Contingency Analysis in Power System
In the past many widespread blackouts have occurred in interconnected power systems.
Therefore, it is necessary to ensure that power systems should be operated most economically
such that power is delivered reliably. Reliable operation implies that there is adequate power
generation and the same can be transmitted reliably to the loads. Most power systems are
designed with enough redundancy so that they can withstand all major failure events. Here we
shall study the possible Contingency Analysis in Power System and remedial actions required by
two main failure events: line outages and generating unit failures.
Figure 1: Base Case AC Line Flow for sample 5 bus system
To explain the Contingency Analysis in Power System problem briefly, we consider the five-bus
system of Reference. The base case load flow results for the example are given in Fig. 1 and
show a flow of 24.7 MW and 3.6 MVAR on the line from bus 2 to bus 3. Let us assume that at
present, we are only interested in the MW loading of the line. Let us examine what will happen if
the line from bus 2 to bus 4 were to open. The resulting line flows and voltages are shown in Fig.
2.
It may be noted that the flow on the line 2-3 has increased to 37.5 MW and that most of the other
line flows are also changed. It may also be noted that bus voltage magnitudes also get affected,
particularly at bus 4, the change is almost 2% less from 1.0236 to 1.0068 pu. Suppose the line
from bus 2 to bus 5 were to open. Figure 3 shows the resulting flows and voltages. Now the
maximum change in voltage is at bus 5 which is almost 10% less.
Figure 2: Post Outage AC Load Flow (LINE Between 2 and 4 is open)
Figure 3: Post Outage AC Load Flow (Line between 2 and 5 is open)
Figure 4 is an example of generator outage and is selected to explain the fact that generator outages can
also result in changes in line flows and bus voltages. In the example shown in Fig. 4 all the generation lost
from bus 2 is picked up on the generator at bus 1. Had there been more than 2 generators in the sample
system say at bus 3 also, it was possible the loss of generation on bus 2 is made up by an increase in
generation at buses 1 and 3. The differences in line flows and bus voltages would show how the lost
generation is shared by the remaining units is quite significant.
It is important to know which line or unit outages will render line flows or voltages to cross the limits. To
find the effects of outages, oontingency nnalysis in oower yystem techniques are employed. oontingency
nnalysis in oower yystem models single failure events (i.e. one-line outages or one unit outages) or
multiple equipment failure events (failure of multiple unit or lines or their combination) one after another
until all “credible outages” are considered. For each outage, all lines and voltages in the network are
checked against their respective limits Figure 5 depicts a flow chart illustrating a simple method for
carrying out a oontingency nnalysis in oower yystem.
Figure 4: Post Outage AC Load Flow (Generator 2 Outage, lost generation is picked by Generator 1)
Figure 5: Flow chart for Contingency analysis