Over Load Capacity Of Xmer

[magdumshirish]

Respeted Sir/ Madum


I Am Using A 315 Kva Natural Oil Cooled

Xmer . What Can Be The Over Load Capacity?

 

[templdl]

This is an ambiguous question, as you have not provided anything other that the KVA.
Please provide the complete nameplate information that is affixed to the transformer in question.

 

[magdumshirish]

Loading A Xmerr

Loading A Xmerr

This is an ambiguous question, as you have not provided anything other that the KVA.
Please provide the complete nameplate information that is affixed to the transformer in question.

RESPECTED SIR/MADUM

THE XMER SPECIFICATION ARE AS FOLLOWS

CAPACIT : 315KVA
VOL. RATIO : 11KV/433V
FL SEC CURRENT: 420A
FL PRY CURRENT : 16A
COOLING. NATURAL OIL COOOED.
LOAD: COMPUTER, INDUCTION MOTOR, UPS,
LIGHTTING, HEATERS

A CONTINIOUS LOAD OF 125A NON MOTORISED
IS THER.
HOW MUCH CAPACITY INDUCTION MOTOR I CAN
SWITCH ON.

 

[templdl]

Mmmmmm, no temperature rise on the name plate?
How old is the transformer? What insulation class may it be?

When a transformer is run into overlad it gets gets warmer and reduced the insultation life. Often times the oveload time period must be balanced by underload time providing the overload does cause the winding temperature to exeed that if the insulation rating.

 

[jghrist]

How big a motor you can start is more a function of voltage drop than transformer capacity. You need to do a motor starting study and need to know:

1. Source impedance.
2. Transformer impedance.
3. Circuit impedance to motor.
4. Sensitivity of other loads to voltage drop.

I don't believe that you can expect to learn how to do a motor starting study from an on-line forum. Neither can you expect to get someone else to do it for you on an on-line forum. Methods are described in IEEE Brown Book?
IEEE Std 399?-1997? Recommended Practice for Industrial and Commercial Power Systems Analysis. See http://standards.ieee.org/colorbooks/sampler/brownbook.html

 

[ENDIX]

calculate spare capacity of transformer before motor connected. rule of thumb total load about 80% of transformer capacity. after selected size of motor, calculate the voltage drop during running and starting using formula:

Percent voltage drop during running =
(TX impedance (%) x MFLA x V x 1.73)/(TX kVA - kVa other load)x 1000)

Percent voltage drop during starting =
(TX impedance (%) x MLRC (lock rotor)x V x 1.73)/(TX kVA - kVA other load) x 1000)

as per NEMA standard, allowable motor voltage drop is max:
- 5% for motor feeder in normal operating condition
- 20% for motor feeder during starting condition
just assumed MLRC=6x FLC, Z Tx = 4-6%.
if theallowable VD exceed reduce size of motor n so forth

 

[petersonra]

Respeted Sir/ Madum


I Am Using A 315 Kva Natural Oil Cooled

Xmer . What Can Be The Over Load Capacity?

My guess is the manufacturer can tell you this. Transformers are pretty tough brutes and can take a lot of abuse. Such abuse does shorten their life span though.

If you can get rid of the heat, you can often load them up a lot more than you might be led to believe by looking at the raw specs.

I would not want to screw around too much with a transfomer of this size. Might get the power minds' panties all bunched up if you happened to damage it and cause havoc at your facility.

 

[magdumshirish]

Loading A Transformer

Loading A Transformer

I suspected it was mostly a language problem. I sort of figured he was an electrican instructor.

RESPECTED SIR/MADUM

I AM A LECTURER IN TEXTILE INSTITUTE.
I AM TEACHING BASIC ELE. ENGG.,ELECTRICAL
MACHINES, UTYLITY ENGG.

BESIDES I AM LOOKING AFTER
MAINTENCE, NEW ELECTRIFICATIONS.SO
AS LOAD IS INCREASED ABOVE 5O HP
WE HAVE PLANED A SUB STATION. SO
I HAVE ERECTED A SUB STATION FOR
MY COLLAGE. AND I HAVE SOME DOUBTS.

THANKS

 

[weressl]

RESPECTED SIR/MADUM

I AM A LECTURER IN TEXTILE INSTITUTE.
I AM TEACHING BASIC ELE. ENGG.,ELECTRICAL
MACHINES, UTYLITY ENGG.

BESIDES I AM LOOKING AFTER
MAINTENCE, NEW ELECTRIFICATIONS.SO
AS LOAD IS INCREASED ABOVE 5O HP
WE HAVE PLANED A SUB STATION. SO
I HAVE ERECTED A SUB STATION FOR
MY COLLAGE. AND I HAVE SOME DOUBTS.

THANKS

Yep, you seem to be doing things that you should not be doing.

 

[petersonra]

I HAVE SOME DOUBTS.

I am not at all surprised.

 

[magdumshirish]

Over Load Capacity Of Xmer

Over Load Capacity Of Xmer

Respected Sir/madum

I Am Lectuer In Textile Institute.

I Am Teaching Basic Electrical Engg, Electircal Machines,
Utylity Engg. I Am Doing Maintenance And Electrifications,
As Expansion Is Taken Place, We Need Have A Sub Station.
I Have Erected 315 Kva, 11kv/440v, 5ohz Xmer.

So I Have Some Doubts.

Thanks

 

[Lxnxjxhx]

Question to Magdum

Question to Magdum

Dear Sir:

Out of concern, I must ask: What is your experience? What is your training? Are you qualified to work at these power levels?

Regards,
Lxnxjxhx

 

[mdshunk]

Isn't the old rule of thumb (if one even believes that rules of thumb exist), that oil-filled transformers can be overloaded 140% almost continuously as long as certain temp limits were not exceeded? After all, isn't that what the Thermotell is all about?

 

[mivey]

Isn't the old rule of thumb (if one even believes that rules of thumb exist), that oil-filled transformers can be overloaded 140% almost continuously as long as certain temp limits were not exceeded? After all, isn't that what the Thermotell is all about?

I don't know that I would word it like that but if you can keep it cool enough, you could probably load it more than that.

With auxiliary cooling, you can increase the capacity. For example, my power transformer table (not all-inclusive) has:
OA = oil-immersed, self-cooled
FA = auxiliary forced air
FOA = auxiliary forced oil & air

so for a transformer with OA/FA cooling:
For 2500 kVA and below = 115% of the OA capacity.
For 2501-9999 kVA 1ph or 2501-11999 kVA 3ph = 125% of the OA capacity.
For 10000 kVA 1ph or 12000+ kVA 3ph = 133% of the OA capacity.

and for a transformer with OA/FA/FOA cooling:
For 10000-16667 kVA 1ph or 12000+ kVA 3ph = 133%/166% of the OA capacity.

You can overload otherwise but probably not continuously. You would have to look at ambient temperature, temperature rise, capacity factor, pre-loading, reduced life allowance, etc.

 

[broadgage]

Hi new member here.

The voltage rating of the transformer in question suggests that the OP is either from the UK, or from a UK influenced country (India? Pakistan?).

Until recently the nominal voltage at the point of use in the UK was 240/415 volts. Substation transformers were often specified at 433 volts in order to allow for voltage drop en route to the load.

The nominal voltage in the UK has recently been reduced from 240/415 to 230/400, though in practice the actual measured voltage has not altered in most cases.

I would agree that the OP may not have sufficient experience in this matter.

 

[iwire]

What is your experience? What is your training? Are you qualified to work at these power levels?

Yep, you seem to be doing things that you should not be doing.

I would agree that the OP may not have sufficient experience in this matter.

Gentlemen, either answer the questions or not.

If you have a problem with a poster, or a thread contact a moderator.

This symbol

at the top right of each post is a there to report posts. Or you can PM a moderator. But don't start questioning members qualifications on the open forum, it is just plain rude.

Treatment of Members

 

[jrannis]

The OP could be in a situation where someone is trying to sell him on something he might not need, possibly due to starting a large motor with a transformer that appears to not be able to handle the load.
I would suggest that the OP hire an engineer to evaluate the proposed design for two reasons. Installing a substation would cost some big bucks for sure, and loosing a distribution transformer would cost big bucks and down time.
I wish the best for you. Let us know how it turns out.

 

[mivey]

Gentlemen, either answer the questions or not.

If you have a problem with a poster, or a thread contact a moderator.

This symbol

at the top right of each post is a there to report posts. Or you can PM a moderator. But don't start questioning members qualifications on the open forum, it is just plain rude.

Treatment of Members

iwire, if you wouldn't mind, could you please explain how the following is different (from http://forums.mikeholt.com/showthread.php?t=99164 )?:

It might be legal.

I question if it's legal for him to be doing this work.



As his zip shows RI for a location he needs to be a licensed electrician to be doing this work.

If it is because you are a moderator, so be it, as I fully recognize your authority. If not, how do you perceive that the questions about qualifications here are different than what you posted in the other thread? I'm not trying to argue with you, I just want to understand the finer definition of "the line". Maybe it is just a perception thing.

 

[weressl]

iwire, if you wouldn't mind, could you please explain how the following is different (from http://forums.mikeholt.com/showthread.php?t=99164 )?:If it is because you are a moderator, so be it, as I fully recognize your authority. If not, how do you perceive that the questions about qualifications here are different than what you posted in the other thread? I'm not trying to argue with you, I just want to understand the finer definition of "the line". Maybe it is just a perception thing.

Yeah,

I think he wanted to be a policeman when he was growing up.

 

[petersonra]

Yeah,

I think he wanted to be a policeman when he was growing up.

Some people are a little more authoritarian, especially when it comes to hot button issues they have.

I wouldn't get too worked up about it.