Breaker (Power System Blockset)

Implement a circuit breaker opening at current zero crossing.

Library

Elements

Description

The Breaker block implements a circuit breaker where the opening and closing times can be controlled either from an external Simulink signal (External control mode), or from an internal control timer (Internal control mode).

The arc extinction process is simulated by opening the breaker device 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 resistive circuit. It is represented by a resistance (Ron). The Ron value can be set as small as necessary in order to be negligible compared with external components (typical value Ron=10m). When the breaker is open it has an infinite resistance.

If the Breaker block is set in the external control mode, a control input appears in the block icon. The control signal connected to this second input must be either 0 or 1, 0 to open the breaker, 1 to close it. If the Breaker block is set in the internal control mode, the switching times are specified in the dialog box of the block.

If the breaker initial state is set to 1 (closed) the Power System Blockset automatically initializes all the states of the linear circuit and the Breaker block initial current so that the simulation starts in steady state.

A series Rs-Cs snubber circuit is included in the model. It can be connected or not to the circuit breaker.

Dialog Box and Parameters

Breaker resistance Ron

The internal breaker resistance, in ohms (

). The Breaker resistance Ron parameter cannot be set to zero.

Initial state

The initial state of the breaker. A closed contact is displayed in the block icon when the Initial state parameter is set to 1, and an open contact is displayed when set to 0.

Snubber resistance Rs

The snubber resistance, in ohms (

). Set the Snubber resistance Rs parameter to inf to eliminate the snubber from the model.

Snubber capacitance Cs

The snubber capacitance, in farads (F). Set the Snubber capacitance Cs parameter to 0 to eliminate the snubber, or to inf to get a purely resistive snubber.

Switching times

Specify the vector of switching times when using the Breaker block in the internal control mode. At each switching time the Breaker block will open or close depending on its initial state. For example, if the Initial state parameter is 0 (open), the breaker will close at first switching time, open at second switching time, and so on. The Switching times parameter is not visible in the dialog box if the External control of switching times parameter is checked.

External control of switching times

If checked, adds a second input port to the Breaker block for an external control of the switching times of the breaker. The switching times are defined by a Simulink signal (0 or 1) connected to the second input port of the Breaker block.

Measurements

Select Branch voltage to measure the voltage across the Breaker block terminals.

Select Branch current to measure the current flowing through the Breaker block. If the snubber device is connected to the breaker model, the measured current is the one flowing through the breaker contacts only.

Select Branch voltage and current to measure the breaker voltage and the breaker current.

Place a Multimeter block in your model to display the selected measurements during the simulation. In the Available Measurement listbox of the Multimeter block, the measurement will be identified by a label followed by the block name:


Measurement	Label
Branch voltage	`ub:`
Branch current	`ib:`

Limitations

The Breaker block is modeled as a current source driven by the voltage appearing across its terminals. When the block is connected in series with an inductor or another current source, you must add the snubber circuit across its terminals. In most applications you can use a resistive snubber (Snubber capacitance parameter set to inf) with a large resistor value (Snubber resistance parameter set to 1e6, or so).

Due to modeling constraint he internal breaker inductance Ron cannot be set to 0.

You must use a stiff integration algorithm to simulate circuits with Breaker block. Ode23tb or Ode15s with default parameters usually give best simulation speed.

Example

A circuit breaker is connected in series with a series RL circuit on a 60Hz voltage source. The switching times of the Breaker block are controlled by a Simulink signal. The breaker device 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 = 3 cycles.

This circuit is available in the psbbreaker.mdl file. Simulation produces the following results.

Note that the breaker device opens only when the load current has reached zero, after the opening order.

See Also

Ideal Switch, Multimeter

Asynchronous Machine Bus Bar