auxiliary generator work done on ge 44-ton – western ...auxiliary generator work done on ge 44-ton...
TRANSCRIPT
Auxiliary Generator work done on GE 44-ton – Western Maryland 75
History and recommendations for 2015
By Robert MacDowell
Western Maryland 75’s battery charging circuits were modernized by a previous owner. This inadvertently removed a protective circuit. Without it, the auxiliary generators hve been overloading whenever an engine is started. This has been destroying generators and regulators at a high rate. A solution has been found but needs to be finished.
GE 44s – two engines, two generators GE 44-‐ton locomotives have two engines. They share one battery bank. The battery bank is 64 volts “nominal” but is charged at 74 volts. They have two auxiliary generators, which recharge the battery. When the unit was built, each auxiliary generator had a mechanical “clack-‐clack” voltage regulator, and some interlocks, including a balancing circuit to assure the auxiliary generators didn’t “fight” each other during operation.
There is also an absolutely critical circuit which disconnects both auxiliary generators when either diesel engine is being started. Otherwise the generator on the running engine would overload itself trying to help start the other engine. This circuit is a very significant factor in the troubles of the last 20 years.
A DC generator has two windings – the field windings around the outside, and the spinning armature windings. Applying current (flow) to the field windings “excites” the generator. As field current increases, armature voltage (pressure) increases. The job of a voltage regulator is to figure out how exciting to be at any moment!
History of WM 75 Western Maryland 75 was purchased in 1994 by SMRS from Railroads Forever in Traverse City, Michigan. When we received the unit, the voltage regulators had been modernized with a transistorized type used on GE “U-‐boat” locomotives. These types cost about $900 to have overhauled. One of the auxiliary generators was burned out, we did not know why. This modernization omitted several interlocks. The auxiliary generator cabinet is inside the cab on the #2 end of the locomotive.
SMRS ran the locomotive with only one auxiliary generator for quite some time. Starting in 2008 there was a flurry of activity. (Please note that the rest of this section is guesswork, from newsletter and member interviews, and may not be 100% reliable.) SMRS replaced one of the auxiliary generators, intending to have both working. In mid-‐
2009, there was a report of “smoking” from an auxiliary generator.1 Since these are under the deck, it was likely a great deal of smoke to be noticed. There were incidents of the auxiliary generator fuses “blowing”.2 Starting in late 2009, member Rob Hall took a look at the fuse problem and determined that the wrong size of fuse was being used. (the correct fuse is 35 amp, and the only other size found on the unit is 60 amp.)
On September 4, 20093, the auxiliary generator #1 was overhauled and replaced. Rob Hall reworked the wiring inside the auxiliary generator cabinet, and replaced the expensive GE transistorized regulators with EMD “black box” types.4 These cost only about $300 to overhaul.
Existing Conditions as of late 2011 In 2011, crews reported that the locomotive pulled poorly, and the voltage meter never went above 65 volts in normal operation and often went below 60 volts. In 2012, Robert MacDowell focused very intensely on this problem. Mr. MacDowell installed a set of gauges to directly observe the performance of the auxiliary generators. He, member Gary Baker, and a friend of Mark Beekel’s also examined the unit and reached the same conclusions.
Neither auxiliary generator was working at all, and had not worked for a long time. When crews saw voltage below 64 volts, that meant the generators were not working. Amazingly, the locomotive was able to function entirely on battery throughout the 2011 and summer 2012 operating seasons, including 3-‐trip Fall Color Tours. Crews and management faithfully charged the battery on a charger every night, unaware this was the battery’s only power source.
The locomotive did not pull very well because of the low battery voltage. The main generator depends on a small “exciter” generator which itself depends on the auxiliary generator’s 74 volt output. Because of this multiplying effect, when the battery voltage was lower, locomotive power was much lower. Both engines were needed, and higher throttle positions were needed as well.
MacDowell and Baker did some testing on generator #1 and determined that it was defective (even though recently rebuilt). Generator #2 had some foreign material on the commutator, but appeared to otherwise work. Both “EMD black box” regulators were broken. One of the regulators was incorrectly installed. 5
1 Email from Cynthia Given, 7/20/2009 and 7/21/2009. 2 Interview with Cynthia Given. 3 Email from Dave Lau, 9/5/2009 4 Railway Express 85, page 2; and Express 88, page 3. 5 Some EMD regulators have 4 terminals instead of 3; those must be installed as described in EMD maintenance instruction MI 9553, and it was not.
The 2012 Diagnostics reveal the problem New gauges
SMRS was able to obtain a replacement EMD regulator. However there was great concern on the part of some SMRS board members that parts kept breaking and nobody knew why, and that we were simply going to break more parts. To troubleshoot a generator, you need to know a great deal about current, and you cannot measure current with a voltmeter. We were all measuring volts and guessing. Voltage is like pressure, but current is flow. To measure flow, the meter must be inline with the flow, which means it must be wired into the circuit.
With that in mind, Robert MacDowell installed a set of gauges in the auxiliary generator cabinet. Here is the gage group. Above, engine #1. Below, engine #2. The left gauge (0-‐30 amps) is generator current and should read between 2 and 20 generally. The center gauge (0-‐100 volts) is generator voltage, which should be 74. The small right gauge (0-‐5 amps) is field current, and we discovered that around 1.0 amp is normal. The field has a 4-‐amp fuse.
In this picture, engine #1 has a good regulator and #2 has a defective one. Pay close attention to the field current gauge on the right. For generator #1, field current is correct, but the other gauges show it is not generating! For generator #2, there is no field current, so naturally the generator is not generating.
Now you see that there is a small voltage on both generators – this is because the generators are spinning. The generator fields are large hunks of iron, and carry some
magnetic charge, that is enough to put a small voltage on the armature. This is a tiny amount of power, and it is used by the regulator to start itself up. (it has no access to battery power because of a diode.) A healthy generator can lose this magnetism, and in that case there’s a procedure called “flashing the generator” to restore it.
Troubleshooting
To start with, Mr. MacDowell spent about 2 days tracing every wire on the locomotive which related to the #1 auxiliary generator circuit. This involved disconnecting each wire at both ends, so that wires weren’t falsely traced, while keeping careful note of how things were assembled. He determined that all the wiring was correct.
Everyone’s diagnosis proved correct when SMRS obtained a new voltage regulator. When Robert connected it to generator #2, it “came to life” and worked normally. Generator #1 did not. Since the other regulators had been tried with generator #2, that meant they were bad too.
SMRS obtained a second spare regulator. This was installed for generator #1, but was disconnected after testing, in case generator #1 is burning out regulators.
Auxiliary generators shouldn’t start engines!
At this juncture, engine #2’s generator works, but engine #1 does not.
Normally you can start either engine on a GE 44, but by convention, SMRS starts engine #1 first and that is firmly enforced. It was unusual that we had engine #2 running, and tried to start engine #1. The new gages on auxiliary generator #2 violently pegged out. It was clear that generator #2 was trying to “help” start engine #1, and was massively overloading as a result.
There is a circuit, #60, which disables both auxiliary generators when either engine is started. That circuit was removed when Railroads Forever upgraded the voltage regulators. That meant whichever engine was started second, the other engine’s auxiliary generator would always overload. Before these gauges were installed, nothing on the locomotive would indicate this was happening.
This explains a lot. It explains the “smoke from the auxiliary generator” earlier reported. It explains why fuses were blowing. It explains why Railroads Forever delivered the unit with a broken auxiliary generator. Since SMRS normally starts engine #1 first, it means generator #1 would constantly suffer this problem, overloading while engine #2 is started. That explains the frequent problems with failures on generator #1.
How severe was the problem? The best evidence is found in a 6-‐gauge wire in the generator #1 circuit, which Rob Hall had installed in 2009. The generator is rated at 30 amps. This wire was code-‐rated for over 100 amps. Mr. MacDowell found the wire was discolored, with black plastic melted into the strands -‐ this was the wire insulation. Clearly the circuit was handling 200 amps or more, cooking the wire and surely the generator as well. They upsized the wires, fuses and diodes to try to stop meltdowns, but this just melted down the generator instead.
The 2012 attempt at Solution When Rob Hall rewired the electrical cabinet, he brought many connections out to a new terminal block. Two of the connections he brought out were wires 60B and 60E, which were part of circuit 60. This is the circuit that disables auxiliary generators during engine startup. However, Rob never hooked these wires up to anything, and there was nowhere on the auxiliary generator wiring to hook it to.
Circuit 60
Figure 1. Circuit 60 as originally built. Follow from the left: circuit 60 comes from control voltage (the left rail) through both engine start buttons. It’s drawn with the controls in the off position, so pressing a button interrupts this circuit, which shuts the generators off. The same kind of interlock is done on the right, with the GS1 and GS2 start contactors (large relays) which are controlled by the start buttons. Yes, it’s redundant, GE did “belt and suspenders”. In the middle, RC1 and A1 worked together.
When Railroads Forever rewired the locomotive, they threw RC1, A1, RC2 and A2 in the trash. Circuit 60 went to nothing at all. The ends were intact but the middle was gone.
In late 2012, Mr. MacDowell updated the circuit as follows.
Figure 2. Robert added two relays called AF1 and AF2. (On these old diagrams, zigzags are coils, not resistors.) These have 36 volt coils, so they are wired in series. The 60B wire was damaged but was fixed in 2015. The diagram has not been updated, but 60C now connects to 60B instead of 21 (always hot). Because of GE’s “belt and suspenders” we were able to get buy on suspenders alone.
You may wonder what RC1, A1, RC2 and A2 did. Here are the diagrams for the generators and regulators, edited in Photoshop to hide irrelevant stuff. This discusses engine 1, but all the same applies to engine 2 as well.
Figure 3: original wiring. It looks scary because it shows the internals of several devices. The RC1 relay coils sensed when the generator was stronger than the battery, and closed the RC1 contact (back on circuit 60) which enabled A1 contact at top center. Note also a bias circuit, #29, which balanced the generators so they didn’t fight.
Figures 4 and 5. Above left is the wiring in 2011. (omitting battery and BR1 resistor for clarity.) The A1 contactor and bias circuit are gone. Diode D1 replaces a lot of stuff – too much stuff as it turns out. Above right is the wiring at the end of 2012, which is exactly the same, but adds 3 gauges for dianostics and a new AF1 relay to disconnect the field.
It didn’t quite work.
Robert’s 2012 approach was not to disconnect the generator, but merely disconnect the generator field with new AF1 and AF2 relays. You saw in the earlier photo what happens when the field has no current. And the field is a low-‐current circuit, typically 1 amp, and fused at 4 amps. Robert used two 30-‐amp, 36-‐volt relays wired in series.
The AF1 relay “tried’, but generators (particularly fields) do not act like resistors. They have a big inductive “kick” that threw an arc across the automotive grade relays. This was somewhat expected, but thought to be worth a try.
How to handle that? One way is a “snubber circuit” – which absorbs the “kick”, but adds complexity and does not guarantee it won’t happen again. The kick may be too severe to solve with a snubber – it is a big generator with a big kick. It’s also possible interrupting the field could cause problems with the regulator. In 2015, AF1 and AF2 were wired in series to reduce arcing, but protect generator 2 only.
The recommended 2015 approach The generator output must be interrupted, which will require a large contactor. Both generators can share the same contactor in this design.
On the left, the 2012-‐14 wiring. On the right, the proposed wiring. AF1 goes away and a new large A12 contactor is added, which disconnects both auxiliary generators (their 21 and 31 circuits) from battery. This A12 contactor is energized by the 60 circuit.
Available contactors and relays
A relay has a magnetic coil, designed for a certain voltage. The coil, when energized, throws an internal switch. The switch can only handle so much voltage or current. It needs to handle a lot more current when switching an inductive load, like a generator field. Like any coil, the field resists changes in current and will spike the voltage, causing arcing. That’s why GE used enormous contactors6 with arc extinguishing features. This can be a problem for automotive grade relays, especially for the generator field.
Automotive relays have coils wound for 12, 24 or 36 volts, and work fine if several same-‐model relays are wired in series to total 72 volts. Robert used Potter & Brumfield T9AP1D52-‐36 relays, which cost $4.28 each. At 30 amps, they are probably too small to replace A1/A2 but may be paralleled.
Electric vehicles need safety contactors on their 300 volt battery packs. They are made in bulk and are “cheap”. We need two (they’re 36 volts) at $200 each for a Kilovac Ev200 series, made to interrupt 500 amps at 320 volts DC.
The original A1/A2 contactors (GE 17CM15CC4) can be had from Western Star for $500. It is wound for 74v so we will need one. It is designed to mount where the diodes are now. The diodes are wildly oversized and can be replaced with much smaller ones.
Damping the generators
Voltage regulators are not designed to drive into an open circuit – they expect a battery there. When we disconnect the generators during engine starting, the regulator could malfunction. My answer is to put a 300 ohm resistor across the generator output to create a “dummy load” of 0.25 amps, and also a capacitor to act like the natural capacitance of a battery. This will also act like a “snubber” to reduce arcing in the disconnect contactor.
Recommended
1. Obtain a GE 16CM15CC4 contactor.
This should be available from companies that scrap GE 44s, such as Western Star. It should be able to bolt up to its original mounting holes in the locomotive. This needs to mount where the current “diode board” is.
2. Downsize the diodes to an appropriate size
The current diodes are far too large, and require a large heatsink that is energized at battery voltage (thus a shock hazard). Much smaller diodes will do just fine, and should be low-‐forward-‐voltage units if possible. Several dual-‐diode rectifiers are made.
3. Add damping circuits to the generators.
Add a capacitor and resistor around the generator output. 6 A contactor is simply a very large relay.
4. Send out the spare auxiliary generator.
SMRS owns a spare auxiliary generator (in the basement of the Clinton building.) There’s just one problem: for some reason, someone removed one of its four field coils. As a result, it is incomplete. The copper wire can be easily replaced by the repair shop. The scarce part is the iron “pole piece” which the coil is wound around. It may be in the basement somewhere.
Then, the generator should be sent out to – specifically – Swiger Coil in Cleveland, division Wabtec (Westinghouse). Electric railroad museums are finding that random local shops do a terrible job, wrecking parts as often as fixing them. Swiger Coil has proven their abilities to the industry and should be used.
5. Swap auxiliary generators.
This is a greasy, messy job – of rotating the generators so the new one ends in the #1 generator position and the currently-‐#2 generator ends back in the #2 position. This should probably be done when we overhaul the fuel pump, as it is in the way.
6. Repair the 60B circuit -‐ DONE