[admin]

demiz said:

dear administrators and all engineers..

i'm a student..

i'm very confused about Load Break Switch and also Fuse..

can you help me please..

i need it for my study..

 

thanx before..

i hope u will..

:-)

---

A load break switch is a device designed to manually switch a circuit on and off. It can be used for manual control and isolation. It is designed to carry a particular current continuously and also to be able to interrupt that current. For example a 400A load break switch will carry up to 400A continuously and interrupt up to 400Amps. This is in contrast to an isolator( or non-load break) switch which is designed to isolate the circuit only. For example a 400Amp isolator will carry 400Amps continuously but the circuit has to be switched off by some other means before the isolator can be opened as its breaking capability is ZERO Amps.

A fuse is a non switchable device which is designed for circuit protection rather than control. A fuse of a given rating will carry the current of that rating continuously but if the current goes above that value, the fuse will rupture and disconnect the load. How long it takes for the fuse to rupture is a dependent on how much above the rating the current that is flowing in the circuit is. As a rough example,  if the current is twice that of the rating the fuse may take a a few minutes, even an hour to rupture depending on the particular characteristic. If the current is twenty times the rating the the fuse will rupture in a a fraction of a second.

Fuses may be in holders with removeable carriers or bolted into a circuit. If in a holder, they can be used for isolation purposes as a removed fuse shows a visible break in the circuit. However a fuse should never be removed from a energised circuit. Doing so could result in the drawing of an arc which may damage equipment or be fatal to the remover.

 

Hope that this helps.

Good luck with your studies

[admin]

pradhyumn said:

Can anybody explain why Seimens Power contactors have nomenclature of 3TF35, 3TF47 ?

---

Siemens have a particular way of providing part numbers for all of their equipment, not just contactors. This was known as the MLFB code which was a German acronym (translated into English I think that this meant Machine Readable Factory Code). Each letter and number in the code had a meaning. If you Google Siemens and MLFB you may pull up the legend.

From memory I think that

3 = switcing device

TF referred to a articular range of contactors

35 (47) etc = the frame or block size of the contactor

There would then be a sequence of numbers and letters which defined the auxiliary contacts and the coil voltage.

Hope that this helps.

[admin]

demiz said:

dear administrators and all engineers..

i'm a student..

i'm very confused about Load Break Switch and also Fuse..

can you help me please..

i need it for my study..

 

thanx before..

i hope u will..

:-)

They are two different things.

A load break switch is a device which can be manually switched by a person. It is there to be able to switch a power supply on to a load or to isolate the load. The significance of the words “load break” is that the switch is designed to be able to interrupt the current passing through it. i.e a 400A load break switch is designed to carry up to 400Amps continuoulsy and also to be able to break (switch off) up to a 400Amp flowing current.

This is in contrast to an isolator (or non load break switch) which is designed to carry the current but not interrupt it. With an isolator there must be another switch upstream to break the current as the isolator is designed to switch at zero amps.

A fuse is a non manually switchable device. It is a fault current  interruption device. It is designed to carry a given current continuously but to rupture when a current higher than that given current passes through it. The time that it will take for the fuse to rupture is dependent on how much above the fuse rating the current flowing is. As an example, a current twice that fuse rating may cuase the fuse to rupture in an hour or two. A current twenty times the rating will cause the fuse to rupture in a fraction of a second. HRC (High Rupture Capacity) fuses are capable of interrupting very high currents (many thousands of Amps) and thus are used for short circuit protection.

Some fuses are unstalled into holders but others may be bolted into circuits. With fuses in holders, you can isolate a circuit by fulling out the fuse. This is handy as you can see a visible break in the circuit. However you should never full out a fuse from an energised circuit. You should always switch the circuit off first. If you were to full a fuse on a DC (Direct Current) circuit which was feeding ai inductive load you could draw an arc which could be damaging to the equipment and even fatal to yourself. 

---

[admin]

HI, jatin333,

 

An automatic PF controller is a 'stepped' PF capacitor bankutilizing canotactors or thyristors to switch PF capacitor groups on and off line according to the PF of the electrical system.  Logic monitors the voltage and current to calculate the phase angle displacement to determine how many steps to add or remove from the system.  Time of step changes may be 10-30 seconds.

 

An active harmonic filter (AHF) is quite different.  The AHF is a power electronic device that utilizes IGBT (very fast semiconductor switches) to inject reactive current – may be harmonics or phase displaced current.  The logic is micorprocessor controlled for ultra rapid speed of analysis and synthesis of a control signal.  The control signal directs the IGBT to duplicate the control signal for injection of the reactive current.  This device works on a per cycle basis. 

 

Regards,  Jim

[admin]

Hi, manh_hoa99,

 

Both harmonic filter banks and SVC (static VAR compensators) utilize PF capacitors and inductors.  They are arranged quite differently and have different logic (control).  The purpose of each is different.

 

Harmonic filter banks are known as “detuned capacitor banks.”  The detuning means series reactors are inserted on the line side of the PF capacitors.   Detuning can be detuned to keep harmonic currents away from the PF capacitors to prevent harmonic overheating.  This device is used for PF correction only.

 

Detuning can also 'tune' the filter bank to remove a specific harmonic frequency and as such are harmonic filters and PF correction banks.  Commonly, the frequency to be removed is the 5th harmonic.

 

These devices can be fixed (all PF caps on line all the time) or stepped.  Stepped banks utilize contactors or thyristors to switch discrete amounts of VARs per step.  Generally, these devices are slow switching – 10-30 seconds on to off or vice versa.

 

SVC use thyrsitor switched PF capacitors and inductors all aranged in parallel with the loads.  SVC logic is designed to inject leading reactive current (leading VARs) to help maintian a short duration voltage sag caused by loads.  The inductors are utilized to prevent resonance conditions that may exist when the electrical system goes leading due to a lot of PF capacitors being added.  SVC are fast operating – cycle by cycle.

 

Thanks for the comments.

 

Regards,  Jim

[admin]

Jim said:

WOW!!! Thank you for your very kind words.

The knowledge expressed here is the result of 39 years of work in the power electronic field. First with AC and DC motor speed controls and then ative harmonic filters. But I have to say a lot of other people have teught me much over the years. Without competent engineers to discuss issues with there would be much confusion and poor assumptions.

Please, do send others to this site. I hope everyone that comes and learns passes it on to another.

Thank you and Regards,

Jim

---

hi jim

i am eagerly waiting for ur reply!

wull i want to know one thing that i am choosing my final year project
on design an fabrication of power factor improvement pannel, well after
reading these all topics i am confused that , in this pannel which is
basically for industries, should i use harmonic filters also or not? and
one important thing what change can i bring in my project?

regards umer

[admin]

Dave
formula is as follows

 

Current = Power/Volts

 

So:

10x( 50/12 ) = ~42A

5 x (100/240) = ~2A

 

So the obvious answer is no! but they will both cost almost the same to run, you will have some extra overhead for the ELV transformers.

[admin]

can anybody please direct me to where i can get standard power factors of various equipment for a hospital? ( example motors,elevators,pumps,refrigirator,medical equipment,kitchen equipment,low current equipment…..

[admin]

Does anyone know where i can get power factor standards of various equipment ?

im sizing the capacitor bank for a hospital so there is a lot of equipment

and does anyone know if nema has standards for power factors of motors?

thx

[admin]

Well to calculate the capacitor bank size,u must determine ur  current power factor and decide on the new power factor to be achieved depending on ur country's regulations but normally its between 0.95 and 1

Judging from the equipment u have,ur power factor is at 0.8-0.9,but better to determine them from the nameplate

to get the kvar for example:

tan(arccos1)-tan(arccos.8)=Y

then KVAR=Y x KW ( and not KVA)

[admin]

taking the project on the new trends elactrical machines like vfds is better idea

[admin]

may be short ckt in the wiring

[admin]

it's depend to tho load, as I thik
let see: U=R*I, where U=12V supplied from the battery, and R is the resistance of the Load supplied by the battery.
the current is given by: I=U/R.

The power of battery is 55mAH
no of hours of a static load, with a Z impedance is = mAh/mA, whare mA is the current truth the load,
so, Time= 0.055/I (I in Amper)

I suppose

[admin]

i am also final year student , wireless electricity is better 4 u , u can watch also on youtube,

[admin]

it's easy…you only use this formula…

I=Q/t

Q=muatan baterai 55mah

So,,,

t=Q/I                                                          I=P/V = 100W/12V = 8,33A

=(55×0,001×3600)/8,33

=23,76 Sec…

 

Regard,,

 

Hendra Marluga

PT.Taikisha Indonesia Engineering

[Author]

Posts