Active Energy, Reactive Energy or just Energy?

Question

I understand the concepts of active power, reactive power and apparent power. I am not sure I am getting the complete concept about the respective energies.

I am using an energy monitor to record only the active power consumption of a CNC machine, as an indication of its power demand.

1. Can I say that using the active power, I can estimate the active energy consumption of the motor or the active energy is something that is not widely used as a term, especially in an industrial environment?
2. If I can use the above term, is it OK if I do not consider at all the reactive energy? Is it even meaningful to talk about reactive energy?
3. What do we generally mean when we talk about electrical energy in a factory? Do we refer to the sum of the active power in kWh? Or do we use the apparent power to calculate the energy in this case?

Answer 1

Motors tend to be the biggest load in the industry and their efficiency must increase with Hp size towards 96% as mandated by stds. The no-load current may be from 10 to 25% of rated but is mostly reactive core excitation current to magnetically couple the rotor and stator.

Since the Power factor, pf is the ratio of real / apparent power or current, the pf goes down with load/rated load. Since reactive energy is stored in the rotating machines it draws some conductive loss in the grid. But more importantly, it raises the apparent load current which must be allocated by costs of the distribution network by selling or buying reserve power to meet the apparent load.

Although load capacitors are expensive as passive power factor (PFC) correction on small motors, it is a major cost-saving on industries using >= 50 Hp motors. So here it is important. Motor inductance causes the current to lag by 90 degrees and capacitance causes current to lead voltage by 90 degrees.

Also, IEC has mandated high pf ratings for high power AC-DC SMPS to reduce the cumulative effects of many AC-DC power supplies. (98% >=100W ) So pf does matter here.

Reactive energy is the inertia stored to get up to and maintain speed yet not consumed to do work while producing real conductive losses from friction and magnetic excitation current needed to create a low impedance real force when a load occurs.

In effect, all big industries with poor power factor pay extra unless they manage their own PF with compensation then get a discount and verified with meters to measure it.

Ref: https://www.cui.com/catalog/resource/power-factor.pdf

Answer 2

In industry everything is important. The current magnitude is relative to apparent power, while only the real power is converted, the reactive bounces back and forth, causing currents to flow without any need. So in industry you get two power meters real and reactive, the price for reactive is higher, since is a product of neglection of the plant. Home users and small shops pay only the real power - only one meter. Industrial plants however have a compensation unit that cancels the reactive power to the mains network.

Answer 3

Can I say that using the active power, I can estimate the active energy consumption of the motor or the active energy is something that is not widely used as a term, especially in an industrial environment?

True power is the actual energy consumption/conversion, so there is no need to estimate it if you already know it. Active or True energy, assuming those are valid terms, would just be quantities of energy that were to be converted to non electrical energy, and the active/true power is the rate of conversion.

If I can use the above term, is it OK if I do not consider at all the reactive energy? Is it even meaningful to talk about reactive energy?

I suspect that would strongly depend on what you are doing. If it's irrelevant to your task, yes you may disregard it, but if you're asking generally if you can ignore power factor or something like that, the answer is no.

What do we generally mean when we talk about electrical energy in a factory?

When we talk about electrical energy in a factory or any other system, we are referring to potential energy available due to a voltage difference that causes current to flow in order to accomplish tasks, electrical in nature or not.

Do we refer to the sum of the active power in kWh?

kWH, or thousand watt hours, refers to the consumption/conversion of energy it is produced by multiplying a rate of energy conversion(a power figure) by the period of for which the energy is being converted, so a figure in kWh expresses a quantity of energy used or available.

Or do we use the apparent power to calculate the energy in this case?

Hmmm I think you might be very hazy on what power and energy mean in the first place. Before I go on, I would just point out it's not clear what you're talking about. Do we use which apparent power figure in which way to calculate what energy figure? Most of your questions are similarly difficult to answer, so I'll add the following:

Hmmmm... Ok, so I think a little clarification might straighten things out for you.

True Power is power that is actually being "used"(converted to some other form of energy and removed from the circuit as heat, kinetic energy, etc)

Reactive Power is power being stored in reactors(inductors and capacitors) and fed back to the circuit at a later time. While this power itself is not used by the circuit it can contribute to waste heat, as it increases current in portions of the circuit as it "rings" back and forth between reactors.

Apparent Power is the power that appears when you simply measure the circuit without separating out the reactive portion of the power. Some fancy guy figured out that the relationship between these figures could be expressed with the mathematics related to the sides of a triangle, as you see here:

Reactive energy, if anything, would be the energy stored by the reactors in a circuit, and its rate of transfer/storage would likely be the reactive power.

Hope this helps.

Answer 4

Active energy, reactive energy, apparent energy and power factor(PF) are all related. Knowing any two of them you can calculate the others just by a simple calculation.

1. Of course you can if you have the right tools. Active energy is the integral of active power over time. If you have only a power meter(an apparatus that only indicates Watts) it's quite hard to estimate energy unless the demand is very stable and you can measure the time it is powered. In that case just multiply the mean active power times time and you get active energy. Also, active energy is very important as it means for the electric service provider how much coal or wind or Sun is needed and they will charge you for that.
2. Insteas you can measure apparent or the PF but reactive energy is also valid. The motivation to measure it depends weather or not your electric service provider charges you for bad power factor or not. If not then you don't have to worry. If yes then you must measure reactive energy so you can figure out your apparent energy or power factor so you know how much it cost or if you want to correct it or whatever.
3. You consumed X kWh(active energy) with a mean PF of 0.95. For a completely description of the demand you must know two of the magnitudes. Not having in account harmonic distortion.