In this paper, we conduct a study to clarify the difficulties which affected the operations of the protective relays in the Oman Electricity Power System and the steps which were taken to overcome these difficulties. A single line to ground fault on the network may cause the tripping of phase loads and reduce the speed of three phase inductive loads. This in turn causes an over current trip on the 11 and 33kV feeders after the fault is cleared. The bank capacitors, used in the system, should not trip during the dip of voltage to avoid any further increase. The settings of the earth fault relays should be adjusted taking into consideration the ground resistance and the length of the distribution lines. A load shedding arrangement for 33kV feeders should be used to avoid the tripping of a second transformer in the feeder transformer arrangement set. Distribution feeders should not be connected with the bus bars of the power stations. Under speed protective devices should not operate on frequencies more than 47.5 Hz. New types of relays should be used after testing it on the existing operating system.

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This paper discusses potential extreme scenarios which could result in unstable conditions on the main interconnected electricity transmission system of Oman. Case studies on loss-of-stability scenarios between different parts of the network are examined. The objectives of the study are to identify possible locations of the electrical centre of swing and to develop an approach for controllable system splitting. A controllable splitting approach has been proposed and sensitivity analysis has been utilised to identify potential locations for controllable system splitting. In the final recommendations, trade-off considerations should compare the introduction of a system-wide out-of-step protection framework and its associated potential complications versus alternatives (e.g. improved protection performance).

This paper presents a literature survey on the subject of voltage stability analysis of power systems. The survey describes several published methods and techniques used to determine voltage stability indices. These indices predict proximity to voltage instability and collapse problems. The Q-V and P-V curves; singular value decomposition; modal analysis; test function; reduced determinant; loading margin by multiple power flow solutions; local load margins; thevenin/load impedance; and energy function are the methods which have been decribed in the paper. The methods described are based on the original work that first proposed them. They are based on the power-flow system model, where the variation of real and reactive powers are assumed to be the main parameters driving the system to voltage instability. Some of the described methods were applied on the IEEE 30-bus power system.

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