Arc Flash/Coordination

[D!NNy]

I am using a 12kv/480v 500kva transformer, I left all the variables constant and changing the transformer configuration from Solid grounded to Delta on the secondary and kept primary side to Delta in both the cases incident energy is changing from 25 to 30. can anyone help me what is the relation between the transformer configuration and IE. where the fault current and fault clearing times are remained to be same......


Thanks in Advance

 

[iceworm]

So, "the fault current and fault clearing times are remained to be same". But the IE changed. Seems odd.

I can't help. I don't know what algolrythms your software you are using:

1. what software you are using.
2. does it do an IEEE 1584 calc
3. Maybe it is doing an NFPA 70E calc.
4. have you looked at IEEE 551 violet book
5. Do you understand the algolrythms your software is using
6. Have you tried doing a hand calc using IEEE 1584.
7. Are both cases looking at bolted 3ph faults
8. What makes you think there is a difference between the two

I've never trusted computer software where I don't know the math model it is using.

ice

 

[GoldDigger]

So, "the fault current and fault clearing times are remained to be same". But the IE changed. Seems odd.

I can't help. I don't know what algolrythms your software you are using:

1. what software you are using.
2. does it do an IEEE 1584 calc
3. Maybe it is doing an NFPA 70E calc.
4. have you looked at IEEE 551 violet book
5. Do you understand the algolrythms your software is using
6. Have you tried doing a hand calc using IEEE 1584.
7. Are both cases looking at bolted 3ph faults
8. What makes you think there is a difference between the two

I've never trusted computer software where I don't know the math model it is using.

ice

If the fault current and fault clearing limits are set on the primary side, then I could imagine that the arc-flash energy on the secondary side for a single phase fault could be influenced, at least in a minor way, by the secondary configuration.

 

[topgone]

I am using a 12kv/480v 500kva transformer, I left all the variables constant and changing the transformer configuration from Solid grounded to Delta on the secondary and kept primary side to Delta in both the cases incident energy is changing from 25 to 30. can anyone help me what is the relation between the transformer configuration and IE. where the fault current and fault clearing times are remained to be same......


Thanks in Advance

IMO, the incident Energy depends only on three things: fault current available, the time fault is allowed to persist (clearing times), and distance the person or object is from the arcflash. If your chosen configuration decreases the fault current level available at that location in your system, then it does decrease the amount of the incident energy assuming other factors the same.

 

[jim dungar]

IMO, the incident Energy depends only on three things: fault current available, the time fault is allowed to persist (clearing times), and distance the person or object is from the arcflash. If your chosen configuration decreases the fault current level available at that location in your system, then it does decrease the amount of the incident energy assuming other factors the same.

You are forgetting about the 'size of the arc' an arc spanning the small bus gap in a panelboard will have a different amount of incident energy than one spanning the larger bus gap in switchgear. This is why the IEEE1584 standard includes a value for gap.

In a similar manner there is an accommodation in the standard for solidly-grounded versus resistance or ungrounded systems.

 

[D!NNy]

Please see my comments in bold and Italic

So, "the fault current and fault clearing times are remained to be same". But the IE changed. Seems odd.

I can't help. I don't know what algolrythms your software you are using:

1. what software you are using. I am using ETAP
2. does it do an IEEE 1584 calc. Yes
3. Maybe it is doing an NFPA 70E calc. No
4. have you looked at IEEE 551 violet book No but does it say anything about the transformer configuration in realation ship to IE.
5. Do you understand the algolrythms your software is using No
6. Have you tried doing a hand calc using IEEE 1584. No
7. Are both cases looking at bolted 3ph faults Yes
8. What makes you think there is a difference between the two Coz of the Incident energy for solidly grounded is low when compared to Delta Delta configuration

I've never trusted computer software where I don't know the math model it is using. No comments

ice

 

[D!NNy]

IMO, the incident Energy depends only on three things: fault current available, the time fault is allowed to persist (clearing times), and distance the person or object is from the arcflash. If your chosen configuration decreases the fault current level available at that location in your system, then it does decrease the amount of the incident energy assuming other factors the same.

For both the transformer configurations it give me same 3 phase bolted fault current but different incident energies??

 

[D!NNy]

You are forgetting about the 'size of the arc' an arc spanning the small bus gap in a panelboard will have a different amount of incident energy than one spanning the larger bus gap in switchgear. This is why the IEEE1584 standard includes a value for gap.

In a similar manner there is an accommodation in the standard for solidly-grounded versus resistance or ungrounded systems.

can you reference me to this formula where it gives me the relation between transformer configuration Vs IE...

Please see the table below for fault currents: This table shows that 3 phase fault currents are same in all the kinds of configuration why is the incident energy different?

Thanks

 

[D!NNy]

Here is what i found from IEEE Section 5.3 but not sure how K1 and K2 are calculated.

Thanks

 

[jim dungar]

Here is what i found from IEEE Section 5.3 but not sure how K1 and K2 are calculated.

Thanks

K1 and K2 are constants, you simply chose the value that fits the installation.

 

[D!NNy]

K1 and K2 are constants, you simply chose the value that fits the installation.

Thanks for everyone for the input

 

[danton]

fault calculation for services equipment

fault calculation for services equipment

Hi I need calculation for fault calculation for services equipment
I have 200 Amps disconnect 208 volt 15feet long and isca at tthe tap can is 12969 amps