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Power electronic control in electrical systems 291

8.2 Electromagnetic transient analysis

The transient response of any natural system is the way in which the response of the
system behaves as a function of time. Mathematically, the transient behaviour of a
given system is modelled by differential equations. However, this approach can be
reasonably applied to systems where the underlying principles are clear and where the
system is sufficiently elementary, so that a `basic' approach can be used. Due to the
high complexity involved in the solution of differential equations by hand-methods,
it has been imperative to develop efficient and reliable numerical techniques imple-
mented on digital computers, which reproduce confidently the transient response of
almost every system provided that these are modelled appropriately.
Electrical power networks like other physical systems are exposed to various forms
of transient phenomena; nowadays, fast variations of electrical parameters such as
voltage or current are very common due to the elaborated equipment and configura-
tions used in the power systems. Bearing this in mind, digital tools have become an
invaluable resource when the transient response of the electrical network is required.
When used for this purpose, digital tools are commonly labelled as electromagnetic
transient simulators.
A considerable percentage of power systems studies rely on electromagnetic tran-
sient simulations. They provide substantial information associated with the perform-
ance of the network under any operating condition and enable the user to identify
and assess the interaction between the various elements encompassing the network.
This information can be used for miscellaneous purposes such as evaluation, plan-
ning, operation, design, commissioning, characterization, etc.
Generally, power networks are very complex all around the world. The enhance-
ment of transmission and distribution systems by means of high-power electronics
technology, such as FACTS and CPcontrollers has increased considerably the
complexity of electrical networks. Consequently, the development of power systems
studies has become more difficult. Moreover, in some cases the only possible way to
carry out the analysis of a given network is by means of electromagnetic transient
simulators. Fortunately, for the electricity supply industry, digital simulators have
equally been developing in order to meet the new system requirements. They are
powerful and provide the user with friendly interface environments. Some of them
have already incorporated models of power electronics-based controllers so that
transient analysis results can be achieved accurately and with high reliability. Some
of the most popular electromagnetic transient simulators currently available are as
follows:
. EMTP/ATP (Electromagnetic Transient Program)
. PSCAD/EMTDC (Power Systems Computer Aided Design/Electromagnetic
Transient Direct Current)
. NETOMAC
. SPICE
. SABER

These simulators provide built-in models for a wide variety of power system
components, which assist users to easily study electrical networks. Although all