Introduction ATP is a universal program system for digital simulation of transient phenomena of electromagnetic as well as electromechanical nature. With this digital program, complex networks and control systems of arbitrary structure can be simulated. ATP has extensive modelling capabilities and additional important features besides the computation of transients. ATP has been continuously developed through international contributions by Drs. W. Scott Meyer and Tsu-huei Liu, the co-Chairmen of the Canadian/American EMTP User Group. The birth of ATP dates to early in 1984, when Drs. Meyer and Liu did not approve of proposed commercialization of BPA (Bonneville Power Administration) EMTP by DCG (the EMTP Development Coordination Group) and EPRI (the Electric Power Research Institute). Dr. Liu resigned as DCG Chairman, and Dr. Meyer, using his own personal time, started a new program from a copy of BPA's public-domain EMTP. Operating Principles Basically, trapezoidal rule of integration is used to solve the differential equations of system components in the time domain. Non-zero initial conditions can be determined either automatically by a steady-state, phasor solution or they can be entered by the user for simpler components. Interfacing capability to the program modules TACS (Transient Analysis of Control Systems) and MODELS (a simulation language) enables modelling of control systems and components with nonlinear characteristics such as arcs and corona. Symmetric or unsymmetric disturbances are allowed, such as faults, lightning surges, any kind of switching operations including commutation of valves. Calculation of frequency response of phasor networks using FREQUENCY SCAN feature. Frequency-domain harmonic analysis using HARMONIC FREQUENCY SCAN (harmonic current injection method) Dynamic systems also can be simulated using TACS and MODELS control system modelling without any electric network. Top Components Uncoupled and coupled linear, lumped R,L,C elements. Transmission lines and cables with distributed and frequency-dependent parameters. Nonlinear resistances and inductances, hysteretic inductor, time-varying resistance, TACS/MODELS controlled resistance. Components with nonlinearities: transformers including saturation and hysteresis, surge arresters (gapless and with gap), arcs. Ordinary switches, time-dependent and voltage-dependent switches, statistical switching (Monte-Carlo studies). Valves (diodes, thyristors, triacs), TACS/MODELS controlled switches. Analytical sources: step, ramp, sinusoidal, exponential surge functions, TACS/MODELS defined sources. Rotating machines: 3-phase synchronous machine, universal machine model. User-defined electrical components that include MODELS interaction Top Integrated Simulation Modules MODELS in ATP is a general-purpose description language supported by an extensive set of simulation tools for the representation and study of time-variant systems. The description of each model is enabled using free-format, keyword-driven syntax of local context and that is largely self-documenting. MODELS in ATP allows the description of arbitrary user-defined control and circuit components, providing a simple interface for connecting other programs/models to ATP. As a general-purpose programmable tool, MODELS can be used for processing simulation results either in the frequency domain or in the time domain. TACS is a simulation module for time-domain analysis of control systems. It was originally developed for the simulation of HVDC converter controls. For TACS, a block diagram representation of control systems is used. TACS can be used for the simulation of HVDC converter controls Excitation systems of synchronous machines power electronics and drives electric arcs (circuit breaker and fault arcs). Interface between electrical network and TACS is established by exchange of signals such as node voltage, switch current, switch status, time-varying resistance, voltage and current sources. Top Supporting Routines Calculation of electrical parameters of overhead lines and cables using program modules LINE CONSTANTS, CABLE CONSTANTS and CABLE PARAMETERS. Generation of frequency-dependent line model input data (Semlyen, J.Marti, Noda line models). Calculation of model data for transformers (XFORMER, BCTRAN). Saturation and hysteresis curve conversion. Data modularization (for $INCLUDE). Top Hardware Requirements Most users, including program developers, use Intel 486/Pentium-based PC's with MS-Windows 3.x/95/98/NT. A standard PC configuration with min. 16-MB RAM, hard disk (20 MB free space) and VGA graphics is sufficient to execute ATP under MS-DOS/MS-Windows. ATP is available for other computers and operating systems, too. At present, the following ATP versions are available: - MS-DOS, MS-Windows 3.x/95/98/NT/2000™ 32-bit, GNU-Mingw32 and Watcom ATP for Windows 95/98/NT/2000/XP/Vista 32-bit, Salford ATP running under MS-DOS, MS-Windows 3.x/95/98 (This version requires Salford's DOS extender DBOS/486) - Linux: GNU version of ATP