ABB 5VHK250 1200A 4160V Breaker Trip

[JBUDA54]

I have a single line that shows a 87 differential relay from the primary breaker of the XFMR and the Secondary main CKT into the 4160V ABB SWGR. I have not been able to find an overcurrent relay for the 4160V Main Breaker. My question is what is tripping that main 4160 Breaker? There are 3 CTs at the back of the Main Breaker compartment that connects to the differential relay, but doesn't the main bkr need to have overcurrent protection or does the differential relay take care of that? Confused? Please advise.

 

[davidbeach]

What is the differential relay? Some have overcurrent, some don't.

 

[JBUDA54]

Good question will find out.

 

[Zogzog]

Post your single line if you can. There are several possible failure causes of a 5VHK, lets assume the breaker is working properly right now and see what inputs and possible faults you have. After those we can discuss the breaker. I work for an ex-ABB MV breaker shop and all my guys are VHK gurus.

 

[racobb]

And...is it actually tripping or are you just trying to find the over current protection for the breaker? Was not sure from your post but you said "what is tripping the breaker" so sounds like it is tripping off line.

If it is tripping, what targets or flags, if any are you getting on the 87?

Like David said, there are three phase relays that have the conplete package built in and you should be getting trip targets. It should also be labelled other than just an 87.

Alan

Democracy is two wolves and a sheep deciding what to have for dinner. Liberty is a well armed sheep!
Ben Franklin

 

[JBUDA54]

racobb: This post was to simply assist me in a SKM CAPTOR Breaker and Relaying coordination study of this power system. This 4160V lineup has four 1500kW syn generators that supply power to the customers grid during certain process requirements. In addition to the generators there is a 500HP water pump. They plan on adding a 950HP water pump in the near future.

Zogzog: I realize that a picture is worth a thousand words so I am attaching the one-line I have for this power system. The 5A and 5B breakers are the main breakers to the 4160 dual bus arrangement. According to the oneline I only see CTs conneted to the load side of the main breakers that go to an 87 differential Relay. I have not seen the 87 relay to determine if overcurrent functions are integral with the relay but I intend on looking into this soon based on Mr. Beach's recommedation. Thank you all for your responses. I look forward to any other recommendations you may provide.

 

[JBUDA54]

I just noticed that the 13.8kV Breaker 6A and 6B has overcurrent protection and is considered the load eventhough it is at the higher voltage. The main breakers 5A and 5B probably do not require overcurrent protection as each of the generators are protected with a Beckwith 3420 gen relay and the 500HP load has it's own overcurrent protection. The main breakers are for switching the generators to the step up XFMRs. I am starting to lose faith in the oneline as I noticed that the 500HP load does not show 50/51 overcurrent relays as I have seen them on the section 10A compartment of the 4160 lineup in the field.

 

[duong12]

Hi!
Read NEC Sec. 384-16(c)it's about sizing your circuit breaker. Usually, Calculate the current:
I= KW x 1000
----------------.
1.73 x Volts x PF
Convert HP to KW in your case to apply
this formula .

On top of my head,Circuit breaker trip will be sized 80% of the rated current.

Son

http://www.electrical-designer-guide.com

 

[jghrist]

It doesn't appear to me that the 4.16 kV switchgear one-line shows relaying. Are the 87 transformer differential relays and the Beckwith 3420 relays in the switchgear? It appears that this one-line is only meant to show typical generator protection and protection of the 13.8kV-480V-4.16kV transformers. There are probably other drawings that show the relaying in the 4.16 kV switchgear.

 

[racobb]

And to add to the previous post, the drawing shows the 3420 as "typical" for the 4 gensets. If so, it has 87, 50/51v and many other functions for the gensets. You can download the manual and specs form the Beckwith site. Don't see any protection specified for the breakers. Maybe shown on another drawing per jghrist? The breakers only show an "E" as possibly an interlock between them? Maybe the area in the cloud is detailed somewhere else?

Alan

Democracy is two wolves and a sheep deciding what to have for dinner. Liberty is a well armed sheep!
Ben Franklin

 

[Zogzog]

I agree with jghirts and Alan, the 87 shown that uses the load side of 5A and 5B is for the relay scheme on the 15kV gear. What is meant by "retrofit" of the breakers? You converting these to vaccuum?

 

[RRaghunath]

It is not a must to have Phase Overcurrent protection on the secondary of transformer. This requirement can be fulfilled by the phase over current protection on the transformer primary (can act as back-up to the outgoing feeder protection on the secondary side switchboard).
I have come across such a practice in some of the major utilities.
However, it is important to have separate Earth fault protection on the transformer secondary side as the Dy transformer cannot have zero sequence currents in primary phases when fault is on secondary side of the transformer.

 

[racobb]

I don't know what specific situation you are speaking of, but I have never installed or seen an installation where the AHJ would not require secondary protection other than the primary of the utility transformer. The primary protection of the utility transformer IMO should never be relied on to protect the secondary equipment as it is not designed to do so.

Alan

Democracy is two wolves and a sheep deciding what to have for dinner. Liberty is a well armed sheep!
Ben Franklin

 

[JBUDA54]

jghrist,

I found a three line drawing that showed the overcurrent protection for the main breakers. You were right the oneline just showed how the powered flowed although some relays were shown as well. Thanks for the tips to dig deeper! I had to put away my hand trowel and use a bigger shovel.