*5.3. Safety Checking*

In the safety checking of the power grid, the participation of the load reduction should be considered, and the maximum reduction is 20% [14]. As shown in Figure 12, the 76th line exceeds the limit, and the limit is 196 MW. In order to ensure the safety of the line flow, two cases were adopted. The cases are described below.

**Figure 12.** Transmission power of the 76th line.

The first case does not consider the participation of flexible loads and directly performs safety checking and correction through unit adjustment.

The second case considers that the load can be reduced to participate in the safety checking and correction. The load that can be reduced accounts for 10.09% of the total load.

The safety checking operation of the 76th line was carried out in the above two cases. We now analyze the differences between the two cases.

Based on the above data, the safety checking line power flow results obtained in Cases 1 and 2 are shown in Figure 13. The diagram shows that both cases can ensure that the line flow does not exceed the limit and can ensure the safe operation of the network; the transmission power of the line does not exceed its upper and lower limits.

**Figure 13.** The safety checking line power flow results obtained in Cases One and Case Two.

The output adjustment results of the two cases are shown in Table 4. Table 4 shows that power plant 52 in Case Two emits 5.61 MW more power than Case One, and power plant 63 in Case One emits 137.89 MW more power than Case Two. The reason is that the reducible loads can participate in the safety checking in Case Two, and balance the power plant output by reducing the flexible load.


**Table 4.** The output adjustment results of the two cases.

The adjustable amount of the reducible load results in Case Two are shown in Figure 14. The total amount of the reducible load after the reduction can be seen, where the total reduction in the flexible loads is 132.28 MW, which makes up for the power shortage of Unit 2 in Case Two.

From the above analysis, we know that the reducible load has a rapid response. By reducing the load and participating in the safety checking, the adjustment amount of the generator set can be reduced. In this way, the role of load reduction can be brought into full play, and the number of start–stops of the unit can also be reduced.

**Figure 14.** The flexible load reduction results in Case Two.
