Grid stability is ability to keep the same voltage and frequency values on the whole network.
On the one hand, it is necessary to keep equal the injunction and withdrawal of current. In other words, electricity production has to correspond with the energy consumption.
On other hand, the power line must be able to regain balance after a disturbance (technical, mechanical or weather incident, for example).
If the electrical stability is not insured, the equipment might be damaged. Moreover, it can lead to a power failure on a part of the grid, or on the whole.
It is very important to be able to continuously control voltage et frequency values in the power lines. There are some automatic and manual solutions.