AC/DC mixed consists

I have no idea what the operating rules are today for DC traction units in an MU'ed consist with AC traction units. When the BN purchased all those SD70MAC units, back in the early 1990s, they first had a policy of not mixing the two different types within an MU consist. A bit later, the "policy" was modified that should DC and AC units be mixed in an MU consist, the DC units MUST be in the lead.

After the merger with the AT&SF and the BN, all such "mixing policies" went out the window! Naturally, it didn't take long for an AC & DC MU consist to be assembled with the AC unit/units in the lead, and again it didn't take long for them to burn the traction motors out of the DC unit! Naturally, the Engineer got the blame! So much for proper training of operating crews and motive dispatchers.

Hot Water posted:

I have no idea what the operating rules are today for DC traction units in an MU'ed consist with AC traction units. When the BN purchased all those SD70MAC units, back in the early 1990s, they first had a policy of not mixing the two different types within an MU consist. A bit later, the "policy" was modified that should DC and AC units be mixed in an MU consist, the DC units MUST be in the lead.

After the merger with the AT&SF and the BN, all such "mixing policies" went out the window! Naturally, it didn't take long for an AC & DC MU consist to be assembled with the AC unit/units in the lead, and again it didn't take long for them to burn the traction motors out of the DC unit! Naturally, the Engineer got the blame! So much for proper training of operating crews and motive dispatchers.

Wow.  The first two managerial decisions were reasonable.  The last iteration was just plain ineptness that also set crews up to fail.  Six burnt out DC traction motors would make my Platinum card melt.  I guess then that management’s answer to my question would be: “The engineer cannot ever monitor the trailing DC units; We don’t care anyway; If things break or go wrong we’ll be happy to blame the engineer”.  

A corporate culture filled with positive reinforcement and exemplary leadership values.  

PRR 5841 posted:

Hot Water posted:

I have no idea what the operating rules are today for DC traction units in an MU'ed consist with AC traction units. When the BN purchased all those SD70MAC units, back in the early 1990s, they first had a policy of not mixing the two different types within an MU consist. A bit later, the "policy" was modified that should DC and AC units be mixed in an MU consist, the DC units MUST be in the lead.

After the merger with the AT&SF and the BN, all such "mixing policies" went out the window! Naturally, it didn't take long for an AC & DC MU consist to be assembled with the AC unit/units in the lead, and again it didn't take long for them to burn the traction motors out of the DC unit! Naturally, the Engineer got the blame! So much for proper training of operating crews and motive dispatchers.

Wow.  The first two managerial decisions were reasonable.  The last iteration was just plain ineptness that also set crews up to fail.  Six burnt out DC traction motors would make my Platinum card melt.  I guess then that management’s answer to my question would be: “The engineer cannot ever monitor the trailing DC units; We don’t care anyway; If things break or go wrong we’ll be happy to blame the engineer”.  

A corporate culture filled with positive reinforcement and exemplary leadership values.  

Apparently you have never worked in the railroad industry.

If the DC units were recent-production (in other words, not SD9's), I'm surprised they didn't have some kind of built-in protection that took the generator offline in the event of an overload.  I've heard of the "short time rating."  How hard would it be to incorporate a timer or a temperature sensor, which would allow the crew to use most or all of the short-time rating without catastrophic damage?

Yes, I thought Dash 2 electronics took care of those issues. I watched a CSX freight stall in front of our house (on the old B&O Johnstown branch) because not enough power. [IIRC] three GP40-2s stalled and producing maximum tractive effort. They pulled for 15-20min like that with no damage and moved maybe thirty feet. IIRC the electronics backs-off main alternator excitation to keep traction motor temps within spec. I got to watch wheel-slip control at work. One axle would start to slip and that end of the truck would bounce a bit. Instantly the brakes would apply on that axle and the wheels would stop slipping. Then another axle would do it. I guess they left it wide-open long enough the DS got it through his/her head that they were gonna' have to double the hill, which is what they then did. I walked the track later and there were the tiniest burn-marks you could possibly see. Never hurt those Dash 2s. So what is with this more modern power not able to protect itself, I wonder?

Ted S posted:

If the DC units were recent-production (in other words, not SD9's), I'm surprised they didn't have some kind of built-in protection that took the generator offline in the event of an overload. 

Why would that surprise you? Neither EMD nor GE locomotives, "back in the day", such as SD40-2s and the like, are going to simply "shut down" in the middle of a long hard pull on a steep grade.

I've heard of the "short time rating."  How hard would it be to incorporate a timer or a temperature sensor, which would allow the crew to use most or all of the short-time rating without catastrophic damage?

That would add more clap-trap stuff, which would need to maintained. Again, neither EMD nor GE designed their locomotives to "shut down" on a steep grade. For another example, when an EMD locomotive over-heated in a tunnel, the only thing that happens was; the "Hot Engine" alarm sounded, but the engine does NOT "shut Down".

Hot Water posted:

Again, neither EMD nor GE designed their locomotives to "shut down" on a steam grade. For another example, when an EMD locomotive over-heated in a tunnel, the only thing that happens was; the "Hot Engine" alarm sounded, but the engine does NOT "shut Down".

 

Would the engineer just try to throttle back a bit to help or would/could just that engine be taken off line in extreme instances? (to help protect it with the train still rolling?)

Did they just carry on and hope for the best? Make it out into fresh air for the engine's conditions to get better?

Engineer-Joe posted:

Hot Water posted:

Again, neither EMD nor GE designed their locomotives to "shut down" on a steep grade. For another example, when an EMD locomotive over-heated in a tunnel, the only thing that happens was; the "Hot Engine" alarm sounded, but the engine does NOT "shut Down".

 

Would the engineer just try to throttle back a bit to help or would/could just that engine be taken off line in extreme instances? (to help protect it with the train still rolling?)

No, as that would surely guarantee a stall, i.e.stopped on the grade.

Did they just carry on and hope for the best?

Pretty much.

Make it out into fresh air for the engine's conditions to get better?

Correct. That was the main reason that EMD developed the "Tunnel Cooling System Modification" for the Southern Pacific, resulting in what railfans and modelers call the "SD45T", "SD45T-2", and "SD40T-2" units (affectionally referred to as 'Tunnel Motors'). 

I think the only situation that WILL trigger an automatic shut-down in most locomotives is low oil pressure.  Jack, is my assumption correct?

PRR 5841 posted:

I think the only situation that WILL trigger an automatic shut-down in most locomotives is low oil pressure.  Jack, is my assumption correct?

Correct.

Hot Water posted:

Ted S posted:

If the DC units were recent-production (in other words, not SD9's), I'm surprised they didn't have some kind of built-in protection that took the generator offline in the event of an overload. 

Why would that surprise you? Neither EMD nor GE locomotives, "back in the day", such as SD40-2s and the like, are going to simply "shut down" in the middle of a long hard pull on a steep grade.

I've heard of the "short time rating."  How hard would it be to incorporate a timer or a temperature sensor, which would allow the crew to use most or all of the short-time rating without catastrophic damage?

That would add more clap-trap stuff, which would need to maintained. Again, neither EMD nor GE designed their locomotives to "shut down" on a steep grade. For another example, when an EMD locomotive over-heated in a tunnel, the only thing that happens was; the "Hot Engine" alarm sounded, but the engine does NOT "shut Down".

 

In fact, when GE loco's DC traction motors started to overheat they would indeed start de-rating themselves to the point of stalling if you didn't stop first, put the unit in neutral and rev the engine up in eighth notch to get the T/M blowers going at full blast to cool the motors down. I have had the screen pulled up and watched this happen many times. As the T/M temp gauge went up above a certain point, you could see the HP rating start to drop. If you weren't right at the top of the hill where the lower power would get you over the hill, you had to stop and cool the traction motors before trying to get up the mountain again!

Hot Water posted:

PRR 5841 posted:

I think the only situation that WILL trigger an automatic shut-down in most locomotives is low oil pressure.  Jack, is my assumption correct?

Correct.

 

EDIT:  In fact there are a number of "events" that will cause the prime mover to shut down, besides low oil pressure:

1) Loss of vacuum in the crankcase, will trip the "CCOP" protector, which causes the governor to see "low oil pressure" and shut down.

2) The "Low Water" protector will also cause the governor to see "low oil pressure" and shut down.

3) The "hot oil" device also causes the governor to see "low oil pressure" and shut down.

4) The engine over-speed trip, which is a mechanical counter-weight system mounted on the camshaft gears at the front of the engine, which causes a shut down.

Hot Water posted:

Hot Water posted:

PRR 5841 posted:

I think the only situation that WILL trigger an automatic shut-down in most locomotives is low oil pressure.  Jack, is my assumption correct?

Correct.

 

EDIT:  In fact there are a number of "events" that will cause the prime mover to shut down, besides low oil pressure:

1) Loss of vacuum in the crankcase, will trip the "CCOP" protector, which causes the governor to see "low oil pressure" and shut down.

2) The "Low Water" protector will also cause the governor to see "low oil pressure" and shut down.

3) The "hot oil" device also causes the governor to see "low oil pressure" and shut down.

4) The engine over-speed trip, which is a mechanical counter-weight system mounted on the camshaft gears at the front of the engine, which causes a shut down.

Excellent info, thanks.  Apparently you HAVE worked in the railroad industry.  
(I already knew that based on your very entertaining “Notch 6” podcasts.)

BIG JIM,

Back in the day when NS, was an 'all DC railroad' and AC units were starting to be used by other roads, did you ever have to handle a consist with a run-through power AC unit on point?

Did you just figure it out as you went along?

EMD posted:

BIG JIM,

Back in the day when NS, was an 'all DC railroad' and AC units were starting to be used by other roads, did you ever have to handle a consist with a run-through power AC unit on point?

Did you just figure it out as you went along?

EMD,
Yes, I guess in a way that I did, although I never thought of it that way. My first experience with AC units were with a set of CSX units and as you say, I figured it out as I went along...just as everyone else had to do. No big deal, there really wasn't any big difference in how they operated.
The one thing that stood out was that the dynamic brake would hold all the way down to almost stopping! That was very impressive! Much more so than any extra tonnage the units were able to haul. 

 I don't have any real RR experience, as you know. I think that we can look back at the change over to AC units as a big deal. I compare it to the original dismissal of diesel units from the steam era. There were RRs that seemed to deny any benefits of using or switching over to AC units. I can only get an idea of what really happened thru reading what's out there.

 It sounded like CN and NS, were two of these big RRs that refused to accept the new tech? I have to imagine there were more including smaller roads. Like the time when steam was the tech, I'm guessing some RRs didn't wish or have the ability to switch over as their assets were tied to what they already owned and ran?

 So to me, the end of the SD60(MAC?) production (test units?) and all of the SD70MAC engines marked the new era and I believe should be thought of as important engines in history. I have to reread GE's production. I believe it was their AC4400's that represented their entries? I'm not sure what other model they first offered or tested in AC? I just remember reading of the tests out of the coal river basins using the EMDs. I don't know the full history.

 Again I'm just a hobbyist and was not part of any RR.

BIG JIM,

Thanks for the reply.

Many years ago, in a diesel locomotive book, I had read that if an engineer would start an AC unit by going directly to notch 2, that the locomotive would 'surge and buck like it's going off the rails'

I guess that is an exageration

EMD posted:

BIG JIM,

Thanks for the reply.

Many years ago, in a diesel locomotive book, I had read that if an engineer would start an AC unit by going directly to notch 2, that the locomotive would 'surge and buck like it's going off the rails'

I guess that is an exageration

Ya think???

EMD posted:

BIG JIM,

Thanks for the reply.

Many years ago, in a diesel locomotive book, I had read that if an engineer would start an AC unit by going directly to notch 2, that the locomotive would 'surge and buck like it's going off the rails'

I guess that is an exageration

Well, depending on the grade, starting out in fifth notch (even jockeying to sixth) may be needed just to get a heavy train started...in the right direction!

PRR 5841 posted:

I was wondering about the mixing of AC and DC locomotives in a consist.  During prolonged slow-speed/high-current operations, and assuming the DC unit(s) are trailing, how does the engineer in the lead AC unit know and respect the traction motor limitations of the DC unit(s) which cannot endure anywhere near what an AC unit can.  

Every DC locomotive has a continuous rating for traction motor current, which is usually marked on the ammeter.  As locomotive development increased horsepower through the 1940's through the EMD Dash-2 and the GE Dash-9 era, the electrical components became more durable and the continuous rating increased.  An F7 could run all day at 750 amps and an SD40-2 could do the same at 1050 amps.  Depending on the gear ratio, locomotives would hit the continuous rating at a particular speed.  So, when speed dropped on a hard pull, amperage increased until the continuous rating was reached.  On a freight F7 that would be around 13 MPH, but it would be 18 MPH on a passenger F7 and 11 MPH on an Alco-GE RSD-5.  An E8 would have a minimum continuous speed of around 24 MPH.

The railroad furnished the minimum continuous speed for each class of its diesel locomotives to employees in the timetable Special Instructions, and the Engineer was governed by the continuous speed for the weakest locomotive, regardless of its position in the consist.

It works the same way today.  And it's a good thing, too, since DC locomotives have a gauge showing amperage, whereas AC locomotives show kilowatts. 

I believe on the Dash 8's you could change a screen (there were three, two for the engineer and one for the fireman (helper)) to show TM amps.  With the Dash 8, there are protections in place so that as traction motor thermal limits are reached, the motor amperage is capped.  This changes.  For example, in low ambient temp conditions the TM cooling air is colder and the motors have more thermal capability.  Similar for altitude, where denser cooler air is available near sea level.  Tunnel operation is another variable, depending of course on the length of the tunnel.  Staring with the Dash 8, GE introduced several new features.  For example, if a motor goes to ground, there is no or truck TM disconnect switch, the control system will isolate that motor and provide a msg to the operator.  The system will even detect and try to dry out a moisture ground anywhere in the motor or braking system by passing a nominal current through it.

I am amused by the MTH ad that states that the SD70 has the piping on one side of the platform and the cabling on the opposite side to aid maintenance.  GE has done this "forever", starting with the U25B in 1963.....

Re operation using units with differing MCS (minimum continuous speeds), I remember when the PRR operated an E7 or E8 equipped passenger train into Erie, as Trains 580 and 581.  That train was always assigned an Alco RS3 helper to get out of the lake basin and south.  The RS3 helper engineer burned up a number of traction motors on the two unit "E"'s on one winter trip with the single RS3 in lead, and local management rode several trips to "reacquaint" the helper crew with the limitations of passenger power on grades.  The local volunteer fire department gained considerable publicity as a result of this problem.  Once you leave Erie and are about three miles south of town, it gets pretty rural.....

  At one time the NS put a bulletin out to have the smaller DC units in the lead. When I first started to run I was told the N&W had the same instructions  ,and  according to my late Dad the C&O done this also.

 Shortly after the NS merged with Conrail and we started experiencing the AC units there was a bulletin out saying "managers" and crews should try to have AC units ahead of DC .

 With todays tonnage and unit rating instructions on our orders , the orders specifically tell us according to our tonnage and our train route , what units in the consist we are to have online from point A to point B .

 The technology is there now for the consist to start dropping units "out"  that you have online while en-route , but I'm not sure if it's being utilized .

 AC's has been a learning curve for the railroads and  crews alike.

 The AC's have had software changes that has helped the "chattering" of the wheels going into dynamic braking and the "surge" that Engineer's have experienced like  mentioned when starting a train out on grade.

 Now with more trains using DP power in the middle  or on the rear some of this AC problems have been eliminated making the trains smoother starting out and operating down the road.

 There's still bugs and learning curves even with the DP trains , especially when using PTC . 

 But the units both AC and DC will limit themselves on amperage when they get hot due to prolonged continuous  amperage or simply will quit loading  . The only way you can see while on the move the information on trailing units such as amperage  , is if the units are say all newer GE's ,then I have seen the lead units computer show you another GE units information . You just cannot "manage' it .Again I believe the technology is there to do so but at this point were not using it on the NS.