Surge Arrester Rating Selection

The posted drawing is practically unreadable here.

You need an expert, or at least someone with a cursory knowledge of electricity and local codes, to do this for you.

Lightning arrester - Wikipedia, the free encyclopedia

http://bayimg.com/IAbAIAAfK

You can see clear image here!!

Do your own work.

Have you searched for a help site?

HowStuffWorks "Surge Protector Ratings"

The Application and Selection of Lightning Arresters

That image is practically unreadable as well.

By clicking, you can see original size of drawing.(readable)

The reason why I ask for this is as below;

In the project that I am in, Surge arrester(S.A) for 6.9kV(L-L Voltage) Switchgear was selected as 9kV, 5kA.(PDV-65) for feeder and incomer both.

As far as I know, in 4.0kV(Line-Ground Voltage of 6.9kV L-L Voltage) system, S.A rating of 9kV cannot guarantee surge/overvoltage,

because residual voltage(discharge voltage) Ures is 30kV, which is 7.5 times of 4.0kV.

Here is what I sketched for S.A discharge characteristic.

Of course I know, S.A will discharge from 9kV point, but 9kV is fairly high voltage for the equipment, I guess.

Please advise if this S.A rating selection is correct or not?

(overvoltage protection for between 4.0kV and 30kV area)

Please identify the local standard against which the <...Surge Arrestor...> in question was selected. The rest of it is second-person-check; is there only one person at the facility who can do that? How peculiar.

Dear Mr.posity,

Pl. open the following links one by one and read. I am sure, Definitely you will get you what you are looking for.

In addition to this there is a Han-Book published by IEEE, COMPRISING 1024 pages, the link could not be located, in my system. I will try to get it and post here.

These details are available in the ELECTRICAL ENGINEERS PORTAL and get registered there and you will get mails regularly LIKE CR4 which is ENRICHING OUR KNOWLEDGE and our CR4 MEMBERS share their knowledge, expertise and advise.

http://electrical-engineering-portal.com/download-center/books-and-guides/siemens-basics-of-energy/basics-of-surge-protection

http://electrical-engineering-portal.com/surge-protective-categories-defined-by-ansi-ieee-c62-41

http://electrical-engineering-portal.com/download-center/books-and-guides/siemens-basics-of-energy/basics-of-surge-protection

http://www.lightningsafety.com/nlsi_lhm/IEEE_Guide.pdf

http://electrical-engineering-portal.com/surge-protection-of-electronic-equipment

DHAYANANDHAN.S

The LA Rated voltage is: Highest System Voltage x Ground Fault Factor

The ground fault factor depends upon the type of system grounding and on the ratio R0/X1 & X0/X1.

Thank you Mr.electricalexpert65 for your response. You have mentioned " the ratio R0/X1 & X0/X1.

I request you to Pl.explain the ratio R0/X1 & X0/X1.the ratio R0/X1 & X0/X1.

DHAYANADHAN.S

Thank you for your idea sharing.

I think as below;

- Highest System Voltage : peak voltage (√2 x Us /√3 = 5.63kV)

- Ground Fault Factor : According to IEC 60099-5, 1.73 for Impedance Grounding system.

=> LA rated voltage = 5.63kv X 1.73 = 9.75kV ??

Am I correct?

LA Rated Voltage is HSV (rms) x GFF

GFF will be 0.8 for effectively grounded systems and 1.732 for ungrounded systems. For impedance grounded systems, GFF will float between these two values of 0.8 & 1.732, depending upon the ratios R0/X1 & Xo/X1 as mentioned by me earlier.

Now, assuming solid earthing in a 11kV system; the HSV for 11kV is 12kV; GFF is 0.8; thus, LA rated voltage is: 12 x 0.8 = 9.6kV; the nearest standard LA one could get in the market is 9kV. Thus, it is 9kV.

But, the case under study is a Low Resistance grounded 6.9kV System. Here, the LA has to be selected duly considering the R0/X1 & X0/X1 ratios only.

Appendix B of IEC 60071-2 throws more light on this. Suggest to go thro the same.

I think, with this I have answered Mr. Dhayanandan (posting 8) too.

THANK YOU Mr.Electrical Expert for yor reply.

DHAYANANDHAN.S

Thank you very much for your further explaination, electricalexpert65

May I ask one more question?

In IEC 60099-5, Figure 23b, it is saying that " Three-wire impedance earthed systems. Earth Fault Factor 1,73"

So, I thought Maximum voltage between phase and earth would be 1.73 x Us / √3 = 6.89kV.

Once again, I really appreciate your comment.

Really helped me a lot understanding overvoltage.