power controllers on improving the network power factor and improving the performance characteristics of induction motors such as torque-speed curves or starting current-speed. The practical purpose of this research is to compare the existence and non-existence of reactive power compensators in the occurrence of different incidents, in terms of voltage stability and power factor of the network, after the implementation and study of the real power system, and according to the advantages obtained, the placement and installation of reactive power controllers by network operators should be carried out.

The necessity of conducting this research, as stated earlier, is the increasing increase of non-linear and mainly post-phase loads in the network. is distribution. These types of loads greatly increase the need for reactive power in the network. This is despite the fact that power plants have been installed and operated according to the needs assessment based on active power. Another important reason that raises the need to control reactive power and study its effect on different loads is the effect of these controllers on improving voltage stability and thus improving the performance characteristics of power system loads, among the most important of which are induction motors.

In order to deal with the effect of reactive power compensation on the performance curves of induction motors, we will first get to know more about the importance of this issue. Then, by clarifying the subject under investigation, we will learn about reactive power compensation and voltage stability issues, and we will also introduce the types of reactive power compensators. Then by implementing the desired distribution network, we will carry out the studies in different scenarios. 1-2 Statement of the problem and the necessity of conducting research The advances made in the field of power electronics as well as the occurrence of new phenomena in distribution networks, such as the presence of distributed power sources, such as wind turbines[2], solar cells[3] and so on. which have changed the distribution network from a passive state [4] to an active state [5], it causes the necessity of many revisions in the studies of the distribution network. Reactive power control[6], which is one of the most interesting and important studies of power engineers in distribution networks, should be reviewed. Reactive power studies, which are mainly discussed with voltage stability, in some cases, are present only to optimize energy consumption and reduce losses in the network. However, conditions may occur in the network that make the presence of these resources necessary to prevent the network from entering into voltage instabilities. On the other hand, it is important to pay attention to the fact that although reactive power compensation can be done in a short time by installing capacitor banks, reactive power planning requires long-term planning horizons, in line with network development, and it cannot be left to short-term and hasty decisions. From this point of view, conducting this research can be useful for network reactive power studies.

On the other hand, the presence of loads such as induction motors which are self-loading and require a lot of reactive power, makes this research even more obvious. Because these motors in different powers account for a large part of the consumption and due to their dispersion in the network, they require special reactive power planning. Note that the issue of reactive power control and voltage control are location dependent. In other words, it is a local quantitative voltage [7] that can have a good profile at one point of the network, while in another part of the network we may face the problem of voltage reduction. While this problem does not exist in the discussion of frequency and active power control. Because the quantitative frequency is global [8] and can be controlled by injecting active power at any point of the network. Therefore, it is very important to control reactive power in industrial centers that have a lot of self-loads (reactive power consumers).

Reactive power control and the study of the effect of reactive power on induction machines can be divided into two areas. In the first case, the goal of compensation and reactive power studies can be to prevent the network from entering voltage instability and blackouts in the network. But in the next step, the goal of reactive power compensation can be considered as reducing energy consumption, improving the power factor of the network, improving the performance curves of induction machines as a large part of industrial loads and increasing their efficiency. Therefore, voltage control (reactive power control) is an essential issue in the power system, both in emergency mode studies [9] of the network and in studies of normal conditions [10]. Because in an emergency situation, by knowing the limits of voltage instability [11], it can increase the margins [12] of voltage stability and thus increase the security [13] of the network, and in normal conditions, it can cause the operation of the network with high reliability [14] and high power quality [15].

1-2-1 The difference of reactive power compensation in distribution and transmission networks rtl;">Voltage control and reactive power control have completely different solutions in two parts of transmission and distribution networks. Transmission networks, which are at high voltage levels, use the reactive power of large generators and thereby control the voltage of the entire network. While in distribution networks, each area as a small part of the larger area has its own independent voltage control, which cannot affect the voltage of the other area much. In other words, high voltage networks have far more effective power than distribution networks, so that the problem of local voltage in them is milder than the distribution network.