critical dc motor starter, any new technology? 1

[byrdj]

a turbine's lube oil feed to its bearings has an "emergency DC oil pump". The urgency in its use requires a starter that is failsafe, relaible and can achieve maximun acceleration with out damaging motor and battery bank. the batterys are nominally 125 or 250VDC and the size is around 50 HP.

the current technology is energized timers that dropout to remove two resistors about every second to achieve full speed in 3 seconds.

The question; Is there modern technology that can control the inrush current to achieve the same starting times (and be failsafe)

 

[waross]

Modern technology may be a PWM drive to the DC motor or an inverter drive to an induction motor.
The most reliable may be the inverter-induction motor combination. No brushes and sealed bearings will make it a very low maintenance solution.
Define "Fail safe".

Bill
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"Why not the best?"
Jimmy Carter

 

[byrdj]

"defined failsafe"

this area is on the edge of my understanding, so that is why I've asked
the question of a "modern" starter for a turbine's emergency bearing oil pump (EBOP) was asked of me today while discussing the OEMs recommendation from 1970 to replace starters that used energized with deenergized to start relays with the OEMs claim of improved reliablity and failsafe design.

Since the last "new" steam turbine I've been on was in the early 90's I was wondering if any thing has changed from that design. I do not have any plans to devolpe a design given the consequencies

 

[ScottyUK]

Hi byrdj,

The old resistor timestarter design is offers bomb-proof reliability and if suitably constructed is capable of surviving very severe overload conditions without failing. I'd always use the old-fashioned bar & shaft type contactors which cost a lot more than the typical AC-3 rated block contactors but are immensely tolerant of heavy switching. Semiconductors can't offer this level of survivability in an economically viable package. The benefits of semiconductors would probably be felt more in a frequent switching role, which doesn't really apply to emergency pumps.

A correctly designed timestarter will ultimately perform an across-the-bars start if the motor is 'tight' and won't accelerate with the starter resistors in circuit. This draws a very high current and may damage the commutator, and usually results in dropping every sensitive load fed from the turbine battery, but if you really need the oil pump in anger then very little else matters. Sacrificing a fews tens of thousands on a wrecked pump and motor is great value to save a multi-million pound turbine.


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If we learn from our mistakes I'm getting a great education!

 

[edison123]

I am with scotty. I have seen even the latest steam turbines have the 'old-fashioned' timed out resistors type of starting for emergency DC lube oil pumps. My dad designed one such system for a 210 MW STG in 80's and it is still going strong.

Some poer stations even have gravity fed oil supply (Overhead tanks in the turbine hall) to the bearings as an redundancy.

Muthu

http://www.edison.co.in

 

[byrdj]

thanks for the replies, it was that i realized it has been a long time since i saw what was current technology.