In newscasts discussing the electricity market, one often sees articles that involve language such as:

• A new transmission line is being built from country A to country B, which will increase country B's ability to import electricity from country A by X MW.
• Electricity prices in (say) Northern Europe are on the rise because power companies there prefer to export their electricity to (say) Central Europe where there is a high demand and therefore better prices per MWh, leaving their home markets with less supply.
• Because of [powerplant maintenance / low hydro reservoirs / declining foreign relations / whatever else the reason], country A will reduce its electricity exports to country B by Y MW.
• Electricity prices vary greatly from region to region in country C because most of the generation happens in a different region than most of the consumption, and transmission capacity between regions in that country is inadequate.

Such news can easily give an impression that electricity is like any commodity that can be transported in arbitrary quantities at will, like you'd export or import grain, oil, or cars, or control how much you water your lawn by turning on the garden hose tap. Anyone who knows something about power grids, however, knows that this impression is wrong: generation and consumption must always be kept in balance, and it's the consuming party that – by its actions that set up a certain impedance (that is, the load) in its part of the grid – determines how much power must flow into it from the producers, not vice versa.

Likewise, since the voltage and frequency must be kept constant, the producers and grid operators in between have to bear with whatever demand occurs within the consumer or, in case the load exceeds their technical or contractually agreed upon capacity, to disconnect. They are not at a position to say that "today we'll sell X MWh" or "tomorrow we'll cut our delivery to B by 50%" – not in a direct "hands on the water tap" way at least.

So I think the newscast examples above should be seen as statements of policy, instead of direct technical actions. However, obviously there must be some technical means to implement them in practice. What are they like? How do grid and transmission line operators regulate the amount of power flowing in their networks, both to utilize the network optimally and to enact delivery policies like those in the examples?

My question:

• How do grid and transmission line operators regulate the amount of power flowing in their networks, both to utilize the network optimally and to enact delivery policies like those in the examples below?

All the following is clarifying material that I've provided to explain what lead me to ask this question.

In newscasts discussing the electricity market, one often sees articles that involve language such as:

• A new transmission line is being built from country A to country B, which will increase country B's ability to import electricity from country A by X MW.
• Electricity prices in (say) Northern Europe are on the rise because power companies there prefer to export their electricity to (say) Central Europe where there is a high demand and therefore better prices per MWh, leaving their home markets with less supply.
• Because of [powerplant maintenance / low hydro reservoirs / declining foreign relations / whatever else the reason], country A will reduce its electricity exports to country B by Y MW.
• Electricity prices vary greatly from region to region in country C because most of the generation happens in a different region than most of the consumption, and transmission capacity between regions in that country is inadequate.

Such news can easily give an impression that electricity is like any commodity that can be transported in arbitrary quantities at will, like you'd export or import grain, oil, or cars, or control how much you water your lawn by turning on the garden hose tap. Anyone who knows something about power grids, however, knows that this impression is wrong: generation and consumption must always be kept in balance, and it's the consuming party that – by its actions that set up a certain impedance (that is, the load) in its part of the grid – determines how much power must flow into it from the producers, not vice versa.

Likewise, since the voltage and frequency must be kept constant, the producers and grid operators in between have to bear with whatever demand occurs within the consumer or, in case the load exceeds their technical or contractually agreed upon capacity, to disconnect. They are not at a position to say that "today we'll sell X MWh" or "tomorrow we'll cut our delivery to B by 50%" – not in a direct "hands on the water tap" way at least.

So I think the newscast examples above should be seen as statements of policy, instead of direct technical actions. However, obviously there must be some technical means to implement them in practice. What are they like? How do grid and transmission line operators regulate the amount of power flowing in their networks, both to utilize the network optimally and to enact delivery policies like those in the examples?