Thank you for the detailed response.
If you are willing to quickly look at Figure 3 of the article in the link from cummins
there is a time after the transient region where the L-L and L-G currents are larger than 3 Ph for the generator in the sample
Any comments on why after some time the LL...
Hello Everyone,
I was reading this article on generator decrement curves created by cummins and its was quite interesting.
On Figure 3 of the article, they show that in there example for a terminal fault at around 0.1 seconds both the line to line and L-G fault currents are larger than the 3Ph...
Thanks for the feedback I get where you are coming from thats its most common 3Ph currents are worst case.
Do you mind elaborating on the 15% allowance for the equipment rating?
Can you maybe break it down in terms of an example, lets say a CB has an SC current rating of 50kA how does the 15%...
Hello Everyone,
In section 7.2 of the IEEE 399 book there is some discussion about 3Ph faults vs LG fault for protective device duty analysis. (see attached image)
Typically its most common to focus on the 3Ph faults however for the special condition where LG faults results are larger than...
@System Protection
The question that comes to mind is why use "3 * I Zero Seq Current" over the other available results (seq or phase currents for example)?
Would one example of this results relevance be for a fault on the secondary of a XFMR with Y-solid grounding since the neutral current...
Hello Everyone,
I am in the middle of trying to further understand symmetrical components.
The SEL paper below has been a great resource.
https://cms-cdn.selinc.com/assets/Literature/Publications/White%20Papers/LWP0010-02_TutorialSymmetrical-Pt2_AH_20201019.pdf?v=20201020-155433
I notice...
Would anyone in this forum have access to the C22.1-21 Canadian electrical code published in 2021?
I’d like to confirm is if any changes have been made to the capacitor discharge requirements shown in red in the image below from the 2018 version.
I have seen some discussions about considering the zero-seq magnetizing current for secondary side fault of a XFMR with Wye grounding on the primary and y solid grounding on the secondary.
I am curious if anyone knows any good references that goes into an example calculation for the LG fault...
@davidbeach
Thanks for sharing such interesting information on what youve seen out in the field.
Based on what you have shared it seems there is some wiggle room in there for error.
However, there is no set guideline to say what to do in all cases as expected.
@thermionic1
Thank you for the feedback from what you have experienced.
From what you have seen where you expect a +/- 3% tolerance it seems considering this in the FCT wouldn't be the worst idea.
However, I do realize an extra 3% tolerance is not going to make a significant impact just...
@dpc
I agree with your statement 100%.
In the relay case the FCT= Breaker Opening Time + Relay Tripping time.
My question is based on the equipment's age could one introduce a "%Tolerance" on the relay trip time?
For example something along the lines of :
FCT= Breaker Opening Time + Relay...
Hello Everyone,
Typically, when running a protection and coordination study or Arc Flash study we use time current curves to determined fault clearing times.
In some older facilities there can be protective devices (Relays, Fuses, etc.) which perhaps have been in service for an extensive...
Hello,
I was looking at the sample PE exam question below.
When solving the question i decided to use the XFMR Secondary voltage and MVA as my base values.
Which then required the Gen imp to be converted to the XFMR MVA base.
When doing so the first time i followed the process below...
Based on what i have read in IEEE C37.20.7-2017 you are bounded to the ratings of the Arc Rated gear.
In other words for you to rely on the gear to work as designed you must not allow the internal arc to last longer than the max arc duration tested by the manufacturer.
For example clause 2.4.3...
Hello Everyone,
I was reading the IEEE C95.6 which is the "IEEE Standard for Safety Levels with Respect to Human Exposure to
Electromagnetic Fields".
In the document they mention the max limit with respect to electromagnetic field exposures as shown below.
What I'm not clear on is we...
Hello,
I was looking at the sample PE exam question below.
When solving the question i decided to use the XFMR Secondary voltage and MVA as my base values.
Which then required the Gen imp to be converted to the XFMR MVA base.
When doing so the first time i followed the process below...
You are correct!
I shouldn't have taken the absolute value of the admittance that was the final issue aside from my Y_22 initially that you pointed out.
Taking the absolute value of each of the elements of the impedance matrix calculated now got me the same Z matrix as the sample calculations...
Hello Xnuke,
Thank you for pointing out Y_22.
Attached is the revised Y and Z matrix however I still don't match the sample document. (see pg 3 of "Summary2.pdf")
I found in the document a summary of the majority of the expected Y matrix components. (see pg 1 of "Summary2.pdf")
All of my Y...
Hello Everyone!
I have a sample SC calculation I'm looking at but can't seem to match the 3x3 impedance matrix found in the sample.
I have formed the Y matrix following the guidelines from Annex B in IEC 60909.
Attached are the system impedance details (pgs 1 to 2 of attachment), the sample Z...
