Transient Analysis Tools Mathematical methods, and Software

1. PRESENTATION EE 6643 - Transients in Electric System - Completed Projects Transient Analysis ToolsMathematical methods, and Software By: KH.M.KAHLED ABO AL EZ PhD student Student No. 3204220

2. Definition of Electric Transients: • A transient is a transition from one state to another. If the voltages and currents in a circuit do not change with time, we call that a "steady state". In fact, as long as the voltages and currents are steady AC sinusoidal values, we can call that a steady state as well. But what happens when the state of a circuit changes, say from "off" to "on"? Can the state of the circuit change instantaneously? No, nothing ever changes instantaneously, the circuit state will go through some transition from the initial state, "off" to the final state, "on" and that change will take some amount of time [1].

3. TECHNICAL DEFINITION [2]: Basically, transients are momentary changes in voltage or current that occurs over a short period of time. This interval is usually described as approximately 1/16 (one sixteenth) of a voltage cycle (in the US, about 1/60th of a second) or about 1 milliseconds (milli = .0 0 1--one thousandths...In laymen's terms, .0166 seconds......or really darned quick.). Voltage transients normally last only about 50 microseconds (micro = .0 0 0 0 0 1--one millionth) and current transients last typically 20 microseconds according to the ANSI C62.41-1991 which is the standard for transients in facilities operating under 600 Volts. • “ANSI std. 1100-1992) A sub cycle disturbance in the AC waveform that is evidenced by a sharp brief discontinuity of the waveform. Transients may be of either polarity and may be of additive or subtractive energy to the nominal waveform. ”

4. FACTS ABOUT TRANSIENTS [2]: 1-  Transient activity is believed to account for 80% of all electrically-related downtime. 2- Lightning accounts at least 5% of Insurance claims and costs an average of $13,000 per occurrence. 3- Effective transient voltage suppression equipment can double or triple the life of electrical and electronic equipment. 4- A systems approach to transient voltage surge suppression can result in dramatic performance in terms of return-on investment. 5- Transient Voltage Surge Suppression is the most immediately apparent, and the most cost-effective means of improving your power quality.

5. OSILLATORY (can be repetitive or for a short period). Impulsive (One shot). TYPES OF TRANSIENTS [2,3]

6. Where do Transient voltages come from? [2] External sources: • Lightning. • Switching operations . • Poor or loose connections in the distribution system . • Accidents and human error. • Another common source FOR EXTERNAL TRANSIENTS, not commonly known, is neighboring businesses. If you share a transformer with other users, any transient activity generated on his premises will be seen at your electrical main. Remember, you are both physically connected at the secondary side (some people call it the "south side") of the transformer. Internal sources”The vast majority of transients are produced within your own facility. The main culprits are device switching, static discharge, and arcing [2].SO, it can be said that the transients are by product of the circuit elements R,L, and C [3].

7. What are the effects of transient activity?[2] • 1- ON Electronic Equipments: • Electronic devices may operate erratically. Equipment could lock up or produced garbled results, at decreased efficiencies. ALSO, Integrated circuits (sometimes called "electronic chips“ may fail immediately or fail prematurely. • 2- ON Motors: • Motors will run at higher temperatures when transient voltages are present. Transients can interrupt the normal timing of the motor and result in "micro-jogging". This type of disruption produces motor vibration, noise, and excessive heat. • 3- ON Lighting: • Transient activity causes early failure of all types of lights. Fluorescent systems suffer early failure of ballasts, reduced operating efficiencies, and early bulb failures.

8. 4- ON Electrical distribution equipments: • The facility's electrical distribution system is also affected by transient activity. Transient degrade the contacting surfaces of switches, disconnects, and circuit breakers. Intense transient activity can produce "nuisance tripping" of breakers by heating the breaker and "fooling" it into reacting to a non-existent current demand. Electrical transformers are forced to operate inefficiently because of the hysteresis losses produced by transients and can run hotter than normal.

9. Transient analysis • Transients are not instant because capacitors and inductors in the circuit store energy, and moving the energy into or out of these parts takes some time. The voltage-current relationships of capacitors and inductors are differential equations, so transient analysis will involve solving differential equations Differential Equation. The differential equations have two parts to its solution, the complementary function (or the homogeneous solution) which is used to find out transient problem and the particular solution describe the steady state value. • But don't panic, MANY SOFTWARE PRGRAMS ARE USED TO DEAL DIRECTLY WITH THE TRANSIENT PHENOMINA. • DC circuits with only resistors also experience transients [3], but these are due to non-ideal capacitance and inductance of the parts and wires that we haven't considered before [1]. These transients happen so fast that we won't worry about them.

10. EXAMPLE ON FORMING D.E for transient analysis: for 1st order RC circuit [1]:

12. The solution of D.Es:

13. 2- Laplace transformation method [4]: • This method is also used widely for transient calculation in the electric circuits. We have to consider the initial condition 0 or this method. The following simple example show how to use this method of RLC circuit.

14. Kirchoff's voltage law Kirchoff's voltage law transformed

15. The series RLC circuit excited by a unit impulse function - that is to say • (The unit impulse always gives the "natural response" of any circuit. Natural as compared to "forced" response.) • This is to be compared to the transform pair

16. Form the table of Laplace transform pairs Therefore, if :

17. THE FOURIER Transform [5]: • The Fourier transform is a generalization of the complexFourier series in the limit as . • Replace the discrete with the continuous while letting . Then change the sum to an integral, and the equations become Where K= and X = t (time)

18. Some Fourier transforms:

19. Software tools used for transient analysis: Some SOFTWARE that can be used to analyze Transient circuits: • 1- PSCAD [6] Reference [6]: Manitoba HVDC Research Centre 400-1619 Pembina Highway, Winnipeg, Manitoba, Canada R3T 3Y6 : • PSCAD is a multi-purpose graphical user interface capable of supporting a variety of power system simulation programs. • EMTDC is a general purpose time domain simulation program for simulating power systems transients and its controls.PSCAD is its integrated graphical user interface. • MATLAB Interface: You can simulate all or part of the controls in MATLAB and interface it to the rest of the system simulation in PSCAD/EMTDC. You can process or plot EMTDC results in MATLAB interactively.

23. 2- ATP (alternative transient program) [7]: • What is ATPDraw? • ATPDraw for Windows is a graphical, mouse-driven preprocessor to the ATP version of the Electromagnetic Transients Program (EMTP). It assists to create and edit the model of the electrical network to be simulated, interactively. In the program the user can construct an electric circuit, by selecting predefined components from an extensive palette. The preprocessor then creates the corresponding ATP input file, automatically in correct format.

24. The main window

25. Example: SINGLE PHASE RECTIFIER BRIDGE: ATP draw of the circuit

26. MATLAB [8] : • THE most important feature of matlab is its ability to use both code programming and in the same time it contains a huge library of blocks in different fields of science. • SIMULINK library and SimPowerSystem library are the two libraries we are very much concerned about in analyzing electric power systems. • MATLAB CAN BE LINKED AS DISCUSSED TO OTHER SOFTWARE PROGRAMS SUCH AS THE PSCAD. • SimPowerSystems LibrariesYou can rapidly put SimPowerSystems to work. The libraries contain models of typical power equipment such as transformers, lines, machines, and power electronics. These models are proven ones coming from textbooks, and their validity is based on the experience of the Power Systems Testing and Simulation Laboratory of Hydro-Québec, and also on the experience of Ecole de Technologie supérieure and Université Laval. The capabilities of SimPowerSystems for modeling a typical electrical system are illustrated in demonstration files. And for users who want to refresh their knowledge of power system theory, there are also self-learning case studies.

28. References: • [1] Arn Stolp, “Circuit Transients”,, ECE DEPARTMENT UNIVERSITY OF UTAH, www.elen.utah.edu/~ece1050/. • [2] “Causes and Effects of Transient Voltages”, Stedi-Power, www.tvss.net/trans/trans-x.htm . • [3] Dr. A. Sharaf, “Electric Transients”,, UNB, Lecture notes, fall 2005. • [4] “Laplace Transforms and Circuit Analysis”, engr.atu.edu/Eleg2111Lab6.doc . • [5] “Fourier Transform”, mathworld.wolfram.com/FourierTransform.html. • [6] PSCAD Manuals. • [7] ATP/EMTP Manuals. • [8] MATLAB Manuals.