Three methods of formulation to increment of load bus voltage magnitude in power system

In this paper, three methods are proposed in order to formulate increment of load bus voltage magnitude in power system during a machine-electric transient process, in which the increment of load bus voltage magnitude is composed of two components. In the first method, one component is proportional to increment of amplitude of current, and another is proportional to increment of module of load equivalent impedance. In the second, one component is proportional to increment of power, which apparent power reactive power and active power can respectively be used to represent, and another is related to variation of load equivalent impedance, which can be formulated in three forms accordingly. In the third, a new term, power per one impedance unit (PPOIU) which is defined by the square of amplitude of current, is proposed. One component is proportional to increment of PPOIU at the bus, and another is proportional to increment of module of the equivalent impedance. In this paper, the three methods are compared with each other. As a result, the third method can universally be used during any machine-electric transient process, is the simplest, link up strongly with existing analysis method, and expediently explain the voltage stability mechanism of power system, so it can be used as a basic method to formulate increment of load bus voltage magnitude for power system voltage stability.