A METHOD FOR CALCULATION OF MARGINS TO VOLTAGE INSTABILITY APPLIED ONTHE NORWEGIAN SYSTEM FOR MAINTAINING REQUIRED SECURITY LEVEL

The paper describes a method for calculating margins to voltage instab ility. The method is based on sensitivity techniques. The measure to v oltage instability can be given in terms of MW, MVAr or MVA depending on the components in the increase in load. The extensions to earlier p ublications of the method are the ability to increase the load and gen eration simultaneously on several buses without increasing the computa tion time. A single forward and backward substitution is sufficient to find the required sensitivities when the load is increased. The produ ctions of the plant can be increased either by a specified profile or by using the turbine droop characteristics. A method for identificatio n of contingencies needing an explicit reserve evaluation is briefly d escribed.