Picking 0.3333333333 of fault current

[mutimuti]

Can anyone tell me the industry standard for protecting radial networks. Some publications for example base the "pick up" on a fraction of minimum fault current, typically 1/3 and the time dial settings based on maximum fault current. Still others use peak load current for pick up and fault currents for time dial settings. I really want to know the preferred method and the reasons for it.

 

[apowerengr]

When you say "radial" network are you discussing a networked system or radial distribution feeders? As for standards, the US COE has their standard, IEEE publishes a standard (currently under review), RUS publishes standards for Electric Cooperatives, .......

Pick your settings based on:

Coordination (source and load devices)
Arc-Flash hazard management
Equipment withstand
Fault detection for normal and contingent switching line length

Whatever you do, make sure the operators understand the settings and how you predict the system will respond to faults. It really helps with troubleshooting.

 

[mutimuti]

Thank you apowereng! You were the only person having the remotest interest in this question. I refer to a radial distribution feeder, with several busses from which loads are drawn. One method involves setting relays based on 1/3 of fault current and time dials at each bus based on maximum fault current near the bus, taking into consideration downstream relays. Another method uses maximum loads as determined from load estimates. What to do?

Can you please advise where I can get the IEEE document.

MM

 

[rbulsara]

http://www.IEEE.org

Refer to the Red book and the Buff book. Look up color series of IEEE standards on the website.

Your question is too vague and at least to me does not make much sense. You do not even mention what type of over current protection you are taking about. Phase or ground? What does the device protect? Cable? transformer? Both? Motor? There are different consideration for different situations and applications.

Fault current comes into play only when setting instantaneous settings. What pick up are you referring to? I suspect it is long time pick up for phase overcurrent protection.

Setting relays is as much an art as science. Bottom line is you must strive to coordinate with upstream and downstream devices. You may not succeed all the time.

Have you compared the curvs of the devices in question on a common plot?? Are you using any software?

 

[apowerengr]

IEEE C37.230 from the IEEE store on their web site. As I stated earlier it is currently under revision. I am not certain when the revised issue will be available for purchase.