Transient Stability: Load Component and CompLoad Characteristic

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Added in Version 20

Using Load Component objects and a special load characteristic named CompLoad allows you to create a fractional combination of other load characteristics. The benefit of this is that most new load characteristic model that are added to the software in the future will immediately be available for use inside the CompLoad model.

 

Load Component Objects

Load Component objects are identified by a name which is a string. They may then have a single load characteristic model assigned to them. The Load Component Objects are then used inside of the special CompLoad load characteristic.

For load characteristics assigned to a load component, there is a restriction is that the load characteristic must be able to calculate its own initial Mvar. See the discussion of Component Initial Mvar for more information.

Load Characteristic: CompLoad

CompLoad is in most ways the same as any other load characteristic model. Just like any other characteristic, it can be assigned to a load, load model group, bus, owner, zone, area or the entire case. What makes the CompLoad special though is its parameters do not define the dynamic behavior but instead only refer to load components by fraction. Thus the input parameters for the CompLoad are described as follows and then show in the figure afterwards.

 

Initialize of Components Initial Mvar

The fractions associated with the model apply only to the MWs. As a result, the initial Mvar associated with each load component's characteristic must be determined by the characteristic from the initial voltage and MW. Thus as of the release of Simulator Version 20 the available models for CompLoad are restricted to CIM5, CIM6, CIMW, IEEL, LD1PAC, LD1PAC_CMP, LDELEC, MOTORW, MOTORX, and MOTOR_CMP. Existing hard-coded composite models such as CMPLDW, CLOD, and CMLD will not be added in the future, as this CompLoad is meant to replace those. As future load models are added this support will be included.

Motor models have always done this because the steady state Mvar of an induction motor is strictly a function of the terminal voltage and the MW output. For induction motors, the mismatch between the Mvar specified in a power flow solution initial condition are made up by placing an internal capacitance to match the initial condition. The same concept is used with each load characteristic used in a CompLoad, except that the internal capacitance is summed up across all the components.

Using these conventions, each component of the CompLoad will calculate its own initial Mvar. As with the stand-along induction motor models, this means that the total Mvar of the initial condition from the power flow solution may not match this summation of calculated initial Mvars. This total mismatch across the entire CompLoad will then be assign to an internal capacitance at the load bus. If a distribution system equivalent is being used in conjunction with this CompLoad, then this mismatch will be used in the calculation of the Bf1 and Bf2 terms as described in the help topic on the distribution system equivalent.

This should be noted that starting in Version 20, to handle this models LDELEC and IEEL were been modified to include additional input parameters that specify the initial condition power factor of the dynamic load model. When used in CompLoad this parameter is used to determine the initial Mvar of the load. If the initial power factor specified with IEEL or LDELEC is set as zero however, then Simulator initializes that components assuming that the fraction of total Mvars is equal to the fraction of MWs.

 

Handling of the Fractional Definitions Degenerate Situations

The expectation for user input for CompLoad are as follows

It is possible that the user input may not conform to this in which case the following logic will be applied. This following logic may result in a validation warning or error and those could be seen on the validation portion of the transient stability dialog.

Any Load Component referenced by a CompLoad which does not have active load characteristic assigned to it will be treated as though the respective fraction is a 0.0. This will not be considered a validation warning and not prevent the simulation from running. Also for any CompAA value which is not assigned (None) , the respective fAA value will be treated as 0.0.

If more than one load component has a negative fraction, then this will be considered a validation and the simulation will abort and not run. Otherwise, Simulator will calculate the summation of all positive fractions assigned to Load Components that have a valid active load characteristic. Call this summation SumFrac.

The SumFrac value and existence of a negative fraction value will be evaluated with the following logic.

None of the above will modify any of the user input data for fractions f0...f9, but the internally modified fractions may be different than specified to conform the input data to the expectation.