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Emmanuel Chimezie Diogu said:
A residential electric power consumer having 53kw installed and connected loads with overall power factor of 0.83 wishes to install an uniterupted power supply,static back up system that will be able to supply some critical loads for 8hours on daily basis.if the percentage of the critical load is 30% ot the connected load and assuming 75% efficiency of the back-up system.determine the capacity i.e ampere-hour,A-hr,of deep cycle cells required.
Dear ;
Plus to that said by SJ, I want to draw your attention that there's another element to define finally the power of needed UPS, this element is the ” Creast Factor ” for these loads, because when the value of CF increase the power the UPS should be increased also.
Regards.
jatin333 said:
up what extent voltage and current harmonics acceptable?
what are effects of current and volt harmonics in system?
Dear Mr. Jatin333 ;
refer to your question and the reply of Mr. Alen, I want to clarify some points :
1 – We know all that the path of any current either Fundamental or Hamonic current is from the load to the source, that means there's no any direct effects from the harmonic currents on the other loads, but, the harmonic currents with the harmonic inpedance of network are reponsable to have a ” Voltage Distrotion ” in the network, and that voltage distortion has a direct effets on the loads even the linear-loads. So, the effetcs of the harmonics current is, as Mr. Alem said, on the : Cables, Transformers, Generators, Motors, Capacitors, ext. where there's many solution for that.
2 – Normally, as the direct effects on the load is from ” Voltage Distortion ” we should look to the percantage of Voltage Harmonic that means ” THD U or THD V “, and when these values exeed some levels, we should find the suitable solution for the network, else we will have problems with some sensitive equipments. Noting that when the ” THD I ” incraese the ” THD U ' will increase also, but be carfull even if we have the same percentages of ” THD I ” in 2 different networks it's not necessary to have the same percantage of ” THD U ” for both, because it dependes on the value of the ” Harmonic Impedance ” of each network.
3 – In some time when the level of Voltage distortion is smaller than standard or definded value, we can accept, as THD I, till ” 40-45% “.
4 – For information, the ” IEC 61000,2 ” defined the percantage of Harmonic Voltage for each harmonic ” Odd & Even harmonics ” in LV networks, and also in some countries the Electricity Co. define the ” THD U ” for their :V & MV networks.
Regards.
3 –
tibbie said:
if a generator is generating 20MW and only 5MW is used where does the other 15MW goes?
Dera Tibbie ;
First, the power of all sources is ” … kVA ” and not in ” …W “.
About your Generator :
As we know all a ” source ” either Generator or Transformer can supply the installed loads, so, the circulated current and consumed power are relative to the loads and not to the source, and we say that the source is ready to supply the loads till to total loads' power will be approximately equal to the source's power with certainly some percentage of reserve.
In your case, you will have some losses of fuel and will have a mechanical damage in the engine, because we should consume at least 45-50% of the generator's power once running and not less.
Regards.
Spir Georges GHALI said:
latafat junaid said:
Dear Sir,
Q1: during making a single line diagram,when i calculated the the total load,then which approperciate cable size i will select,means formula
Q2: For example: f the load s 40 A,Then how i will select MCCB, means i can use the 60A MCCB 3-Phase,but s there s any special arrangement to calculate for MCCB.
Q3: Cable size let say ” 3C,185 mm2″ how capacity of current it will take,any possible formulas r tables for all cable sizes and required MCCB?
A good /satisfaction answers & prompt response will be highly appreciated.
Thanks
Dear ;
Q1 :To do the correct choice of cable, we do as following :
– We calculate the load's current that we called ” Ib “.
– We define the ” Kind ” and the ” Ibtallation Methode ” of cable, then define the correction factors, and multipy them to have the total factor correction ” k “
– We calculate the carrying of current for cable in standard conditions that is ” Iz = Ib / k “.
– Then by the tables of ” IEC 60364-5-52 ” we can do the coorect choice of cable's section.
Q2 :
To de define the specification of Circuit Breaker that shpould be installed, we should do our choice of the main specifications of CB that are : ” Nomber of Poles ; Thermal Protection – Ir ; Magnetic Protection – Isd or Im ; The breaking Capacity “, so, we do as following :
– The nomber of poles will be defined accordongly to the ” kind of circuit & Earthing System used “.
– After doing the above methode to define the Cable's Section, we can define de value of ” Ir ” accordingly to ” Ib ≥ Ir ≥ Iz . k “.
– To define the value of ” Isd or Im “, we should calculate the ” minimum short circuit current – Isc1min ” between ” phase & neutral ” at the end of cable, and calculate the ” Earth Fault – If ” also at the end of cable, then the value if ” Im ” should be msaller than the smalest calculated value.
– To define the ” Breaking Capacity “, we should calculate the ” maximum short circuit current – Isc3max ” at the begining of cable, then the value is ” Breaking Capacity ≥ Isc3max “.
Q3 :
We can know the capacity of current or the carrying of current of cable from the tables of ” IEC 60364-5-52 ” after define the kind of cable that means : Single or Multi ; Cu or Alu ; PVC or XLPE ” and also the ” Methode of Installation ” . Noting that value is in Standard Conditions that means the total correction factors is ” 1 “.
Regards.
Dear ;
Sorry, I forgeten to mention a very importatnt point about ” Q1 : Section of Cable ” that after defining the section of cable as tI explained before, we should calculate the ” Drop Voltage ” for this circuit and add it to the drop voltage from the source to this circuit, if the percentage's result is suitable and equal or smaller than the standard percentage is OK, but oif not, we should over-size the section of cable.
Regards.
Spir Georges GHALI said:
Francois said:
Redondancy of supply is often a must ; protection coordination is not easy to master : case of parallel MV/LV transformers.
This case is typical for hospital and even office building where service continuity constraint is high. (more…)
