Experimental Analysis of Stability and Power Limitations

A method of determining the power and voltage stability limit of a transmission system taking into account the characteristics of the synchronous condenser and load in conjunction with the characteristics of the line is described. The power limit of a straight 500-mile transmission line is calculated by this method. The power limit is also calculated for the same line with a synchronous condenser at the mid-point which divides the line into two sections. The addition of the synchronous condenser at the mid-point increased the power limit 42 per cent. Tests were made on a 625 kv-a. transmission system operated at 2300 volts to determine experimentally the power and voltage stability limit of a transmission line with a synchronous condenser at the mid-point. The tests check closely with the calculated values. Tests on hunting caused by prime mover pulsations, line characteristics and voltage regulator adjustment were made. It was found that the damper windings on synchronous condensers do not have much effect in reducing hunting, particularly at resonant points. There was practically no difference between the standard high-resistance windings used for starting purposes and low resistance copper damper windings. On a high-resistance and low-reactance transmission line hunting was found to occur at high condenser field excitations. The addition of reactance stabilized the system. On high-voltage transmission lines the reactance is high as compared to resistance and no difficulty from hunting due to line characteristics is to be expected.