Question

Explain the modelling of electrical loads using the ( SLY - type ) index based variation curves. What are the error sources ?

Answer 1

• LOAD modeling is essential to power system analysis, planning, and control. The uncertainty and difficulty of load modeling comes from the large number of diverse load components, time-varying and weather-dependent compositions, and the lack of measurements and detailed load information. The goal of load modeling is to develop simple mathematical models to approximate load behaviors.
• Load modeling consists of two main steps: 1) selecting a load model structure, and 2) identifying the load model parameters using component or measurement-based approaches.
• Load modeling refers to the mathematical representation of the relationship between the power and voltage in a load bus. Load models can be classified into two main categories: static and dynamic models. Fig. 1 shows the currently used load models in industry for static and dynamic studies

A. Static Load Models Static models express the active and reactive power at any instant of time as functions of bus voltage magnitudes and frequency. These models can be used to represent static loads e.g., resistive loads, and as an approximation for dynamic loads, e.g., induction motors.

B. Dynamic Load Models Studies in voltage stability require the use of dynamic load models for accurate representation. Dynamic models express the active and reactive powers as a function of voltage and time. Examples of the widely used dynamic models are presented as follows.