I am trying to learn hvac design etc...
I have a doubt as per Ashrae 62.1, is there an ach defined for an office space...it is not directly given..
Problem is that one web site saying it is 2-3 ach .....when I put this this in a small office space of volume (108 cubic meter), I get...
Hi,
For a big shopping center, which has 30 LV Transformers(11KV/415V-system fault level-250mva) in Ground floor Transformer rooms-While designing earthing system how much fault current to be considered-
1)Only One transformer
or
2)Fault curent based on Probability of Failing, since 30 is a...
Hi,
This may be a hypothetical question,But I am glad if somebody can share their insight on it.
If for Electronic trip unit type ACB acts and trip in same manner for Short Circuit and Overload the why we have to segragate on basis of Overload and short cirucit.
For eg: a 2500A breaker set to...
1.What is the difference in 1 second & 3 second rating.For eg: 65ka,3 second.
2.In our plant,11 kv primary feeders (main incomers)busbars is rated for 25ka,3 seocond. But in 11kv secondary feeders(to hv equipment),25kA,1second is allowed.How we can know from theortical point of view,1 second...
Hi,
In GCC Countrie's regulation ,there is a guideline which says Transformer to be rated(KVA) 25% more than Maximum Demand(KW).
How this value came from.If Power Factor is 0.8(1500KVA*0.8=1200KW),this could be possible.But with Capacitor Bank ,a must
we get power factor more than 0.92 minimum...
I had seen busbars going from Transformer to Nearby panels (4000A,415V) supported by very rigid
pillars.I asked suppliers then why you suggest such huge supports..Their answer was to protect
against high short current stress.
Now consider new situation where I encounter is of Bus bars from LV...
But following document mentions if HV & LV Separte keep 8mts distance from Earth Pits;
https://library.ukpowernetworks.co.uk/library/en/g81/Installation_and_Records/Earthing/Documents/ECS+06-0023+Secondary+Distribution+Network+Earthing+Construction.pdf
that is my concern.
best regards
Abraham
Thank you very much for enlightning answers.
One question can I ask witout strating another thread;
Is there any thumb rule for distance between HV and LV Earth pits?for 11k,allowable GPR is around 300V as per IEEE ,I read.
But if there is any distance to be maintained by thumb rules something...
I have two questions regarding earth resistance;
1.For single electrode R=(rho)/2(pi)[1/r] ->here why ressitivity of copper rod (material -copper) has not considered,but only resistivity of soil is considerd?
2.For concrete encased electrode,earth ressitance less than rod alone-How since...
I couldnot exactly remember which BS standard,but it mentions maximum incomer isolator possible for a distribution board is 125A.Whether
such a rule exists-When I look to well known manufacturers productline,I can see it exists.
My question is on what basis such a rule is made?
choice 1...
Hi,
I have a building with three 11/6.6kv, 5MVA transformers with MCC's as loads.Proposed Grounding system is a single row of ground rods at every 8 meter around the periphery of a building interconncted by a cable (of suitable earth fault current carrying capacity).
I want to put this...
Thanks for all thoughtful replies-It helps to gain a partial understanding of subject.
My thinking was this code design was based on old acb standards-not either on considering new electronic trip units or "maximum power,minimum volume concepts" prevalent in switchgear industry.Still question...
I live in middle east,may be a remote place for you-but my question is beyond codes if acb depth is 450mm,what additonal
space I should allow for
1)safe working
2)is some arc/shock hazard etc come into this picture to take away precious space of
architects
regards
Abraham
Hi,
Is there any standard or documents available to get an idea of approximate front space required
for drawing out of ACB (low voltage) like for example-for 1600A ACB ,750mm space is required
infront of switchgear.
Now I would like to know 5000A ACB, what is the minimum distance required...
Hi,
Given datas: 11kv,350MVA Fault level &
11kv is feeding to 11kv/400v,500kva with%z=5%; Transformer;
-------------------------------
Now to calculate Impedances;
primary impedance-->(11000^2)/350-->(equation1)
secondary side impedance-->(5)*400/(100*500)-->(equation2)...
