E+C August 2018

FEATURES: · Electrical protection + safety · Transformers + substations · Cyber security · Power quality, standby + back-up · Temperature measurement + instrumentation

COMMENT

ON THE COVER

FEATURES: · Electrical protection+ safety · Transformers+ substations · Cyber security · Power quality, standby+ back-up · Temperaturemeasurement+ instrumentation

There is energy and power in crisis ...

T he juxtaposition of the energy within our industry and the economic pro- gress of our country is nothing less than fascinating. Yes, there may be some re- markable people batting for the econo- my, but we need no reminder of emerg- ing head winds that, it often seems, we steadfastly continue to produce for our- selves. We worry about state-owned entities and their capacity to deliver while some companies announce ground-breaking developments sure to advance manufac- turing processes. Our world is advancing with or without us. Every day I am encouraged by the competency and commitment shown by younger members of the profession. Their hearts and heads remain committed to this special part of the planet. When engaging with the more mature members of our economy I get a sense of two rather distinct world views and I oftentimes find myself aligning with the latter. The frustration generally allies to per- ceiving a future which is in reach,―but only if we lay the required foundations. We speak glibly about Industry 4.0, yet few people have an actual grasp of its meaning. This was likely to happen whether we like it or not. We have observed organisations that ‘suddenly’ become proponents of Indus- try 4.0 because that is obviously what one has to do – as if that in itself is the solution to all woes. With all due respect to recent proponents of Industry 4.0, this is what the readers and advertisers of Electricity+Control have in fact been ad- vocating for decades – the integration of digital technologies into this analogue world of ours, and the conversion of data into information. This is what we do!

We have consistently argued the fact that energy and information are without doubt the two fundamental commodities of industry. What is intriguing to observe is how business and commerce now latch onto that; how simply appending the ‘4.0’ to any aspect of human endeavour implies progression. What is exciting to observe is how the language is becoming more common across a wider range of industry. This could be viewed as a crisis or an oppor- tunity. For many, 4.0 implies a threat or a risk and we cannot brush that aside. The waves of change now envelop so broad a band of human endeavour that we really do face a revolution. Although the change is quick and mer- ciless, the concept as a whole takes us back to a far more integrated global vil- lage, and the capacity to deploy people into more suitable roles. This is profoundly important, yet the reality is likely to be clouded by fear of change and the perception of crisis. I am of the opinion that one should never waste a crisis. Embrace change. Yes, change may hurt some. Is that not the nature of revolution? We need to ask how we can embrace change and the opportunities it presents while striving to reduce the number of casualties. This will only be achieved with decisive leadership.

ECAUG2018.indd 1 7/30/2018 2:11:22PM www.electricityandcontrolmagazine.co.za

AuCom ’s L-Series MVE soft starter is a powerful and reliable solution for any medium voltage starting requirements. (Read more on page 11).

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CONTENTS

4

Features

ELECTRICAL PROTECTION + SAFETY 4 Lighning and surge protection on solar plants: Alexis Barwise, Lightning Protection Concepts

8 Round Up

TRANSFORMERS + SUBSTATIONS 14 Major factors influencing transformer oil degradation, Corne Dames: Henque 3056 Transformer oil purification

17 Understanding dry-type transformers, David Claassen, Trafo Power Solutions

20 Round Up

CYBER SECURITY 22 Cyber security for industrial automation and control envi- ronments, Ivan Fenandez: Frost & Sullivan

24 Round Up

POWER QUALITY, STANDBY + BACKUP 28 Demanding environments call for robust diesel generators

17

30 Natural gas generators in standby applications, Nalen Alwar, Altaaqa Global

31 Round Up

TEMPERATURE MEASUREMENT + INSTRUMENTATION 34 Improving temperature measurement in power plants, Ravi Jethra, Wika Instrumentation

28

34

38 Round Up

Regulars

1 Comment 11 Cover Article 42 Light+Current 44 Write @ the back 44 Events 44 Advertisers

2 Electricity + Control

AUGUST 2018

ELECTRICAL PROTECTION + SAFETY

Lightning and surge protection on solar plants

Alexis Barwise, Lightning Protection Concepts

It is of great importance to protect the sensitive electronic system components on solar farms or rooftop solar panels, as well as any equipment that is connected downstream, from failure due to lightning flashes and surges.

Take Note!

The three-step protection pyr- amid: Installation of a stable grounding system. Installation of AC and DC surge protection devices. Installation of a well-de- signed structural lightning protection system. 1 2 3

I n recent years, photovoltaic (PV) systems have become a significant sector within the energy market, with the International Energy Agency saying that: "The development of affordable, inex- haustible and clean solar energy technologies will have huge longer-term benefits. "It will increase countries’ energy security through reliance on an indigenous, inexhaustible and mostly import-independent resource, en-

hance sustainability, reduce pollution, lower the costs of mitigating climate change and keep fossil fuel prices lower than otherwise. These advantag- es are global". Given that these costly plants are frequently subject to climatic influence, measures to protect the sensitive electronic system com- ponents from failure due to lightning flashes and surges are essential. Lightning surges in the PV system can dam-

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ELECTRICAL PROTECTION + SAFETY

air-termination system. According to the class of lightning protection system, the height and the quality of the air-termination rods required is de- termined by means of the rolling sphere method. Furthermore, it has to be ensured that the sepa- ration distance is kept between the PV support- ing frames and the air-termination rods. Also, the operation building must be equipped with exter- nal lightning protection. Down conductors must be connected with the earth-termination system by using terminal lugs. Due to the corrosion risk at the point where the terminal lugs come out of the soil or concrete, they have to be made out of corrosion- resistant material or be protected by corresponding measures (applying sealing tape or heat-shrinkable sleeve, for example). Earth-termination system The earth-termination system of the PV system is designed as a ring earth electrode (surface earth electrode); whilst the earth-termination system of the operation building should be designed as a foundation earth electrode. The metal support- ing frames, onto which the PV modules are fixed, must be connected to the earth-termination sys- tem approximately every 10 metres. The earth-ter- mination system of the PV system and the one of the operation building, have to be connected to each other via at least one conductor. The interconnection of the individual earth-ter- mination systems reduces considerably the total earthing resistance; whilst the intermeshing of the earth-termination system creates an equipotential surface that considerably reduces the voltage load of lightning effects on the electric connecting ca- bles between the PV array and operation building. Lightning equipotential bonding In principle, all conductive systems entering the operation building from outside have to be gener- ally included into the lightning equipotential bond- ing. The requirements of lightning equipotential bonding are fulfilled by the direct connection of all metal systems and by the indirect connection of all live systems via lightning current arresters. Light- ning equipotential bonding should be performed preferably near the entrance of the structure in or-

Measures to protect the sensitive

electronic system components from failure due to lightning flashes and surges are essential.

age PV modules and inverters, leading to both high repair costs and considerable profit cuts for the operator of the plant related to system fail- ure. For a complex PV installation, such as a solar power plant, the aim is to protect both the opera- tion building and the PV array against damage by fire (direct lightning strike) and the electrical and electronic systems (inverter, remote diagnostics system, generator main line) against the effects of lightning electromagnetic impulses (LEMP).

Air-termination system and down conductor system

For the protection of the PV array against direct lightning strikes, it is necessary to arrange the so- lar modules in the protection zone of an isolated

Electricity + Control

AUGUST 2018

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ELECTRICAL PROTECTION + SAFETY

Surge protection measures for IT systems

der to prevent partial lightning currents from pene- trating the building.

The operation building provides a remote diagnos- tics system, which is used for the quick and easy function check of the PV systems, permitting the operator to recognise and remedy any malfunc- tions at an early stage. The remote supervisory control system pro- vides the performance data of the PV generator constantly in order to optimise the output of the PV system. Measurements of wind velocity, mod- ule temperature and ambient temperature are performed via external sensors at the PV system and can be read directly from the acquisition unit. The data acquisition unit provides an Ethernet in- terface, which a PC or modems are connected to for remote enquiry and maintenance. Thus, the service engineers can determine the cause of a malfunction by tele-diagnosis and then directly eliminate it. Conclusion In order to provide a reliable trouble-free and con- tinuous transmission of the measured data to the measuring unit, it is necessary to lead the sensor cables entering the building via surge protective devices. When choosing the protective devices, it has to be ensured that the measurements cannot be impaired. Safety in the forwarding of the meas- ured data via the telecommunication network per ISDN modem must be given as well in order to provide a continuous monitoring and optimisation of the performance of the installation.

Surge protection measures in the PV array In order to reduce the load on the isolation inside the solar modules at a lightning strike into the iso- lated air-termination system, thermally monitored surge protective devices are installed in a gener- ator junction box as loosely as possible to the PV generator. On the dc side, a surge protective device is in- stalled in each generator junction box. The surge protective devices in the generator junction boxes assume the protection for the PV modules locally and ensure that no spark overs caused by conduct- ed or field-related interferences come up at the PV modules.

Alexis Barwise is a co-owner and director of Lightning Protection Concepts. He is also a founding member, and current board chairman, of the Earthing and Lightning Protection Association (ELPA).

6 Electricity + Control

AUGUST 2018

round up

ELECTRICAL PROTECTION + SAFETY

Beyond the surge protection device

faced with inexplicable lockups, downtime and even some failures in surge protection caused by low level switching transient events. This is because typical SPDs are voltage triggered only. Their clamping will only oc- cur at a set point above or below the am- plitude of the sine wave, and will therefore not act upon low level switching transient events. While the Sine wave has remained the same since the late 1800s, the sensitivity of equipment connected to the grid is now higher. It is clear that standard SPDs are not doing enough to protect valuable sys- tems, such as in elevators, factory convey-

Around 25% of the world's electrical ener- gy is consumed by electric motors in indus- trial applications. However, as John Mitch- ell, global business development manager at CP Automation explains, installing vari- able frequency drives (VFDs) and surge protection devices (SPDs) are not the final steps in creating ultimate cost-efficiency. By implementing VFDs, many business- es experience an increased bottom line due to increased efficiency and reduced energy costs. However, the VFD is not without its problems – its normal operation can cause negative effects. Issues arise with VFDs as a result of power fluctuation. This could be caused by an anomalous event such as a lightning strike to the grid, or by lower level transient surges caused by VFDs countless times a day. These transient surges are a change in fundamental frequency in a microsec- ond time frame. If not accounted for, they can lead to confusion in electrical systems, such as false zero crossings, false trigger- ing of diodes and timing issues. A basic SPD may be used alongside a VFD to mitigate the damaging impact of high power surges, yet many users are still

ors or petroleum production equipment. The next step is to eliminate low level switching transient events. Surge and tran- sient protection systems such as the Sine- Tamer, offer a new opportunity to protect valuable assets from transient events that can occur millions of times per day. The fre- quency attenuation network of Sinetamer does this by monitoring the frequency, as well as the voltage. CP Automation has partnered with the makers of SineTamer, Energy Control Sys- tems, to supply this equipment across Eu- rope, the Middle East and Africa (EMEA). Enquiries: John Mitchell. Email john.mitchell@cpaltd.net

Next generation hand-held ScopeMeter

After 17 years of leading the 20 MHz and 40 MHz hand-held industrial oscilloscope category, Fluke models 123, 124 and 125 ScopeMeter test tools are being replaced by models 123B, 124B and 125B. The compact ScopeMeter ® 120B Se- ries, is the rugged oscilloscope solution for industrial electrical and electro-me- chanical equipment troubleshooting and maintenance applications. It is an inte- grated test tool, with oscilloscope, mul- timeter and high-speed recorder in one instrument. The ScopeMeter 120B Series also integrates with the Fluke Connect ® mo- bile app and FlukeView ® for ScopeMeter software to enable further collaboration, data analysis and archiving of critical test information. The 120B Series Industrial ScopeMe- ter test tools include innovative functions specifically designed to aid technicians in troubleshooting. Additionally, wave-

forms can be displayed with Connect and View™. Fluke’s IntellaSet™ technology triggers and sets up technology and allows for automatically view related numerical measurements, all without having to make manual measurement adjustments. With Recorder Event Detect capabili- ties, elusive intermittent events are cap- tured on repetitive waveforms up to 4 kHz and logged for easy viewing and analysis. Other features of the Fluke 120B ScopeM- eter include: • Dual-input digital oscilloscope and multimeter. • 40 MHz or 20 MHz oscilloscope band- width. • Two 5,000-count true-rms digital mul- timeters. • Dual-input waveform and meter read- ing recorder for trending data over ex- tended periods. Enquiries:Tel. +27 (0) 10 595 1821 or email sales@comtest.co.za

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AUGUST 2018

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ELECTRICAL PROTECTION + SAFETY

Siemens launches the right soft starter for every application During July Siemens hosted a series of launch events to introduce the South African market to its next generation Sirius 3RW5 range of soft starters. This comprehensive range of devices, developed especially for the soft starting of three-phase asynchronous motors, enables efficient and future-proof machine concepts to be imple- mented easily and cost-effectively. Siemens’ range of SIRIUS soft starters, with intelligent functions, offers a soft alternative for almost any application, from simple to sophisticated drive requirements such as heavy-duty starting. They enable you to start three-phase motors smoothly, easily, and efficiently and implement reliable ma- chine concepts. Furthermore, SIRIUS soft starters are the best solution when direct or star-delta starting doesn’t apply to three-phase motors, because problems can often arise due to mechanical impact in the machine or voltage drops in the line supply. Scalable soft starter offering Siemens soft starters are divided into three categories: basic, gen- eral, and high performance, for easy to difficult starting processes. To make the additional functions of the SIRIUS 3RW52 and 3RW55 soft starters easier to use, the Totally Integrated Automation Portal (TIA Portal) can be helpful for your engineering. Enquiries: ZukiswaTyilana.

Tel. +27 (0) 11 571 2000 or email zukiswa.tyilana@siemens.com

Zameer Thayab and Craig Ryan demonstrate the Siemens soft starters at the launch.

Electricity + Control

AUGUST 2018

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round up

ELECTRICAL PROTECTION + SAFETY

Load pins: redundancy and safety A load pin connects force-transmitting machinery ele- ments while simultaneously enabling the measurement of the force. In addition to the general detection of static or dynamic forces by load pins, the safety that is ensured by various systems also plays an important role in the applica- tion. In safety engineering, a distinction is made between direct, indirect and indicative safety: • Direct safety ensures that, in the event of the failure of a machine, components are shut down in a manner that eliminates further danger to people and does not dam- age the equipment (redundancy, fail-safe or safe-life). • Indirect safety prevents collisions and contact with moving machine parts. • Indicative safety is indicated by signs or symbols dis- played on hazards. Safety through force measurement The role of load pins in the application of safety systems is two-fold. On one hand, the direct physical safety of people involved and, on the other hand, the failure- and hazard-free functioning of machinery. Components must not lose their functionality due to overload or material failure. Load pins and their application People who are in immediate proximity to moving loads face a significant amount of potential danger. Direct safe- ty precautions must be taken to ensure their safety. Load pins and safety electronics The combination of electronics and load pins can gen- erally be used on lifting gear to prevent danger. It pro- tects both the operating personnel and the equipment itself. As a result, the EU machinery directive 2006/42/EC can be easily implemented. This requires that machines with a maximum load capacity greater than or equal to 1 000 kg or a tipping moment greater than or equal to 40 000 Nm are equipped with devices which warn the driver and prevent a dangerous movement. This can hap- pen by exceeding the maximum load capacities, load tor- ques or tipping moments. The use of suitable systems with load pins and safety and overload electronics en- sures trouble-free operation in a wide range of industries, where the protection of people, the reliability of applica- tions and the protection of machinery are important. Enquiries:Tel. +27 (0) 11 621 0000 or email sales.za@wika.com www.wika.co.za

The ultimate tool backpack for maintenance professionals It can be very inefficient, not to mention frustrating, for maintenance professionals to have to go back and forth to the office stores to fetch additional tools. COMTEST offers the new Fluke Pack30 Professional Tool Backpack that makes it easy to organise, transport, and access all tools needed for the day. Designed specifically for an electrician; DMMs, clamps, tools, and accessories, the rugged backpack also protects tools even in the dirt- iest of work sites. For digital users, the Fluke Pack30 offers a way to carry all the necessary tools while keeping one's hands free to use cell phones and tablets. The Fluke Pack30 features: • More than 30 pockets and pouches designed to hold a broad array of tools and accessories. • Six main storage compartments for convenient organisation. • A special pocket for tablets and laptops. • Storage for safety glasses, earplugs, cell phones and valuables. • Rugged, waterproof moulded bottom to protect tools and accesso- ries from the elements. • The moulded base holds the backpack upright, keeping tools organ- ised and within easy reach. Enquiries:Tel. +27 (0) 10 595 1821 or email sales@comtest.co.za

10 Electricity + Control

AUGUST 2018

COVER ARTICLE

FEATURES: · Electrical protection+ safety · Transformers+ substations · Cyber security · Temperaturemeasurement+ instrumentation

Specialists in softstarter technologies

A CDC Dynamics boast a full product offering in low voltage soft starters from 7 kW to 500 kW and in medium voltage from 2.3 kV to 13.8 kV up to 1.7 MW. With an exclusive focus on soft starters, AuCom expertly develops a range of industry-lead- ing control products for industrial applications. Take control from the start The L-Series MVE soft starter is packed with fea- tures including real-language feedback messages, built-in monitoring systems and indicators, together with extensive on-board input and output function- ality. Real-time graphs showing motor operating performance and current quickly and clearly illus- trate motor performance. Powerful and reliable Variables such as altitude, ambient temperature, load and starts per hour all affect selection of the ideal motor starting solution. Aucom employs so- phisticated engineering tools to assist in selecting the right MVE starter for unique site conditions. • A design based on standard components re- duces the need for spare parts and simplifies- support. • An ultra-compact form factor supports vertical or horizontal integration of power electronics, saving valuable space. • Individually removable phase arm design allows for simple installation, service or replacement. • Conformal coating on PCBs for protections in environments up to pollution degree 3 • Shorter lead times owing to a design that lends itself to more automated manufacturing- processes. • Status LEDs for immediate feedback. • Intuitive interface and menu structure for easy setup, with multi-level password protection. • IP54 keypad mounted on cabinet exterior. Panel details L-Series MVE panels are available in either IP4X or IP54 panels, with options for line and bypass devices, as well as earthing and isolation switches.

AuCom can also design and build panels to meet particular specifications, and offers full application engineering support at all stages of the design pro- cess. For customers who prefer to build their own panels, MVE soft starters can be supplied in IP00 format or as a kit for local assembly. Multi-motor solutions are also available for coordinated control of up to four motors. Arc fault Arc faults can occur for a number of reasons includ- ing over voltage, faulty insulation, mechanical failure or failure of a fuse. If an arc event occurs within an AuCom L-Series panel, the fault is contained by solid locking doors and heavy double-layer compart- ment panels. During the emission phase, the pres- sure is safely released using discharge flaps on the top of the panel (or optional ducts), which direct the explosion upwards or vent it safely outside. Even safer with IBT technology AuCom Interface Board Technology (IBT), a unique concept within the medium voltage soft starter- market, separates the core starter control system (including the starter’s HMI and complex, time crit- ical algorithmic processing) from the medium volt- age power section. The interface board is located within a separate, section of the internal arc tested medium voltage compartment. Fibre optic wires connect the control and power sec- tions of the starter through the interface board, eliminating the need for any copper wiring and providing complete galvanic iso- lation of the low voltage compartment.

Enquiries: Dirk Holm Tel:+27 (0)10 202 3300 Email:info@acdc.co.za

Electricity + Control

AUGUST 2018

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round up

ELECTRICAL PROTECTION + SAFETY

Protecting data centres from lightning and surges

Data centres rely on the optimal perfor- mance of equipment, and surges can crip- ple operations. Data centre operators need to be able to effectively manage these energy spikes, as it can cost a significant amount of money to recover from the re- sultant downtime or hardware damage. Across the continent, DEHN AFRICA’s ex- pertise provides surge protection for data centres against various potential causes. According to Julienne Puttkammer, a member of the Technical Team at DEHN AFRICA, there are two main types of risk when it comes to data centres and electrical power surges. “The leading causes of pow- er surges in data centres are direct or indi- rect lightning strikes and internal or external switching surges," says Puttkammer. “In Africa, the foremost causes of surg- es to data centre systems largely depend on the area. For example, in regions with a sta- ble power supply, power surges could most commonly be caused by lightning strikes, while in areas with an unstable supply the most frequent cause may be from on-off switching. Even a nearby lightning strike, and not necessarily a direct hit, can cause a surge to flow on conductors and electrical lines. The factors to look at are whether one is in a lightning-prone area, and the stability of the power grid.” Puttkammer says that because there can be catastrophic consequences for a direct lightning hit, it is common, in DEHN AFRI- Schneider Electric makes selecting a UPS easy. Most homes and small office in South Africa need to have power running continuously, particularly when it comes to computers, security devices or essential electrical equipment. When the power goes out, work can be lost, alarms can start beeping and lights are not available. The answer to this can be an uninterrupted power supply (UPS) that allows you to save your work, power down your computer, run a light and charge a phone. Small UPS systems provide power for a few minutes; enough to power down the computer properly without losing informa- tion, while larger systems have enough

CA’s experience, for data centre designers to opt for lightning protection installation, regardless of whether the normal risk pro- cedure requires it or not. He notes, “Data centres contain sensitive operations, for which all kinds of back-up power need to be implemented to secure a constant stream of power, and no down-time. Even within the data centre itself, one can find on and off switching. For example, a cool- ing system can cause switching surges, which are also a danger to the electronics. On and off switching is the main cause of non-lightning-related surges.” Puttkammer says the main challenges in implementing surge protection measures in- volve coordinating how to implement all the aspects of lightning and surge protection from the beginning of the project. “Ideally, the most comprehensive solution would in- clude all the interlinking systems of lightning and surge protection from the design stage, to have all the components optimised. We need to think about issues such as cable routing or embedding bonding conductors in concrete – these need to be very well coor- dinated from the beginning of the planning and construction phases,” he explains. “To come in once a rollout has been completed or is already underway means that you need to find the space to install and implement surge protection systems, which then requires some sort of compro- mise in most cases. While it is not impos- battery for several hours and can run more than one electrical item. A UPS is also use- ful as a buffer between the main electrical supply and one's computer, protecting it against surges or lightning. APC by Schneider Electric offers many products to power and safeguard critical electronics. This includes access to news and weather updates, important files stored in the Cloud, streaming services and email access. Schneider Electric is so confident in the performance of its products that it stands behind them with a guarantee. Back-UPS and SurgeArrest models include a lifetime Equipment Protection Policy that ensures customers get the peace of mind that only

sible to have a very good system installed later, retrofitting is not ideal. At DEHN AF- RICA we are, however, seeing an encour- aging move towards including lightning and surge protection for data centres from the beginning of projects.” With regards to DEHN's products and solutions for data centres and surge pro- tection, Puttkammer reiterates that it all starts with the planning phase. “We offer all the services required a risk assessment, soil testing if necessary, a detailed design, an earth electrode design for AC system faults, and an inspection and sign off on a lightning safety report. Thereafter we offer all the necessary tested products as well, including the lightning protection, earthing and bonding components as well as the electrical and electronic surge protection devices.” Enquiries: Hano Oelofse.

Tel. +27 (0) 11 704 1487 or email hano.oelofse@dehn-africa.com

Selecting a UPS for your home or office

the market leader can provide. Schneider Electric makes selecting an uninterrupted power supply (UPS) for one's home or small office very simple. Go to select a device and the website will offer you two ways to choose – either by the number of devices you want to protect or the load you want it to carry. Schneider Electric’s worry-free UPS backup and APC surge protectors deliver industrial-strength protection and reliability for your most important electronics. To find a supplier near you, go to Schneider Electric South Africa’s locator web page S A locator. Enquiries: Prisca Mashanda. Tel. +27 (0) 11 254 6400 or email prisca.mashanda@schneider-electric.com

12 Electricity + Control

AUGUST 2018

Informing industry across Africa P U B L I C A T I O N S

We will be at Electra Mining from 10 - 14 September

Visit us in the Link Node at Stand LN 08

Mech hem AFRICA

Phone: +27 11 622 4770 CROWN HOUSE 2 Theunis Street Cnr Sovereign Street Bedford Gardens, Bedfordview, 2007 P.O. Box 140 Bedfordview 2008 www.crown.co.za

Publ i sh ing on mul t ipl e pl at forms

TRANSFORMERS + SUBSTATIONS

Major factors influencing transformer oil degradation

Corné Dames, Transformer Tech Repair

Since oxygen has two free electrons, any in- gress of air in oil makes it more susceptible to an auto-oxidation process. Free radicals can easily break the hydrocarbon chains in oil and produce peroxides. Under heat, the peroxides decay to produce more free radicals, and thus the oxidation process compounds as a chain reaction process. Oxidation inhibitors could be added to slow down the oxidation process in the oil. However, if the sulphur content of the oil is high, oxidation effects on the unit might be more severe as more corrosive by-products form, with adverse effect on the unit. Some oils have natural inhibition proper- ties, depending on the source of the oil. Contamination The presence of water in oil, either in dissolved or suspended form, affects the dielectric properties of oil adversely. Thermal degradation of cellulose and oil will produce water internally, through a process of hydrolysis of the hydrocarbon chains. This can adversely increase if the unit operates at high temperatures. Measuring water content in oil is only a fraction of the total amount of water in the transformer, as the major portion of the water is absorbed by the Kraft paper of the transformer core. If the transformer core heats up, the equilib- rium state between the core and the oil favours movement from the core into the oil. When the unit cools down the opposite is true. Undertaking moisture analysis on a unit that is not operational is of very little value as it is impossi- Major factors influencing the degrada- tion of transformer oil include excessive heating, oxidation, contamination, par- tial discharges, and related by-products.

Thermal degradation Excessive rise of operating temperature is one of the most severe factors influencing the degrada- tion of transformer oil, and it is estimated that an increase of 8 – 10°C in temperature approximately doubles the rate of oil degradation.Therefore, units with higher temperature variations show greater degradation than units under constant load. Tem- perature changes in the transformer cause the oil to push air from the transformer when heating, and suck in air when cooling down, if the unit is free breathing. Chemical reactions in the hydrocar- bon oil take place at a much more rapid rate under high temperatures than in units with cooler oper- ating temperatures. As the oil decomposes, several by-products are formed, which further accelerate the ageing of the oil and solid insulation. As a result, the oil degra- dation rate increases with the formation of degra- dation products as this actually fuels the process. Oxidation Oxidation of oil causes a breakdown of bonds, followed by further chemical reaction. The main oxidation products of oil include water, carbon di- oxide, carbon monoxide, acids, and sludge. In ad- dition, the presence of dissolved metals such as iron, copper, etc, act as a catalyst to accelerate the oil degradation process. Bus bars, leads and wind- ings in the transformer’s tank act as catalysts for oxidation to take place even quicker than would be the case if they were not present.

Take Note!

Typical diagnostic tests used to determine transformer deg- radation include: Testing of new and old oil. Dissolved gas-in-oil anal- ysis (DGA). 1 2

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TRANSFORMERS + SUBSTATIONS

pockets will promote further partial discharges and can cause progressive deterioration of the oil. The severity of an electrical or thermal fault can be determined through Dissolved Gas in Oil anal- ysis, as the daily production rate of the relevant gases individually and in relation to each other may indicate where the problem is located and its se- verity. Electrical faults like arcing and corona can cause severe breakdown of the oil in the region of the fault, going hand in hand with the formation of carbon particles as a by-product of the reaction. Acid Acids are produced as degradation products of cellulose that gets dissolved in oil and also by oil oxidation. Acid levels higher than 0.6 mg KOH/g of oil are considered high and are detrimental to the operation of the transformer. It is recommended

ble to determine if there is free water at the bot- tom of the transformer, or the true percentage of water locked up in the core. Water may also be absorbed from the atmosphere in free-breathing units, which is why it is critical to ensure that no moisture can get into the unit, either through the breather or through any leaks in the unit, as this will cause the oil to deteriorate more rapidly. Partial discharges Gas may evolve in oil as a result of thermal stress or spurious electric discharges due to high elec- trical stress. These gas pockets contain hydrogen and hydrocarbon gases produced by decomposi- tion of the oil. Because of the difference in permit- tivity of the gas and the liquid insulation surround- ing it, the electrical stress across the gas voids will be very high. Such high electrical stress in the gas

In a power grid that is already showing many signs of advanced age, transformer inspection and monitoring is an increasingly important task.

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transformer oil throughout its operational life, es- pecially in humid atmospheric conditions. Howev- er, since paper has more affinity for water than oil, such moisture will primarily be stored in the paper rather than in the oil. During the manufacturing process, the core and coil assembly is heated for many days under vacuum to drive out any possible moisture that may be present. Hot oil is then admitted to the tank under vacu- um to ensure the removal of any gas or moisture remaining in the oil. The whole unit is further pro- cessed by circulating hot oil through a filter plant. At this stage the new transformer has a moisture content of <0.5% by weight in the paper and <5 ppm in the oil. During operation of the trans- former, thermal and chemical degradation of paper insulation also produces water as a by-product of chemical reactions and, in a severely deteriorated system, the moisture content of the paper may reach more than 4%. This process is accelerated by the heat produced when the transformer is on load. If the transformer spends much of its life at low load, its useful life will be greater than a generator transformer, which usually runs close to its nameplate rating. Measures to minimise oil degradation Oxidation is the major cause of oil degradation in free breathing transformer units. To prevent the in- gress of air into the transformer during the breath- ing process, nitrogen gas cushion transformers can be used, where dry nitrogen is used to fill up the tank space above the oil to minimise the expo- sure of oil to oxygen. Changing the silica gel in the breather before it is saturated with moisture can minimise the ingress of moisture via this route. Adding oxidation inhibitors such as DBPC to new oil effectively prevents the ageing of the oil. The ageing process of oil is accelerated by the presence of metals and adding amino group in- hibitors can eliminate this influence. Frequent fil- tration of the oil to remove excess moisture can slow down the degradation rate. Temperature is a dominant factor of oil degradation. The oil temperature can be limited to safe val- ues through the use of cooling tubes that aid in the heat convection and dissipation process. Cooling efficiency can further be improved by artificial cool- ing techniques such as forced fan cooling, forced oil cooling, or water cooling. Large transformers are often equipped with pumps in the oil line, and in the water line, to enhance cooling.

that the oil is replaced before it reaches 0.2 mg KOH/g as the formation of sludge is not irrevers- ible at this stage and it might be flushed from the unit. Acids cause the formation of sludge in oil. Sludge is a solid product of complex chemical composition and gets deposited throughout the transformer. Deposition of sludge can adversely affect the heat dissipation process by blocking oil circulation through the radiator pipes, leading to overheating and subsequent failure of the trans- former. Acid damages the structure of the insu- lation paper, with a subsequent loss of optimal transformer lifetime reached. Undesirable effects of moisture on oil All oil-paper transformers contain some water in their solid insulation. The paper in a transformer acts as the reservoir for moisture content through- out the insulating system. Water remains in a continuous dynamic state within the complex in- sulation system of a transformer. Depending on the operating temperature, water exchange takes place between the liquid and solid insulation. High levels of moisture in transformers can accelerate the ageing process of solid insulation, reducing the dielectric strength of the oil. Since at higher temperature the solubility of wa- ter in aged oil increases, even with an increased amount of water, the percentage saturation of the oil remains low and the dielectric breakdown volt- age of the insulation system remains high. Prob- lems arise in the oil when the transformer cools down again. It is possible for excessive moisture to remain in the oil because it migrates much more slowly back into the paper.This causes the oil to be- come supersaturated with water, leading to the for-

Corné Dames is the Sales and Service Manager at Transformer Tech Repair.

mation of free water in the transformer. The free wa- ter can settle where it will contribute to surface flash- over or could collect at the bottom of the cooler bank. Sudden operation of the oil pumps can direct this wa- ter onto windings, causing insulation failure and result- ing in major electrical break- down or short-circuit failure of the windings. In free-breathing trans- formers, a small quantity of water can enter the

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T he primary factor differentiating these units from the more common liquid-filled transformers is that their electrical core and coils are cooled by normal air ventila- tion, rather than by oil, silicone or other liquid; ducts in the windings allow heat to be dissipated into the air. The construction of dry-type transformers therefore differs considerably from liq- uid-filled units, and separate industry standards apply to the ways they are designed, built and maintained. Containing no oil means higher levels of safety, making dry-type transformers more suitable for indoor, underground and marine applications, but they can operate in a range of hostile outdoor environments as well. They do not require fire-proof vaults, catch basins or facilities to vent toxic gases, and can be easily installed within buildings in close proximity to the load itself; this improves the overall regulation of the system and reduces costly losses in the secondary lines. As a key component of the electrical distribution system, a dry-type transformer must be carefully specified and chosen according to its capacity (its kVA rating), its voltage rating (primary and secondary voltage of the transformer), and its insulation system, which must accommodate the maximum ambient temperature, plus the average wind- ing temperature rise, plus the differential between the average winding temperature rise and the highest temperature of the winding. Voltage ratings There are numerous specifications in which dry-type transformers can be sourced. Large units – commonly available in sizes from 500 kVA to 10 MVA – are usually fed by medium voltage power systems between 3,3 kV and 33 kV, with secondary voltage ratings of 400 V, 550 V, 690 V or 720 V three phase. Insulation methods As the windings of dry-type transformers use air for cooling, there are several treatment techniques to insulate and protect the windings from dirt, moisture, corrosive fumes and conductive dust. Each construction method is suited for particular applications or operating environ- ments; the main types of insulation are open-wound, vacuum pressure impregnated (VPI) and cast coil. Open-wound transformers – open to help ensure penetration of the varnish – are constructed using a dip-and-bake method, in which the conductor coils are pre-heated, The use of dry-type transformers has, in recent decades, extended be- yond niche applications into more universal use, with benefits ranging from safety and reliability to low installation costs and no oil-spillage risk. But what makes a dry-type transformer so different, and what types are available? Understanding dry-type transformers David Claassen, Trafo Power Solutions

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Take Note!

Specifications to consider when selecting a dry-type transformer include: Voltage ratings.

1 2 3

Insulation methods. Classes of insulation.

heated and dipped in varnish at high temperatures. The coils are then baked to cure the varnish. Cooling ducts in the windings provide an effi- cient and economical method of removing heat produced by electrical losses, by allowing air to flow through the duct openings. This dry-type in- sulation system operates satisfactorily in most ambient conditions. A variant of this type is the encapsulated (or sealed) transformer, which is a standard open-wound distribution transformer en- cased in an electrical-grade silica and epoxy, and totally enclosed in a heavy duty style enclosure. VPI transformers are built with high tempera- ture insulation that exceeds the rating of cellulose or 'O' and 'K' class fluids. They contain materials resistant to high temperatures, and the coils are coated with polyester sealant that resists moisture and high temperatures. The varnish coating of polyester resin is applied in interchanging cycles of pressure and vacuum, after which the coils are cured in an oven. The VPI process is better than the standard dry-type insu- lation because it includes pressure in addition to vacuum, allowing better penetration of the varnish in the transformer coil. In a similar but superior process, vacuum pres- sure encapsulated (VPE) transformers undergo several more dip processes during construction, to encapsulate the coil assembly before the coat- ings are cured in the oven. The result is better pro- tection from harsh and wet environments than the VPI type. In cast coil designs , the coils are solidly cast in resin under a vacuum in a mould. To en- sure even distribution of resin and a high level of precision, the winding processes are controlled by advanced electronics. These transformers are particularly reliable and can withstand heavy power surges and frequent overloads. They can also be exposed to extreme conditions in outdoor installations where mois- ture, salt spray, corrosive fumes, dust and metal particles are present in the air. Even in these demanding conditions, they re- quire minimal maintenance and are commonly found in buildings, tunnels, ships, offshore plat- forms, cranes, mines and even nuclear plants. Classes of insulation The level of insulation in a dry-type transformer determines its dielectric strength and capacity to withstand certain thermal limits. There are var-

ious classes of insulation, according to the tem- perature rise rating to be accommodated: Class A (105°C temperature rise), Class B (130°C), Class F (155°C), Class H (180°C) and Class R (220°C). Effi- ciencies are generally better in the lower temper- ature rise transformers, particularly at loadings of 50% and higher. For instance, full load losses for 115°C transformers are about 30% less than those of 150°C transformers, while 80°C transformers have about 15% fewer losses than 115°C trans- formers and 40% less than 150°C transformers. Advantages The growing popularity of dry-type transformers is because of a range of advantages. Safety factors rank high among these benefits, as the technology presents a low fire hazard and is self-extinguishing. Transformer insulation is a mix of epoxy resin and eco-friendly quartz powder, making the wind- ing flame retardant. In addition, it does not produce toxic gases when arcing occurs.These factors elim- inate the need for costly fire extinguishing equip- ment. The absence of oil in the dry-type transformer not only reduces the fire and explosion risk but means that there is no environmental risk of oil leaks, pollution or ground contamination. Several other costs related to the use of oil are also eliminated, such as liquid level checking, oil testing and recycling, and dielectric testing for moisture absorption. Owing to the higher safety levels, there are fewer restrictions on where and how dry-type transformers are installed on site. For instance, no brick or concrete bund wall is required to catch oil spills, and the units can be located closer to the load, reducing the cost of losses and cabling. The reliability of dry-type transformers is high. Cast resin transformers, for example, typically have a service life of over 25 years and an ex- tremely low failure rate. Maintenance requirements are also low, using only air to cool, liquid testing is unnecessary, and the smooth coil surface eliminates heavy dirt build- up even in the most extreme circumstances. Cast resin transformers are designed to meet Class E2 environmental requirements which include resist- ance to consistent condensation and heavy pollu- tion in terms of IEC 60076-011. Conformance to Class F1 ensures that trans- formers meet the requisite fire compliance require-

A multi winding cast resin transformer.

A cast resin transformer with customised terminations.

A freeze chamber used for C2, E2 and F1 tests.

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Dry-type transformers are ideal for indoor, underground and marine applications.

ments including self-extinguishing characteristics as well as non-hazardous gas emissions. The transformers are also suitable for transportation, storage and operation at temperatures as low as minus 25°C, meeting Class C2. Multi-layer winding in dry-type transformers – which permits the easy introduction of extra cooling ducts in the coil – also allows the units to safely handle high surge voltages, and to balance surge voltage stress

across the winding. The larger cooling surface area facilitates a uniform temperature dis- tribution.Dry-type transformers can be engineered to operate in very cold climates, as well as in hot and humid regions. The coil support system in these transformers has uniquely developed spacers, which isolate vibrations from the iron core; this reduces noise levels considerably and makes for much quieter operation.

David Claassen is the Managing Director at Trafo Power Solutions.

Low voltage and medium voltage coils frozen during the test procedure.

A cast resin transformer in a test bay.

View of a transformer inside a freeze chamber being tested for C2, E2 and F1 compliance.

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