Load

A Load is a complicated Power Conversion element that is at the heart of many analyses. It is basically defined by its nominal kW and PF or its kW and kvar. Then it may be modified by a number of multipliers, including the global circuit load multiplier, yearly load shape, daily load shape, and a dutycycle load shape.

The default is for the load to be a current injection source. Thus, its primitive Y matrix contains only the impedance that might exist from the neutral of a wye-connected load to ground. However, if the load model is switched to Admittance from PowerFlow (see Set LoadModel command), the load is converted to an admittance and included in the system Y matrix. This would be the model used for fault studies where convergence might not be achieved because of low voltages.

Loads are assumed balanced for the number of phases specified. If you would like unbalanced loads, enter separate single-phase loads.

There are three legal ways to specify the base load:

1. kW, PF

2. kw, kvar

3. kVA, PF

If you sent these properties in the order shown, the definition should work. If you deviate from these procedures, the result may or may not be what you want. (To determine if it has accomplished the desired effect, execute the Dump command for the desired load(s) and observe the settings.)

The properties, in order, are:

bus1	Name of bus to which the load is connected. Include node definitions if the terminal conductors are connected abnormally. 3-phase Wye-connected loads have 4 conductors; Delta-connected have 3. Wye-connected loads, in general, have one more conductor than phases. 1-phase Delta has 2 conductors; 2-phase has 3. The remaining Delta, or line-line, connections have the same number of conductors as phases.
Phases	No. of phases this load.
Kv	Base voltage for load. For 2- or 3-phase loads, specified in phase-to-phase kV. For all other loads, the actual kV across the load branch. If wye (star) connected, then specify phase-to-neutral (L-N). If delta or phase-to-phase connected, specify the phase-to-phase (L-L) kV.
Kw	nominal active power, kW, for the load. Total of all phases. See kVA.
Pf	nominal Power Factor for load. Negative PF is leading. Specify either PF or kvar (see below). If both are specified, the last one specified takes precedence.
Model	Integer defining how the load will vary with voltage (see “Power Conversion Elements” for more details). The load models currently implemented are: 1: Constant P and constant Q (Default): Commonly used for power flow studies 2: Constant Z (or constant impedance) 3: Constant P and quadratic Q 4: Exponential: and (See CVRwars ans CVRvar) 5: Constant I (or constant current magnitude) Sometimes used for rectifier load 6: Constant P and fixed Q (at the nominal value) 7: Constant P and quadratic Q (i.e., fixed reactance) 8: ZIP (see ZIPV) "Constant" power value (either P or Q) may be modified by loadshape multipliers. "Fixed" power values are always the same -- at nominal, or base, value.
Yearly	Name of Yearly load shape.
Daily	Name of Daily load shape.
Duty	name of Duty cycleload shape. Defaults to Daily load shape if not defined.
Growth	Name of Growth Shape Growth factor defaults to the circuit's default growth rate if not defined. (see Set %Growth command)
Conn	{wye \| y \| LN} for Wye (Line-Neutral) connection; {delta \| LL} for Delta (Line-Line) connection. Default = wye.
kvar	Base kvar. If this is specified, supercedes PF. (see PF)
Rneut	Neutral resistance, ohms. If entered as negative, non-zero number, neutral is assumed open, or ungrounded. Ignored for delta or line-line connected loads.
Xneut	Neutral reactance, ohms. Ignored for delta or line-line connected loads. Assumed to be in series with Rneut value.
Status	{fixed\| variable}. Default is variable. If fixed, then the load is not modified by multipliers; it is fixed at its defined base value.
Class	Integer number segregating the load according to a particular class.
Vminpu	Default = 0.95. Minimum per unit voltage for which the MODEL is assumed to apply. Below this value, the load model reverts to a constant impedance model.
Vmaxpu	Default = 1.05. Maximum per unit voltage for which the MODEL is assumed to apply. Above this value, the load model reverts to a constant impedance model.
VminNorm	Minimum per unit voltage for load EEN evaluations, Normal limit. Default = 0, which defaults to system "vminnorm" property (see Set Command under Executive). If this property is specified, it ALWAYS overrides the system specification. This allows you to have different criteria for different loads. Set to zero to revert to the default system value.
VminEmerg	Minimum per unit voltage for load UE evaluations, Emergency limit. Default = 0, which defaults to system "vminemerg" property (see Set Command under Executive). If this property is specified, it ALWAYS overrides the system specification. This allows you to have different criteria for different loads. Set to zero to revert to the default system value.
XfkVA	Default = 0.0. Rated kVA of service transformer for allocating loads based on connected kVA at a bus. Side effect: kW, PF, and kvar are modified. See PeakCurrent property of EnergyMeter. See also AllocateLoads Command. See kVA property below.
AllocationFactor	Default = 0.5. Allocation factor for allocating loads based on connected kVA at a bus. Side effect: kW, PF, and kvar are modified by multiplying this factor times the XFKVA (if > 0). See also AllocateLoads Command.
kVA	Definition of the Base load in kVA, total all phases. This is intended to be used in combination with the power factor (PF) to determine the actual load. Legal ways to define base load (kW and kvar): kW, PF kW, kvar kVA, PF XFKVA * Allocationfactor, PF kWh/(kWhdays24) Cfactor, PF
%mean	Percent mean value for load to use for monte carlo studies if no loadshape is assigned to this load. Default is 50.
%stddev	Percent Std deviation value for load to use for monte carlo studies if no loadshape is assigned to this load. Default is 10.
CVRwatts	Exponential paramater that defines the relationship between voltage (𝑉) and active power (𝑃) based on the following: P0 is the nominal power of the load at the base voltage V0. CVRwatts default=1 (linear relationship between voltage and active power). Typical values range from 0.4 to 0.8. Applies to Model=4 only.
CVRvars	Exponential paramater that defines the relationship between voltage (𝑉) and reactive power (Q) based on the following: Q0 is the nominal power of the load at the base voltage V0. CVRvars default=2 (quadratic relationship between voltage and reactive power). Typical values range from 2 to 3. Applies to Model=4 only.
kWh	kWh billed for this period. Default is 0. See help on kVA and Cfactor and kWhDays.
kWhDays	Length of kWh billing period in days (24 hr days). Default is 30. Average demand is computed using this value.
CFactor	Factor relating average kW to peak kW. Default is 4.0. See kWh and kWhdays. See kVA.
CVRCurve	Default is NONE. Curve describing both watt and var factors as a function of time. Refers to a LoadShape object with both Mult and Qmult defined. Define a Loadshape to agree with yearly or daily curve according to the type of analysis being done. If NONE, the CVRwatts and CVRvars factors are used and assumed constant for the simulation period.
NumCust	Number of customers, this load. Default is 1.
spectrum	Name of harmonic current spectrum for this load. Default is "defaultload", which is defined when the DSS starts.
ZIPV	Array of 7 coefficients: 1. First 3 are ZIP weighting factors for active power (should sum to 1) 2. Next 3 are ZIP weighting factors for reactive power (should sum to 1) 3. Last 1 is cut-off voltage in p.u. of base kV; load is 0 below this cut-off No defaults; all coefficients must be specified if using model=8.
%SeriesRL	Percent of load that is series R-L for Harmonic studies. Default is 50. Remainder is assumed to be parallel R and L. This has a significant impact on the amount of damping observed in Harmonics solutions.
RelWeight	Relative weighting factor for reliability calcs. Default = 1. Used to designate high priority loads such as hospitals, etc. Is multiplied by number of customers and load kW during reliability calcs.
Vlowpu	Default = 0.50. Per unit voltage at which the model switches to same as constant Z model (model=2). This allows more consistent convergence at very low voltages due to opening switches or solving for fault situations.
puXharm	Special reactance, pu (based on kVA, kV properties), for the series impedance branch in the load model for HARMONICS analysis. Generally used to represent motor load blocked rotor reactance. If not specified (that is, set =0, the default value), the series branch is computed from the percentage of the nominal load at fundamental frequency specified by the %SERIESRL property. Applies to load model in HARMONICS mode only. A typical value would be approximately 0.20 pu based on kVA * %SeriesRL / 100.0.
XRharm	X/R ratio of the special harmonics mode reactance specified by the puXHARM property at fundamental frequency. Default is 6.

Inherited Properties

Spectrum	Name of harmonic current spectrum for this load. Default is "defaultload", which is defined when the DSS starts.
Basefreq	Base frequency for which this load is defined. Default is 60.0
Like	Name of another Load object on which to base this one.

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