FUNCTION BASED OPTIMIZED PROTECTION SCHEMES FOR DISTRIBUTION SUBSTATIONS

Abstract

A power system is vulnerable to faults, either due to natural disasters or by mis-operation of the system due to operators' negligence. This can result in permanent damage to power system components leading to considerable costs for their replacement and in longer disconnections of power supply to customers, which is highly undesirable. This sets a requirement for a power system to sustain faults, while protection systems should minimize the damage in important components and the effect of faults as much as possible. This is achieved by using power system protection techniques and methodologies. Microprocessor-based relays have their own algorithms for monitoring the power system through current and voltage inputs from CTs and VTs respectively. Protection relays are thoroughly tested using relay test sets to confirm their reliability and safe operation before commissioning them in a substation. With the advent of Real-Time Simulators and compact reconfigurable input /output (I/O) controllers, large power systems can be simulated and their behavior can be analyzed in both steady state and faulted conditions. The purpose of protection relays is to detect a fault and give a trip order to the switching device that is closest to the fault location. However, in several cases, the commonly used algorithms of the digital relays fail in practice to cope with their functions. Therefore this thesis presents a programmable microprocessor based relay for enhancing the operation of the main protection functions. The investigated modifications for this objective have been applied to EL-KOBBA 66/11kv substation in Cairo to check the reliability of the suggested models. Thus, the basic over-current protection is simulated for different standard