OT: 110V DC Motor Starter

[Saffa]

Hi All,

Not strictly PLC, but I'm sure someone works with this stuff and might be able to point me in the right direction.

I'm designing a replacement control panel for a hydro generator, and the lubrication system utilizes a 12.5 HP, 81A, 110V DC pump for their backup if they lose the 3 phase 400V supplied primary lube oil pumps.

I have very little experience with DC Motors larger than a few watts.

The existing panel, built in the early 90s, starts this pump DOL with a 100A contactor and a 0.56 ohm resistor in series which is then bypassed by another contactor after a few seconds.

Original drawings also show a 7.5ohm resistor in series with another winding in the motor which is supplied with 110V when the line contactor is pulled in.

My question is... are there any more modern solutions for starting this Motor? 110V DC soft starter of some kind?

I can find a fair few Motor controllers aimed at 24V DC but not at 110vDC.

The existing panel has what looks like 2 x 1000W wire wound resistors for that 0.5ish ohm start resistor. These are expensive and long lead time, so am keen to hear if anyone has any suggestions.

 

[robertmee]

What's generating the DC power feed? If its coming off the same 480v feeder somewhere and not some special battery backup, I would bite the bullet and install an AC motor.

 

[joseph_e2]

I would investigate a DC drive...but...I'm finding that larger ones are rarer than smaller ones. I would still probably head in that direction. They generally have ramp functions that would serve as a "soft start". I see some offerings from ABB, but don't have any experience with larger DC drives other than replacing them with AC. Is that an option?
I know that Reliance makes a line of AC motors in DC frame sizes that are designed to be drop-in replacements for DC motors (with an appropriately sized/designed/tuned VFD of course). That's another option.


edit:
I see that robertmee posted while I was typing and asked the question that hit my brain as I hit submit. Where does the DC come from? If possible, I would also lean towards an AC replacement.

 

[Ron Brown]

I agree that if at all possible change this motor out with an AC motor and get a smaller drive to control it so you have the ramp times. It will be easier to find replacements moving forward also.

 

[lfe]

Surely that is an authentic DC motor with brushes and commutator.

I think the most appropriate control panel is the one you already have installed.

 

[Steve Bailey]

Is the 110 VDC backup power a bank of 12 volt batteries in series? Can you tap from two of them to connect to a 24 VDC bus inverter? Will doing something like that impact the life of the batteries you choose?

 

[GaryS]

Wow for the original system designed in the 90’s that was a very poor design
For a standby system using batteries it was not well thought out
Batteries are high maintence item if they are not exercised regularly they will go bad and not hold a charge. Over time they will have to be replaced and you will only have a limited run time with batteries. No need to mention the maintence requirements for a DC motor.
I would redesign the system to use a propane power generator. Change the dc motor to an ac motor. As with all standby systems they must be run at regular intervals to insure operation when needed but propane can be stored long term without going bad. So you would have a good reliable energy supply on hand

As for your original question for a contactor in this application I would look at Ward Leonard but be sure you get a pure DC motor starter rated contactor
A lot of companies have DC contactors but they are for use in scr rectified dc not pure dc as with a battery I have seen the high inrush of the motor starting and long arch when they open destroying contactors the one you need is getting harder to get.

 

[Steve Bailey]

It is fairly typical, at least here in the US, for small, run-of-the-river hydroelectric generating stations to have a bank of lead-acid batteries as their backup power source. Utilities are notoriously conservative and slow to adopt newer technologies. Many hydropower stations date back to a time period when the lead acid battery was the state of the art.

 

[Saffa]

Thanks all for the responses.

The 110V DC is from a separate backup source which is a large battery bank. As Steve Bailey said, that's pretty typical for these plants. The original power station was built in 1904 I believe.

Unlikely to be able to change this or the motor, as the 110V feeds multiple services around the plant. This panel upgrade is for only one of 3 generators.

Main reason for the upgrade is to modernize the controls. Back in 1990, it was full relay logic with 110V DC relays.

I did have a bit of a look online for DC Motor VSDs as have worked with ABB ones for much larger (600kW) DC pumps in an old installation. The 110V input plus motor size seems to be the sticking point.

The 110V pump is only a backup in a 3 phase failure situation to keep the generator bearings lubed until the machine is shutdown, so it runs very infrequently. May just copy the last design.

Thanks for the suggestions GaryS, Site requires Schneider brand contactors & breakers so will be using those, they have a good document for rating correctly at various DC voltages if you break using 2 or 3 poles in series.

 

[lfe]

If the pump can stop for a few seconds without problems, a diesel or gas generator can be installed to restore the three-phase voltage.

There are those prepared to start and give 100% power in a few seconds, they have an electric pump that circulates the engine oil even when stopped.

 

[I_Automation]

Can you get a split power off the battery system?


My thought is use a Y-Start/Delta-Run contactor (or a reversing contactor with the top rails removed) and if you can tap say 60 or 90VDC off the batteries have the Y-Start power the motor with that, then switch to Delta-Run that gives it the full 110.

 

[Saffa]

I think if we were designing a brand new station then a standby diesel generator would be the way they would go, or a large industrial UPS.

Space is very limited outside the plant for fitting a generator and getting new cabling down to the turbine hall would be much more costly than the entire panel replacement.

For the very infrequent number of times this pump will run, I think maybe the original starting method will have to do.

I think the battery bank going to be hard to modify for a reduced voltage start, I do like the idea though I_Automation!