Softstarter on Pump
Softstarter on Pump
(OP)
Due to our equipment inventory and operation evaluation, i found out one of 250KW, 460V SCIM uses Softstarter with bypass contactor which i observe is somewhat unusual, that in turn often damages pump assembly.
I was assign to take a root cause failure of the pump but i prefer to investigate first on electrical operation.. i am not well verse of such configuration of this Starter, i know you guys would clear me up.
Here are the following i observed;
1.) At starting, the starting current reaches 4-5 times the FLA then settle down to 75% FLA for about 6 seconds and eventually bypass contactor closes.
2.) Upon Stopping, the SS(Softsatarter)again activated as in "starting sequence" (1.) while bypass contactor open up, it coasts down for about 10 seconds, then machine stops.
I think this action or sequence never satisfy the ramp up/ ramp down feature of Softstarter; that is, not configured to its design feature as for pump application. Anyone would like to share his views on this matter?
Please suggest possible sequence for pump application.
thanks,
bil





RE: Softstarter on Pump
In general, the operating sequence that you should use depends upon what your goal is. If you want to reduce the pressure shock wave that can happen with a check valve slamming shut, then the Soft Stop function should be used. If however, you already have a pressure reducing valve that closes slowly in order to do the same thing, then perhaps you do NOT want the soft stop feature enabled. If it is a positive displacement pump, you do NOT want that feature either. Again, it mostly depends on the nature of your application.
Also, if your duty cycle is high, using Soft Stop may become another problem because each stop operation must be counted the same as a start operation when determining the starts-per-hour capability of the equipment. For example if your motor is rated for 6 starts per hour, that becomes only 3 if Soft Stop is used. If you are using it 6 times per hour then you have exceeded the rating of the motor and you will likely experience rapid insulation breakdown.
Describe the entire pump system as best you can and also see if you can tell what your soft starter settings are.
JRaef.com
"Engineers like to solve problems. If there are no problems handily available, they will create their own problems." Scott Adams
For the best use of Eng-Tips, please click here -> FAQ731-376
RE: Softstarter on Pump
Thanks jRaef, a Star for you! i bet you know exactly about my query. Well, your on the right track!
Upon my thorough seach of PMS and related documents of this unit, i found out that SS is installled against frequent mechanical failures like; check valve damage, twisted shaft,worn out pump bearing, motor burn out, etc but this time the situation is worse in terms of mech'l failures.
I beg an apology to limit you the description of the SS, since i'm not involve in configuring/setting its parameters. I can describe only its operation as posted above.
Nevertheless, here's the entire pump system;
PUMP-MOTOR Assembly:
Vertical Mounted centrifugal pump, 252m^3/hr, 1750 rpm, 4.5 mtrs Head, driven by 250KW, 460V SCI Motor with SS unit (Altistart 48 Telemecanique) with bypass contactor. Upstream pipe equip with Butterfly check valve, pressure build up of 1.7 bars.
Jraef, could you give me a typical configuration for this specific application? And perhaps prove me the Operation sequence as i describe above isn't suitable for such application.
I hate to argue with our maintenance sup't noting that he assure that all configuration(SS), Starting/Stopping sequence are best suited for pump application. I guess his afraid when the root cause is the SS itself.
With regards to number of start, we regulate this strictly.
Big Thanks!
Bill
RE: Softstarter on Pump
The start sounds OK. The current is going a little high but you would have to trade off a longer starting time for less current.
You say on stopping that it coasts - as in the starter just turns off and there's no power to the motor? Or does the starter provide output power even though the motor seems to just coast to a stop? If it's the first you need to turn-on the decel feature and if it's the second then you need a longer decel time.
The soft-starter should ramp the output to bring the motor to a stop to gently close the check valve. If I understand correctly, the butterfly check valve will open and close by pump flow and will slam shut if the pump is suddenly stopped.
Now, I have never seen an Altistart 48 work. Not all soft-starters are equally capable of decelerating a motor driving a centrifugal water pump. Some cause current and torque transients or oscillations as they try to decel the motor. Some only work on certain applications. I do know the Altistart 48 has a torque control that should work well for water pumps but maybe it just isn't working for your application.
RE: Softstarter on Pump
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Softstarter on Pump
I agree with what LionelHutz has said. You still have not described what your pump failures are. Is it the motor that is failing or the pump itself?
Your complete sequence of operation should be as follows:
On a Start command, the SS should energize and ramp the motor to full speed. After reaching full speed, the Bypass Contactor (BC) should close, shunting power around the SCRs.
On a Stop command (assuming the Pump Control option is enabled), the BC would immediately open, putting the motor back into the control of the SS, which then begins slowly reducing the output torque by primarilly reducing the voltage. As the voltage is reduced, the motor current will initially increase. Then as torque is lost and the motor slows down, eventually pressure drops and the butterfly valve begins to close. As flow drops with the butterfly valve closing, so eventually does current (because current and flow go hand in hand). When the SS detects that the lowest torque setting has been reached, it will (should) automatically turn itself off.
JRaef.com
"Engineers like to solve problems. If there are no problems handily available, they will create their own problems." Scott Adams
For the best use of Eng-Tips, please click here -> FAQ731-376
RE: Softstarter on Pump
" as in the starter just turns off and there's no power to the motor? Or does the starter provide output power even though the motor seems to just coast to a stop? "
When Stop pushbutton is pressed, a current raises comparable to starting current as i mention above. With a time delay 10secs, then goes to complete stop. In both cases, Starting and stopping sequence, the check valve slamming badly until it fails, frequently.
Itsmoked, i beg an apolology for such blank lines.
Jraef, upon stopping does the current necessarily reaches as similar to starting current?
Failure often occurs on pump. These are check valve, twisted shaft of pump, severe vibrations and pump bearings.
In comparison to other units (SS other brand), they run with minimal failure.
I'm convince that a fine tuning or refining the configuration of this SS is necessary to attain its specific application, what do you think Jraef?
RE: Softstarter on Pump
RE: Softstarter on Pump
RE: Softstarter on Pump
However, I don't understand why the check valve would slam on pump starting or why you would see severe vibrations. This certainly sounds abnormal to me, almost like there is a fault with the starter. Are the voltages and currents balanced? Do you get a smooth acceleration from the motor?
If the starter isn't programmed correctly or incapable of properly decelerating the motor I typically see a speed oscillation or speed hunting in the motor and pump, not severe vibrations.
If the starter has a firing or SCR fault the motor will really growl on starting or stopping (like it's angry, which it likely is when you feed it bad voltages). Otherwise, the motor sound should be more of a smooth hum.
RE: Softstarter on Pump
billybry,
The level to which current will rise is completely dependant on the application, there is no hard rule on that. In most soft starters you must manually program the starter for Decel control. If nobody did that it is just allowing the motor to coast to a stop. If all they did was select Decel, they still did not do enough. In the ATS48, you should also manually activate the Torque Control ramping parameters in what they call the Advanced Settings menu if you want the smoothest deceleration profile. That then takes some additional knowledge for setting it up along with some trial and error to fine tune it.
If not, then the default Decel mode is a simplistic voltage decel which is very tricky to set up properly without a lot of experience. The ATS48 also does not provide all of the necessary adjustments to make it as smooth as possible for use with a pump. It only allows programming of the time and final torque levels, which means it always starts at 100% voltage and that is not good for some applications. If the pressure differential at which the check valve closes is very small, by always starting at 100% voltage you often end up with the output pressure passing through that band too quickly, making the valve slam anyway. You can extend the decel ramp time as cbarn24050 mentioned, but then you often run up against the thermal overload curve of the motor and trip off line, which also causes the valve to slam. Also, in this simplistic mode of the ATS48 if someone sets the final torque level too low (below 20%) in an attempt to make it work, it will disable the feature altogether and freewheel stop, which of course ALSO slams the valve!
Either way, the starter settings must be matched individually to each application, leaving it at the factory default settings is not adequate for setup because every pump system is different. Even 2 identical pumps sitting side-by-side will sometimes need different settings.
DickDV,
Good point also. On the ATS48, the difference between setting it up for Decel and Braking is that the display reads "d" or "b", altered by a simple Down keystroke. I have often though that this could easily be misread if done in a hurry, especially by those who's native language doesn't use "d" or "b" in the associated words (although interestingly enough, Braking in French is Freiner).
JRaef.com
"Engineers like to solve problems. If there are no problems handily available, they will create their own problems." Scott Adams
For the best use of Eng-Tips, please click here -> FAQ731-376
RE: Softstarter on Pump
LionelHutz,
"This certainly sounds abnormal to me, almost like there is a fault with the starter. Are the voltages and currents balanced? Do you get a smooth acceleration from the motor?"
Operating parameters like voltage and current were normal. Acceleration.. i'm hesitant to confirm i'll still verify this issue soon when i came back in the field.
cbarn24050, i think your right ramp down is too short. During stopping, i never notice a "gradual increase of current" but rather it is comparable to starting current about 4-6 times the full load.
DickDV, i dont think if dc injection is configured, the fact i never seen any record on its setting.
Jraef:
Upon my investigation, i restrict myself on check valve issue.
I bet you're right, Voltage Boost feature - if i'm right, it is similar to pre-select voltage level starting of 30, 60, 80, 100% voltage starting or other way around. But in my case, it starts around 80 to 100% voltage where starting current raises to 4-6 times FLA. While stopping, it goes as in Starting Mode no difference on current profile.
With this scenario, i think, this causes the "severe slamming" of check valve that lead to its failure that is; quick open(at starting) and quick closing (at stop). Give me your views in this.
Voltage boost or kick start are interchageable?
I get through the details of all your advices on tuning and
re-configuration issues on this matter. I urged my colleague to check it.
Well, thank for your helpful and witty advice.
Regards,
bil
RE: Softstarter on Pump
RE: Softstarter on Pump
RE: Softstarter on Pump
RE: Softstarter on Pump
JRaef.com
"Engineers like to solve problems. If there are no problems handily available, they will create their own problems." Scott Adams
For the best use of Eng-Tips, please click here -> FAQ731-376
RE: Softstarter on Pump
RE: Softstarter on Pump
OK, a Soft Starter can't "decelerate" a motor, it slowly chokes off the voltage, which slowly reduces the torque. Yes, it technically is the load that is "decelerating" the motor but that is referred to by everyone in the industry as "decel" in a soft starter.
The torque speed curve of that motor, as the voltage is being reduced, looks exactly like the torque speed curve does as it is being increased during acceleration. At some point in that curve, the torque is reduced enough to drop the slip back to where the motor is producing Breakdown Torque again and at that time the current can, depending on conditions, reach 400-500% FLC, which is damned near LRC. So OK, I took a shortcut and overstated it a smidgen. I was addressing his question as to why he was seeing 4-5X FLC by pointing out that this could be entirely explained as an expected phenomenon if his adjustments were such that it made it happen. I have witnessed this on countless occasions.
Misunderstanding of this set of facts has led to a lot of motors being abused and damaged during deceleration with soft starters. Current rises as the Decel function is activated.
[Reposted with minor correction]
JRaef.com
"Engineers like to solve problems. If there are no problems handily available, they will create their own problems." Scott Adams
For the best use of Eng-Tips, please click here -> FAQ731-376
RE: Softstarter on Pump
RE: Softstarter on Pump
Jraef, seeing the manual it has "3 type of stop mode" namely
Decceleration, Braking, and Freewheel. As i found, noted on manual, Deceleration mode is suitable for pump application, i think the ramp time should be set to specific time until torque is at 20%, then a short freewheeling will follow and eventually motor completely stops. I'm also doubtful with the BRAKING enable. Could this be also applicable to pumps? How about Freewheeling mode?
i would rather furnished a final setting of the SS controller.
Thanks,
bill
RE: Softstarter on Pump
In the Decel mode, power is maintained on the motor and slowly reduced; this is the OPPOSITE of braking. The intent with Decel is to control the reduction of torque so that the motor does NOT coast to a stop as fast as it normally would. This SS comes with 2 forms of Decel; a "default" mode and also an "advanced" mode. As I said above, the default mode is a simplistic voltage reduction; it just ramps the voltage down linearly. In the an advanced form of Decel the SS estimates the actual motor shaft torque and uses that in a closed-loop fashion to control the Decel better. I suggested that you should probably use that advanced mode because the default mode is somewhat crude compared to other brands and may be difficult to get adjusted correctly.
Braking means that they inject DC power into the AC motor and replace the rotating magnetic field with a stationary one, so the rotor "follows" that field and comes to a stop FASTER than if it were freewheeling. Braking mode is NEVER appropriate for a centrifugal pump. Remember, they sell these starters for all kinds of applications. DickDV and I mentioned braking from the standpoint that someone may have [i]accidentally/[i] programmed it for Braking instead of Decel; I was pointing out that this would be somewhat easy to do because of the way that unit programs.
As to the settings for the Decel mode, that 20% is just the factory default, any given application may need to be higher or possibly lower. Unfortunately, in the default Decel mode on this particular unit, you CANNOT set it any lower than 20% because at 20% it just automatically shuts off (freewheels) anyway. This means that IF you needed the shutoff point to be 15%, at 20% the starter turns off and may be allowing the check valve to slam anyway.
JRaef.com
"Engineers like to solve problems. If there are no problems handily available, they will create their own problems." Scott Adams
For the best use of Eng-Tips, please click here -> FAQ731-376
RE: Softstarter on Pump
There is a setting for the torque control in the Altistart manual(code CLP). Factory setting is torque mode. If it is a voltage ramp that starts at 100% and ramps down then it is totally unsuitable for pump applications. I don't even know if the torque control works on pumps. There are some soft-starter manufacturers who have created quite different control modes and some never worked and others either don't work well or only work on certain applications.
Billy, if you want to try different settings then set the acceleration and deceleration ramps to 30 seconds with the rest of the controls at factory defaults. Possibly try setting the current limit to 300% as well. If these adjustments don't help at all then i'd be highly suspect of proper starter operation. If you have any further descriptions of how the motor starts and stops it may also help.
One last note, I've never heard a complaint about a check valve being damaged on opening before. How is that possible? Won't the check valve even be OK if the motor was started full voltage?
RE: Softstarter on Pump
Thanks, Jraef that's cool and concise definition.
LionelHutz,
"The motor has to be running at a reduced speed to actually draw that much current and it typically doesn't happen with a pump while stopping but it is possible"
As i understand from it, do you mean while pushing the stop button motor draws current as much as 4-5 times FLA? However, it typically doesn't happen when pump is stopping but possible. So you confirm that SS parameter setting is somewhat poorly configured? If possible, what particular setting needs to be reconfigured in order not to draw current as a startting current does.
Well, you pointed out Torque Control (CLP). I suspected that this mode creates incompatiblity with Stop mode (Dec,Braking, Freewheel) when both modes are activated as TC and Decelerate selected.
Guys, for me to consolidate your opininions. The basic setting that affects SS for pump application in order to lessen slamming of check valve and to extinguish current while stopping; Starting Torque, Acceleration ramp time, deceleration ramp time, and Stop(Decel) but i'm doubtful with Torque control mode. Any comment?
Lionelhutz, i agree with your suggestion but ATS has "test small motor" mode feature can i use this mode upon altering such ramp time.
"I've never heard a complaint about a check valve being damaged on opening before. How is that possible? Won't the check valve even be OK if the motor was started full voltage?"
Upon starting, i haven't seen any abnormalities. I can't support you of how it was possible.
Nevertheless, the description of SS operation that would likely to attain is smooth start and smooth stop in order to
reduce valve slamming (lead to damage), to extinguish drawing high current as much as "4-5 x FLA" upon stopping.
My ultimate goal is to define the root cause failure of pump system failures and damages that might rooted from SS.
Thanks,
bill
RE: Softstarter on Pump
BASIC SETTING
Acc. ramp time: 15 sec
Initial Starting torque: 30% of Tn
Stop mode: Deceleration
Decel. ramp time: 15 sec
final decel. torque: 20% of estimated torque
current limit: 430% of In
ADVANCE SETTING
Torque limit: OFF
Voltage Boost: 64% of main voltage for 100msec
Torque control: ON
Decel. gain: 40%
Cascaded function: OFF
INPUT/OUTPUT SETTING
L13: L1A (force freewheel)
I think Force freewheel contradicts with STOP MODE - Deceleration. I presume this input was configured and wired to stop button. How Torque limit affects the torque control where it controls without seeing the torque limit reference? The setting appears that braking is disable so we discard our thought out of it.
On operating manual it says; "Deceleration ramp starting at the "motor load torque point", to maximize the linear deceleration ramp for all pump loads." As qouted, "motor load torque point" At this point, does it something to do with slight high current drawn when stop command is initiated? (Noting SS has Torque Control enable)
Any comments?
RE: Softstarter on Pump
Your voltage boost should not be turned on.
I don't know what the freewheel input does. If you're seeing current after pressing the stop though it's not freewheeling.
I believe you should increase the decel ramp time. As you do so the pump should take a longer time to decelerate (it will not slow down as quickly) and it should also reduce the check valve slamming as you do so. If you get up to 45 seconds or so and this isn't helping then the soft-starter is either bad or not suitable for the application.
HAve you listened to the motor when starting and stopping. Does it have a smooth hum as it accelerates or a angry growl. If it's growling then the starter has a problem.
Can you not get someone who knows what they are doing with the soft-starter to come out and look at it?
RE: Softstarter on Pump
While I stated (and later had to defend) that the motor current could go up to 400% on Decel, I didn't mean to say that it should; that would be unusual and definitely not desirable. Misfiring could also explain that as well.
I agree with LionelHutz that the Decel time probably needs to be longer and the voltage boost should DEFINITELY be turned off. There is no need for that feature in a pump. of course if the starter is misfiring, changing the Decel time will actually make the problem worse, so check that out first.
That "Freewheel Input" worries me as well. Is there something that is using that input to possibly override the soft starter's Decel routine and force it into freewheel before it is finished? Sometimes an input such as that is tied to the NO aux contact of an external Overload Relay, which interprets the Decel current increase as an overload condition and shuts the motor down immediately, which would cause the valve to slam.
By the way, some Torque Control algorithms cannot coexist with Current Limit, so in order to have a "closed loop" ramp of torque, current must be allowed to go wherever it will, given the desired torque profile. Torque Limit has nothing to do with ramping, it serves as an "electronic shear pin" to trip the starter off-line in the event of a severe load spike so that mechanical components are not damaged. You would rarely (if ever) need that on a pump.
I also second the notion that you need to find someone who is familiar with soft starters to take a look. Your other thread about the damaged soft starter indicates to me that you may have some issues at your site.
JRaef.com
"Engineers like to solve problems. If there are no problems handily available, they will create their own problems." Scott Adams
For the best use of Eng-Tips, please click here -> FAQ731-376
RE: Softstarter on Pump
I am thankful with your expert suggestions. I would then agree about such SCR misfiring. I'll check first the hard wire configuration about the "forced freewheel contact" that might override the deceleration stop.
Anyway, guys im thankful,this would clear up my confusion. I bet there would be great deliberation over my colleagues about this issue. I'm convince myself to track down the root cause failure about pump system and SS with your help.
regards,
bill
RE: Softstarter on Pump
Here's our new setting,
SETTING
Acc. ramp time: 20 sec
Initial Starting torque: 30% of Tn
Stop mode: Deceleration
Decel. ramp time: 30 sec
final decel. torque: 20% of estimated torque
current limit: 430% of In
ADVANCE SETTING
Torque limit: OFF
Voltage Boost: disable
Torque control: ON
Decel. gain: 40%
Cascaded function: OFF
Operating parameters:
At start we obtain: 4.7 X FLA
At running: 95%FLA
At Stop (decel): 2.2 x FLA, then ramp down to 95% FLA until it completely stop.
A slight slamming of check valve was notice.I'm not getting any 4-5 X FLA upon stopping..
Any comment on this data? will this sounds a smooth tuning?
RE: Softstarter on Pump
Is this happening at the very moment you give a start command, and then the current drops? The reason I say this is that most digital soft starters must read current and react to limit it by moving back the phase angle, a process that can sometimes take 1 or 2 seconds. When the initial voltage is enough to cause a rapid surge in current right from the start, the current can often overshoot the limit setting before the starter has a chance to react. If that is the case, the only possible remedy is to lower the initial torque setting. Mind you, 30% is fairly low already, so that may not make enough of a different here, but it may be worth a try.
If your starting current is going above the limit setting sometime AFTER the initial start command, then you may have a problem with your soft starter. It should be able to catch and limit the current to whatever the setting is. One way to find out is to lower the current limit setting, to maybe 350%, and see if the starter still goes to 470%. If it does, there is a problem. If the current is limited, but still over the limit setting by a similar ratio, then it may just be a measurement error inside of the starter.
Another possibility is that, as I said earlier, some Torque Control algorithms are not capable of executing torque control AND current limit at the same time. It might be that the ATS48 is one of them, but Schneider just fails to mention that little detail in their manual (something often done on purpose because it can interfere with marketing efforts). To test that theory, turn the Torque Control feature Off and see if it attains control of the Current Limit setting. If it does, then that was your problem.
Good luck. It will be interesting to see the outcome. Please report back.
JRaef.com
"Engineers like to solve problems. If there are no problems handily available, they will create their own problems." Scott Adams
For the best use of Eng-Tips, please click here -> FAQ731-376
RE: Softstarter on Pump
About TC, this is interesting! I would be little experimental on this.