Reactive power compensation

THD - Definition by AcronymFinder

A1) No. It isn't right.

A2) -

A3) The most commony-known definition of THD has a lot to do with audio amplifier circuits, and there is no overlap into <...reactive power compensation...>.

The reactive power needed to be compensated is a function of the inductive and capacitive loads that are attached to a supply at any moment, and vary depending on what is connected at any moment. The job of a <...reactive power compensation panel...> is to best match that load to the supply for the purposed of avoiding a charging penalty on the incoming power tariff. It does it by adding and subtracting capacitance across the supply to compensate for the (usually) inductive lag that part of those those loads present, and it does it automatically.

A4) No It isn't correct.

If in doubt, the <...we...> should consult a qualified Electrical Engineer.

Why should anyone contact a certified professional when it's more ego-satisfying to run with erroneous misunderstandings?

Birds Aren't Real

Some loads like fluorescent lighting, which conducts at the peaks of the voltage waveform, can generate third harmonic distortion in the current waveform (THD). Loads that are inductive in nature (motors, etc) cause the current to lag behind the voltage in phase (reactive power).

In both of these cases, you have currents that are not contributing to real power. Only the current that is in phase and frequency with the voltage contributes to real power.

Phase error can be corrected with capacitors. THD, as far as I know, can only be filtered to prevent it from affecting other circuits. I would think you would want to investigate the THD first.

https://resources.system-analysis.cadence.com/blog/msa2020-total-harmonic-distortion-thd-power-factor-measurements-for-voltage-and-current-distortions

https://www.allaboutcircuits.com/technical-articles/understanding-thd-total-harmonic-distortion-in-power-systems/

In large data processing centers,it is a requirement to double the neutral size to compensate for these"stealthy" currents.

More modern switch mode power supplies have circuits that are in sync with the line frequency to eliminate these problems.

Many recent data centers are using DC to supply their computers from a central dc supply,eliminating all of the individual supplies,reducing heat loads and reducing overall costs.

Friend,

Generally speaking, THD (Total Harmonic Distortion) and power factor are two different parameters you may need to evaluate in an electrical distribution system and at the service.

THD: Electronic devices repetitively switch their load on/off at various places in the AC power's sine wave, according to the amount of power needed "downstream" and the required voltage "downstream". (Devices such as LED lights, computers, variable frequency drives, and many more.) This creates a non-sinusoidal wave form which can mathematically described as a sum of many sine waves with frequencies that are multiples of the incoming voltage. These imposed frequencies can be as high as 20 or more times the main voltage frequency. This is called the THD, and can be from a few % to well over 100%. This THD can put a substantial heat load on transformers, so its removal is desirable--bu active filters, special transformer designs, series inductors, and more.

Power factor (PF) is expressed as cosθ where θ is the number of degrees by which the voltage and current waveforms are not simultaneous. Capacitors cause a leading PF (I before E) while inductors cause it to be lagging (I after E). To get the most power through a wire, you want the PF to be close to 1 (higher than 0.9). Only a few common loads are capacitive, so PF correction is typically by adding capacitors to a circuit. Ideally they can be put into each large motor's circuit but this requires care in selecting overcurrent protection, etc. If the load is varying or is going to be increased later, then an active capacitor bank can be chosen with contactors to add units of capacitors as needed (using meters and controls to automatically measure the PF and do the work). You may see a few places where they have a large synchronous motor with a starter which can vary the excitation to make the motor put a leading power factor back onto the line (and again one can use automatic controls to do this).

Keep learning, ask a lot of questions like you have here, and be careful that the mistakes are not BAD. Contact your manufacturers and their engineers for more information. Many companies make test tools to measure THD, PF, voltage spikes or dips, and more (and even give a chart record of the events....) --JMM

BAD - Definition by AcronymFinder

Beware Amateur Design.

Reactive power compensation vendor assumes the THD in the facility is within IEC stipulated limits, unless otherwise stated by the Owner in the Tender.

If the THD is high, it is owner's responsibility to provide suitable filters in the facility.

Having said that, it is possible to integrate harmonic filtering with reactive power compensation provided, the same is planned early.

It is also well known that many a capacitors of Reactive power compensation panels have failed due to overloading by excessive harmonics in the facility.

An in line choke is very effective at elimination of high frequency harmonics,and are used in many large back up power supplies.

Isolation(1:1 ratio) transformers are also pretty effective.

Of course,this creates a lagging power factor,but that is easily corrected by capacitors.

OT Note:↓

An old fashioned trick used by TV repairmen to help reduce lightning surges was to put several knots in the line cords feeding the TV,a primitive choke.

I apprecipate all your answers, but it's only theories about reactive power. I asked for principle, how to determine the size of compensation in TENDER phase. So, how to determine the size of compensation, before some building is built, how to know how much compensation will be needed in, for example future market?

You need to know the type and quantity of equipment that is to be installed,initially,as well as in the future,as well as the power factor rating of each piece,which makes it very hard to accomplish.

Motors,data processing center,etc.

The NEC says that for data centers,the neutral size should be doubled after making the initial calculation.Capacitors can be added or subtracted after installing equipment,but if you double the neutral size, it is usually adequate for harmonic currents.