30 hp pump, black start, need help on starting methods???

[kiffcommando]

Hello, I am new to the forum. I have an interesting problem. I have been given the task of figuring out how to start a 30 hp, 250 VDC motor off of a battery backup system. The pump will be used to pump hydraulic fluid to operate the wicket gates of a generator on a dam project. I am a little perplexed about how to start the motor. I am looking for an off the shelf starter. Most DC drives require a 3 phase input (480v) then output the required DC voltage, varying the frequency to control the speed. My application does not require much speed control. It will just be used to build and maintain hydraulic pressure to start the generator unit. Any ideas on a manufacturer that may provide a starter?

 

[byrdj]

Would a simple DC motor starter with dropping resistors to limit inrush as motor accelerates . There would be no "speed control" once at speed though. "an emergancy oil pump starter?"

 

[MintJulep]

Is the entire motor/pump system a backup to the main motor/pump, or is only the battery a backup system?

How quickly after you lose main power do you need hydraulic pressure?

 

[sreid]

If you haven't purchased the DC motor yet, I'd consider using a three phase induction motor and a VF Inverter drive. The primary reasoning for this suggestion is that AC motors and inverters are main stream technology where DC motors and drives are legacy products.

Inverters can be powered from a DC Bus. You then have all the inverter control inputs and parameters for controlling the motor.

 

[kiffcommando]

Thank you for all of your replys. First, the suggestion of a DC motor starter with dropping resistors sounds good. However, I am not sure where to buy one. Are they available, and who manufacters them? Second suggestion. Yes, the DC motor would act as a backup to build pressure in the Accumulator in the case of a total lose of AC power at the site and a failure to start the generator unit using residual hydraulic pressure. Third suggestion, we have not purchased the motors yet, however there is a requisition for them at the moment. I am not sure about using the backup batteries to power a three-phase drive. Problem is that the batteries are used in a black out condition to power relays, sensors etc....I am afraid that we will run down the batteries if we apply that much load.

Again, I appreciate all of your replies. I am not the one who came up with idea of DC pumps in this application, only the poor sucker asked to fix the problem. If I had my choice I would use either a portable gasoline pump directly to the hydraulic system or use a backup generator and power up the bus that supplys the existing AC pumps.

 

[byrdj]

I googled and could not find info on GE (Salem) starter that is use for turbine emergancy oil pumps (that was the norm 10 years ago, don't know what now using).

these motors were shunt wound. I'll did through some old files and see if i can find more liturature

 

[sreid]

As you mention, large DC drives are SCR phase controlled and require AC power in to operate.

I would contact Uninterruptable Power Supply manufacturers (UPS) and see if they can do a custom unit for you.

 

[Philrock]

Try searching on "heavy duty DC contactor". My understanding is that motor starting current is typically around 600% of full load current.

 

[sreid]

Although small, low voltage DC motors are started all the time by applying full DC voltage, in larger motors this will result in brush burning, shaft snapping currents.

You might call Peerless-Winsmith for their recomendation.

http://www.peerlesselectric.com/

I strongly believe that what you are going to find is that the technology has moved on and that DC motor starters are simply not available today if they ever were. DC motors were used in industrial applications where variable speed was required. Early, Ward-Leonard drives were used and later SCR phase controlled drives. For fixed speed applications, Induction Motors have been used for 100 years since Tesla invented them.

 

[unclesyd]

Out of my area of expertise but here goes.
We have (32) 30 HP Dc drives running at this very moment. The motors are paired and synchronized with each set is driving a twin shaft common discharge positive displacement gear pump.
The motors were originally controlled off motor-generator sets. The motor-generators where phased out to a purpose built solid state system.
Then the last time I was in MG room the equipment was mostly in Louis Allis cabinets. The motors in normal operation are controlled by a pressure setting using a Provox Process Control System. This current control system allows a very soft start, the motors start to creep with a 3% (possible of 100) on the operators control panel.
This system now works very well though initial there were several bugs, like you had to get to 20% to get the motors to turn, at which time they immediately attained the corresponding speed. Initially the controller had to be manually returned to a 0 setting on the control panel or they would start at the shutoff speed.
Since it is critical that all pumps keep running once started the MG Control Room has the capability of reducing the motor speed by 25%,50%, and 75% in the event of a power outage or an individual process line upset. This was done with a gear box on the MG sets and now is accomplished electronically.

I'll try to see if they will give me some details on the motor control scheme or at least who is the supplier of the equipment.