MEP-002A Left Connected when Main Power was Restored

[Turbinetester]

I was able to test all six diodes without removing any additional covers. I did it by bumping the starter switch and letting the spinning set come to rest until i could reach each one. Three of them correctly passed current from the wire to the threaded stud with no current flow the other direction, and the other three passed current from the threaded stud towards the wire with no current flow in the other direction. Do I test the voltage regulator circuit next?

 

[Guyfang]

I started reading from the top. I have found a place we made a mistake, or a typo.

In post #29 I wrote this.

Roger. That looks good. Now you want to hook up the cable. Then find TB3-5 and TB3-6. You want to measure between those two terminals, on start up. You need to see 24 volts DC there.

In post #30, You answered this.

Running genset gives these measurements inside the AC control box:

L0-X14A4 = 70V
L0-X15A4 = 8.3V
L0-X16A4 = 72V

Across Terminals 3 and 5 on the TB3 gives 115mv DC

I wrote Terminals 5&6. You wrote terminals 3&5. Was this a typo, or is that where you measured?

 

[Turbinetester]

I started reading from the top. I have found a place we made a mistake, or a typo.

In post #29 I wrote this.

Roger. That looks good. Now you want to hook up the cable. Then find TB3-5 and TB3-6. You want to measure between those two terminals, on start up. You need to see 24 volts DC there.

In post #30, You answered this.

Running genset gives these measurements inside the AC control box:

L0-X14A4 = 70V
L0-X15A4 = 8.3V
L0-X16A4 = 72V

Across Terminals 3 and 5 on the TB3 gives 115mv DC

I wrote Terminals 5&6. You wrote terminals 3&5. Was this a typo, or is that where you measured?

I did originally measure at terminals 3 and 5, and i also measure with the engine runnign and the S1 switch in the "Prime and Run position." Several days later I realized my mistake when I was reading back through all the responses as well. I redid the measurement across the correct terminals AT STARTUP and posted the results

Ok, first thanks for sticking with me this far. Second, i need to back up a step, i did not check those two terminals at TB3 for 24V "ON STARTUP". I misunderstood what you meant and was checking them with the generator STARTED and running. My apologies. So I came back out and tested again at TB3-5 and TB3-6 reading only while S1 was engaging all the way to the “Start” position and I do not get 115 mV. I also still do not get 24V, I get around 8-9 VDC. It may be hitting 24 VDC it i cant see it because it’s happening too fast and it’s auto-ranging, but it seems to settle at 8-9 V after about 1 second. I’m not sure what that means but there it is. Where do I go after the A4 board trying to find this 24 VDC?

I did just go back and measure across the terminals 5 and 6 (based on the marking on the panel near TB3 i am measuring the two terminals closest to the outside of the box, farthest away from S1. ) with the engine started and running and I still get something less than 1V, in the 100-200mv range. With the engine running and engaging the S1 switch to the Start position (which earlier in the thread someone said would "flash the field") i still do not get 24V on those two pins. Additionally, flashing the field did nothing to fix the problem. I still get ~60-65V from L0 to L1 and L3.

10:07 EST 12/3: Edited to be more clear in what i measured and the sequence of events.

 

[Turbinetester]

@Guyfang or anyone else still tuning in, what else can i check? Does the low voltage on TB3 Pins 5 and 6 indicate another component that should be tested? Could i hook up a constant voltage power source to those pins and see if that improves the output on L0,1 & 3? I have 2x12v server power supplies i use in series that could provide up to 40A of current at 24v to those pins if needed. I'm not sure where else to go in the TO and nothing looks bad inside the unit except the parst that have been exposed to weather and have started to rust. Thanks for any help!

 

[Guyfang]

@Guyfang or anyone else still tuning in, what else can i check? Does the low voltage on TB3 Pins 5 and 6 indicate another component that should be tested? Could i hook up a constant voltage power source to those pins and see if that improves the output on L0,1 & 3? I have 2x12v server power supplies i use in series that could provide up to 40A of current at 24v to those pins if needed. I'm not sure where else to go in the TO and nothing looks bad inside the unit except the parst that have been exposed to weather and have started to rust. Thanks for any help!

Sorry, been over my head a bit.

If you apply 24 VDC to TB3, Pins 5&6, while the set is running, the main gen should make voltage. If it will not, then the problem is in the Main gen.

 

[Turbinetester]

Sorry, been over my head a bit.

If you apply 24 VDC to TB3, Pins 5&6, while the set is running, the main gen should make voltage. If it will not, then the problem is in the Main gen.

Ok so i'f i'm getting ~60v on each leg now, does that mean applying 24v on those pins should bump it up to 120v? Also, which pin shoudl ahve the + and the - for the 24v?

 

[Guyfang]

The 60 volts should only be inductive voltage I think. Terminal TB3-5 should be pos.

The problem I see, is we have not tested the CT's. Or for that matter not the rest of the output box parts. There could be more then one problem here. When you back fed the gen set, all kinds of things can happen. I supose it it were me, I would try and get a known good output box, and hook it up. That way if it doesn't work, the problem is in the main gen. If this happened to me in the Army, I would have gotten a box to "system check" or pulled every item out of the box and tested it.

 

[Turbinetester]

The 60 volts should only be inductive voltage I think. Terminal TB3-5 should be pos.

The problem I see, is we have not tested the CT's. Or for that matter not the rest of the output box parts. There could be more then one problem here. When you back fed the gen set, all kinds of things can happen. I supose it it were me, I would try and get a known good output box, and hook it up. That way if it doesn't work, the problem is in the main gen. If this happened to me in the Army, I would have gotten a box to "system check" or pulled every item out of the box and tested it.

Unfortunately, i left my working output box in my other pants . I'm still learning the lingo so i'm assuming CT is current transformer. Is there a simple way to test the raw output of the generator, without having a known good output box? Simultaneously, i can work on checking out the CTs. How do i test the CTs?

 

[Guyfang]

(7) Current Voltage Transformer (CVT1). Using
an ohmmeter check three primary windings of
transformer (figure 1-1, 6-7.1 and 6, figure 6-9) by
measuring resistance from terminals H1 to H2, H3 to
H4, H5 to H6, Resistance must be 2.27 ohms ± O.227
ohms. Check resistance in three secondary windings
of transformer by checking from terminals X1 to X2,
X1 to X3, X2 to X3. Resistance must be 1.68 ohms
±0.168 ohms. Check resistance in control windings by
checking from terminals C1 to C2. Resistance must be
9.6 ohms ± 0.96 ohms. If any of the windings do not
show the proper resistance, replace transformer.

( Current Transformer (CT1). On the current
transformer (figures 1-1, 6-7.1 and 7, figure 6-9) only
the secondary windings can be checked. Using an
ohmmeter check resistance in secondary windings by
checking from terminals 1A to 2A, 1B to 2B, 1C to 2C.
Resistance must be 0.5 ohms ±0.05 ohms. If any of
the windings do not show the proper resistance,
replace transformer.

(9) Bridge Rectifier Assembly (A4) (see figure
6-11 ). Tag and remove leads to terminal board and to
each diode (3) separately by checking between terminals
(6) shown in table 6-6. Resistance in one direction
should be very high in one direction and very low
in the other. Measure resistance of R1 (4). It should
be 56 ohms.

 

[Turbinetester]

(7) Current Voltage Transformer (CVT1). Using
an ohmmeter check three primary windings of
transformer (figure 1-1, 6-7.1 and 6, figure 6-9) by
measuring resistance from terminals H1 to H2, H3 to
H4, H5 to H6, Resistance must be 2.27 ohms ± O.227
ohms. Check resistance in three secondary windings
of transformer by checking from terminals X1 to X2,
X1 to X3, X2 to X3. Resistance must be 1.68 ohms
±0.168 ohms. Check resistance in control windings by
checking from terminals C1 to C2. Resistance must be
9.6 ohms ± 0.96 ohms. If any of the windings do not
show the proper resistance, replace transformer.

( Current Transformer (CT1). On the current
transformer (figures 1-1, 6-7.1 and 7, figure 6-9) only
the secondary windings can be checked. Using an
ohmmeter check resistance in secondary windings by
checking from terminals 1A to 2A, 1B to 2B, 1C to 2C.
Resistance must be 0.5 ohms ±0.05 ohms. If any of
the windings do not show the proper resistance,
replace transformer.

(9) Bridge Rectifier Assembly (A4) (see figure
6-11 ). Tag and remove leads to terminal board and to
each diode (3) separately by checking between terminals
(6) shown in table 6-6. Resistance in one direction
should be very high in one direction and very low
in the other. Measure resistance of R1 (4). It should
be 56 ohms.

Ok, finally got enought time when the weather cooperated to get back into the transformer checks. Here are my readings:

CT1
1A-2A .5 Ohms
1B-2B .4 Ohms
1C-2C .5 Ohms

CVT1
C1-C2 9.3 Ohms

X1-X2 1.9 Ohms
X2-X3 1.8 Ohms
X3-X1 1.9 Ohms

H1-H2 1.8 Ohms
H3-H4 1.8 Ohms
H5-H6 2.1 Ohms

So clearly some of the readings are a bit lower than spec. But is that enough to account for the voltage discrepancy?

 

[Triple Jim]

If it were mine, I'd assume you're within measurement error of correct. But I'm going my experience with transformers in general, and not the very special CVT1. (leaving an excuse in case I'm wrong)

 

[Turbinetester]

If it were mine, I'd assume you're within measurement error of correct. But I'm going my experience with transformers in general, and not the very special CVT1. (leaving an excuse in case I'm wrong)

Thats kind of along the lines of where i was thinking, but i have no experience with transformers at all. Could be that anything out of spec from a resistance perspective is indicative of large scale performance changes. I'm getting close to the point of just going out to buy a name brand new deisel generator, but i feel like we have to be close to finding the cuplrit component that has failed and maybe it won't be too bad to change out.

 

[Turbinetester]

@Guyfang just wanted to give you a gentle nudge and see if you had any ideas where i should go next?

 

[Triple Jim]

One has to think along the lines of "What did a huge current spike damage?" Does your reconnect switch work as it should, allowing you to select single phase and 3-phase configurations? The contacts in that switch had to take some abuse during the "event".

Forgive me if this was covered earlier... I'm starting to forget what's been done so far.

 

[Turbinetester]

One has to think along the lines of "What did a huge current spike damage?" Does your reconnect switch work as it should, allowing you to select single phase and 3-phase configurations? The contacts in that switch had to take some abuse during the "event".

Forgive me if this was covered earlier... I'm starting to forget what's been done so far.

Thanks Triple Jim! My selector switch is stuck in the 120/240 single phase mode, and that is new since the power was sent through the gen. But @Guyfang did walk me through testing the actual connections on that switch and the voltage was low even on those terminals.

One has to think along the lines of "What did a huge current spike damage?" Does your reconnect switch work as it should, allowing you to select single phase and 3-phase configurations? The contacts in that switch had to take some abuse during the "event".
Forgive me if this was covered earlier... I'm starting to forget what's been done so far.

My selector switch is stuck in the 120/240 single phase mode, and that is new since the power was sent through the gen. I think either you or @Guyfang asked about that earlier and i think i tested it correctly on the terminals on the switch inside the AC control box cabinet. Here is what i got earlier:

Running genset gives these measurements inside the AC control box:

L0-X14A4 = 70V
L0-X15A4 = 8.3V
L0-X16A4 = 72V

Across Terminals 3 and 5 on the TB3 gives 115mv DC

Is there a way to determine if the selector switch itself is causing the low voltage? Is there a quick way to hard wire the system to remove the voltage selector from the circuits and have it only produce 240v/120v single phase?

 

[Guyfang]

In the Army, I would have had calibrated test equipment. That's one of the big differences between our worlds. Our test equipment were calibrated at least once, if not twice a year. So if a meter read 0.01, you knew that was was there. I simply do not know if your gear is calibrated.

For instance, H1-H2 and H3-H4 are not close to spec, IF your meter is "right".
X1-X2 and X3-X1 are also out of spec. All other readings I would probaly have accepted.

In the Army I would have replaced anything not in specs. At the user level, I would not have tested anything. Simply replaced the AC out put box and gone from there. It was only later at the Direct Support level, when I really TESTED much of these things IAW the -34 TM. We simply did not have the luxury of being able to take the time. If you can not get another AC out put box to do a system check, then I would say to start at the beginning and test every part of the system. Like Triple Jim wrote, "What did a huge current spike damage?"

Even a 003A AC out put box would work for a quick system test.

 

[Guyfang]

Thanks Triple Jim! My selector switch is stuck in the 120/240 single phase mode, and that is new since the power was sent through the gen. But @Guyfang did walk me through testing the actual connections on that switch and the voltage was low even on those terminals.



My selector switch is stuck in the 120/240 single phase mode, and that is new since the power was sent through the gen. I think either you or @Guyfang asked about that earlier and i think i tested it correctly on the terminals on the switch inside the AC control box cabinet. Here is what i got earlier:



Is there a way to determine if the selector switch itself is causing the low voltage? Is there a quick way to hard wire the system to remove the voltage selector from the circuits and have it only produce 240v/120v single phase?

Wire #X1A8 on the S6 should be straight out of the main gen to L1
Wire #X3A8 on the S6 should be straight out of the main gen to L3
Wire #X2A8 on the S6 should be straight out of the main gen to L2

Measure from ground to these wires, on S6. What do you get? If I can read the diagrams right, this should give you 120 VAC?

 

[Turbinetester]

Ok so i checked the three wires as best as i could. I was able to find the terminal for X1 and i think X3 on S6. Both of these registered the same ~65 volts that i was getting on the L1 and L3 lugs. X2 was completely unreachable without removing S6 from the control cabinet which i did not want to attempt. Since these wires were connected directly to the J9 connected at theh back of the cabinet i decided to disconnect the J9 plug with the genset running. Once disconnected I checked every pin inside the connector coming from the genset. I got readings of less than 1 volt on all the female pins inside that connector end. Thinking "That's weird because at least two of them should show ~65v..." i plugged it back in and check the X1 and X3 terminals again, and this time i didn't get the ~65 volts on either. So basically I'm getting nothing on any of those wires now and i'm worried that disconnecting the J9 while the genset was running may have damaged something else entirely as i'm getting no line voltage on X1 or X3 like i was just a few minutes ago. So it seems like whatever problems i have are in the genset itself, not in the control box right? If so what did removing J9 while the geset was running do to drop the voltage output of the genset to 0v?

 

[Chainbreaker]

...My selector switch is stuck in the 120/240 single phase mode, and that is new since the power was sent through the gen.

I'm wondering if the selector switch being stuck, which from your comments above, was not the case before the power restoration event is a symptom that's being overlooked. If that's the case, I would take off the side panel and just loosen the nuts on the wafer switch and spray contact cleaner (Deoxit, or CRC, etc.) on the wafer/contact sections and work the switch back and forth to free it up and break any oxidation points.

If by chance the switch somehow arced or became pitted the switch may be damaged or worst case toast. However, you did indicate in your posts that you tested the outputs off that switch and the outputs were correct if in fact you read the voltages off the correct output wire terminals.

Regardless, a stuck switch can be problematic in that it could have oxidation on the wafers/contacts and lead to intermittent contact behavior.

 

[tobyS]

You might want to check the contacts on the switch to make sure they didn't burn off...

Or maybe the breaker tripped from the reverse feed. Hmmm