Cycloconverter Upgrade info

[mchaisson]

Hello all

I am new to this site. I have currently been tasked with developing a budget/project scope for upgrading a cycloconveter drive on an ocean going icebreaker.
I am looking for similar type upgrades that can give an idea of the type of equipment out there. Due to privacy/competition rules where I work I am expected to come up with a realistic budget figure for a drive upgrade. I am not allowed to contact possible vendors for information/pricing as it would be viewed as those companies having prior advance notice of contract and having unfair advantage over other companies. The main companies from my research are GE/Converteam, Siemens and ABB. There are some smaller companies that may be able to perform the work but are not known to me.

The current drive was installed in 1987 and has been quite reliable. Spare parts however are getting harder and harder to obtain . The drive is fed from 2 4160/1200volt transformers and outputs a max of 1900volts at 18HZ to a 8000HP Synchronous motor. The existing system consists of a control module which fires thristors through the use of fiber optics. The control scheme is very similar in scheme to a rolling paper mill drive of the same size with the main difference being the drive can operate from 25-180RPM in either direction. The system also uses a brushless exciter. There are two of these drives used, a port and stbd of the same size and configuration.

The system bus is fed from 3 5MW 4160 diesel generators.

From my viewpoint I have several options from lowest cost to highest:
1) Upgrade the existing control scheme including the firing circuits
2) Upgrade the control, firing circuits and power package (SCR's) in the existing cabinets
3) Upgrade the drives with COTS(commercial off the shelf) utilizing the existing voltages
4) Get rid of the input transformers and connect directly to the 4160 bus with new COTS drives( possibly 2 in parrallel), retain the 1900volt motor voltage
5) Same as option 4 but rewind propulsion motors to a higher voltage or replace motors.

I know that this is a tall order, but if anyone has gone through anything similar, any pertinent info would be great.

Thanks

Mike

 

[jraef]

Cycloconverters are a dying breed, in short order you may find that nobody will make and support them any longer. That's not the case yet, but marine propulsion is about the only remaining use and even there they are being replaced with more readily available and supported drive technologies.

I'm not sure you will need to change anything with regard to the motor voltage, because your output is only 18Hz at 1900V. That may easily correspond to a somewhat standard base motor design. If we look at 1900V at 18Hz that is approx. 105 V/Hz, so if we extend that out to 60Hz, that is 6300V. So your motor might be a 6300V 60Hz base design (typical for 6600V power systems and very common on marine propulsion). However I'm not sure if you mean it is producing 8000HP at that speed, or that is the base motor design HP of the motor at it's rated full speed. You will have to confirm that by looking at the actual motor nameplate data. If that is the case, you can easily retrofit what you are referring to as a 'COTS' drive (at MV, no drives are really Commercial Off The Shelf, but I know what you meant) without the need for any additional transformers or motor rewinding.

"Will work for (the memory of) salami"

 

[mchaisson]

Hello

The motor does produce up to 8000Hp at 180Rpm or 18Hz. It is not able to run much beyond that speed due to damage that would occur from centrifigal forces. This is very basic desciption of course. I understand nothing of that size is COTS but as it stands now we have the only 2 versions of that drive ever produced. It was a special one-off design. The interest from the OEM is no longer there to maintain the drive.

We want to stay away from going this route again. An example of drives I have been considering would be Siemens SL150 series and GE/Converteam MV7000 series type PWM drives in that HP range

 

[Drivesrock]

Hi mchaisson.

I would say that you have correctly identified in order of cost your options. Added to options 3, 4 and 5 will be the considerable shipyard cost of removing the existing equipment and installing the new - especially if the hull has to be cut open. This will be typically more than your most expensive option of replacing equipment - transformers and the drives. And, of course then there's the downtime of the vessel.

Three questions immediately come to mind;

1. Do you need a more powerful propulsion system to warrant a new drive, transformer and motor?
2. Can the power thyristors and exciter diodes still be sourced easily? or
3. Based on thyristor/diode failure rates over yr many years of the equipment how many do you have in stock for another similar period of use?

(which "spare parts are getting harder to obtain"?).

Cycloconverters may be 'a dying breed' for new drive options but the three companies you cite should be able to provide you with an upgrade path for the existing equipment and especially if it is one of theirs already. These upgrades may quite possibly be based on control H/W that is used in their current drive offering so they will have engineers familiar with the H/W.That would be preferable. All that will be different is the basic S/W and perhaps thyristor gate pcbs. Thus making spare parts easier to source for sometime to come.

If you don't need more power and you can still source the thyristors and diodes your cheapest and quickest option overall by far will be an upgrade. You won't have any issues to overcome about a PWM drive on an existing motor too, for example.
And the new control H/W may be able to provide new features as standard, such as fibre-optics in the firing circuits, increased diagnostics down to individual thyristors, remote access and others.

In my experience an upgrade might take 20-25 days (forgetting nights). That's 7 days for stripping down and installing the new H/W by good wiremen and a supervisor. Perhaps some seven days commissioning (two engineers) and then running/startup with integrated tests to automation and DP systems that you might have ready for seatrials and handover.

A) Do your existing transformers have pre-magnetization to eliminate the 4.16kV inrush? Might be good to include if possible.
B) Are harmonics an issue that a change to the transformers could be justified?
C) To conform to latest Class requirements you may need individual protection relays on your main transformers secondaries. This means CTs right on the output of the secondary windings.
D) Anything else like cooling method issues?

I have been on the other side - commissioning upgrades.

 

[mchaisson]

Hi Drivesrock

To answer your three questions:

1) The power is fine for the application. More power of course would be nice but then the hull strength, shafting, propellors and available power from the Propulsion generators come into play.

2) The power Thyristors can still be purchased ( long delivery, 3+ months ) Exciter package about the same.

3) The largest issue is that the control section ( controls firing of the Thyristors), the first digital drive ever produced by that manuafacturer is no longer interested in producing spares. We have what we have and that is it...

A) The existing transformers (2 per drive) port delta/delta, stbd delta/wye ( done this way to help with harmonics) do not have pre-magnetization.
B) Harmonics reduction would be a secondary benefit of going with a newer PWM drive but not a nessesity.
C) The existing transformers have differential protection and this will be upgraded as well from the existing FPE scheme.
D) There are no cooling issues

The time frame for the install is not a problem as this will be part of a larger upgrade/downtime 8-10months for the vessel. Having to cut a hole in the ship which sounds bad is not something to be scared of. In this instance only a ballast tank is in the way, with minimal piping and non-essential wiring etc associated.

One of the biggest issues of going with another custom upgrade is 3-4 years down the road, being back in the same situation( no parts support). We have been very lucky in that we have some very talented service personnel on staff that have been able to repair the existing scheme.

So far I have some budget figures in mind, from some other similar jobs I have come across of smaller size and have adjusted for inflation and increase in horsepower
1) Upgrade the existing control scheme including the firing circuits ~ 3.5 Million US
2) Upgrade the control, firing circuits and power package (SCR's) in the existing cabinets (more up front engineering)~ 6 Million US
3) Upgrade the drives with COTS(commercial off the shelf) utilizing the existing voltages ( Less engineering) ~ 7 Million
4) Get rid of the input transformers and connect directly to the 4160 bus with new COTS drives( possibly 2 in parrallel), retain the 1900volt motor voltage ~ 9 Million
5) Same as option 4 but rewind propulsion motors to a higher voltage or replace motors. ~12Million

Do these figures seem realistic?

Regards

 

[rhatcher]

The presence of the two transformers per propulsion motor indicate that you have either two VFD drives per motor or a single VFD drive with two input rectifier sections and one inverter section per motor. This is done to reduce harmonics on the power source and the other loads, if any, that are operating on the same generators.

So, the question is; are the generators dedicated "propulsion" generators or are they also "ship service" generators? If they are dedicated propulsion generators then you may be able to eliminate the dual transformers and accept a single six pulse rectifier input section to power a single new VFD (per motor). The question here will be whether the heavy harmonic content of a six pulse input rectifier will interfere with the voltage regulators.

If the generators are dual purpose and supplying both propulsion and ship's service, then you probably will be forced to have some sort of dual transformer / dual input rectifier setup (12 pulse rectifier) to reduce harmonics to an acceptable level for the other ship's service equipment.

I cannot offer specific advice or evaluation of your budgetary figures. However, I will say that, IHMO, there does not seem to be an obvious benefit to rewinding (to a higher voltage) or replacing the existing motors. This is true even if you can eliminate the transformers and operate with a 4160V VFD.

If you do keep the existing motors, I will strongly recommend having them pulled for complete testing and service during the yard period.

 

[ScottyUK]

rhatcher,

The existing cycloconverter doesn't really have a rectifier and inverter as such, it is closer to being a group of interacting phase angle controllers whose gating is sequenced to synthesise a reduced frequency output. The output is direct from the input without any DC link, and is very crude. If you're unfamiliar with them here's a half-decent link:

http://www.uv.es/~emaset/iep00/cycloconvertertutorial.pdf.

ABB's old promotional material lists a few of the advantages of higher pulse counts here:

http://www05.abb.com/global/scot/sc...d004deb49/$file/ACS 6000c Cycloconverter.pdf.

 

[mchaisson]

Hi

The generators are common to the hotel bus. The ship can run in split bus mode however it rarely does due to fuel efficiency. The ship can steam at 12 Knots on one Main engine for example with all services available.

To ScottyUK, you are correct. There is no DC link. The CCV is a 12 pulse unit/phase. By a CCV's design you can only get a max of 1/3 the input frequency, which in this case is 60 to 18HZ.

The idea of getting rid of the existing transformers would be good as the existing voltage is 1200V.
Utilizing a current PWM drive with an input of 4160 (the ships main bus voltage) would be an easly fit. Utilizing the existing voltage with a new drive would mean the drive would have to be way oversized to compensate for the lower input voltage or at least thats what I`m led to believe.

The existing motors transformers and generators are due to have extensive testing done in the near future to ensure the reliability of the units. By all indications they are in perfect condition but detailed testing will confirm this.

Anyway, gotta go... training the next 3 days...budget stuff....wish is was a little more exciting..

 

[powerjunx]

scot, nice link for cyclo-converter..Though, i am confuse with synchro-converter.

"..the more, the merrier" Genghis Khan