This paper shows that normal power system operating data may be used to determine the power-frequency characteristics in power systems. Data are processed as random signals using spectral analysis techniques, and the results estimate the generator and load power-frequency characteristics as transfer functions. The generator characteristics
Kg are determined as a transfer function of the system in which input signals are frequency fluctuation Δ
F and generator power setting signal Δ
Pg, and output signal is generator power output Δ
Pe, To estimate the load characteristics
Kl, a difficulty arises. There is a relation Δ
P/ = Δ
Lo +
KlΔ
F between actual load Δ
Pl, ideal load under the state of nominal frequency Δ
Lo, and fluctuation of system frequency Δ
F. Because it is impossible to measure Δ
Lo directly, ΔL
o and
KlΔ
F cannot be separated. With regard to a partial system, when its capacity is small enough compared with the total system capacity, the contribution of Δ
Lo in a partial system to Δ
F of the total system may be ignored, that is, Δ
F and Δ
Lo are considered as independent phenomena. Thus the cross spectrum of Δ
F and Δ
Lo decreases to zero according to the increase of data in number, and
Kl of the partial system can be estimated.
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