The interruption cost for one hour of a petrochemical plant is 33 times higher than that of
the average interruption cost for industrial plants across all industries. In addition to the
high cost of loss of production, interruptions to the operations of petrochemical and gas-toliquid
plants pose safety and environmental hazards. Thus it is necessary to better
understand the reliability requirements of petrochemical and gas-to-liquid plants.
This study investigated the reliability of electrical distribution networks used in
petrochemical and gas-to-liquid plants compared to those used in other industrial plants. A
model was developed that can be used to establish the adequacy of the reliability of a
distribution network in terms of the components and network topologies used. This model
was validated against data that had been collected by the IEEE and applied to an actual
Over 19 years’ worth of data regarding the trips that have occurred on the distribution
network of an existing petrochemical plant was collected and manipulated in order to
calculate the reliability indices associated with the equipment used to make up thisRecommended Practice for the Design of Reliable Industrial and Commercial Power
The cost of loss of production and the capital costs associated with increased reliability
were calculated for a section of the existing petrochemical plant. The reliability associated
with different network topologies that could possibly be used to supply power to this
section of the plant were modelled using an appropriate software package. The resulting
total cost of ownership over the life of the plant associated with each topology was then
calculated in order to establish which network topology is the most appropriate for
petrochemical and gas-to-liquid plants.
It was concluded the components that affect the reliability of an industrial distribution
network are different to those that affect a utility distribution network. These components
were listed and compared. It was found that the reliability indices that were calculated for
the components that affect the reliability of a petrochemical plant were similar to those
provided by the IEEE. 17 out of 20 of the indices that were calculated were within the
required factor of deviation. Generally the failure rates of components used in
petrochemical plants were very similar to those given in the IEEE Gold Book, while the
MTTR’s for the components used in petrochemical plants were found to be slightly better
than those given in the IEEE Gold Book. The effect of network topology was found to be significant, with small changes in the
topology of a network resulting in large variations in the reliability of the network. It was
also found that the most appropriate type of network topology to use in the design of the
electrical distribution network of a petrochemical plant is the dual radial network. This is
the most conservative of the commonly used network topologies and is the one that is
currently used in the existing plant that was studied.
Due to the high cost of loss of production in petrochemical plants it was established that
any incremental improvement in the reliability of the dual radial network would be
beneficial to the total cost of ownership of such a plant. Such incremental improvement of
the reliability of the distribution network could be cost effectively achieved by adopting a
conservative maintenance strategy and the establishment of a conservative spares
inventory. Before this study was undertaken, there was no literature around the reliability of electrical
distribution networks that focused specifically on petrochemical and gas-to-liquid plants.
This study produced a set of reliability indices and a model that electrical engineers can
use in the reliability analysis of petrochemical and gas-to-liquid plants. Furthermore it
shows that, because the cost of loss of production in petrochemical plants is so high, the
most conservative distribution network design and maintenance philosophies should
always be used.
distribution network. These reliability indices were compared to those given by the IEEE
Dissertation (MEng)--University of Pretoria, 2014.