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Abhilash said:
DEAR SIR,
In this case we can go for
Rated insulation voltage for the DB: Ui …… how much for doing Asta type test with this DB as per IEC61439.
Dear ;
As we use ” Ui ” to do the tests for ” Dielectric , Clearance & Creepage “, and if the DB contains RCCB where for some of them ” Ui : 440V “, in this case we should use ” Ui : 440V ” to do these tests.
But :
– If there's ” MCB ( C60… & C120… )+ Vigi-block ” we can use ” Ui : 500V “.
– If there's ” MCB ( only NG125… )+ Vigi-block ” we can use ” Ui : 690V “.
Dear ;
If we talk about the ” Power Fcator ” of loads, we can improve it only by using a ” Capacitors bank “, but as the inrush current of capacitor is too big, we should be careful if there's in the capacitors bank a big step or big steps.
By the way, the changing of the engine's full system and the alternator's exitation doesn't chang at all the power factor of the loads, because the load's power factor is depending on the specifications of the load itself.
manh_hoa09 said:
dear Spir Georges GHAL
According to your formulae, the compensation sysem only have capacitor. but It is only use for transmission gird and normal load. there are problem when use in industry plant which use a lot of big mortor or nonline load. We have to add reactor connect in series with capacitor, these reactor's function is protect capacitor. plz see the drawing in following:
But I don't know, with this compensator system, how do you caculate? how do you choose reactor?…ect
plz show me?
Thank you very much
Dear ;
As before, we calculate first of all the needed capacitors power, then accordingly to the ” Poluation ” of the network, we can decide which kind of capacitors we should use, and we do that as follow :
– We should calculate the percentage ” Gh / Sn ” where :
– Gh : the total power in ” kVA ” for all equipments that generate the harmonics like : UPS, Variable Speed Drives, … ext.
– Sn : the power in ” kVA ” of the tansformer.
then :
– If ” Gh/Sn = 0 … 15% ” : we can use the ” Standard Capacitors ” without any thing.
– If ” Gh/Sn > 15 … 25% ” : we should use the ” Overrated Capacitors ” without any reactors.
– If ” Gh/Sn > 25 … 50% ” : we should use the ” Detuned Capacitors ” that means ” Overrated Capacitors + Reactors “.
To define the type of reactors that we should use, as we have normally 3 types, we should analyze the network to know the existed harmonics, then the ” Tuning order ” for ” Reactors + Capacitors ” should be smaller than the smallest harmonic.
Rem. 1 : if you should use the Standars Capacitors, it will be better to know from the manufacture the percentage ” Gh/Sn ” that can withstand, because for some manufactures this percentage is ” 10% “.
Rem. 2 : if you should use the Detuned Capacitors, please be careful because the combination generates also some harmonics that we can know from the manufacture.
Regards.
Dear All,
Kindly help for my below query,
We want to type Test our final DIstribution board as per IEC 61439. we are using the MCB/ELCB's schneider make. I want to know what will be the Rated insulation voltage for the DB: Ui
= ??? if other parameters are as followsRated voltage: Un = 415V
Rated operational voltage: Ue = 690V
Rated impulse withstand
voltage: Uimp =
6kVWhen I checked in the MCB catalogue Ui for MCB is shown as 500V
If anybody can help me in this matter, I am verymuch thankful.
Dear ;
First, as all MCB are designed and tested accordingly to ” IEC 60898 “, so, the ” Ui = 500V ” because it's defined by ” IEC 60898 “.
About ” MCB's for ” Schneider Electric ” :
– For all ” MCB : C60… & C120… ” the ” Ui = 500 V “.
– For ” NG125… ” the ” Ui = 690 V “.
About ” ELCB's ” for ” Schneider Electric ” :
– If you use ” Vigi block ” with ” MCB ” the Ui is equal that for ” MCB “.
– If you use ” RCCB “, be careful because for some of them ” Ui = 440 V “.
Regards.
said: Abhilash
Dear ;
The VMM ikram shehzad said:
Hello all,
i want to ask a question to all of you that what is VMM (voltage monitoring module )? how it work,s? i heard somewhere that it compare 1 phase voltage to other phase voltage. but there is also some setting on it. how to set it,s setting. please tell me briefly.Thank,s and Regard,s.Muhammed Ikram.
Dear ;
the ” VMM ” are ” Electronic Relays ” with 1 or more of auxiliary contacts , and have many functions that are :
– ” Monitor & Compare ” each voltage phase's value with a ” References values ” for ” Up & Down “, and when the difference exceeds a ” References levels ” also for ” Up & Down “, the auxiliary contacts will change their states from ” NO to NC ” or ” NC to NO “.
– ” Monitor & Compare ” the rotation of phases with a ” Reference Rotation “, and when aren't the same, the auxiliary contacts will change their states from ” NO to NC ” or ” NC or NO “.
About the settings, there are many kinds, but normally :
– A special setting for ” Up level ” of voltage given in ” % ” of the designing value.
– A speical setting for ” Down level ” of voltage given in ” % ” of the designing value.
– In some VMM there's also a ” Timing delay ” in seconds.
In some ” VMM ” the references values are fixe by ” 10 – 15% “, so, there's no need to do any setting.
Regards.
Dear ;
Adding to that said by Mr. Samman, be sure that the cables can carry their nominal currents defined by ” IEC 364-5-52 ” but with one condition that the selection of cable's section have been correctly done by taking into consideration :
– All correction factors accordingly to the working & installation conditions.
– The cables can withstand the short circuit currents specially at the 1st & 2nd levels of electric networks, or when we should use a small section of cables installed to the MDB.
Regards.
Hemant Arora said:
BS 7671 Table 54G indicates Earth cable sizing for Power cable size.
If the Electrical Sub Panel is far away & local earth electrodes (Eart Pit) is provided, is it medatory to run earth continuty conductor with the cable feeding to Sub Panel
Dear ;
To decide if the PE cable should be run to a far Sub-Panel or not, we should know the used ” Earthing System ” for the project. For exp. in ” TT system ” it shouldn't be, because in this sytem we can use 2 or more different earth electrodes, but in ” TN-C & TN-S ” it should be, because we can't use more than one earth electrode.
By the way be carful if you are using ” TT ” that means at least 2 different earth electrods, these 2 different earth electrods shouldn't be connected, because when we connect them the earthing system will ” TN “.
nani said:
i need some help on breaking capacities on mcb, about 16ka and 85 ka..can you pls. guys, give some idea about it..tnx
can i replace 16 kA to 85 kA? what is the effect on it..
Dear Nani ;
The ” Breaking Capacity ” for a Circuit Breaker means :
– The CB should withstand a certain value of short circuit current during a time, and the CB is able to trip this short circuit current without any damage on his components.
Normally, to select the value of Breakaing Capacity for any CB, we should know the value of the maximum short circuit current ” Isc3max ” in the place of CB's installation, that means a short circuit current between 3 phases with or without neutral, this value can be knowing by doing the calculation of all Short Circuit Currents. for exp. if this value is ” Isc3max = 13.5 kA ” the value of the relative CB should be bigger than this value that means 16 kA
You can replace any CB by another CB with bigger breaker capacity but not vise vera, and in the same time when the breaking capacity be bigger the CB will be more costly.
abrahan said:
There is a transformer which has primary is Delta and Secondary also Delta. this transformer is used for light & other single phase & 3 phase supply.
415 Delta/ 435 / 240 Delta
my question is
How we can use this transformer single phase purpuse ( where is the Neutral in Delta system)
Dear Mr. Abraham ;
In some case, we use a transformer ” Dd… ” where we haven't a neutral in secondary, but in this case we should select the output voltage of secondary accordingly to the supply voltage of the loads that will be electrified by this transformer. Asume that all loads are ” single phase – 230V “, so, the secondary output voltage should be ” 230V ” between ” 2 phases ” and each load should be connected to ” 2 phases “.
For exp. we use the ” Dd… transformers ” in ” LV/LV ” when we change the earthing system from ” … ” to ” IT without neutral “, because with this kind of transformer we decrease the number of earth fault that can happen, but we should be carful of the loads' supply voltage.
Regards.
erickench said:
The earth should never be used as a ground fault current return path. I's resistance is too high and may therefore be unable to operate the overcurrent device in case of a fault.
Dear Erickench ;
1 – Excuse-me to say, I can't understand where the Earth Fault will be circulated, asume that we use ” TN-C ” as Earthing System, that means ” 4 Wires : L1, L2, L3, PEN “, or we use ” TN-S ” that means ” 5 wires : L1, L2, L3, N, PE “, and in both the earth fault is with ” L2 “, please let me know where the Earth Fault Current will be circulated ?
2 – Normally, once we have an ” Earth Fault “, and accordignly to the Earthing System, we have 2 possibilities to trip the Circuit Breaker that are :
A – Use the ” Magnetic Protection ” built-in the Circuit Breaker, if the value of the Earth Fault Current is bigger than the setting of this protection, or, if possible, modify the setting to be smaller than the Earth Fault Current.
B – Use an ” Earth Leakage ” Protection when we can't realize any condition mentioned in A.
Noting that :
– We can use the ” Earth Leakage Protection ” with ” TN-S ; TT ; IT “.
– We can't use the ” Earth Leakage Protection ” with ” TN-C “.
– The value if the ” Impedance Fault Loop ” is big ” … Ω “ in ” TT ” and ” IT with many different Earth Points “, where in these cases the Earth Fault Current's value is small and we should use the Earth Leakage Protection to trip the circuit breaker.
Regards.
Sudeep said:
What is the basis of selection of different sizes of PE conductor w.r.t. Phase conductor sizes ?
If the phase conductor is incresed to restrict voltage drop, is it also necessary to increase the PE conductor size by the same ratio?Question by eproengg
– Moderator Team
Dear ;
The basic rule to select the PE's section is as follow :
– SPh < 16mm2 we should use the same section for PE
– SPh > 16mm2 we can use for PE ” 1/2 section of pahse “, but not more than ” 300-400mm2 ” because the effect on the Earth Fault Current value will be too small.
But it's not suitable for all cases, as the selection of PE's section is depending on the Earthing System because :
For ” TN-C ” :
As we can't use the Earth Leakage Protection with this system, we should, after selection of PE, calculate the Earth Fault Current ” If ” where this value should be bigger than the adjustment value of the Magnetic Protection ” Im ” of the Circuit Breaker, if not, we have 2 possibilities : either minimize the magnetic adjustment ” Im ” ( if it's possible ) to be smaller than ” If “, or over-size the PE's section, and in some case the pahses' section, till the ” If ” be bigger than the magnetic adjustment ” Im “.
For ” TT ” :
As the resistances' values of the Earth Points are big ( a few ohms ) and are integrated in the Earth Fault Impedance Loop, and the cables' impedanse are too small ( … mΩ ), the value of Earth Fault Current is limited, and the effect of changing the PE's section is negligible. For this reason the maximum section of PE in TT system is ” 50mm2 ” for phases' section more than ” 50mm2 “, and ” 1/2 section of pahse ” for smaller than ” 50mm2 “.
For the 2nd question : it's not necessary to modify the PE's section when we chang the pahses's section, because the Earth Fault Current will be bigger.
In all case, the Earth Fault Current ” If ” should be calculated, then we can decide what we should do.
Regards.
REY said:
Bonjour,
Pouvez-vous me dire quelle est la section minimale du câble que l'on peut introduire et serrer dans une borne de terre ? Par exemple la terre fonctionnelle d'un produit peut elle se faire avec un câble de section inférieure à 1 mm ² (0,75 mm² ou 0,5 mm²) et quelle est la limite minimale ?
merci,
Jean-François
Bonjour ;
La norme ” CEI 364-… ” a bien défini que la section minimale du câble ” PE “ doit être ” 2.5mm² “ même si la section des câbles ” Phase et neutre ” est inferieur.
Spir Georges GHALI
nagaraju said:
Hi,
thanks for reply.
If you dont mine can you send the photos (i.e is how to connect elr to125 kva)
your regards
nagaraju
Dear ;
Please send me your e-mail to provide you in details the principal methode if installation of ELR.
Regards.
Matthieu said:
Hello
I would like to get a feedback from
your community regarding the reliability of electronic trip unit controlling low
voltage power circuit breaker:Electronic trip unit are not new on
Air Circuit Breaker but I have the feeling that new products (see for instance
Larsen Tubro UPOWER + OMEGA) include more and more new technologies like
wireless communication, touch screen, metering, communication.I wonder if such electronic product
can last as long as electro-mechanical part of the breaker.Does anybody have reliability figures
(MTTF) of the trip unit itself ?Do you know if some manufacturers
propose trip unit replacement during maintenance operation?I went through the documentation of
the following:
* Larsen & Tubro UPOWER OMEGA + Matrix
Protection & Control Unit* Schneider Electric Masterpact +
Micrologic* ABB Emax + PR121/122/123
* GE EntelliGuard + EntelliGuard Trip unit
* EATON Magnum + Digitrip
* Siemens Sentron 3WL + ETU
and I don't find a lot of information on
reliability and life expectancy of trip units. I think simplest trip unit is more reliable and easier to maintain, and
usage of external devices for metering or advanced protection is still
possible. But I don't have a long field
experience of such advanced trip units.
Do you?
Dear ;
I used a lot of CB either ” MCCB ” or ” ACB ” equiped with Electronic Protection Units, and I can say that their reability and advantages are good, but I have some comments :
– We should be carfull when we do the adjustment.
– I hade, in some time, a connection's problem between the Protection Unit and the the connection base in the CB ( specialy in MCCB ).
– A few CB and after a long time of istallation, tripped at a value smaller than adjustment one ( specialy in MCCB ).
– The big problem that we can't replace these units, because that needs an authorization from the manufacters, and also the electric connection between the Protection Unit and the CB should absolutly be tested, if not, we aren't sure that the trip order from the Protection Unit will trip the CB.
Regards.
nagaraju said:
what is the purpose of earthing leakage relay(ELR) ?
>How to fix the ELR in 125 KVA (i.e connections)
Dear Nagaraju ;
We use ” ELR – Earthing Leakage Relay ” to realize the ” Earth Fault Protection ” for an electric notworks, where in the most of case all protection were been installed before without this kind of protection and we want to add it, so, instead to change the circuit brekaer to have a new one built-in with this protection, we can add ” ELR ” where the output order of the ELR should be connected to a ” Shunt Trip ” installed in the circuit breaker.
For exp, if you want add an ” ELR ” to the main protection of your installation, that means to the main circuit breaker, you should add to the circuit breaker a ” Shunt Trip “, and install the ” Torroide ( special current transformer delivered with the ELR ) ” around the main cable ” 3 phases + Neutral ” but without the PE cable , connect by a special wire between the Torroide and the input of ELR, supply the ELR by the necessary voltage, then connect the output of ELR to the Shunt Trip. Nothing that there's many kind of ELR that are : Fixe, adjutable with or without a timming delay, and many Diameters of trhe Torroide ( depending the cables ).
Once there's a earth leakage current above the adjustment one in te ELR, a trip order to the shunt trip will be delivered and the circuit brekaer will trip.
Regards.
