Implement a circuit breaker opening at current zero crossing
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Elements Library
Description
The Breaker block implements a circuit breaker that is controlled by a Simulink signal applied on its second input. The control signal must be either 0 or 1, 0 for open and 1 for closed. The arc extinction process is simulated by opening the breaker when the current passes through zero (first current zero-crossing following the transition of the Simulink control input from 1 to 0).
When the breaker is closed, it behaves as a series RL circuit. The R and L values can be set as small as necessary in order to be negligible compared with external components (typical values Ron=10m
, Lon=10µH). When the breaker is open, it has an infinite impedance.
If the breaker's initial state is set to 1 (closed), power2sys automatically initializes all the states of the linear circuit and breaker initial current so that the simulation starts in steady-state.
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Limitations
The circuit breaker is modeled as a current source driven by the voltage appearing across its terminals. Therefore, it cannot be connected in series with an inductor or another current source. You can avoid this by connecting a large resistor across its terminals. The internal breaker inductance cannot be set to zero. However, a null resistance is allowed.
It can happen that a breaker is connected across a capacitor. Depending on the capacitor value, breaker resistance and inductance, a high-frequency poorly damped oscillatory voltage, and current oscillation can be produced when the breaker closes. If the breaker parameters (Ron, Lon) are not properly selected, this will result in a slow simulation speed. This situation can arise, when a circuit breaker is used to simulate a phase-to-ground fault at one end of the PI line section.
To damp this high frequency mode, set the inductance of the circuit breaker sufficiently small. A good practice is to achieve a damping factor z<0.5 for the RLC circuit formed by the circuit breaker and the capacitor. This condition is obtained for
For example, for a capacitor C=1µF and a breaker resistance Ron=0.01, the breaker inductance Lon should be selected so that:
You must use a stiff integration algorithm to simulate circuits with a circuit breaker. Ode15s usually gives the best simulation speed.
Example
A circuit breaker is connected in series with a series RL circuit on a 60Hz voltage source. The breaker is initially closed and an opening order is given at t = 1.5 cycles, when current reaches a maximum. The current stops at the next zero crossing; then the breaker is reclosed at a zero crossing of voltage at t = 5 cycles.
This circuit is available in the psbbreaker.mdl file. Simulation produces the following results.
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