AeroCable

Aero Cable

The AeroCable class uses lookup table data based on real world cable metrics (resistance, inductance, and mass per unit length as well as ampacity), as a function of wire gauge. Sizing logic is included and used during on-design runs, that selects the lightest possible cable assembly (bundle of n number of parallel cables) that meets the ampacity requirements (on-design current).

Usage

• The input design parameters that must be specified by the modeler when creating an instance of the AeroCable component are cable length (length), maximum number of parallel wires (n_parallel) and voltage drop tolerance, expressed as a percentage of the cable input voltage (drop_tolerance) When this component is run ONDESIGN, it will select a wire gauge and number of parallel wires that comprises a cable assembly rated above the cable current seen during this ONDESIGN run. Outputs generated by ONDESIGN runs include the cable resistance and inductance (R and L), the cable mass (Mass), and mass specific ampacity (SpecificAmperage).

• This component supports DC and AC (single or multiphase) power. At instantiation, this component's power type is unspecified. NPSS Power System Components need to have a power type in order to correctly run power calculations. For this component, the power type is typically set by calling the findSourcesAndPropagate() method at the top level assembly (see ElectricPort).

• The data used in this design logic was obtained from lookup tables constructed using realistic cable data. Note that this data is based on terrestrial medium voltage power cable, and not flight-weight, medium voltage aircraft cable. This cable does not yet exist (as of 2020), and so be aware that the cable designs produced by this sizing logic may over predict mass.

• This component does not contain a node, and so starts each iteration with its port voltages unknown. The NPSS Power System Library requires that all components that contain nodes all have a prePass() method specified that pushes node voltage information, via their ports to all components that do not contain nodes and so do not know their voltages. The intent is that after all component prePass methods are automatically called, all components in the system will then have port voltages specified. Then during the normal iteration, components that don't contain nodes such as this one, will execute first. These components typically transmit power from one node to another and do not transform it from one kind to another (e.g. cables and breaker). These execute first in the solver sequence, and inside their calculate() methods, they calculate their currents, which are then passed via the ports, to all other components in the circuit. So after these nodeless transmission components execute, all electric port voltages and currents should be specified, and so all other components are free to run.

• This component, like other power system components in the NPSS Power System Library, can optionally include thermal models. An optional thermal model is enabled by setting switchThermPort to TRUE, and plugging an EThermalMass subelement into the S_eThermMass socket. Doing these will add a temperature state (existing within EThermalMass) and a thermal port to the model. The thermal port is intended to connect this component to a second component that represents the mechanism by which heat is extracted from this component. This second component could represent a heat exchanger, cold plate, or just model heat transfer from the first component to the surrounding environment. For more information see EThermalMass.

• Solver independents and dependents are only used during ONDESIGN. In ONDESIGN, the cable's impedance (resistance and inductance R and L) is not known. Because of this, the cable will run with only its input and output voltages specified via its input and output ports (see Electric Port - Nodal Component prePass()). With no other parameters, the cable cannot know the design current (ampacity) it must be sized to. For this reason, the cable includes solver variables for ONDESIGN. The cable's real current (and also imaginary current if the cable carries AC) is set up as an independent. A dependent is used to ensure that the voltage seen across the cable's ports, equals the voltage drop according to the guessed current and designed impedance (dV = dVCalc = I * Z). Imaginary dependents are also included if the cable power type is AC (AC1 or AC3).

• The AeroCable OFFDESIGN logic does not need solver variables because during OFFDESIGN, the cable knows its complex impedance (Z = R + j*2*PI*frequency*L), and knows its voltage as specified at its input and output ports. Current is calculated from I = dV/Z, and this current information is updated in the cable's input and output ports.