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I am learning about grid level stabilization services. My native language is German and I am translating the specific terminology. If I use the English terms incorrectly please edit my below sentences.

Context:

I have read that consumers are using energy mainly inductive. In my understanding, inductors are coils of wire that build a magnetic field.

This can be used in electric motors to create motion from electricity.

So, pumps (e.g. fridges), washing machines, electric lawn mowers and air conditioners are inductive electric devices.

Sidenote: PCs, TVs, stoves, ovens and lamps don't produce motion. Are they mainly inductive or are they capacitors? With stoves and lamps I guess that they are only resistors and therefore neither.

If you use electricity via an inductor or a capacitor there is a phenomenon, where the device is sending electricity back into the grid, but current and voltage are phase shifted by 90°.

This phase shifted electricity can't be used by other devices, but needs to be transported via the electric grid. This is not good because in that case we transport unusable power we have to account for. Transmission lines, transformers and other equipment needs to be bigger to handle the flow of current.

The unusable power from inductors and capacitors cancels each other out. So, there are service providers who feed electricity into the grid to balance the shifts from inductors and capacitors. At least in Germany, household end users don't pay for this service (or at least the costs are hidden in the electricity price.) Companies must pay for the phase shift they are responsible for.

Questions:

  1. Why do inductors and capacitors cause this phase shift?
  2. Why can the phase shifted electricity not be used anymore?
  3. How can you balance this phase shift as a service provider? Which devices do they use?
  4. What happens to the electricity that is fed back to the grid? Is the phase shift corrected at some point or does the current flow in circles until all the electric energy has been turned to heat in the conductors?
  5. Why are there no policies to force electric equipment designers to prevent current backflow into the grid? If a device has an inductor you could add a capacitor to prevent the problem, right?

Please mark your answers with the number of the question that you are answering to, to avoid confusion.

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  • \$\begingroup\$ 1) Consider inductors a caps as energy storage but they are not able to store this energy immediatelly. It alway take some finite time. In inductors if you apply voltage on it a current starts rise from zero very slowly. That´s why the current lags voltage and cause a phase shift. The caps do opposite. \$\endgroup\$ Nov 24, 2023 at 13:48
  • \$\begingroup\$ I have read that consumers are using energy mainly inductive That's wrong. \$\endgroup\$ Nov 24, 2023 at 13:55
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    \$\begingroup\$ PCs, TVs, stoves, ovens and lamps don't produce motion. Are they mainly inductive or are they capacitors? Neither. They are fed by switch-mode power supplies, which need to have active power factor correction. So they look like resistive loads, just like your water kettle, or your oven. \$\endgroup\$ Nov 24, 2023 at 13:56
  • \$\begingroup\$ device is sending electricity back into the grid, No matter how well-intended I try to interpret that sentence, it keeps being wrong, sorry. Electricity is current flowing in closed circles; there's no "sending back" here. The current through the device might lag or run ahead of the voltage across the device (which is imposed by the grid), but the net power flow here is always grid->device, otherwise you'd be a electricity producer. \$\endgroup\$ Nov 24, 2023 at 13:58
  • \$\begingroup\$ Other than that, this is 6 questions in one. Don't do that – it makes your question "lacking focus". We can only answer one in an answer you could accept. So, remove all but one question. \$\endgroup\$ Nov 24, 2023 at 13:59

1 Answer 1

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  1. Why do inductors and capacitors cause this phase shift?

Consider this simple circuit.

schematic

simulate this circuit – Schematic created using CircuitLab

Figure 1. Capacitor across mains supply.

Thought experiment:

  • V1 is producing a sinusoidal voltage waveform.
  • The rate of change of voltage \$ \frac {dV}{dt} \$ will be maximum at zero-cross. The capacitor is charging / discharging to keep up with V1. The current will be at a maximum when V1 = 0!
  • When V1 reaches maximum or minimum the rate of change will be zero. Therefore the current in or out of C1 will be zero when V1 is at maximum!

If you plot the points for the full mains cycle you will get a current waveform that is 90° out of phase with the voltage waveform.

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