MATLAB: Does the model show a non zero voltage when I have the breakers open in SimPowerSystems 5.1 (R2009a)

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Refer to the attached model. Even though both breaker components are open there is a non-zero voltage reading on the scope.

Best Answer

The reason that there is a voltage across the lower branch of the circuit when both breakers are open is because the open breaker, in SimPowerSystems, is modeled as a very large resistance (not actually a true 'open' circuit).

By connecting the two breaker/ resistance pairs in series and opening both breakers you have effectively turned your circuit into a very large voltage divider. Where half of the input voltage appears across the lower branch, albeit with a very tiny current.

In a more realistic model you would probably have some kind of load attached to your system that would provide a path for the current when the breakers are open. In this case you should see a more acceptable voltage level on the scope. You can modify the example model to show this by adding a 1 Ohm resistor in parallel with the voltmeter.

Related Solutions

MATLAB: Does the “power_battery” link from Battery block in SimPowerSystems documentation take me to the “power_breaker” model instead in SimPowerSystems 5.1 (R2009a)

This change has been incorporated into the documentation in Release 2010a (R2010a). For previous releases, read below for any additional information:

This is a bug in the documentation for SimPowerSystems 5.1 (R2009a). To open the correct model type

power_battery

in the MATLAB command window.

MATLAB: How does using multiple SimPowerSystems Ideal Switch blocks in series with snubber impedances compare with reality in the power network in SimPowerSystems 4.3 (R2006b)

If you build a real circuit with two switches connected in series as in your example "Basic_network_topology.mdl", the voltage appearing across switches when both switches are opened will be dictated by the stray capacitance of each individual switch and by their capacitances to ground. We can assume that the resistive leakage current is negligible.

For a mechanical switch this stray capacitance can be evaluated based on the

switch geometry or it can be measured.

In your example, if you replace the resistive snubber by capacitive snubbers

by setting

 Rs=0 and Cs=10e-12

(assuming 10 pF stray capacitances), you will still obtain 50 V across each switch. See example model "Basic_network_topologyGS.mdl".

Now, if the capacitances are

 Cs1= 10 pF and Cs2=30 pF
 you get 
 Vsw1= 75 V  and Vsw2 = 25 V.

Naturally, if you use a Voltage sensor with given input impedance, the voltage sharing will be affected. For example, using a voltage sensor with 10-Megohm resistive input impedance to measure Vsw1 and Cs1=Cs2= 10 pF will give

 Vsw1| ~0  V Vsw2=100 V

If the voltage source is an AC source of 60 Hz and 100V peak voltage, you would get Vsw1 = 3.8 V peak and Vsw2 = 99.8 V .

In other words, the voltage sharing is highly dependant on the stray capacitances and voltage sensors input impedances as it would be in the real life.

Best Answer

Related Solutions

MATLAB: Does the “power_battery” link from Battery block in SimPowerSystems documentation take me to the “power_breaker” model instead in SimPowerSystems 5.1 (R2009a)

MATLAB: How does using multiple SimPowerSystems Ideal Switch blocks in series with snubber impedances compare with reality in the power network in SimPowerSystems 4.3 (R2006b)

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