Equipment Damage Curves 1

[Shavner]

Trying to find some reference material on 15 kv switchgear damage curves. I am trying to convince a client to install a partial bus diferential protection and want to quantify the possible damage to the equipment without it.

 

[jbartos]

Suggestion: 15kV switchgear damage curves are not that much wide spread as the transformer, generator and cable damage curves. Actually, the switchgear Close & Latch (C&L) value should not be exceeded, continuous current rating should not be exceeded, interrupting capability should not be exceeded, etc.

 

[busbar]

See IEEE Std C37.97-1979 (R1990) Guide for Protective Relay Applications to Power System Buses. Description at standards.ieee.org/reading/ieee/std_public/description/relaying/C37.97-1979_desc.html Often, bus-protection schemes have evolved from hard-won experience, and will not show up requested by a client unless outage(s) have caused significant loss in production and restoration-expense outlay.

 

[jbartos]

Suggestion: Visit

http://www.usace.army.mil/publications/armytm/tm5-811-14/chap5.pdf

for damage curves

 

[alehman]

Bus differential protection is usually applied where the concern is to minimize damage from arcing faults. Switchgear bus is designed so it can be adequately protected with time-overcurrent devices.

 

[jbartos]

Suggestion: In many instances, the bus is important in the power distribution. Therefore, the bus differential protection is applied. I may have a fast differential protection to minimize damages caused by shorts.

 

[alehman]

Clarification to my previous post: I meant to say that switchgear bus can be adequately protected from _thermal damage_ with time-overcurrent devices.

Bus differential protection is advisable for applications where personnel may be injured by sustained faults, where downtime for repair is costly, where fault levels are high or where upstream overcurrent protection is suspect.

 

[jbartos]

Suggestion: Protective relay textbooks show bus protected, under the bus zone protection. This implies the differential bus protection.
Visit

http://www.geindustrial.com/pm/notes/artsci/?SMSESSION=NO

for The Art and Science of Protective Relaying by C. Russell Mason

 

[DiscoP]

Partial differential protection is normally applied when you want to close a bus section breaker, but don't have enough grading margin available for three overcurrent stages - ie feeder then bus section then incomer. If you have a copy of the GEC Measurements PRAG, this is discussed in sec. 9.23.3
It is different to bus zone differential which operates instantaneously for a fault on the busbar and requires CTs on all breakers.
Partial differential only requires CTs on the Incomers and Bus section breakers, and will operate for faults on the feeders so a time delayed grading is required.
It is very common for these terms to be confused (some on this thread have also thought inst bus zone diff !)- perhaps your client has also misinterpretted your proposal.
However fast operation to limit damage is not normally the reason for applying this scheme, rather providing good selectivity is it's benefit.

 

[neps3]

Jbaretos

Could you please give me the web access to all the mil chapters on the protection. Have been quite useful.

Ta