Since the 1890s, electricity networks and devices all around the globe have used alternating current (AC) systems, which means that the flow of electricity in the system is repeatedly changing direction.
Supplying electricity at a consistent frequency is very important because appliances and electronics on the network are designed for a specific frequency/voltage input. Therefore, they can be damaged by the wrong electricity supply.
As a rule, networks would rather supply no electricity than bad electricity. Automated controls through the electricity system will disconnect the supply if the frequency or voltage is “off-spec.”
Frequency Control is an often neglected topic and worth getting a good mention.