Power Quality in practice

This course deals with the power factor correction (PFC) units design and related problems in case of harmonics rich environment. Particularly it provides an overview of the sizing approach in a real case of PFC units design for steel factory where the new PFC units replaced old ones after a fault with catastrophic damage to the existing compensation equipment.

Plant load, estimated at around 80 MVA, consists of large amount of small loads fed by power converters. They are significant disturbance source in terms of harmonic content. In particular, because of typical lack of real harmonics content data log, the main issue was to define generic harmonic distortion spectrum for installed loads, based on:

  • installed power converters
  • available literature about power converters spectra
  • field verification for PFC optimization, with three measurement campaigns aiming to verify real harmonic distortion together with risk of series and parallel resonance.

This kind of problem is real and constantly growing also in other industries, not only in steel factories where harmonics content has always been a key problem. Now, due to the continuous increase of power converters use, type of power consumption and because of increase of equipment sensitivity to disturbances, a deep measurement campaign is the key solution during PFC units design stage.

Students will receive guidance how to prepare installation of PFC equipment.

The voltage system in any three phase electrical installation is expected to be balanced (voltages equal in magnitude and displaced to each other by 120o). In practice, it is not possible to have the full balance at all nodes of the power system.

The main sources of the long-term unbalance are unbalanced loads, primarily single-phase loads existing mainly in low-voltage and medium-voltage networks. These loads cause non-equal phase currents to flow in the power system and unbalanced voltage drop on the system components. As a consequence, voltage balance at the nodes is lost. Voltage unbalance can also result from different self- and mutual impedances of individual phases of transmission system components, and particularly those of overhead lines. In this case, different voltage losses are produced even when a load is symmetrical.

This course describes the voltage and current unbalance phenomenon in electrical power networks. Considerations relate mainly to long-term unbalance occurring in normal steady state conditions due to operation of loads or asymmetry of network elements. Short-time unbalance can appear only under disturbance conditions, for example during an unsymmetrical short-circuit. Effects of unbalance on the main electrical equipment together with mitigation techniques will be presented.

Some years ago Power Quality issues were a problem concerning engineers working mainly in power stations, operating arc furnaces and data centers. The approach was just to focus on faults and reliability of the electrical installation while nowadays PQ phenomena have to be linked also to energy and economic efficiency.

Different PQ devices have conversion losses and may distore power and have adverse effects on energy efficiency. At the same time PQ solutions may help to reduce energy losses. Global competition and economical efficiency require to take into consideration also PQ implications to energy efficiency.

The course helps to analyze various PQ issues and solutions from the perspective of energy efficiency. The discussed concepts can be applied to utility networks as well as to customer installation and equipment. Course participants will receive guidelines how to keep energy efficiency in mind when applying PQ solutions.>

The nature of electrical power failures, interruptions, and their duration covers events which take from microseconds to days, but even for the shortest interruption the result could be fatal for facilities and systems that cannot operate without power. The choice of schemes for electrical plants is one of the keys of primary importance in the electrical project to mitigate, if not eliminate all power interruption effects. However it requires full knowledge of the loads and the characteristics of supplies. This lesson discusses the most common basic schemes of electrical grids, general criteria for scheme choice, redundancies of components and circuits and selection aspects of electrical installation power supply and distribution.

Nowadays the residual current device (RCD) is universally considered as an effective measure of guaranteeing protection of people against electrical hazards in low voltage, both in case of indirect and direct contact. Of course its choice and optimum operation requires deep knowledge not only of the electrical installations and in particular of the earthing systems, but also existing technologies and their possibilities of these devices.

All these aspects are deeply investigated in this lesson, which in addition, will provide knowledge on RCD behavior when using it in case of PQ phenomena, allowing users to make the optimum choice of the protective device in any installation environment.

A good earthing arrangement is required for the correct operation of electrical networks and is important for the quality of electricity supplied to consumers. Main functions of an earthing system are safety, correct operation of equipment and network, good power quality, achievement of a given electromagnetic compatibility (EMC). All these functions are provided by a single earthing arrangement that has to be designed to fulfill all the requirements.

Standards require all earthing conductors within the installation to be bonded together, forming one arrangement. Moreover, the growing proliferation of electronic equipment generates the need for new requirements and bonds when designing an earthing system.

This course provides overview of requirements and practices needed for the correct earthing of electronic devices.

Electrical equipment is designed to operate optimally with a supply voltage that is within rated values and within frequency tolerances. Operation outside these limits can result in increased losses, poor efficiency and unpredictable operation. Large deviations can cause disruption due to the false operation of protection devices. Voltage quality has therefore a decisive influence on the operation of equipment and risk coming from a power failure could be very serious. Such disturbance affects safety, as in hospitals and any public building or causes economic losses, as in manufacturing industries, especially continuous process manufacturing or high technology manufacturing . There is a big variety of devices and reserve power supply equipment available on the market and the choice of mitigation depends on the characteristics of the load equipment and the type, duration and severity of the power disturbances. In this wide framework this lesson aims to provide information on how to approach reserve power supply choice by giving a detailed overview on available solutions, sizing criteria and safety implications.

The wide usage of microelectronic components for control and operation results in the increasing importance of power quality in distribution systems. These components are very sensitive to voltage dips and power interruptions. Motor drives, including variable speed drives, are particularly susceptible to voltage dips. Similarly lighting equipment. Considering also that protective systems are often used for the purpose of supply disconnection in event of the voltage undervoltage (voltage value drop below a preset level, the effect will be the conversion of a voltage dip into a long supply interruption. The cost implications are very serious. This lesson gives an overview of voltage dips and interruptions causes and effects on electrical equipment, mitigation measures and measurement techniques, all in order to provide students with the in depth understanding of this serious PQ phenomenon.

Today, nearly every piece of electrical equipment generates harmonic currents and voltages. Unfortunately harmonic currents and voltages cause many problems in electrical installations, including overheating of equipment and cabling, reduced energy efficiency, and reduced functionality due to loss of electromagnetic compatibility. Designers and technicians must therefore consider harmonics and their side effects very carefully to ensure safety and resilience of installations and to meet harmonic emission limits. This course gives a comprehensive and up-to-date overview of the subject. It explains why harmonic problems have been increasing over recent years, how they are generated and what kind of equipment is responsible for these problems. It also presents an overview of the various problems harmonic currents and voltages can create and an overview of the available solutions.

Power quality is a relatively new issue for industrial and commercial electricity users. Up to a few years ago, it was a problem concerning only power stations and heavy industry (e.g. arc furnaces). It is only recently that the electrical engineering community has had to deal with the analysis, diagnosis and solution of PQ problems. This lesson provides an introduction to the concept of PQ which consists phenomena definitions, effects, problems and mitigation techniques. It will allow students to enter the courses about particular PQ disturbances and PQ practice in earthing, relibaility, protection and as well as understanding their implications for energy efficiency and distributed energy sources.