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Spir Georges GHALI said:
farang said:
I have a oil filled 3 phase transformer 315 kva on a pole pripary voltage is 33 kv secondary is 220/380.
What would be the rated output in amps per phase. Here everyone brings in 3 phase to thier pannel there are hardly any 3 phase loads, maybe a pool pump motor or two. The rest are 1 phase A/C and lighting loads.
Our ampient temperature is 35C
What can I safely draw in current per phase on this transformer?
Thanks
farang
Dear Farang ;
Each transformer hase an ” S : Apparent Power ” in kVA, either for single phase with neutral or for 3 phases with or witout neutral (depending of the connection).
The formula for Single phase + neutral is : S = V x I where :
– S : apparent power in kVA
– V : the nominal voltage between phase & neutral without load.
– I : the nominal current for the transformer
and for 3 phase + neutral, the formula is : S = 1.73 x V x I
So. using one of these formula accordingly the the kind of transformer, we can calculat the nominal current for any one, noting that the ” I – nominal current ” for 3 phases with or without neutral means the value of current for each phase, in this case, when we have single phase loads we will distribute them to the 3 phases of the transformer trying to have approximetly an equivalant installed power on each phase.
Normally, we try to have the maximum load on any transformer not more than 80-85% of the apparent power.
Regards.
Dear Farang ;
I', very sorry for this typing mistake, but in 3 phases we use the formula :
– S = 1.73 x U x I
where ” U ” is the voltage between 23 phases.
Regards.
RAFI said:
Dear Engineers,
iam working as a trainee engineer in a stone crushing plant where it has a load of 750KW AND 630KVA TRANSFRMR….IAM NOT ABLE TO UNDERSTAND THE CONNECTIONS GIVEN IN THE PANELS LIKE NO,NC,CONTACTORS,MCCB,MCB'S,RELAYS,DRIVES……HOW TO UNDERSTAND THE CONNECTION DIAGRAM AND HOW TO TROBLE SHOOOT WHEN A PROBLEM RISES?
HOW TO UNDERSTAND ABOUT KWH,KVAH,KVARH,KVA,MD,PF…..HOW TO DECIDE THE MULTIPLICATION FACTOR….HOW TO CALACULATE REQUIRED KVAR?
PLEASE HELP ME OUT
Daer Mr. Rafi ;
You asked about a lot of points and if we will expailn all in details we need many pages, bu I will try to explain shortly:
NC : Normal Closed, that define the stat on a contact in normal calse ” not working “
NO : Normal Open, that define the stat on a contact in normal calse ” not working “
MCCB : is a Circuit Breaker using to protect a network ( cable ), and contains cormally 2 kind of protections ” Themal & Magnectic Protection “, where there's an adjustable protections and fixed protection, many sizes and frames from ” 16A ” up to ” 1600A”, ans some company have till 3200A, the breaking capacities are from ” 10kA ” up to ” 150kA “, all MCCB are tested accordingly to ” IEC 60947-2 “
MCB : is a Circuit Breaker using to protect a network ( cable ) installe on ” Din-Rail 35mm “, and contains cormally 2 kind of protections ” Themal & Magnectic Protection “, where protections are fixed, 2 sizes from ” 0.5A ” up to ” 125A”, the breaking capacities are from ” 1500A ” up to ” 25000kA “, all MCB are tested accordingly to ” IEC 60898 ” and for breaking capacities can be tested accordingly to ” IEC 60947-2 “
Contactors : they are using to commande ” Running & Stoping ” the motors, there's no protection inside, but the Thermal preotection Relays will be installed with the contactors to realize the necessary protection to the motors. inside of any contactor there's a ” main Contacts ” and ” Auxiliary Contacts ” where the main contacts are used to commande the motors, and the auxiliary for the control circuits, also inside the contactor there a ” Coil ” and by applying the supply voltage to the coil the main contacts close to electrify the motor, and the auxiliary contacts chang their sitation, the nominal currents of contactors are from ” 6A ” uo to ” ≈ 800A “
Drives : I think you mean the drives used to Commande & Protect the motors, if yes, we called ” Variable Speed Drives “, they are Electronic Equipments that can ” Run, Stop, and Chang the speed ” of motors with all necessary protection, and they have also many advantages, the powers oh these drives are from ” 0.5kW ” up to ” 630kW “, and there's, accordinglt the the output torque, 2 kinds ” Standard Torque & High Torque “
There's alos ” Soft Starters ” that we use to ” Run & Stop ” the motors without changing the speed, that means with them the motor should run allways at his normal speed, inside there's in some of them the necessary protection and in others no protection.
I will try to explain the other points in other time.
Regards.
ikram shehzad said:
Dear all,is ther any body who can tell me about the setting of ACB(air circuit breaker ). what kind of it,s setting is and how to do it,s setting. also please tell me the setting of VCB(vaccume circuit breaker) . please tell me their setting,s.i will b very thank ful to all of u.Thank,s and Regard,s.Muhammed Ikram.
Dear Mr. Ikram ;
VCB :
They are Circuit Breakes, but the volume of tripping is done in a small empty room that means inside this room there's nothing, becuase in the standard circuit breakers the tripping is done in Air. This technology is using for MV circuit breakers and useed also from some companies for low voltage circuit breakers, and I thing for LV it's finiched.
Regards.
ikram shehzad said:
Hello dear,s
please tell me that what is “Residual protection, magnetic protection, instantaneous protection.
Is Any body can explain?
Dear Mr. Ikram ;
Residual Protection :
We use this kind of protection against any Indirect Earth Faulf, that means any short circuit betwwen any phase and the protection line, where normally the current fault value is small or too small from ” 0.01 mA ” up to ” 30 A “. We can obtain this protection by many kind of protection equipments like : RCCB, RCD, MCCB equiped by Residual Protection, and even ACB equiped by Residual Protection. Also, in some equipments we have ” Timming Delay ” for this protection.
Magnetic Protection :
We use this kind of protection against any short circuit that can happen between : 2 phases, or 3 phases with or without neutral, or 1 phase with neutral. There's adjustabe magnetic protection that means we can adjust it accordingly to the results of study of short circuit currents, and others have a fixed values. we find this protcetion in all circuit breaker : MCB, MCCB, & ACB. Some of this protection have ” Timming Delay ” to realize the Discriminitaion or Selectivity. In some kind of Earthing Systems we use this protection also against Direct Contact ( short circuit between phase and the protcetion line where the value of earth fault current is big ).
Instantaneous Protection :
This main role of this protection likes the role of magnetic protection, but there's some differences that are :
– We find this protection in all ACB and in w few type of MCCB.
– In some cases, the value of this protection is ” Fixe “, and in other cases are ” Adjustable ” and also we can switch-off.
– No timming delay for this protection.
Normally, we try to do adjustment value of this protection more than the Magnetic protection in circuit breakers that have also ” Timming Delay ” for the magnetic protection to realize the discrimination, so, once the value of short circuit current ” Isc3 ” is equal that of the magnetic protection, the circuir breaker will trip after the timming delay adjustment, but when the ” Isc3 ” is bigger and we don't want to delay the tripping the instantaneous protection trip the circuit breaker without delaying. This protcetion is very important in the networks specialy in the 1st level.
Regards.
RAFI said:
Dear Friend,
In our plant we have load of 750kw we are using 400kvar capacitor bank ….we are getting 0.91-0.97 pf sum tymes we are getting less pf like o.87….why getting like this>is capacitor bank has to increase ?
Dear Mr. Rafi ;
Firts, you should do the calculation, as I mentioned before for the same topic, to know if ” 400kVAR ” is enough or not for your installation.
In all case, there some reasons for your case that are :
– Normally, and depending to the connection's type of the controller, the Controller of capacitors is connected to ” one phase or 2 phases ” accordingly the the connection's type, but allways with ” one Current Transformer ” that's installed on the same phase ( for the 1st connection type ) or on the third phase ( for the 2nd connection type ), that means the measuring of the angle ” φ ” is doing between the current of one phase only and the voltage.
– In some time we have on the same controller the value of PF ” 0.91 or 0.96 or 0.87 ” but we adjusted the controller to achieve ” 0.95 ” : as the methode of working of Capacitors bank is doing by a controller where it needs a time ( at least 50sec ) to Switch-On or Switch-Off ” the steps accordingly to the difference between the measuring value and the reference value, in these times it's possible to see on the controller a smaller or bigger value than the reference one.
– If you compare the PF value of the controller with the PF value mentioned on the Bill, there's certainly some difference, because the ” kVARh meter ” works on 3 phase for currents & Voltage.
Regards.
ikram shehzad said:
Dear all,is ther any body who can tell me about the setting of ACB(air circuit breaker ). what kind of it,s setting is and how to do it,s setting. also please tell me the setting of VCB(vaccume circuit breaker) . please tell me their setting,s.i will b very thank ful to all of u.Thank,s and Regard,s.Muhammed Ikram.
Dear Mr. Ikram ;
An ” ACB ” is a circuit breaker dedicated to protcet the Electrical Low Voltage Networks, that are equiped of many kind of protections noting that are all Electronic Protection installed in the ACB and internaly connected with ” Current Transformers ” that are also istalled in the ACB, these protections are :
– Thermal Protcetion against ” Overload faults ” : it can be adjusted ” Ir : 0.4 to 1 x In “, where ” In ” is the nominal current of ACB like : 2500A or 3200A or 4000A, so, if we adjusted it at ” 0.5 ” for ” ACB – 4000A “, the thermal protcetion value is ” Ir = 0.5 x 4000 = 2000A “
– Magnetic Protection for ” Short Circuit Faults ” : it can adjusted ” Isd : 1.5 to 10 x Ir ” or for some manufacters to ” 12 “, so, if we adjusted for the same ACB at ” 6 “, the magnetic protection value is ” Isd = 6 x 2000 = 12000A “.
– Earth Fault Protection against direct fault between any phase and the protection line, it can be adjusted ” Ig : 0.3 to 1 x In “, so, if we adjusted it for the same ACB at ” 0.7 “, the earth fault protection value is ” Ig = 0.7 x 4000 = 2800A “.
-Residual Protection against ” Residual Faults ” that means against indirect fault where the fault current's value is normaly small ( a few Amps ), it can asjusted ” IΔn : 0.5 to 30A “.
– Instantaneous Protection against ” Short Circuit Faults ” when the fault's current value will be very big, and in the same time we want that ACB trip quickly without delaying, it can adjusted ” Ii : 2 to 15 x In ” and we can also switched-off, so, if we adjusted it for the same ACB at ” 6 ” the instantaneous protection value is ” Ii = 6 x 4000 = 24000A “.
In some ACB there's also a ” Timing Delay ” for the thermal protection and for the magnetic protection, where the ” Timimg delay ” for thermal protection can be adjusted is ” Seconds “, but the ” Timing Delay ” for the magnetic protection can be adhusted in ” mili-Seconds “, and we use these ” Timing Delay ” in ACB to realize the ” Discrimination or Selectivuty ” between 2 ACB's or between ACB and MCCB .
Regards
ikram shehzad said:
Dear all,
can anybody explain diversity factor. what is it,s defination. please tell me briefly. i have no concept about this.
Dera Mr. Ikram ;
The ” Deversity Fcator – Kd ” or the ” Simultaniety Factor – Ks ” are the same, and we apply this factor to ” Panels “ not to each load.
This factor means : if we have a panel with 10 different loads, certainly these loads don't cosume in the same time 100% of their powers, because some of them consume 80%, another 100%, other 65%, so, the percantage of the Diversity Fcator means the percentage of the loads that comsume in the same time 100% of their powers.
By experience, we use the following percentages :
– For ” 3 ” Loads or Outgoing : 0.90
– For ” 5 ” Loads or Outgoing : 0.80
– For ” 9 ” Loads or Ourgoing : 0.70
– For ” 10 or more ” loads or Outgoing : 0.60
Regards.
paule said:
Thanks, if its exceeds the maximum value of 5 % for n=3 and 6 % for n=5, what will be the impact in the connected instrument or devices, does it will damage the instrument?what precaution or protection we can apply.
Dear Mr. Paule ;
If the Voltage Harmonic Distortion for each harmonics exceeds the value defined by standard, that means the Total Harmonic Distortion of Voltage ” THD U or THD V ” will be globaly more than standardrized valeus, that can creats some disturbances in working of instruments, and even the currents for lieanr Loads will be distorted.
By the way, when we have these high percentages of THD U, that means we have big percentages of current distortion ” THD I “, that leads to increase the losses in transformers, generators, cables, and also the heating of these equipments will be more. In some cases when we have a big value of ” THD I ” but the ” THD U ” is less than the stadard value, we should in this case dereat the power of Transformes and Generators, and also over-size the section of cables.
In the same time, the most dengarous harmonics are the Double Third Harmonics, that means : 3, 9, 15, …, because these harmonics have the same vector,so, the sum of them aren't ” 0 ” and they run in the neutral cables, for this reason once we have this kind of harmonics in the network, we should calculate the value of them and do correctly the choice of the neutral cable's section. But most of the maufacters of some elctronic equipments like : Virable Speed Drives, UPS, try to minimize the percentages of them in their euipments. Noting that in some equipments of serious manufacters the percentages of this kind of harmonics are ” 0 “.
Regards.
Freeknow said:
if upgrade meter from 100amperes to 150amperes, can I use the exsiting cable with out pulling new cable.
Please I need advices thnx
Dear ;
First, you should know if the exicting cable can withstand 150A in the working conditions, noting that all tables of Current's Cables give the nominal current for each section coordingly the the cable's type & kind in the standard conditions that means the correction factors equal ” 1 “. If the nominal currnet if this cable in the working conditionbs is less than 150A, you have 2 solutions :
– You can chang completly the cbale by another suitable one.
– Or, lay another cable withe the same section, type, and kind, and connect them in parallel, but be carful, because the 2 cables should have the same length.
Regards.
jatin333 said:
if there is three phase power system we calculate power kw= sqrt(3)*V*I*CosØ so what is formula for two phase system?
Dear Mr. Jatin333
To calculate the power value accordingly to : Voltage, Current, and Power Fcator, we have the following formula :
– For 3 Phases plus or withour neutral :
P = sqrt(3) x U x I x Cos Ø
– For 2 Phases :
P = U x I x Cos Ø
– For 1 Phase + Neutral :
P = V x I X Cos Ø
where :
U : Voltage between 2 pahses in ” Volt “
I : Current line in ” Amp “
V : Voltage between phase & neutral in ” Volt “
Regards.
lecto said:
I know that 110 and 220 volts are available in a three phase installation what other voltage is normally available in the installation? I'm getting mix up with 500 and 400 volts.
Dear Mr. Lecto ;
You know that we have multi kind of supply that are :
– Single Phase + Neutral for 127V ( accordingly to the kind of source )
– Single Phase + Neutral for 220V ( accordingly to the kind of source )
– 3 phases + Neutral for : 127/220V that means : 127 between any phase & neutral, 220 between any 2 phases
– 3 phases + Neutral for : 231/400V that means : 231 between any phase & neutral, 400 between any 2 phases
So, you should know the kind of your network.
Beside, we can , accordingly to the kind of loads, mix 2 kinds of network, but we should be carful.
Regards.
nathan said:
Hi. sir me again.i just wanna ask about CB rating 1250 Amperes 3 pole. there is a humming sound and i touch the CB and the wire in a line side its very hot. the wire size is 500 AWG .3 sets of 500 AWG.what will be the cause why there is a humming sound? why the wire is so hot? i am afraid that will be a cause of burning or the CB will tripped off.what will i do.
i hope sir you will answer my question. Thank you very much. God bless.
nathan
Laurent said:
I'm not familiar with AWG cable sizes, difficult for me to tell if sizing is ok or not.
Did these noises and over-heating appear only recently? If yes, did anything change in your installation recently?
Some extra questions:
– Do you know the actual (rms) current going through this breaker? What kind of loads are fed by this CB ?
– Do you have the possibility to make an infra-red measurement, to show the temperature values around this CB ?
– Is there any relation between this CB and the transformer you mention in your other topic, which also makes noise? Is this CB fed by this transformer? How are they connected together, cable or busway?
What I'm thinking about is that you might have a high level of harmonics in your installation, which could be a reason for vibrations and over-heating. Or maybe a connection getting loose…
Dear Mr. Nathan ;
All reasons were been defined by Mr. Laurent are possible to have a hot circuit breaker, but refer to my experience, to say about CB is hot is not enough, because you should measure the temperature of the circuit breaker that means : the temperature of connection points and the temperature of the body, them we can decide if the CB is hot more than standard or not. noting that the ” IEC 947-1 & IEC 947-2 ” said the the heating of connection points above the ambiant temperature should ” maximum + 60°C “, and for the touchable body ” maximum + 50°C “, with one condition that the maximum value of the ambiant tenperature is ” maximum + 40°C “.
You replyed to Mr. Laurent that the sention of cables are ” 3 x 250 mm² “, and to say it's enough or not we should know the working conditions that means : the kind of cables, the methods of installation, the ambiant temperature, and if there's another circuits on the same way, but also from my experience i think it's not enough. Noting that if the heating of cables can affect the conection points of CB
You also replyed to Mr. Laurent that the measured temperature is ” + 40°C “, if it's realy like that the CB is not hot, or you mean that's the ambiant temperature ? Please re-check again.
Rem. : I measured the temperature of ” CB 1600A ” with ” 1450A ” as the total load, in ambiant temperature ” + 30°C ” the temperature of connection points were ” + 84°C “, and regarding the standard values it's OK.
Regards.
Abdul Jabbar said:
WHY REACTIVE POWER IS RETURNED TO SOURCE
Dear Mr. Abdul Jabbar ;
I thnik you are talking about the reactive power that we have from ” Capacitors Bank “.
First, we should know that the ” Capacitors ” are like other ” Loads ” installed on the network, so, as we have an ” Inductive Loads ” and a ” Resistive Loads “, we have also a ” Capacitive Loads “, so, the current of the capacitve loads will run to the source. But from the point of view of the source we have the ” Vectorial Sum ” of 3 currents that are ” Inductive, Capacitive, and Resistive currents “.
Regards.
Freeknow said:
I have 8 meter in the 1st floor , the rate in the meter 3×127/220 and 3×220/380 also 40/160 Amper the Breaker is 150 A
Can I get the KVA from these information, and the the right size of the cable.
best regards
Dear ;
First, we can calculate the power in kVA by the following formula :
– For 3 phases network : S = 1.73 x U x I
where :
– S : Ther Power in ” VA “
– U : The voltage between 2 phases in ” Volt “
– I : The line's current in ” Amp “
About the cable, if you have a circuit breaker ” 150A ” that's means you should use a cable that can withstand in the working conditions at least 150A, so, to know the relative section, you should know the working conditions : type & kind of cable, methode installation, and the ambiant temperature, then accordingly define the correction factors, so you can do the correct choice of cable's section from the table of ” IEC 364-5-52 “.
Regards.
Issa A said:
Hey
How to calculate the pump hp
For example I Have motor N/P is
Voltage = 2393 Amps = 39 Hp 150 @ 50 Hz
Pump size is 5.40 type S5000N 134 Stages
What is the hp of each stage in the pump?
Thanks and appreciated
Issa
Dear Mr. Issa ;
There's some thing rong, because you said : Voltage = 2393 Apms = 39 Hp 150
Please clarify what do you want to ba able to answer.
Regards.
