Generator/DSLC Question 1

[safspir]

As some of you may have surmised, I work for an agency which operates marine commerce vessels. Please forgive me for not providing additional details, as I am in a very politically charged situation.
I was called in to troubleshoot an event which popped up recently. The vessel normally runs with a 200kw Vital Generator sharing via a bus tie the load with an 800 kw Ship's Service Generator. The event was a reported simultaneous opening of the Vital circuit breaker, opening of the tie breaker, and a high current trip of the SS breaker. My understanding of the system is that in the event of a Vital failure, the tie should remain closed and the SS takes up the load. The sharing is controlled via a DSLC unit.
Prior to my arrival, the steps taken were a megging of the vital gen, a wiring "tug" test, and a controlled running of the vital only, carrying full load until the excitation current of propulsion generators exceeded the vital's capacity. The details provided were a bit hazy. Beyond that there were no failures noted.
I looked over the system (don't get out of the office much anymore), and the only anomaly I found was that the contacts of both the SS and vital "circuit breaker open" push buttons were all over the place. That is, for a NC contact, with control wiring disconnected, I was getting between 0.4 ohms to over 800 ohms. I replaced the contacts and ran the plant in normal operating mode for over an hour. No problems, even load on all phases.
To complicate things just a bit, I searched through the MicroLogic units for history and found nothing. Unfortunately, the batteries/time stamps were at default. (PM anyone?) Actually, I did find the SS showed a trip fault of 1700 amps, but no time/date stamp.
The alarm/monitoring system showed only a multitude of faults related to the loss of power generation.
Wish I could give you more info on this, but I must tread carefully.
A question lingers in my mind....is the DSLC looking for purely binary input, and could the introduction of a variable resistance have an effect? Perhaps I am way overthinking this, and am off on a strange tangent. I suggested sea trials under full load to replicate or not the occurence. Management has ordered a megging of the individual windings of the vital. Huh?
Anyway, random thoughts will waiting for the SO's new kitchen paint to dry enough for a second coat!
Also, would like to say that I have enjoyed immensely belonging to this group. I have learned so much just by following the threads here. A special shout out to Waross and CatServ for their awesome contributions. You guys are my idols, and I've been in this industry for 40+ years. Think I would have learned something by now? LOL!
So, if anyone has some input in their spare time, it would be much appreciated. Thank You. Retirement in 523 days. But who's counting?

 

[dpc]

I'm not sure why the DSLC would be the prime suspect. Sounds more like miscoordination between the circuit breakers. Have the breaker settings been reviewed?

 

[waross]

One thing to suspect is an out of phase closure of one of the breakers.
That could trip all three breakers.
Possibly a drop out and re-closure of the tie breaker?
Could the vital generator have been closed in out of sync?
The high contact resistance could have played a part in this.
Does the sync check relay drop out of the circuit after a successful closure?
Thanks for the kind words.
Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[safspir]

Thank you for the responses. (DPC) One of the first things I did was ask for the breaker settings. The CG 835 also questioned this. These were not available onboard. However, this would not seem to account for it running for a long time without issues.
(Waross) I will check to see if there is a record of this. I will also inquire about the sync relay. Perhaps if the out of sync scenario had indeed happened, it might explain why the trips happened when propulsion excitation increased. Contact resistance has not been checked, as we do not have the equipment to perform a loaded resistance check.
I will keep you all updated when the accepted RCA has been published.
Thanks again for your input. Your knowledge and discretion is highly valued. The best thing this outfit could do would be to keep one of you on retainer. Less costly than missed sailings. IMHO.

 

[davidbeach]

Badly coordinated breaker settings can lay dormant for a very long time. All may work perfectly well over the broad range of load plus some fault conditions. Past performance is no predictor of future performance. Give it the right conditions and an otherwise benign set of miscoordinations becomes a bomb waiting for the fuse.

 

[catserveng]

Still hard for me to picture the exact setup, so the Vital Gen and the Ships service gen both have DSLC's, right? What device manages the tie breaker?

Normally the DSLC's breaker OPEN and CLOSE outputs are wired in parallel to any other breaker operating circuits, but if the breaker opened for some reason and the DSLC inputs are asserted to make it want the breaker closed, it will try to reclose as long as the paralleling parameters are met.

Is there anyway you could maybe provide a single line of the ship's power system?
Is this a diesel electric vessel?
How many actual busses? Last research vessel I was on had four busses, propulsion, "house", "lab" and emergency. Since any of the 6 generators could feed any bus, it was quite an arrangement.
How many generators? are DSLC's used on all generators?
Any MSLC's in the mix?

How familiar are you with the DSLC controls? There are a lot of settings and not all features are used in all applications. I have some training material on them if the manual doesn't provide the info you need.

MikeL.

 

[dpc]

As David said, miscoordination often happens only for certain magnitudes of fault current. In this case, if the ICCBs have instantaneous trip elements (required in US), if there is enough fault current, they can all trip.

 

[waross]

I understand that a fault was not found. It could have been a one-time fault such as rodents between some bus bars in an out of the way place.
If a fault location can not be found then I would check if an out of phase closing of one of the breakers is possible.
Are there any breakers not controlled by the sync check device?
If you can not support an out of phase closure after investigation, then look harder for the location of a flash-over or other one-time fault.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[safspir]

Thank you all for your input to this thread. Found the culprit last night. Actually it was several things which led up to a chain of events. First off, circuit breaker settings were too low. This contributed to the drop out of all three. The initiating problem turned out to be dirty power feeding back from aging propulsion generator exciters. There is a Crompton protective relay which tripped out when reaching a certain level of excitation. I could visually see this after attaching a scope to the sensing power leads on the relay. It was one very ugly, spiky waveform near the trip point. We achieved a temporary work-around by bridging the contacts of the relay, and programming the Micrologic trip unit on the CB to take over this function. Now it is up to the powers that be (and the CG) to determine which permanent path to take. I can think of three options: 1) Stay with the Micrologic setup, 2) Install filtration on the sensing leads coming from the PT's, or 3) rework/renew the exciters to eliminate or at least reduce the noise to levels acceptable to the protective relay. Joys of old boats and delayed PM's! Thanks again for all of your great ideas.

 

[itsmoked]

I would caution you that I see bigger problems around the bend, of course, during high seas with crossing waves and storm force winds. That is the generator exciter(s) is/are failing. The trips are just a harbinger of imminent failure and the spiking nasty waveform are a cry for help. Rectifiers are failing or capacitors or the commutator or the brushes - something needs attention.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[safspir]

Thank You Keith,
I share your concern here, and have passed along said concerns to the "uppers" in charge. Not sure when it happened, but it twas a sad day when the politicians and bean counters took over maintenance priorities.

 

[edison123]

Congrats on finding the culprit the old fashioned way.

Muthu

http://www.edison.co.in

 

[waross]

Thanks for sharing your solution with us.

Bill
--------------------
"Why not the best?"
Jimmy Carter