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 Post subject: Generator Alternator Protection with Tthermal/Magnetic Trip.
PostPosted: Sun Jun 23, 2024 6:31 am 

Joined: Mon Feb 09, 2015 8:48 am
Posts: 3
I am using latest ETAP to model the Diesel Generator Protection for the Generator Alternator 515kW, 600VAC, 3Phase. 0.8 pf, Xd"=10%.

Cummins common practice is advising that using fully rated molded case breaker(s) with thermal/magnetic trip may not protect generator and only molded case circuit breaker with fully adjustable electronic trip unit or other UL listed protective device would be needed to protect generator as required.

I am having a hard time modeling NoArc M5N800T3L (800A, thermal/magnetic) circuit breaker unit with 30 kA short circuit capability to be tripped the simulated Generator Alternator Bolted Fault @6kA for the Arc Flash study, which gives me:
1. Circuit Breaker trip @752.23 seconds of Arc Flash Clearing Time (FCT)
2. 138.3 feet of Arc Flash Boundary (AFB) and
3. 1656.1 cal/cm2 at 18" Incident Energy (IE).

Has anyone had any luck protecting the Diesel Generator System (i.e. Alternator) with the Molded Case Circuit Breaker with the thermal/magnetic trips (both adjustable) only. Any response appreciated. Thanks.


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 Post subject: Re: Generator Alternator Protection with Tthermal/Magnetic T
PostPosted: Mon Jun 24, 2024 5:43 am 
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Joined: Fri Jul 08, 2016 10:01 am
Posts: 323
Location: Indiana
I don't have this breaker in my library to check but Google seems to show it is adjustable.

https://shop.forcesinc.ca/products/noar ... gIBLfD_BwE

Does the breaker in your model have an instantaneous adjustment? If yes, can you lower the setting to get an acceptable trip time?

Do you have the instantaneous even turned "on" in the model. Even if it is not adjustable, I would think 6000 amps would trip well before 752 seconds. Can you post a pic of the TCC?

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 Post subject: Re: Generator Alternator Protection with Tthermal/Magnetic T
PostPosted: Mon Jun 24, 2024 9:41 am 
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Page 40?:

https://www.chint.com/uploads/20220916/ ... 4b862b.pdf

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 Post subject: Re: Generator Alternator Protection with Tthermal/Magnetic T
PostPosted: Mon Jun 24, 2024 2:28 pm 

Joined: Mon Feb 09, 2015 8:48 am
Posts: 3
Hello bbaumer,

The breaker is adjustable, and yet, with the curves you saw, its tripping FCT at arcking current of @1500 Amps is 752 seconds.


1. Circuit Breaker trip @752.23 seconds of Arc Flash Clearing Time (FCT)
2. 138.3 feet of Arc Flash Boundary (AFB) and
3. 1656.1 cal/cm2 at 18" Incident Energy (IE).

Without the ETAP FCT preset.


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 Post subject: Re: Generator Alternator Protection with Tthermal/Magnetic T
PostPosted: Mon Jun 24, 2024 2:28 pm 

Joined: Mon Feb 09, 2015 8:48 am
Posts: 3
Hello bbaumer,

The breaker is adjustable, and yet, with the curves you saw, its tripping FCT at arcking current of @1500 Amps is 752 seconds.


1. Circuit Breaker trip @752.23 seconds of Arc Flash Clearing Time (FCT)
2. 138.3 feet of Arc Flash Boundary (AFB) and
3. 1656.1 cal/cm2 at 18" Incident Energy (IE).

Without the ETAP FCT preset.


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