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I'm trying to figure out how to measure energy consumption with a power meter.

It reports for the three phases:

  • Total Active Energy
  • Forward Active Energy
  • Reverse Active Energy
  • Total Reactive Energy
  • Forward Reactive Energy
  • Reverse Reactive Energy

Where: Total Energy = Forward - Reverse, for both Active and Reactive versions.

The question is what is Forward Reactive Power and Backward Reactive Power?

My understanding is that reactive power is casued by inductive elements in the machines, causing a "backward" flow (from machine to generator). What is then the Reverse Reactive power?

If I'm interested to find out my energy bill cost then (if I understand correctly):

  1. for residential consumers: I should look at total active energy
  2. for industrial consumers: it varies, but sometimes also the reactive part is billed. Would this be the total reactive?

Thank you! I'm not an engineer, apologies if the question is nonsensical.

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  • \$\begingroup\$ It can be reactive by both inductive loads and capacitive loads. The likelihood of it being inductive is far greater since we like to run lots of motors and coils. The "backward flow" is incorrect, an inductive load lags the phase of the AC source, and a capactive load leads the phase of the AC source. Reactive loads will consume power. How you would get "backward flow" is by running a generator. \$\endgroup\$ – klamb Aug 7 '17 at 12:44
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for residential consumers: I should look at total active energy

Worldwide, every supplier has their own billing scheme. In some places or at some time in the future, residential consumers may be concerned with reactive energy. Today few if any consumers should be concerned with reactive energy. Net energy seems to be the most-used term for forward or positive energy, energy going to the consumer minus reverse or negative energy supplied by the consumer. Consumers who supply energy from their own generation or storage may be concerned only with net energy, but they may also need to consider forward and reverse energy separately. Suppliers may (1) simply bill for forward net energy, (2) bill for forward energy and give partial credit for reverse energy, (3) give credit for reverse energy but carry net credit to the next billing period, (4) pay the consumer for net reverse energy, (5) base the billing policy on the time of day, (6) do something else.

for industrial consumers: it varies, but sometimes also the reactive part is billed. Would this be the total reactive?

Net reactive energy is always zero. Reactive energy supplied during one half-cycle of the waveform is returned during the next half-cycle. The charge is often called a power factor penalty or a demand charge. The charge is often based on the minimum power factor during a given time period or the maximum current during a given time period. I don't have any further details of example billing strategies.

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My simplest explanation is reactive power is the difference of power between two points, these being the position of supply in terms of its frequency and the position of the device as it is trying to keep up with the supply frquency.

Think of it as the supply frequency is dragging the motor around with it and the more load the further behind the motor gets.

As for the 2nd and 3rd qus

Residential customers are not (normally) charged for reactive power - who knows may change in the future, but this is basically because they only use small devices

Business customers are charged for their reactive power and it can get expensive - so some fit power factor control units (had to calculate the size of one in the past...) which switch in capacitors to reduce the effect and, so, the bill.

Apologies to the more technical for the details that are missing or glossed over....

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Reactive power just current with less power. The power factor is not 1. (Amps without Watts)
The power company still has to carry the current to your premises, it loads the grid with without selling any actual power. So you get penalized.

Reverse is when you supply the grid. And you can supply the grid with the "wrong" power factor if you have your generator or PV inverter configured incorrectly.
Do that, and get penalized as well.

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