10 second rating of resistor in a neutral grounding transfomer?

[topgone]

you'll never pass if you keep thinking like that
he gave us the total reactance Xc

by you calculations a 7kva will do
but charging kva is 17kva
that xfmr won't last too long
using your numbers charging kva is 50
you 7 kva will last even less

keep trying
he asked the ngr current value, not the xfmr kva

We don't spoon-feed people here, we assume posters are big enough to do some calcs of their own, that's why!:lol:
Given the grounding transformer kVA, you can compute for the resistor values (power rating and resistor current). The resistor power rating will be matched with the transformer kVA.

BTW, you won't pass your subject if you're lazy and don't do honest research.
Here's an additional literature re grounding transformer primary voltage rating. LINK
Proceed to p. 12 for the "primary voltage rating" of the grounding transformer. Come back here and say again how "silly" old people are, will ya?:rant:

As to the "overload factor" (10.5 for 10-second rating) on transformers used in grounding, please spend some more time researching. Tip: it's an IEEE document.

Remember, engineers stand on the shoulders of the giants of their trade!

 

[Ingenieur]

We don't spoon-feed people here, we assume posters are big enough to do some calcs of their own, that's why!:lol:
Given the grounding transformer kVA, you can compute for the resistor values (power rating and resistor current). The resistor power rating will be matched with the transformer kVA.

BTW, you won't pass your subject if you're lazy and don't do honest research.
Here's an additional literature re grounding transformer primary voltage rating. LINK
Proceed to p. 12 for the "primary voltage rating" of the grounding transformer. Come back here and say again how "silly" old people are, will ya?:rant:

As to the "overload factor" (10.5 for 10-second rating) on transformers used in grounding, please spend some more time researching. Tip: it's an IEEE document.

Remember, engineers stand on the shoulders of the giants of their trade!

You need to get a better grasp of the subject matter before you assume you have anything to share
according to you ngr A = 7000/240 = 29
primary 240/10400 x 29 = 0.69 << charging current lol

you realize I posted that link in post 3?
and it proves you are incorrect?
it is a single phase eq ckt on the neutral lol not a 3phase

excerpt

The primary of the transformer is connected fromthe system neutral to ground. The loading resistor is connected across the transformer secondary..
The resistor should be sized the same way as a neutral grounding resistor, except that it will be reduced in value by the square of the turns ratio of the transformer.


Read it!!!! Lol
it tells you how to size the xfmr
basically ngr i x v
no reduction of 10.5

I'm older than you
and better trained

 

[Ingenieur]

Btw: Engineering is a profession
not a trade
lol

 

[topgone]

SKIRTING THE ISSUES DOESN'T WORK

SKIRTING THE ISSUES DOESN'T WORK

Egads!
You posted the NGR manufacturer's paper and it is clear you're lazy by not reading your posted link.:happysad:
Here's the phrase you purposely skipped (again, it's on p. 12):

The transformer primary voltage rating should be
the same as the system line-to-line voltage. The
secondary voltage is normally 240 or 120 volts.

Please stop spreading false information to others who wanted to learn from this forum. By telling people to use a grounding transformer primary voltage rating equal to the line to neutral voltage, you are going to get the grounding transformer into saturation during SLG faults. LINK1 LINK2 LINK3

As to specifying a smaller grounding equipment especially if the system is designed to trip on ground fault, that is a logical design. It is the amount of energy dissipated that matters and if the system is designed to isolate in a few cycles, it's correct to design the grounding equipment to withstand for just a few seconds, say, 10 seconds. The equipment will be smaller (cheaper) but does the job of conducting the rated fault current for the fault duration.

But, if you don't know how to size the grounding equipment, you can go ahead and follow your continuous-duty idea. But I'm sure you'll never win a single bid in your lifetime.

 

[Ingenieur]

Egads!
You posted the NGR manufacturer's paper and it is clear you're lazy by not reading your posted link.:happysad:
Here's the phrase you purposely skipped (again, it's on p. 12):


Please stop spreading false information to others who wanted to learn from this forum. By telling people to use a grounding transformer primary voltage rating equal to the line to neutral voltage, you are going to get the grounding transformer into saturation during SLG faults. LINK1 LINK2 LINK3

As to specifying a smaller grounding equipment especially if the system is designed to trip on ground fault, that is a logical design. It is the amount of energy dissipated that matters and if the system is designed to isolate in a few cycles, it's correct to design the grounding equipment to withstand for just a few seconds, say, 10 seconds. The equipment will be smaller (cheaper) but does the job of conducting the rated fault current for the fault duration.

But, if you don't know how to size the grounding equipment, you can go ahead and follow your continuous-duty idea. But I'm sure you'll never win a single bid in your lifetime.

even a stopped clock is correct twice a day
Keep trying
If you read the paper I posted ( and you re-posted) you'ld be ahead of the game
or at least not so far behind

You never did give the ngr ampere rating?
the voltage across the xfmr (and ny n^2 across the ngr) is line-neutral
It is sized for that
it is insulated for ph-ph V

you typically want the ngr 5-10 times the protective relay setting

you are talking a lot of gobblty-gook but convey little information and even that is inaccurate

as far as $$$
already made all I need
and I don't 'bid'
I submit fee proposals

http://apps.geindustrial.com/publibrary/checkout/System NGR?TNR=White Papers|System NGR|generic
As a rule, the value of ground fault current is chosen to provide enough current for the ground faultrelay to operate at 10% of rated ground fault current. This will allow the detection of a fault to within10% of the neutral point of a motor or transformer.

this will ensure tripping if voltage sags or fault impedence is higher limiting current well below the ngr value

 

[Ingenieur]

btw
on a gen install the cost difference of an ngr gnding xfmr will not cost you the job

burning one open will cost you your business and livelyhood
and depending on fault scenario and location may cause injury or worse
penny wise poind foolish

 

[topgone]

even a stopped clock is correct twice a day
Keep trying
If you read the paper I posted ( and you re-posted) you'ld be ahead of the game
or at least not so far behind

You never did give the ngr ampere rating?
the voltage across the xfmr (and ny n^2 across the ngr) is line-neutral
It is sized for that
it is insulated for ph-ph V

you typically want the ngr 5-10 times the protective relay setting

you are talking a lot of gobblty-gook but convey little information and even that is inaccurate

as far as $$$
already made all I need
and I don't 'bid'
I submit fee proposals

http://apps.geindustrial.com/publibrary/checkout/System NGR?TNR=White Papers|System NGR|generic
As a rule, the value of ground fault current is chosen to provide enough current for the ground faultrelay to operate at 10% of rated ground fault current. This will allow the detection of a fault to within10% of the neutral point of a motor or transformer.

this will ensure tripping if voltage sags or fault impedence is higher limiting current well below the ngr value

You do your math and we will have a look at those calcs. We will tell you if its wrong ot right. So far, you got it wrong. Also, we're not allowed to do student's homework here. Bluntly, we're not even obliged to feed you the figures.

It could have been nicer if you politely asked. Since you have an attitude problem (enlarging the texts is shouting for us), strive on your own to learn. We've done it, and it works fine for us everytime!

 

[Ingenieur]

You do your math and we will have a look at those calcs. We will tell you if its wrong ot right. So far, you got it wrong. Also, we're not allowed to do student's homework here. Bluntly, we're not even obliged to feed you the figures.

It could have been nicer if you politely asked. Since you have an attitude problem (enlarging the texts is shouting for us), strive on your own to learn. We've done it, and it works fine for us everytime!

already did it
you never gave a current rating for the ngr

I graduated 30+ years ago and been licensed for over 20

it's not 'my' math
it's Kirchhoffs, Ohms, Newton, Liebniz, Fortescue, et al

you are in no position to judge my work considering you've been incorrect at every turn

The Dunning–Kruger effect is a cognative bias in which relatively unskilled persons suffer illusory superiority, mistakenly assessing their ability to be much higher than it really is. Dunning and Kruger attributed this bias to a metacognitive inability of the unskilled to recognize their own ineptitude and evaluate their own ability accurately. Their research also suggests corollaries: highly skilled individuals may underestimate their relative competence and may erroneously assume that tasks which are easy for them are also easy for others.

I'm typing on an ipad and text size/font gets garbled at times
I am typing/writing, not speaking or yelling
But nice attempt to avoid the crux of the matter
redirect and obscure
you are incorrect
making a mistake is not a problem
not seeing it is lol
seeing it and not owning it is even worse

 

[Sahib]

The grounding transformer, whether it be zig zag or wye-delta, is sized based on its rated phase to neutral voltage and neutral current. So what is the problem, guys?

 

[Ingenieur]

The grounding transformer, whether it be zig zag or wye-delta, is sized based on its rated phase to neutral voltage and neutral current. So what is the problem, guys?

No problem
rated on phase to neut/gnd voltage for current limitation
rated for ph-ph re: insulation

 

[topgone]

The grounding transformer, whether it be zig zag or wye-delta, is sized based on its rated phase to neutral voltage and neutral current. So what is the problem, guys?

There's more to that than simply considering what you've mentioned!

If you are designing for a grounding equipment of a generator, you also take into consideration the effect of the field exciter. Field excitation control could have altered the excitation in the span of time the abnormality persisted (10 seconds). Please see GEC Alstom Protective Relays, Application Guide, Section 17.2 where field forcing is considered when calculating grounding transformers (fault voltage multiplied by 1.3).

Attention to details is the key here.

 

[Ingenieur]

Lol
phase-neut/gnd V
desired limitation of fault current > charging current
duration that fault is allowed to persist before clearing

that is all you need to size the ngr

the OP has a good understanding of this subject matter