What are the options available for breaker/switch open actions in RMS and EMT simulation?
In dynamic simulations, a breaker/switch can be opened via the Switch Event (EvtSwitch). The Switch Event can be parameterised in order to configure the opening process. Furthermore, the breaker itself may be modelled in detail via the available options within the Breaker Type (TypSwitch). For both RMS- and EMT-simulation types, the breaker open delay (type parameter) will be considered as an added delay between the breaker open command action and the actual opening of the breaker. The switch event can be configured to open a given selection of the phases of a breaker e.g. if a three phase breaker is targeted, then either all, one or a combination of the phases can be configured for opening.
Within RMS-Simulation, the breaker opening is largely idealised/simplified: the instant of current zero crossing cannot be observed within an RMS simulation, neither can the electro-magnetic transients created by the event. Therefore, the breaker opening occurs exactly at the moment of triggering the breaker open event. All poles that have been configured to open in the Switch Event will open immediately. If, for example, all three phases of a three phase circuit breaker have been configured to open, then they will open immediately - with no time delay in between. This is, surely, a simplification with respect to an actual opening of a three phase breaker. If, due to any reason, the opening sequence of the breaker poles needs to be simulated, then three individual switch events should be defined - one for each phase. In such a situation, an accurate representation of the positive/negative/zero sequence system can be obtained during the opening period of each phase within the breaker. Note, that an unbalanced RMS-simulation is required in order to represent unbalanced systems and events.
Within EMT-Simulation, the opening of the breaker poles can be done using the following options:
- current zero crossing (where a certain procedure of the opening scheme of the individual phase poles can be selected)
- current threshold (where a certain logic can be chosen on the evaluation criteria, as well as an particular procedure of the opening scheme of the individual phase poles)
- execution time (immediate opening of the targeted breaker poles, independent of momentary value of phase currents). This option may be useful for the simulation of vacuum circuit breakers. Cautious use of this option is advised for any other case, since opening an purely inductive path with non-zero current may generate unrealistically high overvoltages at the terminals.
Moreover, the Breaker/Switch can hold additional settings relevant for EMT simulation which may influence the behaviour of an open event:
- Transient Recovery Voltage characteristic (breaker type parameters) and usage configuration (breaker element parameters)
- Non-linear characteristics for DC breakers (type parameters)
- Additional passive components of a detailed breaker (type parameters)