Element Models

A great number of element models are available in OpenDSS; among those models the user can find power conversion elements, power delivery elements, protection devices, and control models. All element objects are initialized with a default set of parameter values; when a new instance of an element is created, the default values are overwritten by those specified in the new instance definition. Due to the default parameter initialization, it is not necessary to define all parameter values for a new element, only those that are necessary. Some of the most important elements and their main parameters are summarized in this Section [A.1].

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Figure A.3. Default solution loop [A.2].

Load

A Load is a power conversion element that represents the power consumption of distribution system customers. It is defined by its nominal kW and PF or its kW and kvar. Nominal power values 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. Loads are assumed balanced for the number of phases specified. For unbalanced loads, it is necessary to define separate single-phase loads. The main parameters are presented in Table A.1.

Property Description

bus1 Bus to which the load is connected (it may include node specification) conn Connection type (Wye or Delta)

kv Nominal rated (1.0 per unit) voltage for load kw Total base kW for the load

pf Load power factor (use negative value for leading power factor) model Integer code for the model to use for load variation with voltage phases Number of phases

yearly Loadshape object to use for yearly simulations Table A.1. Load object properties.

Generator

A Generator is a power conversion element similar to a Load object. Its rating is defined by its nominal kW and PF or its kW and kvar. Rated power values 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. For power flow studies, the generator is usually modeled as a negative load that can be dispatched. The main parameters are presented in Table A.2.

Yprim 1 Yprim 2 Yprim 3 Yprim n

Y

= Iinj I2 Im I1 ALL Elements PC Elements Comp. Currents V Node Voltages Iteration Loop

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Property Description

bus1 Bus to which the load is connected (it may include node specification) conn Connection type (Wye or Delta)

kv Nominal rated (1.0 per unit) voltage for load kw Total base kW for the load

pf Load power factor (use negative value for leading power factor) model Integer code for the model to use for load variation with voltage phases Number of phases

yearly Loadshape object to use for yearly simulations Table A.2. Generator object properties.

Line

The Line element is used to model most multi-phase, two-port lines or cables; it is a power delivery element described by its impedance using a Pi-model with shunt capacitance. Impedances may be specified by symmetrical component values or by matrix values. Alternatively, the user may refer to an existing LineCode object from which the impedance values will be copied. Furthermore, line impedances can be computed from an existing Geometry object. The main parameters are presented in Table A.3.

Property Description

bus1 Name of bus to which first terminal is connected bus2 Name of bus to which 2nd terminal is connected length Length of line

phases Number of phases

linecode Name of linecode object describing line impedances

geometry Geometry code for LineGeometry Object (use instead of linecode) Table A.3. Line object properties.

Transformer

The Transformer is implemented as a multi-terminal power delivery element; it consists of two or more windings, each defined by one of the available connections (Wye or Delta). Transformers have one or more phases; the number of conductors per terminal is always one more than the number of phases. For wye-connected windings, the extra conductor is the neutral point. For delta-connected windings, the extra terminal is open internally. The main parameters are presented in Table A.4.

Property Description

buses Specifies all bus connections at once using an array conns Specifies all Winding connections at once using an array kVs Specifies all kV ratings of all windings at once using an array kVAs Specifies all kVA ratings of all windings at once using an array phases Number of phases

windings Number of windings

Xhl Percent reactance, H-L (winding 1 to winding 2) %Rs Specifies all winding %resistances using an array

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Capacitor

The capacitor model is implemented as a two-terminal power delivery element. However, if a connection for the second bus is not specified, it will default to the ground reference of the same bus to which the first terminal is connected. That is, it defaults to a grounded wye shunt capacitor bank. If the connection is specified to be Delta, then the second terminal is eliminated. The main parameters are presented in Table A.5.

Property Description

bus1 Bus to which the capacitor is connected conn Connection type (Wye or Delta) kV Nominal rated (1.0 per unit) voltage kvar Total kvar

phases Number of phases

Table A.5. Capacitor object properties.

PVSystem

PVSystem is a power conversion element that aims to replicate the behavior of a photovoltaic generator. The model output will depend on the solar irradiance, panel temperature, and panel and inverter efficiency. Nominal irradiance and panel temperature values may be may be modified by a number of multipliers, including the yearly load shape, daily load shape, and a dutycycle load shape. The main parameters are presented in Table A.6.

Property Description

bus1 Bus to which the PVSystem element is connected (it may include node specification)

conn Connection type (Wye or Delta) irradiance present irradiance value in [kW/m2

] (used as base value for shape multiplier) kV Nominal rated (1.0 per unit) voltage for PVSystem element

kVA kVA rating of inverter

Pmpp rated maximum power of the PV array in [kW] pf power factor for the output power

yearly Dispatch shape to use for yearly simulations Tyearly Temperature shape to use for yearly simulations

Table A.6. PVSystem object properties.

Vsource

A Vsource object is a two-terminal, multi-phase Thevenin equivalent. The data are specified as it would commonly be for a power system source equivalent: Line-line voltage (kV) and short circuit MVA. Voltage sources are used to initialize the power flow solution with all other injection sources set to zero. The main parameters are presented in Table A.7.

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Property Description

angle Phase angle in degrees of first phase basekv Base Source kV (usually phase-phase)

bus1 Name of bus to which the main terminal is connected frequency Source frequency

phases Number of phases

pu Actual per unit operating voltage MVAsc1 MVA Short Circuit for one-phase fault MVAsc3 MVA Short circuit for three-phase fault

Table A.7. Vsource object properties.

Fuse

The Fuse object is a protective device that is connected to one terminal of a circuit element. All circuit elements have switches on each of its terminals, the Fuse object controls the terminal switches according to the current flowing through the monitored element. The monitored and switched circuit element must be explicitly defined, even if they refer to the same circuit element. The main parameters are presented in Table A.8.

Property Description

FuseCurve Name of the TCC Curve object that determines the fuse blowing RatedCurrent Multiplier or actual phase amps for the phase TCC curve

MonitoredObj Full object name of the circuit element to which the Fuse is connected MonitoredTerm Number of the terminal of the circuit element to which the Fuse is

connected

SwitchedObj Name of circuit element switch that the Fuse controls

SwitchedTerm Number of the terminal of the controlled element in which the switch is controlled by the Fuse

Table A.8. Fuse object properties.

Relay

The Relay object (like the Fuse object) is a protective device that is connected to one terminal of a circuit element; it can monitor currents and voltages at the terminal to which it is connected. The Relay object can use the current and voltage values to operate the terminal switches of the switched circuit element; it also has the capability to perform reclosing actions. As in the Fuse object, the monitored and switched element must be defined explicitly; moreover, for reclosing actions, the total number of opening actions and reclosing intervals must be specified. The main parameters are presented in Table A.9.

Recloser

The Recloser object is a protection device similar to the Relay and Fuse object. It controls the terminal switches of the switched element according to the current flowing through the monitored element. The Recloser object also has the capability to perform reclosing actions; furthermore, two different time-current curves can be defined (one

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fast and one slow/delayed); these can be used to implement a fuse-saving scheme. The main parameters are presented in Table A.10.

Loadshape

A LoadShape object consists of a series of multipliers (typically ranging from 0.0 to 1.0) that are applied to the base kW values of the load to represent variation of the load over some time period. Load shapes are generally fixed interval, but may also be variable interval. For the latter, both the time and the multiplier must be specified. The main parameters are presented in Table A.11.

Property Description

kvbase Voltage base (kV) for the relay

MonitoredObj Full object name of the circuit element to which the relay's PT and/or CT are connected

MonitoredTerm Number of the terminal of the circuit element to which the Relay is connected

Phasecurve Name of the TCC Curve object that determines the phase trip PhaseTrip Multiplier or actual phase amps for the phase TCC curve RecloseIntervals Array of reclose intervals

Shots Number of shots to lockout

SwitchedObj Name of circuit element switch that the Relay controls

SwitchedTerm Number of the terminal of the controlled element in which the switch is controlled by the Relay

Type Relay type

Overvoltcurve TCC Curve object to use for overvoltage relay Undervoltcurve TCC Curve object to use for undervoltage relay

Table A.9. Relay object properties.

Property Description

Numfast Number of Fast (fuse saving) operations

MonitoredObj Full object name of the circuit element to which the Recloser's PT and/or CT are connected

MonitoredTerm Number of the terminal of the circuit element to which the Recloser is connected

SwitchedObj Name of circuit element switch that the Recloser controls

SwitchedTerm Number of the terminal of the controlled element in which the switch is controlled by the Recloser

PhaseTrip Multiplier or actual phase amps for the phase TCC curve RecloseIntervals Array of reclose intervals

Shots Total Number of fast and delayed shots to lockout

PhaseFast Name of the TCC Curve object that determines the Phase Fast trip PhaseDelayed Name of the TCC Curve object that determines the Phase Delayed trip

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Property Description

mult Array of multiplier values for active power (P) or other key mpts Max number of points to expect in load shape vectors interval Time interval for fixed interval data

hour Array of hourly values

UseActual If true, signifies to circuit element objects to use the return value as the actual kW, kvar, kV, or other value rather than a multiplier

Table A.11. Loadshape object properties.

In document Analysis of power distribution systems using a multicore environment (Page 183-189)