Motor Question for DickV

[elevmike]

Steve,

Yes! The pump motor is started under no load, after we get a uts (up to speed) signal from the motor starter (soft start) we then energize the valve coils that divert the pump flow to the elevator jack. This is the normal starting cycle, so were already there.

We have a 50 hp motor, directly belted 2 to one to a rather large pump. The total mass is about 300lbs, so starting - even under no load is high. The overall efficency of a hydraulic elevator system is about 45%, depending on the piping, and other factors.

Mike

 

[elevmike]

Vic,

You seem to understand my prediciment, but:

My question really boils down to:
Who makes a two ramp soft starter? I've never seen one.

If you know of a brand, or model please let me know.

Thanks, Mike.

 

[Old Timer]

I use soft starts on stationary and mobile mining equipment. I have used up to 500HP @ 480 V, the C-H "IT" is a good choice. Remarkably small for capability, all surface mount electronics and integral bypass. Fraction the footprint and volume of equivalent Motortronics, Saftronics, or Tele Altistart. My applications start 1-2 times per day, then run in continuous bypass so the SCRs are not generating heat. With an elevator, I suggest you size for severe duty due to the large number of start/stop cyles.

 

[elevmike]

Old Timer,

As you surmised a bypass contactor to disengage the SCRs during the same run cycle isnt practable due to my application (up to 80 starts per hour).

If im going to have a prayer, its a soft start with two seperate ramps. One for starting on normal power, and one for starting on gen power.

Thanks, Mike

 

[Alan Case]

Hi Mike. AB SMC flex is a dual ramp soft start. (got to get them when their young) Regards Alan Case

 

[elevmike]

Thanks Alan,

I'll check with my local AB guy, I just hope someone else answers the phone this time.

By the way, ADC will start selling soft starts, just wait and see..

Thanks, again, Mike

 

[Vic]

Mike

Motortronics, Saftronics and Benshaw all have models of starters with dual ramps. It is generally the microprocessor controlled straters which have this feature.

 

[Rick Densing]

Is the pump variable or fixed displacement? Unloading the pump is different between the two. At least according to our hydraulics guy.

 

[elevmike]

For all you guessers out there (not ment in a derogatory way), a quick lesson in Elevator Hydraulics.

IMO is the predominant manufacture of 3 screw pumps used in the elevator industry today. These are positive displacement-continuous flow type pumps. The pump/motor are run at 1 speed. For most applications the motor runs at 1700 rpm & the pump runs at 3400 rpm.

The pump runs only when the elevator is traveling in the UP direction.

The acceleration ramp, slowdown, and stopping of the elevator is controlled solely by the hydraulic valve.

The Hydraulic valve has 4 coils, UP Fast; UP Slow; DOWN Fast; & Down Slow.

The UP run sequence is as follows:

1) Start Pump (run motor)

2) Either time the start, or get feedback from soft starter to tell the PLC that the pump is up to full speed and volume. (at this time the pump is bypassing)

3) After the pump is up to speed, energize both up valve coils, The oil will then be diverted from the pump to the elevator jack in such a way as to provide a smooth take-off, and acceleration.


4) when it comes time to start stopping the UP Fast coil is De-energized, causing a partial bypassing of the flow from the pump back into the tank.

5) when the elevator reaches the floor level the UP Slow coil is De-energized, and the control valve goes into full bypass.

6) after the elevator has come to a complete stop the pump is shut down.

The down valve circuit operates in the same manner, however the motor/pump is not used, the elevator is lowered solely by gravity.

So there you have it.

Alan, I have received your pdf. Thank you very much! I may have swollow this one a little hard, but what the hey!

I will investigate all leads provided on this thread, Thank you all very much!

Off to study soft starts...again.

Mike

 

[Tom Jenkins]

Mike, you indicated that the pump has a dump valve or bypass valve. Can you get a contact that indicates the pump is running on emergency generator?

If so, can you get the pump started once, and keep it running with the dump valve open so the system isn't pressurized but you aren't loading up the generator with starting current. Then you could use a soft start with a very long acceleration time for the initial start up where the long acceleration would not be objectionable, and keep the pump running so your normal response time is within reasonable limits, and not be constantly loading up the generator.

You would probably want a time delay after you get the generator contact so you aren't trying to start that pump at the same time every other load is coming on line.

 

[elevmike]

Tom,

Your solution would seem to make sense, however in the case of a closed hydraulic system, continual bypassing would heat the hydraulic fluid beyond acceptable limits. That would pose a wholenother set of problems to solve. I'm checking into the two ramp starters suggested on this thread.

As it turns out we have 5 AB starters of the type Alan suggested. I didnt realize that they could do this. They were intended for another job, but that job had minor power bumps that would fault the starters and cause unnessary shutdowns so we had to replace them with Wye-Delta starters.

Regards, Mike

 

[Rick Densing]

Is the bypass direct to tank or through a pressure relief valve?

 

[APB]

Other problems

Get your documentation in order. The lawyers are definitely coming and here’s why.

1) You may be able to get the motor started using a softstart, but at the expense of overheating the motor. Any time the elevator is used during an outage, the motor will have to start slowly. How many and how often will it have to start is a question. The hydraulic syste might not respond correctly (or safely) during prolonged startup.

2) While you are heavily loading the gen set by starting the elevator, all the other loads that are running will also get bogged down. This leads to a couple problems
- Burning out the HVAC motors. At the very least aging the insulation with heat or voltage spikes.
- Damaging or tripping any VSD drives in the HVAC system.
- Even more likely, damaging a power supply that runs one of the other systems controls. Now you have a building that can not be used.
- I have had AB SLC500 supplies burnout when on a generator and a heavy load was started.
- Voiding warrantees on light ballasts.

3) Is the elevator a required emergency system for egress? It may be to meet ADA requirements. If so, the bldg running off the generator may not be code compliant. If something goes wrong the bad press alone can put you of business.

You need to do a couple things
1) Record F and V and FLA to the elevator pump during normal start. You will likely need some form a of real time RMS recording to get this correctly.
2) Now turn the generator on and repeat the test.
3) Send results, registered mail to owner and indicate the system as installed is not adequate, and.
3) Politely suggest that the owner retain a qualified EE PE to get an independent opinion.
4) Do EVERYTHING in writing.
5) Keep a complete personal file. If the s___ hits the fan, the lowest person on the pole will get the blame.

Yes, I spend most of my time dealing with litigation. The winner (if there is such a thing) will be the person with the best documentation in writing.

As for a technical fix. Can you drop all the other loads off the generator while you start up the pump motor?

The hydraulic bypass valve sounds interesting, but I would be very very careful before making changes to a hydraulic system designed to carry people safely. I would call the elevator mfg and ask them what they would do.

Another issue with generators is the power factor. With lots of nonlinear loads (flour. lights, HVAC) you may have a poor or unbalanced power factor. The generator rating is likely with a good PF (typically 0.8 or better). VFD drives can, depending on age (as in what generation of technology) and use, create a nonlinear load. WE do not care most of the time as the utility line is very stiff. A generator is a soft load.

Good luck

 

[Eric Nelson]

APB brings up a good point, Mike. Since you've been in this business a while, I'm sure you've dealt with emergency standby systems in the past. Those were probably sized CORRECTLY, so you didn't have any issues. If this is true, the the real PROBLEM here lies with the generator guys. Yes, it will be up to you to prove that, but I think that's a better approach than trying to rework your system to accommodate their lack of knowledge...

Still worthwhile to look at alternative ideas to reduce your power requirements for furure systems though... :nodi:

Just my 2¢...

beerchug

-Eric

 

[Doug_P]

from left field

The pump motor is started under no load ...

Mike

I'm way out of my depth here but, would it be possible to add a smaller HP motor to run the main motor up to speed before applying power to it (the main motor)? There'd be some extra controls needed.

Just a thought.