The purpose of insulation coordination is to insure that insulation used in an electrical power system is adequate
for the environment in which it is applied and to understand the probability of insulation failure under transient
Typical studies include the analysis of a substation to determine the probability of post insulator flashovers.
This is generally measured in flashovers per hundred years. Another important analysis is to determine that the
insulation contained within transformers has an acceptable margin of protection. Since the internal insulation is
not self-restoring a failure is completely unacceptable. An insulation coordination study of a substation will
present all the probabilities and margins for all potential transients entering the station. The studies include
both switching surge analysis and lightning surge analysis. Even though stations are usually shielded, the
lightning surge finds its way into a substation when there is a backflash on any incoming line. The resulting
current levels in the station are quite low relative to direct strikes, but all that is needed to fail insulation
is voltage and not current.
Transmission Line Studies
Insulation coordination studies of a transmission lines fall into two categories. A very common study in recent times is
to determine the proper locations and ratings of arrester applied on lines that do not have pre-insertion resistors
installed on their breakers. A second type of study is to determine where to install arresters to reduce the
back-flash-over rate of a line. This type of study also indicates what the new flashover rate will be after
installation of the arresters.
Methods of Analysis and Resources
Studies completed by ArresterWorks use both time domain software (ATP) and Hileman software that accompanies the well known
"Insulation Coordination of Power Systems" text by Andrew Hileman.
Numerous standards are used in analysis including IEC 60071-1 and 60071-2, along with IEEE 1313-1, 1313-2, 1243, 1410,