Welcome to the South African ATP User Group Page

The Alternative Transients Program, ATP, is probably the most widely used simulation tool for the study of transient phenomena in power systems. It shares its roots with EPRI's Electromagnetic Transients Program, EMTP, in the early work performed by the Bonneville Power Administration but differs in a number of key aspects, one of which is licensing. ATP licensing is royalty-free and involves the approval by a recognised user group of a license agreement, which the interested party has signed. ATP licensing has been distributed geographically amongst User Groups around the world. The South African version of the License Agreement can be found Here.

ATP Features

The ATP provides the user with a host of pre-defined elements that can be incorporated into the study. These include :

  •  Lumped elements such as resistors, inductors and capacitors.
  •  Multiphase Pi-equivalents.
  •  Multiphase distributed-parameter transmission lines with propagation time representation. Frequency-dependence of the line parameters can be incorporated into the model.
  • Nonlinear resistors, where the v-i characteristic is single-valued.
  • Nonlinear inductors, either with a single-valued characteristic or with hysteresis and residual flux.
  • Time-varying resistances.
  • Switches that can be used to simulate changes in the network configuration. The modeling of power electronic circuits is possible with the specification of diode and thyrister characteristics by the user.
  • Voltage and current sources. Standard mathematical functions such as sinusoids, surge functions, steps and ramps are available. Additionally, the user may specify the source in an external FORTRAN routine or point by point as a function of time.
  • Dynamic rotating electric machinery including,
    • 3-phase synchronous machines
    • 1, 2, or 3 phase induction machinery
    • dc-machinery
  • Control of the machines can be realised using TACS models.

Nonlinear and logical control of the electric network variables can be achieved with the use of either TACS (Transient Analysis of Control Systems) or the MODELS language. Inputs and outputs may be interfaced with the electric network of the ATP, thereby providing hybrid computer capability.

ATP provides the following support routines: Calculation of electrical parameters from the geometry of overhead lines, calculation of input data for frequency-dependent line modeling, calculation of model data for transformers, mapping procedure for the conversion of saturation and hysteresis curves.

Solution method

The ATP employs a time domain based solution method to calculate the unknown variables. The ordinary and/or partial differential equations resulting from the connection of the above mentioned components are solved using trapezoidal-rule (second-order) implicit integration. The resultant simultaneous equations are placed in nodal-admittance form, with new unknown voltages as variables, and are solved by ordered triangular factorization.


Execution of a data case involves providing the ATP with the name of an ASCII file containing the circuit information in a very specific format that involves the grouping of elements of one type together. Additionally, ATP requires the ordering of these groups in a prescribed sequence. However, there is an alternative to creating these ASCII files with a text editor:


ATPDraw is a graphical, mouse-driven pre-processor to the ATP on the MS-Windows platform. The user compiles an ATP case by creating a graphical picture of the electric circuit and then exporting the file into an ATP compatible format. The ATP elements are available to the user through menus. Additionally, the program provides the user with the capability of saving the circuit objects for re-use in other circuits. ATPDraw allows the user to perform editing operations between open circuit windows. Printing to paper or metafile/bitmap format is supported.


In addition to providing output options through printed lists and character plots, the ATP supports a number of graphical output formats including HP-GL (Hewlett-Packard Graphic Language), CGM (Computer Graphics Metafile), PostScript and GNUPLOT. Each of these formats can be processed by one of the plotting programs accessible through the ATP license. Certain plotting programs are available only for the more popular PC operating systems.

Operating System and Hardware Requirements

ATP maintainers are concentrating their efforts around popular PC operating systems, in particular Linux, Windows NT and Windows9x, as their primary target platforms . However, the ATP has proven compatibility with a number of OS's among others: Unix System V, VAX ULTRIX, OS/2 Warp and DOS.

For acceptable execution of typical simulations an Intel 486/Pentium based system with a minimum of 8 MB RAM is recommended. A complete ATP installation, including pre- and post-processing programs, occupies less than 10 MB of hard disk space.