2013年2月23日星期六

Week 4

It is only remaining one week to the end of this project. And the main objectives in this week is to simulate four types of fault occurring in the power system which are three-phase fault, single-line to ground fault, double line fault and double line to ground fault. 

Firstly, we have to design our own circuit for a simple power system which is demonstrated with specific physical values in the Figure 1 below. In addition, the base power and base voltage for this power system are regarded as 100 MVA, 154 kV respectively.

Then, the corresponding schematic of the power system can be built in the model of MATLAB (Figure 2) on the basis of the painted circuit above(Figure 1). 


Figure 2
The only difference between the two circuits above is that whether a fault is produced or not. In theory, the normal operation for a power system is either the three phase currents or three phase voltages all present steady alternating signals through the whole system. If a fault appears at a certain time, there will be an abnormal phenomenon with unstable current and voltage signals during the transition time.

Next step is the most significant part which is to set the properties for each element properly in terms of those given messages. Moreover, the nether screenshots are the exact settings for our  design.
  
Series RL Branch
 
Transformer 1
Source
          
Transformer 2
Series R Load
     
Three Phase Fault
   













After everything is ready, the simulation can be started. For the normal operation, the measurements for Vabc, Iabc are shown below:   
No Fault
Besides, the three phase fault is the primary pattern for consideration in this project. Since, the three phase short-circuit (to ground) fault belongs to the symmetrical fault, each phase is identical. And the Vabc would become 0(GND) immediately after the fault occurs, whereas  Iabc would increases rapidly towards a very large value during the transient time. As the simulation for three phase fault shown below, the theory can be verified by reality, so using MATLAB software to solve the power system fault is efficient and reliable.
Three Phase Fault
In the same way, the another three unsymmetrical short-circuit faults can also be simulated and the result of simulation is demonstrated below.
SLG Fault
LL Fault
DLG Fault

  • Calculations (Per-unit System - Three Phase Fault)


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