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2013/01/31 at 3:05 am #10950saipurushothamParticipant
sir , can i know what are the different types of harmonics in power systems and can you please list out the power factor ranges in different industries such as lighting,textile industry etc..2013/02/05 at 11:09 am #12794Spir Georges GHALIParticipant
sir , can i know what are the different types of harmonics in power systems and can you please list out the power factor ranges in different industries such as lighting,textile industry etc..
About The Harmonics :
The “ Harmonics Currents ” generating by “ Non-linear Loads ” are different depending on these loads, where we found hereafter some of Non-linear loads and the relative generated Harmonics Currents :
– Computers with single phase power supply : 3rd, 5th, 9th
– Computers with three phase power supply : 5th, 7th
– DC power supply with three phase power supply : 5th, 7th
– Electronic Ballasts : 3rd, 5th, 9th
– Variable Frequency Drives with 6kHz switching : 5th, 7th
– Variable Frequency Drives with 12kHz switching : 11th, 13th
– Greatz Rectifiers : 5th, 7th, 11th
– Single Phase Welding machines : 3rd, 5th, 7th, 9th
– Fluorescent Lamps : 3rd, 5th, 9th, 11th
Rem. : each of these Non-linear Loads generates also another Harmonics Currents but their amplitudes are too small.
So, depending on the types, numbers, and powers of installed non-linear loads, the amplitudes of some Harmonics Currents will be bigger than others, and if we know exactly the specifications of these loads, especially the VFD and UPS, we can estimate which Harmonics Currents will have an important amplitudes, because the serious manufactures of VFD and UPS add in their catalogues a special tables contain : the percentage of each generated Harmonic Current, and also the percentage of the Total Harmonic Distortion of Current “ THD-I ” where that value should be “ ≤ 48% ” accordingly to “ IEC 61000-3-12 ”, also, these manufactures try to minimize or eliminate all Multiple Third Harmonics “ 3, 9, 15, … ”, because these harmonics are “ Zero Sequence ”.
In practice way, it’s better to carry out some currents and voltages measurements in multiple places of network to know exactly which Harmonics Currents injected in the network and their amplitudes or percentages compared with the fundamental current, and in some case knowing which non-linear load or loads generate these Harmonics Currents, then decide which should be minimized or eliminated, and at any level of network or where the treatment of Harmonics should be done.
Normally, if some Harmonics Currents have a big amplitudes, we try to minimize them by using in the most of case “ Passive Filters ” and/or “ Active Filters ” depending on the site’s type, and also the currents’ values of these harmonics, as the “ Passive Filters ” can be manufactured by a big capacities of current, where the “ Active Filters ” has a limited capacity.
By the way, using of “ Passive and/or Active Filters ” will correct also the Power Factor’s value but certainly not to the target’s one, so, after doing the Harmonics Currents’ treatment, another measurements should be carried out to decide : the Type & Power of Capacitors that should be used, and where should be installed to achieve the target value of Power Factor. Noting that we shouldn’t install the Capacitors to the same point where the Filters are installed.
About the Power Factor :
It’s too difficult to estimate the Power Factor value of any site because this value depends on the types, numbers, and powers of installed loads, as for exp. : the power factor values for big motors are bigger than the small motors, and even for the same motor this value depends on the load’s percentage, where we found hereafter some loads and the relative Power Factor :
– Motor of medium power :
- ≈ 0.85 at 100% of load
- ≈ 0.80 at 75% of load
- ≈ 0.73 at 50% of load
- ≈ 0.55 at 25% of load
– Fluorescent Lamp without capacitor : ≈ 0.50
– Fluorescent Lamp with capacitor : ≈ 0.85 – 0.90
– Discharge Lamp without capacitor : ≈ 0.40 – 0.60
– Induction Furnace with capacitors : ≈ 0.85
– Arc Furnace : ≈ 0.50 – 0.55
– Arc Welding machine : ≈ 0.75 – 0.80
So, it will better to measure The Power Factor’s value in the MDB, and also in the SMDB especially if one of them or more supply a big machines or motors, then depending on the value or values of these measurements we can choose the suitable solution of Power Factor Correction. Noting that we should also have an idea about the Total Harmonic Distortion of Current “ THD-I ” or the percentage of Non-linear Loads comparing with the total installed loads to be able to define the Capacitors’ type that should be used.2013/02/08 at 10:41 am #13174samueljordanParticipant
Power system harmonics are integer multiples of the fundamental power system frequency. Power system harmonics are created by non-linear devices connected to the power system. High levels of power system harmonics can create voltage distortion and power quality problems. You can get more information about it on the wiki.
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