The one way generator problem.
The one way generator problem.
(OP)
I have a problem with two private railcars. Let's call them "A" and "B".
Each car has several ways to be powered.
1) 52KW generator: 240Vac 3Ph. Delta
2) Shore power: 240Vac 3Ph. Delta
3) HEP (Head End Power from locomotives) 460Vac 3Ph. Delta
In each car there is a 240VAC 3Ph. bus that feeds everything. This includes refrigeration, (railcars are essentially refrigerated as apposed to "air conditioned") and heating loads that are all 3Ph loads.
To create the 120V 1Ph power car A has a bank of three dry type transformers hooked in delta on the 240V side and star on the 120V side creating the neutral. (208V L-L)
The B car also has a bank of dry type transformers that are hooked up to the 240V 3Ph as delta and on the LV side as 120V 3Ph delta. That's line to line 120V. This is to run existing 120V 3Ph motors. This gives 55Vac to ground
from any phase. Outlets are Line-Line to get 120V out of them.
The 460V HEP comes in thru a plug to a bank of transformers to be dropped to 240V to feed the buses.
The shore power feeds the 240V bus directly.
They each run independently perfectly well on HEP, or shore power, or on their respective generators.
That's the set up.. Here's the problem. These cars can find themselves entrained anywhere, in any weather. Not infrequently they are grouped out of reach of HEP in freight service,(no HEP), or in passenger service, (HEP) but at the back of a train behind "express baggage" cars meaning they have been cut off from the HEP by high speed box cars. This means they must run on generators. The environment these cars find themselves in is so physically violent and temperature abusive that on a regular basis they lose generators. This can be from snow packed radiators,blowing leaves, 130 degree, -40 ambients, adverse wind from motion, physical slamming, etc ,etc. It has become obvious that the ability to run both cars from one car's generator would greatly increase reliability and power availability.
To test this the HEP cables were connected between cars A and B. Car A's generator was run, the lock out system was defeated connecting car A's bus to the HEP transformer bank while the generator was feeding the buss. This is normally prevented for obvious reasons. Next car B was selected to get HEP power, (artificially created by car A feeding backwards thru its HEP transformer bank. All worked as expected NO surprises.
However, if the same exact procedure is followed in reverse with car B's generator driving car A's 240V bus everything is fine until ANY load of ANY kind is applied to car A's 240V bus. This truly hammers car B's generator! It goes from steady state no load, to no rotation, in about 2 seconds sometimes the breakers go, sometimes not.
We thought there may be some HEP transformer bank "situation", (tho we can't think what),so we instead linked the cars with a shore power cable. This resulted in exactly the same result.
This is baffling me.
Ideas?
Each car has several ways to be powered.
1) 52KW generator: 240Vac 3Ph. Delta
2) Shore power: 240Vac 3Ph. Delta
3) HEP (Head End Power from locomotives) 460Vac 3Ph. Delta
In each car there is a 240VAC 3Ph. bus that feeds everything. This includes refrigeration, (railcars are essentially refrigerated as apposed to "air conditioned") and heating loads that are all 3Ph loads.
To create the 120V 1Ph power car A has a bank of three dry type transformers hooked in delta on the 240V side and star on the 120V side creating the neutral. (208V L-L)
The B car also has a bank of dry type transformers that are hooked up to the 240V 3Ph as delta and on the LV side as 120V 3Ph delta. That's line to line 120V. This is to run existing 120V 3Ph motors. This gives 55Vac to ground
from any phase. Outlets are Line-Line to get 120V out of them.
The 460V HEP comes in thru a plug to a bank of transformers to be dropped to 240V to feed the buses.
The shore power feeds the 240V bus directly.
They each run independently perfectly well on HEP, or shore power, or on their respective generators.
That's the set up.. Here's the problem. These cars can find themselves entrained anywhere, in any weather. Not infrequently they are grouped out of reach of HEP in freight service,(no HEP), or in passenger service, (HEP) but at the back of a train behind "express baggage" cars meaning they have been cut off from the HEP by high speed box cars. This means they must run on generators. The environment these cars find themselves in is so physically violent and temperature abusive that on a regular basis they lose generators. This can be from snow packed radiators,blowing leaves, 130 degree, -40 ambients, adverse wind from motion, physical slamming, etc ,etc. It has become obvious that the ability to run both cars from one car's generator would greatly increase reliability and power availability.
To test this the HEP cables were connected between cars A and B. Car A's generator was run, the lock out system was defeated connecting car A's bus to the HEP transformer bank while the generator was feeding the buss. This is normally prevented for obvious reasons. Next car B was selected to get HEP power, (artificially created by car A feeding backwards thru its HEP transformer bank. All worked as expected NO surprises.
However, if the same exact procedure is followed in reverse with car B's generator driving car A's 240V bus everything is fine until ANY load of ANY kind is applied to car A's 240V bus. This truly hammers car B's generator! It goes from steady state no load, to no rotation, in about 2 seconds sometimes the breakers go, sometimes not.
We thought there may be some HEP transformer bank "situation", (tho we can't think what),so we instead linked the cars with a shore power cable. This resulted in exactly the same result.
This is baffling me.
Ideas?






RE: The one way generator problem.
This is something I do not understand: "That's line to line 120V. This is to run existing 120V 3Ph motors. This gives 55Vac to ground
from any phase."
With a delta secondary, I would not expect any significant voltage line-ground. At least not that can be loaded. And if all capacitances are symmetrical, I would expect around 70 V in a three-phase 120 line-line V system. Could that be a clue?
RE: The one way generator problem.
RE: The one way generator problem.
Draw complete wiring diagram and trace the issue. Review each gen and tranfromer winding configuration and phase markings.
RE: The one way generator problem.
RE: The one way generator problem.
You're right, the math sez 70VAC I have not checked to see if the measured value is just capacitive leakage or "real" current.
I will soon be able to.
e5fornow,
Remember, the car with the 120-3Ph motors can be run by the "other" car. It can not itself run the other car. So even though car B has the weird 120-3Ph it can be run by the other car just fine.
We keep thinking phase rotation too... but all the motor loads we have can be run backwards and will in fact draw less in this state!! Fans, blowers, etc. The refrigeration compressor can be run backwards also briefly, (oil pump). So we don't see why a phase reversal would cause the generator to be hammered.
rbulsara,
Why would reverse phase cause "a locked rotor" condition? This car is dead until HEP is selected so there is no
rotation present at the time of power up. Or am I missing your point?
I agree a phase map isn't a bad idea!
Your second point is that somehow in the effort to "jury rig" these systems the A car's generator may still be
online and power up is essentially trying to motorize a 52KW generator into turning the diesel over? Hmmm
that makes a certain kind of sense as we can think of no other load capable of hammering B car's generator
without being obvious, (breakers, smoke, etc). We'll look into that too.
Thanks for the thoughts!
RE: The one way generator problem.
I meant to say that the symptops are of a locked rotor condition or heavy current draw and you are coorect that not all motor loads creat locked rotor conditions in reverse. I thought may be some of your loads can not run in reverse without some intervention.
Good luck with your trouble shooting.
Do the loads on B bus work ok, while on B gen with voltage available on unloded A bus or you don't even reach that point?
RE: The one way generator problem.
RE: The one way generator problem.
You would still need the 240 volt the 480 volt transformers to run on 240 volt shore power.
Your generator that does not want to power both rail cars seems to have an internal or nearby ground fault that interacts with a ground fault in the othe rail car.
RE: The one way generator problem.
The same running generator runs its own car just fine. It's when you're standing in the other car and load its 240 bus that the sky falls. So I still am wondering how that could effect the other car's DC generator control.
mc5w; Changing the bus to 480 would require junking of a whole bunch of contactors and a few transformer banks at present. Also the 240 generators would then have to run everything thru a transformer bank instead of the big loads directly. The normal 480 supply is 3000HP Inverter that seems to have no problems doing the job. It does trip out on ground faults and won't even energize if senses one.
Either and both of these rail cars are run by the HEP without any GFI complaints. I do wonder how the Head End Power source even knows there is a ground fault because there is NO ground wire passed thru the massive cables that run the length of the train on both sides.
I was wondering if there could be some ground fault that causes these two cars to have this problem. They each weigh about 100 tons and are sitting on polished steel rails that essentially connect them together.
Also the two cars were hooked up 240 bus to 240 bus directly bypassing the 480 transformers with the same negative result.
RE: The one way generator problem.
RE: The one way generator problem.
Thanks for jumping in.
This is in no way solved yet. We just missed a bullet.
The cars are in service thru snow country 4 trips a week
and unavailable for testing. The "A" car just blew it's
supercharger and a lot of stress came up fearing a non-HEP
return with 45 passengers (no power) but HEP was luckily
available allowing time for a replacement blower to be
installed.
No one has been standing near A's generator.. This is a
great bit of info! We will have someone stand there the
very next opportunity we have for troubleshooting this.
No digital display, but we have ammeters on all three
phases.. I don't remember if they display properly during
one of these jury rigs I will check. After these checks
we will be lifting connections.
Once we get a troubleshooting opportunity I will feedback
to this thread.