Breaker

Breaker

The Breaker class represents the performance (losses) of a circuit breaker. On-design, the breaker runs at the design efficiency and computes its impedance. Off-design, it runs with the impedance. Supports DC, 1-phase, and 3-phase.

Usage

• The input design parameters that must be specified by the modeler when creating an instance of this Breaker component are mass specific power (SpecificPower) and design efficiency (eff). When this component is run ONDESIGN, it will select the necessary resistance such that it runs with the specified design efficiency. It then calculates its component mass (Mass) by dividing its ONDESIGN input power by its specific power.

• 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).

• Note that for purposes of mass calculation, a DC breaker is assumed to consist of two physical breaker units (one protecting the positive rail, and one on the negative). Multiphase AC breakers typically include 3 breakers within one physical breaker unit, and these protect the three phases (no return or ground need be protected). This is why the DC breaker mass calculation bookkeeps the total breaker component mass twice.

• 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 in the Breaker component during ONDESIGN. In ONDESIGN, the breaker's impedance (resistance and inductance R and L) is not known. Because of this, the breaker 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 breaker cannot know the design power it must handle, and so cannot calculate the impedance it should have such that it runs with the specified design efficiency. For this reason, the breaker includes solver variables for ONDESIGN. The breaker's real current (and also imaginary current if the breaker carries AC) is set up as an independent. A dependent is used to ensure that the voltage seen across the breaker'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 breaker power type is AC (AC1 or AC3).

• The Breaker OFFDESIGN logic does not need solver variables because during OFFDESIGN, the breaker 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 breaker's input and output ports.