Darbe generatörü veri alma ve işleme yazılımı
Data acquisition and processing software for impulse voltage generator
Yazar: EMRAH DOKUR
Danışman: PROF. DR. AYDOĞAN ÖZDEMİR
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Elektrik Mühendisliği Ana Bilim Dalı
Derece: Yüksek Lisans, 2013
Konu: Elektrik ve Elektronik Mühendisliği = Electrical and Electronics Engineering

Özet:
Güç sistemlerinin kapasitelerinin artmasının yanısıra çalışma güvenilirliği de büyük önem taşımaktadır. Güç sistemlerinde kullanılan bir elemanda meydana gelecek arıza, sistemin büyük kısmının devre dışı kalmasına ve güvenilirliğinin azalmasına neden olabilmektedir. Arızaların önemli bir kısmı yalıtım kaynaklı arızalardır. Yalıtım bozulmaları, yüksek gerilim altında çalışan cihazlarda, çeşitli nedenlerle oluşan aşırı gerilimler nedeniyle yalıtımın zorlanmasından veya zamanla yalıtımın zayıflamasından oluşur. Sistemde meydana gelecek aşırı gerilimler şebeke kaynaklı olabileceği gibi, yıldırım vb. şebeke dışı kaynaklı da olabilmektedir. Bu nedenle yüksek gerilim elemanlarının aşırı gerilimlere karşı dayanımları sağlanmalıdır. 
Yüksek darbe gerilimleri, atmosferik dış aşırı gerilimlerin yol açtığı zorlanmaları deneysel olarak saptamak, yalıtkan malzemelerin yüksek gerilime dayanım şartlarını araştırmak ve üretilen ürünlerin ulusal ve uluslararası standartlara uyumluluğunu deneysel olarak belirlemek için kullanılırlar. Bu tez çalışması kapsamında da, İTÜ Fuat Külünk yüksek gerilim laboratuvarında bulunan 6 katlı 1 MV, 10 kJ'luk darbe gerilimi üretecinden elde edilen yıldırım darbe gerilimi işaretinin bilgisayar ortamına aktarılarak analizinin kolaylıkla yapılabilmesi amaçlanmıştır. 
Yüksek darbe gerilimlerinin, standartlarda öngörülen parametrelerinin belirlenmesi ve yorumlanması gerekmektedir. Standart osiloskoplar ile darbe gerilim ölçümlerinde, genlik ve zaman parametrelerini ölçmemiz mümkündür. Fakat kullanıcı, genlik ve zaman parametrelerini belirlerken osiloskobun yakaladığı işaret üzerinde, genlik ve zaman ayar düğmelerini elle hareket ettirerek bazı kritik noktaları tespit eder ve çeşitli matematiksel işlemleri yaptıktan sonra işaretin istenen genlik ve zaman değerlerini hesaplar. Bu yöntem uzun zaman alan ve hataya açık bir yöntemdir. 
Tez çalışması kapsamında  oluşturulan yazılım sayesinde yüksek darbe gerilimi işaretleri, 2 GS/s örnekleme frekansına sahip 200 MHz'lik bir osiloskoptan .CSV formatında MATLAB GUI ortamında oluşturulan arayüze aktarılmıştır. Yazılım ile yıldırım darbe gerilim parametreleri bilgisayar ortamında otomatik olarak belirlenebilir, işaretler zaman ekseninde ve frekans ekseninde ayrı ayrı çizdirilebilir, istenildiği takdirde yazılım vasıtasıyla işaret üzerindeki gürültü bileşenleri yok edilebilir ve girilen çevirme oranına göre darbe gerilimi çizdirilebilir. Ayrıca alınan darbe gerilim parametreleri Microsoft Excel ortamına aktarılarak kayıt edilebilmekte ve raporlanabilmektedir. Yazdırma önizleme, direk yazdırma özellikleri ile raporlar alınabilir, aynı zamanda büyütme özelliği ile grafik üzerinde istenilen noktada analizler yapılabilmektedir. 
Çalışma kapsamında diğer darbe gerilimi ölçüm sistemlerinden farklı olarak, yıldırım darbe gerilimindeki gürültülerin nedenleri de araştırılmıştır. Yazılımın frekans ekseninde analiz yapma özelliği, hangi frekans bileşenlerinde gürültülerin meydana geldiğini bizlere gösterebilmektedir. Yine araştırılan makaleler ve bildiriler doğrultusunda elektromanyetik girişim kaynaklı gürültüler, yıldırım darbe şekli üzerinden belirlenmiştir. Savitzky-Golay yöntemi referans alınarak, işaret üzerinde gürültü bileşenleri ayrıştırılmıştır. Gürültülü veya gürültüsüz işaretin gözlemlenmesi tuşlar vasıtalasıyla kullanıcıya bırakılmıştır. Frekans analizinin getirmiş olduğu üstünlüklerden biri de; gürültünün ölçüm sisteminden veya sistem elemanlardan kaynaklandığına ilişkin yorum yapabilmesini sağlamasıdır.
Yıldırım darbe gerilimleri ile yapılan deneylerde, kullanıcının okuma hatalarından uzak, kolaylıkla kullanabileceği böyle bir yazılım ile bilgisayar destekli analizlerin yapılabilmesi ve işaretin işlenebilmesi ile çalışma, hedefine ulaşmıştır. Ulaşılan bu hedef ile bundan sonraki çalışmalarda, yazılıma otomasyon sisteminin de eklenerek geliştirilebilmesine ve gürültünün çeşitine göre otomatik olarak süzme işlemini yapabilen özelliklerde bir programın oluşturulmasına temel hazırlayarak bu alanda çalışanlara yeni ufuklar açmıştır.

Abstract:
An uninterrupted supply of electricity is of supreme importance in our daily activities. Transient overvoltages and overcurrents due to lightning and switching surges are the main causes of interruption of the continuous supply of electricity. They cause discharges in the insulation of the transmission lines and various power apparatus thus resulting severe damage to these equipments. So, power apparatuses are generally subjected to several insulation tests to demonstrate that the equipment fulfills the specified requirements of the quality standards. High voltage laboratories are an essential requirement for making research as well as performing the acceptance tests for the equipments those will be the part of the high voltage transmission systems. 
This study was carried out at Istanbul Technical University Fuat Kulunk High Voltage Laboratory. All tests are performed by using 1 MV, 10 kJ, six stages impulse voltage generator. Istanbul Technical University, Fuat Kulunk High Voltage Laboratory is the biggest high voltage laboratories in Turkey where high voltage tests are performed for industrial utilities as well as academic researches are conducted. The laboratory consists of several blokes that perform various tests. Six stages, 10 kJ impulse voltage generator that is located in B block of the laboratory can perform lightning impulse voltage tests up to 1 MV.
There has been a major change in waveform recording devices and methods of high-voltage impulse tests over the last four decades. Nowadays, digital waveform recorders have become dominant although, prior to 1970, virtually all impulse recordings were performed using oscilloscopes. This change has been driven by five factors: technical improvements in digitizers, economical benefits of using digitizers, elimination of subjective judgements by the operator, growth in the use of quality systems, and the use of digital signal processing to extract more information from the test records.
Early digitizers had limitations that prevented them from being fully utilized in impulse measurements. However, they sparked widespread interest and several organizations developed programs to evaluate digitizers and digital techniques. Further developments have led to a large number of models, made by different manufacturers, which are as good as oscilloscopes for impulse measurements. Indeed, several of these digitizers are better than oscilloscopes for some applications.
The economic benefits include: automated reading of records (usually on a desktop computer), easy transfer of the results to reports when compatible software is used, and the ability to compare several different analysis algorithms without compromising the record. The application of standardized reading algorithms for smooth impulses has eliminated subjective judgements by the operator (standardized algorithms for distorted impulses are under consideration).
The standards on high-voltage tests define all parameters in terms of a smooth impulse. High voltage impulse generators are dominated by the values of resistance and capacitance used and usually produce smooth impulses that are approximately double-exponential in form when used with a capacitive test object. 
The main amplitude parameter is the peak voltage.  Time parameters are defined in terms of the differences between the two times at which the impulse crosses particular fractions of the peak value, e.g., the front time is defined as 1.67 times the difference between when the impulse first crosses 30% of the peak value and the time when it first crosses 90% of the peak value. Lightning impulses have standard front times of about 1.2 µs. Standard peak values for tests range from 50 kV to 2 MV. 
The voltage divider is the most important component of the circuit, and the quality of the measured waves is closely related to its performance. However, recent reports have shown that using appropriate materials with the correct design and construction technique can lead to a performance suitable for the measurement of almost all HV impulses. Moreover, the new philosophy of using a chain of reference dividers to improve the traceability of test results ensures that divider performance is adequate for a given measurement.
After dividing the high voltage signal to the measurable low voltage level, evaluation of this signal is made by high voltage measurement systems such as peakvoltmeters, digital recorders or oscilloscopes. It is not enough to use the peak voltmeters alone at impulse high voltage measurements since they can not measure the time parameters. It is possible to measure the amplitude and the time parameters of the impulse voltages with standart oscilloscopes. However, such a measurement involves moving the voltage and the time cursors of the oscilloscope manually on the screen. After having determined the relevant places of voltage and time parameters with cursors, the user have to make some mathematical calculations to determine the impulse signal parameters. Such a measurement is a time consuming process and also includes high user errors. Recorders are the most ideal measurement device for the impulse voltage measurements.
Digital recording systems contribute to the analysis of the wave shape during the test. The noise can be found by the analysis which can also give information about the reason of disturbances to the user. The operator then can take the relevant actions to avoid those disturbances.
The corruption due to interferences in the measuring system is produced by electromagnetic radiation generated by the HV impulse, that runs in the test circuit, and is picked up by the measuring system. The disturbances have, again, an oscillating nature, but its characteristics are now closely attached to the shape of the HV impulse and, so, their characteristic frequency is higher than 500 kHz. In many occasions the durations of this type of disturbances are limited and their influence on the registered waveform is only localized in a short time gap.
Beyond the difference in what concerns their characteristic frequency, the two types of disturbances have very important differences between them: The first type of disturbance  presents in the HV impulse that is applied to the equipment under test, whereas the second type of disturbance only presents on the recorded waveform and, so, does not have any correspondence in the applied HV impulse. Having this fact in mind, the characterization of the impulses must only take into account the disturbances due to the test circuit, but not those due to electromagnetic interferences. The international standard specifies that the oscillating phenomena with frequency above 500 kHz has to be discarded before the impulse characterization.
Working in the time domain, or in the frequency domain, several methods were proposed, by different researchers, for digital processing of HV impulses recorded during the tests. However, those methods do not allow an efficient processing. The time domain methods are basically based on fitting techniques and, so, they become very heavy and very dependent on the skill of the operators. To improve the efficiency a large set of standard curves must be used in the fitting procedure and the choice of the best standard curve to be used requires the presence of a skilled operator. The frequency domain methods are based on the analysis of the classic spectrum of the impulses, which can inform about the presence of the undesirable frequencies, but do not give any information concerned with the duration of the disturbance phenomena. Without that information and assuming that the disturbance phenomena are present in all the time duration of the impulses, the processing procedure may, in many cases, have an erroneous action on undisturbed zones of the impulse.
This thesis presents such a software which is written in Matlab Gui. The software yet can calculate the peak value, the timing of peak value, front time (T1), and time to half value (T2) of impulse voltage.
Software can represent the impulse voltage both in time domain and in frequency domain. It consists of noise filtering option using Savitzky-Golay method. Impulse voltage magnitude can be calculated using the divider ratio.
Impulse voltage parameters can be exported as an Microsoft Excel file automatically. If required, the datas and graphics can be printed either by using direct print or by using print preview buttons.
Impulse voltages are generated by six stage impulse generator and mesaured by a digital oscilloscope. An output from oscilloscope's usb port is applied to the computer's usb port. Oscilloscope data is sent to Matlab Gui interface in .CSV format. Then,  the software is converted to data matrix form automatically.
Time domain and frequncy domain analysis can be performed by clicking the appropriate buttons. Graphics can be zoomed in or out easily. Intended time and frequency values can be zoomed  thanks to zoom button.
As a result, the software can analyse  impulse voltage signal in time domain and frequency domain. This will anable to differntiate noise types and the user can take the necessarry precautions with respect to appropriate domain analysis.