itsmoked
Electrical
- Feb 18, 2005
- 19,114
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?