case studies

By Dragomir Vasic

In this reader article, Dragomir Vasic introduces a basic technique of frequency regulation for preparing the fuel-air mixture in hot water boilers used for district heating. This simple and relatively low-cost measure saves 25,000 euro per year, with a payback of just 0.6 years.

With such compelling economics, one would expect most old boilers to be retrofit in this way, but according to Dragomir, this is often not the case. It's often easier to charge customers for high losses rather than to engineer change.

An energy service company would be a solution, bringing in specialised expertise to facilitate the project. But it's often a barrier to companies to open up their operations, and expose their inefficiencies to a 3rd party.

These 2 case studies demonstrate that high-quality rewiring of domestic electrical systems in older residential buildings can yield a significant increase in home comfort.

We describe some examples of electrical refurbishment work aimed at illustrating how electricians can tap into this market.

We begin in the city of Jena in Thuringia in the east of Germany. Many of the residential areas in Jena are situated on the slopes of the Saale valley. One such development comprises detached and semi-detached houses all built in the 1930s and 40s.

These solid, comfortable residences were built with typical German thoroughness, but with electrical systems that reflect the requirements of that time.

For its time, the electrical installation work was fairly modern using copper wires within a protective metal sheath. However, each house was fitted with only a few wiring circuits comprising two copper conductors with a 0.5 mm² cross-section and protected solely by a 6 A fuse.

One such semi-detached house is owned by the seventy-year-old pensioner Herta Engels:

The second case takes us to the Rapp family from Jena that owns a detached house built in the 1950s that is situated on the slopes of the Saale valley.

The original quote for the electrical installation work was for €3,500. The final bill, however, totalled €10,000 – not because the electrician failed to do the costing properly, but because he succeeded step by step in explaining to his customer the added value and long-term benefits of carrying out a comprehensive electrical modernization programme.

This article demonstrates that the big challenge facing electricians today is convincing their customers that, when comparing quotes, the bottom line is not enough – they have to ensure they are comparing like with like:

By D Mueller

Transmission systems around the world are increasingly applying capacitor banks on their transmission systems, primarily to support transmission systems and avoid voltage collapse issues leading to blackouts. Another trend is the utilization of underground cable to obtain right of way in corridors sensitive to overhead lines. These trends both lead to harmonic resonance issues. This paper presents three separate case studies of different situations and concludes with some of the general principles that can be derived from an examination of diverse case studies.

By C Zuniga

This paper is presented by Chilectra, a subsidiary of the Endesa Group Spain and the biggest electric utility in Chile. It sets out a methodology for estimating and determining control parameters for the voltage quality to be delivered to its end customers. The methodology is able to estimate the voltage at each end customer location in the low voltage (LV) distribution network, using measurements of voltage, current and power factor in real operating conditions at the feeder substation bus bars in the medium voltage (MV) distribution network. The available information sources, the assumptions used for analysis and the partial results at each stage of the methodology are described. A case study shows the main results of the methodology: the number of end customers with voltage quality problems and the geographical location of these customers. Finally, it shows the improvement obtained as a percentage decrease in end customers subject to bad voltage quality when applying the methodology.

By Roeland De Meulenaere

But how much do energy savings cost? How long does it take until you recover your investment? Where can you save energy? And how much CO2 emissions are actually avoided?

This document provides answers to questions such as these, based on commonly used methods of saving energy. Various possibilities for saving energy are discussed in detail.

The five case studies presented in this document are:

By A Baggini at al

The installation of non linear loads determines the presence of current and voltage harmonics and interharmonics. Components particularly sensitive to this kind of phenomena are power factor correction equipments. This paper describes the design process of a centralized PFC system under harmonic pollution conditions pointing out the key role of measurement campaigns.

Summary

This paper deals with PFC units' design related problems in case of installation in harmonics rich environments: in particular, the paper contains an overview of sizing approach used in a real case of PFC unit design for installation in a steel factory where new PFC units installation has been necessary after a fault with catastrophic consequences for the existing ones.

The document contains a report on stress calculation on PFC units due to harmonic currents generated by non linear loads installed in the above mentioned plant. Plant load, estimated to be around 80 MVA, is formed by a large number of small loads fed by power converters. This is a big disturbance source for the installation in terms of harmonic content.

In particular, due to the usual lack of real harmonics contents data availability, the main issue has been the process of definition of a generic harmonic distortion for installed loads, based on power converters installed and literature available data on power converters spectra and its on field verification for PFC optimal design, with three measurement campaigns aiming to verify real harmonic distortion and series and parallel resonance risk.

This kind of problem is very real, and, most of all, is constantly growing in other industries as well, not only in steel factories where harmonics content has always been a key problem.

Now, due to the continuous increase of power converter usage and equipment power consumption, and most of all to the increase of equipment disturbances sensitiveness, to avoid potentially tragic faults, a deep measurement campaign is the key solution at PFC units' design stage, also considering the usual lack of data on installation harmonic distortion.

The experience described in this paper constitutes the first detailed example of in-the-field verification of harmonic disturbance effects on two 8.4 Mvar, 13 kV PFC units in a harmonics critical environment aiming first of all at a detailed fault analysis (referred to pre-existent PFC Units) and then to a correct new unit design.

In the paper, the different design stages and related issues are described, including: installation network analysis, load analysis, harmonic distortion evaluation, PFC units stresses analysis, PFC units sizing, on field stresses verification.

This work highlights the strong need for deep measurement campaigns in harmonics rich industrial environment as the only way, in addition to a correct distortion pre-analysis aiming to a careful PFC design strategy to prevent potentially catastrophic faults.

A new case study by Michèle De Witte, Laborelec.

A steel manufacturing plant was experiencing a flicker problem. Lights in the office areas of the plant were often flickering, affecting productivity and creating an irritating nuisance for employees.

A Power Quality consultant was called in to investigate the case. He carried out measurements to gain a better understanding of the problem and to enable him to identify the source of the flicker phenomenon and the operating conditions in which it occurred. Once this information in hand, he was able to propose an appropriate solution.

A new case study by :

Nowadays, energy is one of the most important prime materials in industrial processes. Highly automated industries need to have a reliable power supply and efficient energy utilisation in order to maintain both a high productivity and to be competitive. On the other hand, in industry automation, designing the automation process has an important influence on the later energy consumption. In the following case study an automated pneumatic waste collection process was studied for its energy efficiency assessment and its improvement.

Industries in Europe are generally connected to the distribution grid. Specific companies, though, are great energy consumers and have been directly connected to the transmission grid.

While the distribution grids are ruled by strict standards concerning quality of supply, comparable standards aren’t available for transmission level. Consequently, transmission grid operators determine perturbation emission limits for each grid user separately.

In this case study, a transmission grid operator is worried about the perturbation level at a specific connection point in the grid. Three metallurgical companies are connected in this point, whose main energy consuming installations are three arc furnaces; one is of the AC-type, two of the DC-type.

Using a number of measurements and a specific calculation algorithm, the goal is to evaluate the responsibility of each company for the deterioration of grid quality.

By Didier Empain, Laborelec

In this new case study, a large plant in the transport sector was experiencing a general voltage interruption caused by a local short-circuit inside the plant’s electricity network. This happened because of a non-selective tripping of the general protections at the plant’s connection point. The company decided to take action to identify the origin of the malfunction and implement corrective measures. An electricity consultant was called in to investigate the case.

By Conrad Bottu, Laborelec

Download case study (pdf)

Description of the site

The Belgian site being studied in this paper is connected to the public transmission grid (380 kV) by a High Voltage (HV) station. This HV station incorporates a 25 kV substation linked to a second substation via 25 kV underground cables. The second substation supplies the electric installations on the site.

The substations contain 25 kV circuit breakers in interior type HV cells with a metallic casing (see pictures below). The insulation is realised by SF6 gas. The safety relays and control devices are located in cabinets situated on the front panel of the cells. Their LV supply (110 VDC and 24 VDC) is provided by cabinets situated in an adjacent room.

Description of the problem

When operating the new circuit breakers, the control circuits received over-voltages and broke down. The same thing happened during other operations and events, including in-line short circuits, section switch closures, and above all the connection of the 25 kV cables to the earth to discharge them.

Thousands of Euros were going up in smoke every time one of these events occurred. The poor EMC of the installation was generating voltage surges between the LV equipment and the earth, causing the breakdowns.

Solution

The company called in an EMC consultant to study the phenomenon and propose a solution.

Since the earthing concepts of the HV station with the incorporated substation and the second substation are different, part of the consultant’s study had to be executed separately. The first substation contained an earth loop connected to the mesh of the 380 kV public grid earthing system, while the second substation earthing system consisted of earth rods.

The EMC consultant provided the company with a solution to bring the surges below the 500 V limit tolerated by the LV equipment. He recommended, among other things, building a meshed ground grid and improving the continuity of the cable shielding. In the solution, all connections to the earth were kept as short as possible and the installation of data cables and power cables next to each other was avoided.

After implementing the proposed measures, a thorough inspection and test of the substation was carried out. The measures reached their objective and no more breakdowns have occurred.

A power quality case study

By Michiel Van Lumig, Laborelec

Various departments at a car manufacturing plant are suffering from regular process outages due to voltage dips. These dips are causing production losses in the Metal Operation, Spray Coating, and Assembly departments that directly affect the productivity of the plant. The cost of those losses is directly related to the profile of the voltage dip (duration and depth).

Various options to reduce these costs are investigated, with particular emphasis upon the Spray Coating and Assembly departments. The following conclusions can be drawn:

1. The number and type of dips occurring at the point of connection of the plant is regular. It is similar to what is monitored at other medium voltage stations that have the same grid structure.

2. A detailed analysis of the spray coating process reveals that installing a ‘restart on the fly’ system on the large conditioning fans substantially reduces the related voltage dip losses.

3. A detailed analysis of the Assembly department shows that there are two main bottlenecks that determine the restart time after a dip (the ‘Drive’ sub-process and the ‘Cockpit’, ‘Marking’, and ‘Transport chain’ users). These bottlenecks can be removed by installing a Dynamic Voltage Restorer (DVR), which results in a payback time of 1.4 years.

... to increase the electric power availability, reduce running costs and prevent damage to people & property

Leonardo Energy launches its case study series with this first one about maintenance as a tool to increase the electric power availability, reduce running costs and prevent damage to people & property by Matteo Granziero, Socomec.

A lack of preventive maintenance on electrical systems can cause poor quality and wasted power or even danger for people and property. Scheduling annual inspections by experienced personnel is the solution to maintain high levels of electric power and safety for the enterprise.

A number of economic case studies on the application of energy efficiency measures in an industrial environment:

1. variable speed drive for water pump
2. variable speed drive on combustion air fan
3. energy savings in compressed air systems
4. steam valve insulation
5. condenser set point in cold storage room

By Ton Van der Wekken, KEMA Consulting

The initiation and feasibility phase section includes site selection criteria and a discussion of the methodology for the assessment of the likely energy yield – a critically important factor in the investment decision. Often, several sites will need to be investigated before making a selection.

During the pre-building phase the necessary planning and building permissions must be obtained and a connection contract negotiated with the local network operator. The feed-in tariff – the money received for the energy produced – must also be negotiated. Decisions made during these early stages determine the return on investment of the farm.

Building and Operation and Maintenance follow with details of the steps to be taken to ensure rapid commissioning and reliable operation. The note concludes with a financial analysis highlighting the importance of an accurate energy yield assessment and adequate feed-in tariff.

Related:

• Application Note - Wind Power
• Webinar - Business opportunities for wind power development

EPQU and LPQI are pleased to introduce Volume 2 No 1of EPQU Magazine, now available online. We hope this issue meets your expectation, and welcome your comments or contributions for the coming issues of EPQU.

Content

• Experience with Regulation of Network Quality in Italy, the UK and The Netherlands >>
• Classification Methodologies for Power Quality >>
• Effect of PQ-Monitor Connection on Voltage Dip Indices: PN vs PP Voltages >>
• Low Voltage Fault Detection and Localisation using the TOPAS 1000 Disturbance Recorder >>
• Analysis of a TSC Failure in a Steel Mill Industry >>
• New Fault Detection Techniques for Induction Motors >>
• Conducted EMI Propagation in Inverter-Fed AC Motor >>
• Impact of Multi-Cycle Symmetrical Control on Power Systems >>
• Harmonic Analyses and Mitigation in Large Industrial Steel Plants - A Case Study >>
• Predicting Harmonics by Simulations: A Case Study for High Power Adjustable Speed Drives >>
• Electrical Diversions and Amusements >>