It is helpful to understand the applications of load
modeling before discussing particular load characteristics.

The applications are divided into two broad categories:
static (‘‘snap-shot’’ with respect to time) and dynamic (time varying). Static
models are based on the steady-state method of representation in power flow
networks. Thus, static load models represent load as a function of voltage
magnitude.

Dynamic models, on the other hand, involve an alternating
solution sequence between a time-domain solution of the differential equations
describing electromechanical behavior and a steady-state power flow solution
based on the method of phasors.

One of the important outcomes from the solution of dynamic
models is the time variation of frequency. Therefore, it is altogether
appropriate to include a component in the static load model that represents
variation of load with frequency.

The lists below include applications outside of Distribution
Systems but are included because load modeling at the distribution level is the
fundamental starting point.

Static applications: Models that incorporate only the voltage-dependent
characteristic include the following.

* Power flow (PF)

* Distribution power flow (DPF)

* Harmonic power flow (HPF)

* Transmission power flow (TPF)

*Voltage stability (VS)

Dynamic applications: Models that incorporate both the
voltage- and frequency-dependent characteristics include the following.

* Transient stability (TS)

* Dynamic stability (DS)

* Operator training simulators (OTS)

Strictly power-flow based solutions utilize load models that
include only voltage dependency characteristics.

Both voltage and frequency dependency characteristics can be
incorporated in load modeling for those hybrid methods that alternate between a
time-domain solution and a power flow solution,such as found in Transient
Stability and Dynamic Stability Analysis Programs, and Operator Training
Simulators.

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