Railroad Generator Breaker discussion.
Railroad Generator Breaker discussion.
(OP)
Situation:
108Hp Turbocharged 4cyl Cummins, approx 108hp.
Nameplate:
55.0kW
68.8kVA
240V 3-Phase
Generator is underslung on a railcar.
It is mounted in an enclosure with a protection circuit breaker.
This circuit breaker originally was a thermal/magnetic 150A 3Ph
breaker. It's relatively large:
8" high, 6"wide, 4"deep; handle 2" long, 1" wide, 1/2" thick.
Making me speculate it's a 600V breaker.
Anyway, it regularly tripped. This required the train to stop so someone could reset it. <big frown>
Someone changed it to a 200A breaker. Now it nuisance trips whenever the car is running in high ambients; 105+.
This breaker, as mentioned, is in the enclosure with the turbocharged diesel, its turbo, its radiator, and the exhaust manifold.
Questions:
1) Why is the factory breaker on this 55kW generator 150A?
Isn't 55kW/240 = 230A?
Isn't 230A/3phases = 76A?
2) Can this scheme ever be made to work based on a breaker in an weather ambient that swings regularly from -30F to 120F meaning the breaker ambient probably swings from 70F to 300F?
3) Any suggestions?
108Hp Turbocharged 4cyl Cummins, approx 108hp.
Nameplate:
55.0kW
68.8kVA
240V 3-Phase
Generator is underslung on a railcar.
It is mounted in an enclosure with a protection circuit breaker.
This circuit breaker originally was a thermal/magnetic 150A 3Ph
breaker. It's relatively large:
8" high, 6"wide, 4"deep; handle 2" long, 1" wide, 1/2" thick.
Making me speculate it's a 600V breaker.
Anyway, it regularly tripped. This required the train to stop so someone could reset it. <big frown>
Someone changed it to a 200A breaker. Now it nuisance trips whenever the car is running in high ambients; 105+.
This breaker, as mentioned, is in the enclosure with the turbocharged diesel, its turbo, its radiator, and the exhaust manifold.
Questions:
1) Why is the factory breaker on this 55kW generator 150A?
Isn't 55kW/240 = 230A?
Isn't 230A/3phases = 76A?
2) Can this scheme ever be made to work based on a breaker in an weather ambient that swings regularly from -30F to 120F meaning the breaker ambient probably swings from 70F to 300F?
3) Any suggestions?






RE: Railroad Generator Breaker discussion.
132A*1.25=165A (Minimum CB size), round up to 200A.
My guess is that the breaker is applied in an ambient temperature far higher than the 40 deg C for which it is rated. Thermal Mag breakers needed to be derated for higher ambients; best bet would be to separate the breaker from the heat.
RE: Railroad Generator Breaker discussion.
RE: Railroad Generator Breaker discussion.
I am bothered by further derating because in cold weather the breaker may actually run at its nominal value providing poor protection.
Anyway I think you guys are correct, the breaker should be moved out of the engine compartment. Even if it's only into a Hoffman box a foot away.
Thanks for the sqrt(3) reminder David! Makes a bit of a difference...
RE: Railroad Generator Breaker discussion.
Does the US code use generator kW for breaker sizing or kVA? Does this explain the 1.25 multiplier to account for the typically-quoted 0.8pf for small gensets?
I agree with moving the breaker away from the engine, and additionally suggest putting an anti-condensation heater and a stat in the breaker enclosure to keep the cold and damp at bay. This is just good practice for electrical panels in cold environments. If the box is a sealed type, put a breather in the base to prevent condensation forming.
The electronic tripping units typically offer much more flexible protection than a thermal-mag unit can: loss of phase (or phase imbalance) and G/F protection are usually included for a relatively small premium over a thermal-mag type.
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One day my ship will come in.
But with my luck, I'll be at the airport!
RE: Railroad Generator Breaker discussion.
The plan is to now remove the breaker and move it into the car's electrical closet 50ft away, which is part of the air conditioned space.
Scotty, the breaker is mounted in the generator wiring box (the sheetmetal hump on the generator) which is never wet when the generator is running and is open 5 ways from Tuesday.
RE: Railroad Generator Breaker discussion.
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One day my ship will come in.
But with my luck, I'll be at the airport!
RE: Railroad Generator Breaker discussion.
http:
I beleive its Siemens JD series Sentron breaker that has electronic trip. So does GE's Spectra series with Microversa trips and Square D or Merli Gerin's with micrologic trips.
RE: Railroad Generator Breaker discussion.
rbulsara thanks for the Siemens link I shall study it.
I'll check the Square D and Merli Gerin's :)
RE: Railroad Generator Breaker discussion.
RE: Railroad Generator Breaker discussion.
RE: Railroad Generator Breaker discussion.
RE: Railroad Generator Breaker discussion.
For this situation it is possible to use some form of differential protection and place the cables from the generator to the switchgear as part of the protected zone. Big sets typically use a true differential scheme with a CT at the neutral end of each winding and another at either the line end or at the switchgear. Small sets tend to save a couple of CTs at the neutral end by employing restricted earth fault protection. A protection relay like Areva's P342 would be well suited to a small set.
David,
Those must be the US breaker range - they're definitely different to the new European range although they have a passing resemblance to the older 3VF series, which itself has an uncanny resemblance to the even older Westinghouse HCMP breakers. The US range is probably more use to Mr. Smoked than the one I was searching for - thanks.
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One day my ship will come in.
But with my luck, I'll be at the airport!