Transient Stability: Load Characteristic

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For more detail on specific models, see the Transient Stability Block Diagram PDF document. This help topic describes the general behavior of these models.

 

Each load has information related to the amount of MW and Mvar. The simplest transient stability models are purely an algebraic function of voltage and frequency at the terminal of the load. Other stability models model the rotor dynamics of induction motors.

There are also a few transient models that assign a fraction of the load while the remaining would be assumed by the algebraic model used by the load. For example you may assign both a MOTORW model and a WSCC model to a load. The parameter Pul then termines the fraction of the load assigned to MOTORW while (1-Pul) is assigned to WSCC. There are also several models that are an aggregation of other models.

Finally, there are also several composite models that create a combination of hard-coded models by fraction (For example CMPLDW and CMLD typically have 3 induction motors, 1 single phase aircondition, 1 electronic load, and 1 static load). For future composite loads the CompLoad model (Added in Version 20) will be used as it can define a any combination of most of the other load models.

  1. Dynamic models that always apply to the entire load: CIM5, CIM6, CIMW, LD1PAC_CMP, MOTOR_CMP, BRAKE, DLIGHT, EXTL, LDFR
  2. Dynamic model that have fraction terms: LD1PAC, MOTORW, MOTOR
  3. Static (algebraic) models which can be used in combination with fractional dynamic models: IEEL, WSCC, and the default model (Transient Stability Dialog's Option\Power System Model)
  4. Composite Models: CLOD, CMLD, CMPLDW, CMPLDWNF, CompLoad

Special Rules for when to Ignore Load Models

For any load smaller than 0.001 per unit (0.1 MW when using System Base of 100 MVA), any dynamic load model will be ignored and the load will be treated as purely algebraic.Added in Version 18, build on Sept. 27, 2014.

For complex load models that represent a composite of various load types (for example, CLOD, CMPLDW, MOTORW, and CompLoad) there are additional options for when to ignore these models as described in the Transient Stability Analysis Options for the Power System Model. Added in Version 19, build on Sept. 14, 2016

CompLoad and LoadComponent objects Added in Version 20

A Load Component is a special object used by the load characteristic named CompLoad. These together give you the ability to create any combination of other load models and give the user more flexibility that exists in the older composite load models such as CLOD, CMPLDW, and CMLD.

See the help topic Load Components for more details.

Determining which Load Model Characteristic Models to Use

Load Characteristic Models may be applied to either a load, Load Model Group, bus, owner, zone, area, or the entire system. During the dynamic simulation, a particular load record will use the following priority when determining what to use as the load characteristic in the stability simulation. Note that this same logic is used to determine which Static and which Motor load model characteristic to use.