# How exactly does the grid handle small deviations in power consumption?

I've heard many times that the grid electricity production and consumption must be balanced and imbalances lead to overvoltage or undervoltage. I've never seen an explanation of that phenomena from energy conservation law standpoint.

Suppose I have a grid with exactly one gigawatt generation and exactly one gigawatt consumption. Let's pretend there're no losses - all the conductors are superconductors. So whatever is generated is fully consumed.

Now someone switches his one thousand watts space heater off. Generation now exceeds consumption. Although it's a relatively small increases there's still some imbalance.

What happens? Where does this excess power go?

• I think in your scenario the frequency goes up (less load to generators, they tend to spin up) and the guy begin the (country's) control panel quickly switches of some generators. Saw a documentary on tv showing how it's done. – Dan Feb 24 '15 at 8:27
• The "superconductor" part of the question interferes with the normal mechanism for load adjustment. – Ignacio Vazquez-Abrams Feb 24 '15 at 12:42
• @IgnacioVazquez-Abrams I'm not sure I see the difference. If a heater is connected with resistive wires we just have to add their resistance to the resistance of the heater. So when the heater goes off both it and the wires are excluded. – sharptooth Feb 24 '15 at 12:48
• The transmission wires are part of a resistor divider. With no resistance, things go strange. – Ignacio Vazquez-Abrams Feb 24 '15 at 12:50
• @IgnacioVazquez-Abrams: Even a superconducting generator has a source impedance, which allows the terminal voltage to vary with load. But it's true that the resistance of a real transmission system plays an important role in damping out disturbances caused by load variations. A purely inductive (and capacitive) distribution system would be no fun! – Dave Tweed Feb 24 '15 at 12:58