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Chapter: Power Quality : Over Voltages

Computer Analysis Tools for Transient – PSCAD and EMTP

1. Digital computers 2. Analog computers 3. PSCAD 4. EMTP

Computer Analysis Tools for Transient – PSCAD and EMTP


The following computational tools are used in general to solve different electrical network problems:

ü   Digital Computers


ü   Analog Computers


ü   Transient electrical network analyzers


ü   Special purpose simulators such as HVDC simulator


The types of studies usually conducted are as follows:


ü   Power flow studies


ü   Dynamic Simulation


ü   Control System parameter optimization studies


ü   Harmonic studies


ü   Switching transient studies


1. Digital Computers:


Digital computers are the most versatile and can be used to solve all the earlier mentioned problems, although in particular cases and depending on the facilities available, other methods can be more advantages and economical. As very large and fast digital computers are available today, invariably all large problems are solved using digital computers with commercial software packages or locally developed special purpose computer programs.


2. Analog Computers:



A n analog computer is a form of computer that uses the continuously changeable aspects of physical phenomena such as electrical, mechanical, or hydraulic quantities to model the problem being solved. In contrast, digital computers represent varying quantities symbolically, as their numerical values change. As an analog computer does not use discrete values, but rather continuous values, processes cannot be reliably repeated with exact equivalence, as they can with Turing machines. Analog computers do not suffer from the quantization noise inherent in digital computers, but are limited instead by analog noise.

Analog computers were widely used in scientific and industrial applications where digital computers of the time lacked sufficient performance. Analog computers can have a very wide range of complexity. Slide rules and monographs are the simplest, while naval gunfire control computers and large hybrid digital/analog computers were among the most complicated.

Systems for process control and protective relays used analog computation to perform control and protective functions.



3. Power System Computer Aided Design – PSCAD / EMTDC



PSCAD/EMTDC is a general-purpose time domain simulation program for multi-phase power systems and control networks. It is mainly dedicated to the study of transients in power systems. A full library of advanced components allows a user to precisely model interactions between electrical networks and loads in various configurations. A graphical user interface and numerous control tools make PSCAD a convenient and interactive tool for both analysis and design of any power system.


PSCAD seamlessly integrated visual environment features all aspects of conducting a simulation, including circuit assembly, run-time control, analysis and reporting. Users can easily interact with the components during the simulation because of the variety of control tools. The solution meters and the plotting traces are also visible and available during the simulation. Signals can be analyzed in real time.


PSCAD features a broad range of models for power system and power electronic studies such as:


ü   Frequency dependent transmission lines and cables,


ü   Transformers (classical model with saturation/Umec model)


ü   Various machines, (synchronous, asynchronous, DC)


ü   Various turbines (hydro, steam, wind),


ü   Converters & FACTS,


ü   Drive & control blocks,


ü   Relays.



3.1 Fast and Accurate



The time steps interpolation technique combines accuracy and quickness: it allows the simulation to precisely represent the commutations of breakers and switches in the electrical model, for any model’s size, up to extremly large models. PSCAD results are solved as instantaneous values, and can be converted to phasor magnitudes and angles via built-in transducers and measurement functions such as true-rms meters or FFT spectrum analyzers. The PSCAD simulation tool can duplicate the response of a power system at any frequency, because the computation step chosen by the user can go from several nanoseconds to several seconds.


3.2 Optimization:



PSCAD features multi-run capabilities, enabling a user to run a case multiple times with a set of parameters changed each time in a predetermined manner. This facility makes optimization an easy game as the optimum results (according the criterion the users defines before) are highlighted by the software.


3.3 Customization:



Create custom components? PSCAD features the built-in Component Workshop, the tool used to create all the Master Library components. The look of the components and the data forms are all designed graphically. It allows each user to easily create their own component library.


3.4 Applications:


1.     Power lines & cables


2.     Large non-linear industrial loads


3.     Transformers with saturation


4.     Power electronic systems & drives


5.     FACTS/HVDC systems


6.     Protection relay coordination


7.     Arc furnace flicker


8.     Distributed power generation


9.     Rotating machines


10.                        Embedded systems



4. EMTP:



EMTP is an acronym for Electro Magnetic Transients Program. It is usually part of a battery of software tools targeting a slice of the spectrum of design and operation problems presented by Electric Power Systems to the Electrical Engineer, that of the so-called "electromagnetic transients" and associated insulation issues.


Originating in the habilitation (postdoctoral) thesis of Dr. Hermann Dommel in Germany in the mid sixties, and brought up to its present robust and industry strength status by the cooperation of many professionals of power engineering led by the two champions: Dr. Dommel (currently with the University of British Columbia, in Vancouver, B.C., Canada), and Dr. Scott Meyer (from the Bonneville Power Administration in Portland, Oregon, U.S.A.). Both have been awarded the highest recognition that the Institute of Electric and Electronic Engineers (IEEE) grants to some of its members: they are both FIEEE (Fellows of the IEEE).


There are two basic streams of EMTP programs: "EMTP" as known such originates from the program development at BPA - an agency of the U.S. Department of Energy - and those written from scratch. The EMTP-ATP and MT-EMTP programs, for example, are based on the original BPA and DCG-EMTP versions.

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