On behalf of the technology department at Preemraff, a system analysis of the electrical distribution system has been performed. The work consists of two parts, and its main purpose is to give a better knowledge of the plants status. In the first part, a model of the refinery’s electrical distribution system is built in a program for network analysis. The model is intended to help Preemraff’s technology department in both the daily operation but also for expansion projects and changes in the electrical distribution system. In the second part of the work, an analysis of a limited part of the plant is performed. The analysis consists of verification of short-circuit currents, selectivity and simulation of voltage drop during start of electrical motors. A rough check of free capacity in respective part of the plant is also performed.
Theory to give the reader understanding of the various components function and mutual interaction is presented. Existing standards and their calculation methods are discussed. Additional attention is paid to calculation of short-circuits. The technical configuration of the electrical plant is introduced, followed by a description of the modelling with respect to suppositions and some special cases.
The results show that the short-circuit currents are in an acceptable level in most part of the plant. In one switchgear, the short-circuit current are somewhat exceeded. Start of electrical engines does not contribute to a voltage drop above acceptable levels in the part of the plant that was investigated. With respect to selectivity the plant has the potential to achieve selective disconnection at most of the investigated points. It is shown that the present operation mode, with switched on breakers between the switchgears A- and B-side prevent selective disconnection. The selectivity analysis is performed with the premise that A- and B-side is sectioned. With those premises, it shows that some adjustment is needed to achieve good selectivity.
The electric distribution system is mainly constructed to permit redundancy for the n-1 criteria. The results show that a few switchgears are loaded to the point that their transformers will be overloaded with a single transformer fault.
At the end of the report, proposal on operation diversions that is considered to optimize the plant is given. Suggestions on investments that would improve the plant in an energy term perspective is also given.