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Soft Starter Thyristor Burns


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#1 Quazi Haque

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Posted 08 August 2007 - 01:43 AM

Can someone please answer why Thyristors in Soft starters burn?
We are using a 400 KW AC3 (690V 60Hz) rated soft starter to start a 300KW (690V 60Hz) motor. Power is supplied by a 750KVA Generator set. The soft starter is configured according the motor datasheet. The soft starter manufacturer is saying that we have to use power form the grid; the generator set is not big enough for this application. I don't quite understand the reason though. The motor starts with no load. Soft starter is bypassed using a bypass contactor after top of ramp is reached. So far four soft starters are burnt during testing with seperate motors.

#2 marke

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Posted 08 August 2007 - 03:27 AM

Hello Quazi Haque

Welcome to the forum.

Some soft starters do not perform well on the out put of a generator, especially if it is marginally sized.
The normal cause of failure on the SCRs used in soft starters, is either a severe overcurrent, or overvoltage. Both failures result in a shorted SCR. A suitably trained/skilled person can determine the cause (over voltage or over current) by opening up the SCR and studying the actual die and failure mode.

If the generator is marginally sized, some soft starters can go unstable and this can result in current and voltage surges which can do some damage.
If the alternator is self excited and fitted with a half wave, single phase peak reading AVR, the output regulation will not be good under the starting conditions of the soft starter. In effect, the soft starter and AVR can "chase" each other.

If the generator you are using has a PMG excitation and a three phase averaging AVR, then it should not be a problem with that motor size as long as the soft starter is suitable for operation on a generator.

Best regards

#3 jraef

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Posted 08 August 2007 - 04:17 AM

What brand of soft starter is it out of curiosity?
"He's not dead, he's just pinin' for the fjords!"

#4 Quazi Haque

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Posted 08 August 2007 - 05:01 AM

Hi Mark,

Thanks a lot for the info. I am impressed by the quick response. I already added this site to my favourites list as I am sure I will be using this forum much more often from now on.

I am checking with the generator supplier if the generator has a PMG excitation and a three phase averaging AVR. We are using ABB PST210 690 soft starter (answer to jraef's question). It has built-in over-current protection according to its datasheet. So I will be surprised if the thyristors are burnt out due to over current. By the way, we connected the soft starter inside delta of the motor winding, but it can still measure the phase currents.


Best regards,
Quazi



#5 marke

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Posted 08 August 2007 - 05:07 AM

Hello Quazi

The overcurrent protection will not protect the SCRs. That is for motor protection only. The problem is that once an SCR is turned ON, you can not turn it OFF. It will self commutate when the current passes through zero.

If voltage wave form distortion is causing SCR miss triggering, it is possible to get DC in one phase and the current can go high enough to damage the SCR. Similarly, the voltage spikes can be very high.

I have no experience with the ABB units on generators, so I can not comment on that one.

Best regards,

#6 SCIM

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Posted 09 August 2007 - 02:51 AM

Hi Quazi,

Just interested to know if the the motor failed together with the SCRs? You might want to do a meg test on the phases of the windings.

There has been a couple of inside delta failures of late with compressors applications on my end...



Marke and Jraef,

Just like to know your views on if a soft starter is wired inside delta with settings on parameters on soft starter - Line, would that caused SCR to fail and in turn caused the motor to fail? There is no bypass contactor in the system.

I do understand that the triggering timing will be different but what kind of effect would it caused?

We currently have a failure as per above on screw compressor application and soft starter supplier is saying a overvoltage that caused a blow to the motor windings and the soft starter would not have caused that even with above settings.

Application was running with the wrong parameters for 3-4 months before changing over before 1st motor and soft starter failed.


I can't name companies here... So please take soft starter as a general big in the market soft starter.

This case above is just one off the I have gone thru with.... I still got others that are unsolved which I am still waiting for more information.

Thanks
SCIM






#7 marke

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Posted 09 August 2007 - 03:54 AM

Hello SCIM

Welcome to the forum

The answer is yes and no, it depends. How is that for being evasive??

Actually, it depends on the actual starter and the way is works internally.

At one extreme, we have soft starters that will handle that with no problems. You do not need to set them up for three wire or six wire (inside delta) connection. At the other extreme there are soft starters that can be installed in inside delta connection provided that you have the correct phase sequence and wiring of each winding from the output of a phase to the input of the preceding phase, and then there are the starters that can not be wired inside delta at all.
There are issues with firing overhang, initial phase angles etc etc that must be set correctly depending on the connection.

If the starter is not able to auto configure for inside delta connection, then there is a good possibility that there will be some mistriggering that could cause DC to flow in one or more windings and that could cause the winding to fail and the SCR to fail. This is totally dependent on the starter being used.

Similarly, if the starter is connected inside delta and there is no line contactor, then any line transient is blocked by the SCRs and in the inside delta connection, the OFF state transients applied to the SCRs are equal to the line to line transients, whereas in three wire connection, the transients applied to the SCRs are equal to the line to neutral transients and so are significantly lower.
If a high transient occurs, then the SCR could be damaged and this would in turn cause the motor winding to fail.

Analysis of the failed SCR and the failed motor winding can give clues as to the cause.
If one whole winding is badly burnt, that would suggest to me that the motor failure could be due to an SCR failure. A skilled technician can give a good indication of the mode of SCR failure from the damaged die.

Do you have an indication of when the failure occured? was it while the starter was OFF, while it was starting or while it was running?
Was the motor damaged on one phase or all phases?
Was the winding burnt, or was there a whole blown in the winding?

Best regards,

#8 jraef

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Posted 09 August 2007 - 04:58 AM

I personally am not a fan of using soft starters inside the delta, and I have written two papers on the subject for my previous employer, who did not offer it as an option. To me, the risks far outweigh the advantages. There is only one advantage; lower cost of the soft starter power components. There are however multiple risks above and beyond what is normal for all soft starters. Here is my (not so) short list:
  1. High risk of a single shorted SCR causing motor damage. In a normal connection if one SCR fails it isn't a big deal. The motor will not ramp properly and a shorted SCR detection scheme may lock you out from re-starting next time, but there is no inherent danger of damaging the motor. You would need for there to by multiple SCRs shorted in at least 2 legs for the risk to present itself (the risk being unimpeded current flow though one set of windings in the motor). Once you connect inside the delta however, even one shorted SCR presents an immediate opportunity for that unrestricted current flow through the winding, because 1/2 of the current path is already there. So the only way to ensure it doesn't happen is to use an isolation contactor (called a Fault Contactor by some manufacturers). Ironically though, the cost of this extra contactor is usually MORE than whatever you saved by using inside the delta anyway, so hardly anyone puts it in. That means they are at a much much greater risk of losing the motor.
  2. Higher risk of SCR failure as well. SCRs should technically have a higher PIV (peak inverse voltage) rating when used inside the delta, yet nobody does that, which means SCRs are more likely to short on faults. When SCRs are picked for a soft starter application, a major consideration is that the PIV rating should be 3X the line peak voltage. So on a 480V Y system, the maximum voltage to ground is 277 so the maximum peak voltage across the SCR in a fault can be 277x1.41=390V. Therefore the PIV needs to be at least 1170V, which is rounded up to 1200V. Because a lot of IEC countries use 415V, 1200PIV has become the minimum rating in use all over the world (it never hurts to have a little extra). So that rule ends up equating to the PIV being based on 2.5x the nominal line RMS voltage (1200/480=2.5) and over time, that is how many people have come to interpret the rule and have even come to believe that IS the rule. Most of the time it works out fine to do it that way, exceptwhen you put the SCRs inside the delta! If used inside the delta, the peak fault voltage potential to ground that the SCR can see becomes theoretically the line voltage. So on a 480V system, the peak voltage is 480x1.41=677V, which means if you want to select the SCRs correctly, they SHOULD have a PIV of 679x3=2030V! But nobody does that because the SCRs would be extremely expensive. The values would of course be lower for 415V Y systems (1755PIV) and that's why you see inside the delta used more freely in IEC countries, but there is a significant extra risk for users in the US. Even with the 1755PIV value in IEC countries, 1800PIV SCRs are readily available and there have been arguments in the soft starter manufacturing community that this should be the minimum rating when used inside the delta. But as soon as one manufacturer ignores it and uses 1200 or 1600PIV, his pricing becomes incrementally better and everyone else has to follow suit. The loser in this argument however is the end user. At the very least, users with 415V maximum systems should select the 690V class soft starters, because they will have (should have) 1800PIV rated SCRs. But salesmen are not educated on this issue so they sell the 500V class products and put the users at risk.
  3. Risk of having a technician in the future not understand the unique nature of the connections, and do something catastrophically wrong. Having to connect 6 leads in the correct pattern is not too bad when the equipment is first installed and the manual is right there. But 5 years down the road, the reality is that the manual will be lost and the technician who has to work on it may have never seen this odd-ball arrangement before. One mistake and all the savings will go up in smoke.
  4. Can't use low firing angles, so initial torque may always be higher than you want, which may end up negating one of the best benefits of soft starting anyway. I'm not really sure about this one, it was related to me anecdotally, I have never seen it.

Now I'll admit that I have not been as intimately involved in the ground up engineering of soft starters from scratch as Marke has, so he may have some corrections to what I have come to believe, but in general, inside the delta will always have no attraction for me just based upon point number one.


"He's not dead, he's just pinin' for the fjords!"

#9 SCIM

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Posted 09 August 2007 - 09:34 AM

Thanks for the replies guys,

Marke,


This soft starter that failed does not have auto configuration and when it failed, manufacturers were 1stly quick to point out the there is no effect and could not have contributed to a motor failure. (If they see this, they will most likily know who I am)

After questioning them that the triggering timing would be different (that's why the parameter settings) and questioing them as to if that would lead to more harmonics which in turn caused the motor to fail, they agree that it might caused more harmonics but only at start and they do not know what kind of effects it would caused on the motor. They are also not very willing to supply the PIV rating of their SCR.

I have just received a letter from them stating that the Soft Starter would not have caused the current situation we are seeing in the winding failure of this motor.

This motor failed on start. There is no discolouration in windings and the only blow is just between 2 phase. It's along 2 smaller leads at 11O'clock covered with fiberglass between two phases on a leased up point and the blow isn't a big blowout. Most who had seen the failure commented that it looks more like a high spike in voltage without any high current or it would have blown alot of copper out. I am still quite young in analysing winding failures and been in the industry for 4years but am not convice that the wrong parrameter settings with a correct inside delta connection who have no effect to winding insulation.

Could you please explain on how mistriggering can caused DC to flow and inturn caused winding failures?
Do you mean DC voltage? or Direct current? Is there a way to prove so? The SCR will be taken apart soon and we are waiting for the soft starter manufacturer to organise for a time.

We currently have on the same site, another motor that failed last week with failure being like an explosion of windings with copper everywhere. The motor was opened today and I have yet to see the photos but will get them tommorrow. Base on the explaination on the phone with someone who saw it, my believe is that it will be totally different from the winding failure of the 1st motor.

As said earlier, there have been other failures elsewhere on other sites. Others I am led to believe that they have the correct settings and correct connection of Inside Delta with fingers cross.
All failues(6-7 so far till date) are after commissioning of about 4-6months. My thinking is, could inside delta connection actually be determital to the insulation system or breaking it down slowly. There have been cases whereby SCR failed but motor was still fine and after SCR was replaced, motor failed together with SCR. Does this mean that for Inside Delta Connection, motor to be supplied should have the best insulation system possible? e.g ISR Wires only?

I only happen to chance upon that SCR were failings together with motor as well only after the 4th failure!


Jraef,

Yes, I have read alot or almost all of your writings with regards to Inside Delta Connection (Of coz, Marke's as well and GSOSSS) and I agree with your saying that for Inside Delta Connection, there is a higher chance of failure rate than line connection. I have actually been talking to many soft starter manufactuers and reliease that most of them do not know what they are selling only for a rare few in my current place of location. I am impressed by the rare few breed that actually knows what they are selling and marketing.

I do believe that I will make a better salesman than some if I will to join the soft starter industry here.


1:High risk of a single shorted SCR causing motor damage

Could you please tell me what kind of fault isolator contactor are you taking about? Are you saying the contactor between 3phase source and soft starter?


2: Higher risk of SCR failure as well.

It's 415V 50Hz here.

I believe industry here is telling their customers that Inside Delta is good on their 415V drives with increase in amps by 1.73 by some.
Till date I have yet to seen any that they will recommend their 690Volt system for inside delta connection with 415V supply.

The rating of PIV is a very well guarded information here, in fact some don't even know what the PIV stands for.

There is one case that I know of whereby a customer has complain about knowing of these failures and the soft starter manufacturer has changed all soft starters to suit Inside Delta to Line. From what I hear, it's FREE OF CHARGE! It only leads me to think that manufactuers themselves are unsure of what might happen and can't guranttee their products for Inside Delta.

3. Risk of having a technician in the future not understand the unique nature of the connections

It has happen here, correct connection but the parrameter settings wrong on the soft starter.



I am actually quite worn out by this current situation but it's affecting alot of companies in terms of dollars of damage done. I have even been threaten by a big company saying they will consider sueing me for not recommending inside delta connection with their products!!! I said it's due to the number of failures that it was said..


It's a bloodly crazy world today....

#10 marke

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Posted 09 August 2007 - 11:48 AM

Hello SCIM

The details in the SCR control and effects of incorrect triggering angles and overhang angles gets quite involved and is beyond what can/should be discussed here, but if the triggering angles are set up incorrectly, it is posible to get 1 SCR turning on only in one phase. This results in a burst of DC current. This could cause a high back emf on that winding, or for a high voltage to be induced in an other winding.
I have seen some pretty nasty currents and voltages occur with incorrect triggering. - if it was not a problem, they would not have the settings!!

Your description of the motor failure indicates that the SCR did not fail first. The initial problem was the punch through on the insulation of the motor and this fault will have damaged the SCR.
As the fault occurred at start, I would suggest that the possibility of the failure being a misfire problem can not be discounted. A line transient problem in an inside delta installation would probably damage an SCR before damaging a winding and would be most likely to occur when the starter is powered up but not running.

Other comments:
1) I believe that ALL soft starters wired inside delta must have an isolation contactor that disconnects the incoming supply when the motor is not running. If you do not have the isolation contactor the chances of an SCR being damaged by high voltage line transients is much higher than in the standard three wire connection. More important however, if you install the soft starter inside delta, and just rely on the soft starter to start and stop the motor, then you are leaving full voltage on one end of the motor tails when the motor is not running. In the event of a fault, you can not disconnect the motor from the supply. - It is very much like using a two contactor star delta starter.
If you do have a high voltage transient on one phase, it could easily cause one SCR to fail. This puts full voltage on one winding only and this will result in a high current flow on that winding until something breaks. - usually the smoke coming out of that winding.

2) The same PIV rating is used for both thre wire and inside delta connection and this is appropriate, however in the OFF state, the SCRs are blocking 415 volts rather than 230 volts in a three wire connection. - less margin for transients.
As far as the current is concerned, in a situation where there is a continuous sinewave (Full voltage) applied to the motor windings, the current inside the delta loop is 1/rt(3) of the current in the line. However, when you have a discontinuous sinewave, (during start) the thermal effect is very dependent on the wave form and the conduction angles. In inside delta connection, the conduction angles are very different from the conduction angles in standard three wire connection. The correct re rating of the unit for thermal reasons, is to increase the motor size by about 50%. If you increase by 73% as most suggest, you are actually heating up the junction of the SCRs by a much higher value during start than you would in three wire connection.

3) Inside Delta connection is OK and is not a major problem with correctly designed starters. I have done many, but I believe that you must rate correctly, and you must use a line contactor that opens when the motor is not running. It is definitely preferable to use an auto setup starter so that there can be no problems with incorrect configuration or wiring.
I have experienced problems with earlier systems that were not intelligent where the installers were also not intelligent and got the installation and configuration out of synch.

Best regards,

#11 chaterpilar

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Posted 12 August 2007 - 03:58 AM

Dear Quazi,

Your generator 750 kva is definitely undersized for the application even if you use a softstarter of appropriate size.

I am using a 1250 kva generator for with Reduced voltage starter for a 450 hp motor.

The starting current would be high causing a severe voltage drop and hence the softstarter would be under lot of stress.

Check the voltage at the input of softstarter, after you give the start command.

Resize your generator.

regards,

Chaterpilar

#12 marke

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Posted 12 August 2007 - 08:32 PM

Hello SCIM

QUOTE
could inside delta connection actually be determital to the insulation system or breaking it down slowly

I do not believe so, provided that the SCRs are correctly controlled. This is supported by many installations that have been running successfully for up to and beyond 20 years.
If there is mis firing of the SCRs such that there results a large DC component for a short period, then yes, at the expiration of the DC current, there will be a very high back emf generated and this will cause a high voltage transient that could damage SCRs and/or windings.

To be more specific on the risks, I would need to know the topology used for controlling the SCRs. I have found that it is important to use a different algorithm for inside delta connection than for line connection in order to ensure the correct triggering of the SCRs.

Best regards,

#13 SCIM

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Posted 13 August 2007 - 01:07 AM

Hi Marke,

I forgot to add with regards to 2nd failure on site is that the soft starter was on wrong settings for 3 months before Soft starter's technical engineer went to change to the correct settings and increasing the starting current to 580%. The reason they claim for not being able to start the compressor was due to it being set at 380% for limitation of start current. Therefore, this motor failed with right settings after about 3 months on site with right settings and 3months with the wrong settings and only had running hours of less than 50Hours.
The first motor failed after 3 months on site with wrong settings.


Soft starter company is currently claiming with regards to 1st motor that failed with incorrect parameter settings:

" The soft starter can not cause an over voltage to the motor. The initial incorrect settings could have lead to additional motor heating during starting, but the physical nature of the soft starter will not significantly increase the voltage levels "


The electrical company that did the installation for both motors has also make mention that when they tried to do a test run with "Inside Delta parameters" , the motors were rocking and couldn't seems to get to speed. I am unsure of what their starting voltage settings are.


1.
With regards the "correct" triggering of the SCR on inside delta or line connection, does that mean that there is actually no way of determining so if the manufacturer has the right programming for timing of the triggering.

I am led to believe so because manufacturers involved in the situations that I am involved in could not provide a reply as to where went wrong other than stating that the winding insulation failed first that caused the SCR to fail. unsure.gif

Another problem I been thinking is, if it's transist voltage to be in the system that's causing these problem, it would be the same for DOL or Star/Delta system and it would still take the motor windings out if insulation system is unrated for it.

Question being now is that why are we seeing these failures only with Soft Starters with Inside Delta? Due to the source or due to Others like installation? unsure.gif



2.

With regards to the rating of soft starter being rated Line Connection x 1.732 or x 1.5 for inside delta connection:
When I raised the questions to soft starter manufacturers on why the difference in ratio for inside delta connected,

One of the Manufacturer Product Manager (MARKETING) response laugh.gif ,
(Nothing mention of the PIV rating other than with regards to thermal rating)

" ...However, there are many variables which can be taken into account during a design phase which allows for someone to take full advantage of the connection. A couple of those variables revolve around SCR thermal capabilities and there ability to handle peak surge currents. One of the reasons we maximize our ratings is because of the way we have tested the device. Most of our thermal tests and models were done with motor/loads set up in a inside-the-delta connection.

Some could argue the point that we may not be maximizing our line ratings, however I would point out the fact that our line connection ratings are already significantly more heavy duty than both (Company A )******* and (Company B ) *****. When you design a product to very tight thermal tolerances, you are subject to many types of application considerations including ambient temp, elevation, cycle rates, high motor LRA, and even the connection type. The bottom line is that we have more tolerance built into the product to allow for these types of deviations without the need to derate or more importantly impact the life of the product.
"

Cheers,
SCIM


#14 Quazi Haque

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Posted 13 August 2007 - 05:04 AM

Dear Chaterpilar,

Thanks a lot for your comment on the generator size. We are now using a 2700KVA generator and there is no new incident of soft starter burn so far. smile.gif

May be this was the only reason behind four soft starter burn. I will keep you guys updated if I find anything more on this. Thanks everyone for your input. You guys are GREAT!!!

Best regards,
Quazi

#15 anu_rags

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Posted 25 August 2007 - 08:03 AM

QUOTE(jraef @ Aug 9 2007, 10:28 AM) View Post

I personally am not a fan of using soft starters inside the delta, and I have written two papers on the subject for my previous employer, who did not offer it as an option.


Dear Jraef,

Im interested to read your papers on this subject. Is it possible to get it somewhere?

Regards,
Anurag

#16 marke

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Posted 25 August 2007 - 09:58 PM

Hello SCIM

I wonder if you have made any progress? I suspect that you are up against a brick wall with a he says, they say stalemate!!

As far as I am concerned, from my experience and knowledge, there is no reason why a properly designed and commissioned soft starter installed inside delta, should increase the risk to the motor or the SCRs provided that it is used with an isolation contactor that disconnects the motor when it is not running.

I would put strong emphasis on the properly designed requirement however as I have witnessed poor performance because things are not done properly internally.
There are many inside delta (6 wire) installations out there that have run faultlessly for many years.

QUOTE
if it's transient voltage to be in the system that's causing these problem, it would be the same for DOL or Star/Delta system and it would still take the motor windings out if insulation system is unrated for it.
I agree provided that all things are equal. If there are DC pulses occurring due to incorrect SCR control, then there will be much higher transients than usual and these could lead to premature failure. For example, if a positive SCR is triggered ON on two or more consecutive cycles and negative SCR on that phase is not triggered ON, then in effect you have DC current flowing through that winding. When the current stops, there will be a high back emf.

QUOTE
" ...However, there are many variables which can be taken into account during a design phase which allows for someone to take full advantage of the connection. A couple of those variables revolve around SCR thermal capabilities and there ability to handle peak surge currents. One of the reasons we maximize our ratings is because of the way we have tested the device. Most of our thermal tests and models were done with motor/loads set up in a inside-the-delta connection.

Some could argue the point that we may not be maximizing our line ratings, however I would point out the fact that our line connection ratings are already significantly more heavy duty than both (Company A )******* and (Company B ) *****. When you design a product to very tight thermal tolerances, you are subject to many types of application considerations including ambient temp, elevation, cycle rates, high motor LRA, and even the connection type. The bottom line is that we have more tolerance built into the product to allow for these types of deviations without the need to derate or more importantly impact the life of the product. "
At the end of the day, they can claim what they like, but to suggest that they are able to use the root three factor for inside delta because of the SCR overload capacity, or because they have oversized the SCRs, sounds like "marketing license" to me.
Many SCR users out there believe that the SCRs have a overload capacity which allows you to start the motor. I used to get hounded by one SCR supplier who maintained that I should be using his SCRs and relying on the overload capacity to start the motors.
If you study the SCRs, you find that the "overload" capacity is there to cope with transient overload very occasionally, not every start. In many data sheets, this overload capacity is rated as eight time in the life of the device.
If you wish to have reliable long term operation, then you must ensure that the junction temperature of the device never goes above 125 degrees C under any circumstance.
I also note that some of these manufacturers of soft starters believe that 400% current is severe duty. I would estimate that apart from submersible pumps, the majority of soft starters require more than 400% current to get modern motors and loads away. To me, 400% start current is light duty, an 550% start current is heavy duty. I would class 600% for 50 seconds as severe duty!!
Unfortunately, there are no real standards covering how the ratings for soft starters are derived. We do have AC53 ratings, but how are they derived? do you just connect up a soft starter and try it a dozen times in the lab, and if it survives, it must meet the ratings? I prefer a full thermal analysis of the junction temperatures and I know that this works. I have over 25 years of experience with this technique and the results to prove it.

Good luck, I do not expect it to be an easy answer!
Best regards,


#17 marke

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Posted 25 August 2007 - 10:22 PM

Hello Jraef

Just a few comments on your thoughts on inside delta.
QUOTE
High risk of a single shorted SCR causing motor damage.
I totally agree, I believe that it is imperative that a line contactor must be used with inside delta starters, and the line contactor must operate to isolate the starter when the motor is not running.

QUOTE
Higher risk of SCR failure as well.
I agree with this if the starter does not use a line contactor to disconnect the motor during the non running state. With a standard installation, during the off state, the SCRs are subjected to phase - neutral voltage. In effect, the SCRs create a star connection with the motor at the star point. In the inside delta connection, the SCRs are constantly blocking line to line voltage. In order to gain the same transient blocking capability, the SCR voltage rating would have to be increased by root 3. If a line contactor is used, this is not necessary. During start, the SCRs in both configurations are subjected to line to line voltages. The normal ruole is that the SCR voltage rating should be at least 2.5 times the line to line voltage. By virtue of it's connection, the standard connection provides additional transient immunity in the non operating state, as it is subjected to less than line to line voltage.

QUOTE
Risk of having a technician in the future not understand the unique nature of the connections
Where the wiring is critical, and in some cases you must have the wiring correct and the phase sequence correct, then this is a major issue. At the other extreme, if you have a system that is able to analyse and calibrate to the connection used, and just give an installation trip when it is not possible to run, then this is not an issue. It depends on the design of the unit.

QUOTE
Can't use low firing angles
My experience is that you can get much better control with low conduction angles than in the standard connection. The control can go from 1 degree to 180 degrees with reliable control. This is not possible in "three wire connection". For motor starting, you are rarely interested in good control at much less than 50% voltage, so it is not a major issue, but I would rather attempt 10% voltage in inside delta than otherwise.

Best regards,

#18 SCIM

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Posted 26 August 2007 - 03:12 AM

Hi Guys,

Yes, I am up against a group of so call soft starter EXPERTs that has little knowledge of what's going on in terms of causes and failures. From my point of view, they shouldn't be selling/marketing something they don't know 100%.


Company A - Soft Starter Failed together with motor with correct settings.
Company A - Company that sent out "marketing report".
Company A - Someone from their office rang up and told me to make proper comments/statements or they will think of suing me.
Company A - Has stopped all talking/response to me.... Due to questions/request/statements I want! I believe I am on the phone call ban listing.


Company B - Soft Starter failed together with motor with incorrect parameter settings.

Company A has come back with a report on the SCR dismantling. They have done it wrong without opening up the wafer so as to see the actual fault caused. They have only cut up the body which can't tell anything and they concluded that there don't seem to any fault of the soft starter. The only fault I could see is HV has gone into the LV path. I have gone back to them asking them to open their wafer in a very polite and political manner... (I hope I don't get sued for asking questions)... I might got to ask a lawyer before I see if I can post those pictures on this site. I have also not been invited to witness it....

I find it extremely odd that I am not a soft starter expert nor am I any expert in internal parts of soft starter but I am sort of teaching or leading them how to look into it.....

I can only comment that their "technical engineers" do not know what they are doing base on the report provided!!!

Company A is a big organization in the Electrical business globally and I really doubt their REAL abilities.
Of coz, we can't determine 1 or 2 person's knowledge on what the whole company really is.


Company B has not got back to me other than the report that they concluded that their Soft Starter will not create an Over voltage to the motor.

Still waiting for them to organize a time for dismantling of the SCR. They are pretty keen as well to know what's going on as well but are relying on their engineers overseas in ****** to response.



Marke,

I believe I am up not just against a simple brick wall but the BERLIN WALL plus Great WALL upsized combo.

Is there any way to proof incorrect SCR control? I am thinking that it might be due to incorrect control that caused a back EMF and in turn caused the motors to fail.

Reason for thinking so -
There is another company that supplies Compressors with similar kw/pole motors that has no failures and they use auto trans and star/delta set up only. That should be more detrimental if it's due to transient voltage if that's the reason for failures.

I do agree that there are applications out there that have been running for years without fault/failure but....
We have decided to no longer supply equipments if Inside Delta is being used because of the risk on not knowing who is doing and how they are doing the Installation. Also, we do not know whose Soft Starter has the correct control seq.

I do not have the knowledge on how to determine on how one differs from another in terms of SCR control and you are right that there is no regulating body to determine others either.

All I currently have an idea of which company has (or have not) the knowledge and knows what they are doing. And also those who are just following the crowd to what Others supply and "I will supply as well" without knowing how/why than reduction of cost!

I believe most End-users are currently still unaware of this situation on Inside Delta Connection, most thinking it's a motor problem.

On selection of equipments, they mainly rely on quotes sent out by Electrical or equipment manufacturers for any new jobs and most would only look at costing as the selection factor.


wink.gif If end users can't think for themselves and just want to save cost at setup, we have to think for them from start to avoid further grief for everyone.



Jrasef,

I wish to take a look at the 2 x written report as well. It would be "For My Personal Information Only".
If possible, could you please send it to my email: stupidnp@yahoo.com



That's the progress so far till date and I am also relying on someone in the local soft starter industry who's company is not involved in these failures to comment my findings. I have been quite a bother to him asking Questions/comments from basics to in-depth.

Till date, he's the only one from another company who is talking sense and making logical comments about the problems I am facing!! The comment made by him has line up with what you guys are saying here.

Big Thanks to everyone on inputs and sharing the knowledge.
I will update you guys further if I will to get any results.


More digging for now biggrin.gif ,

Cheers,
A DIGGER TO SCIM INDUSTRY








#19 marke

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Posted 26 August 2007 - 05:31 AM

Hello SCIM

I personally, would be setting a unit up in the lab with some test gear to measure exactly what is going on at the beginning of the start and as the motor reaches full speed.
Knowing what to look for, is a major benefit and probably something that needs the right skill and experience, however there is a good chance that it could uncover what is actually happening.

Good luck, but do not expect them to help you to prove them wrong, they will not do so!!

I like threats to sue, it usually means that the other party has something to hide and is running out of options.
I have had plenty of threats over my website and in particular, my paper on energy savers. - it amazes me how 24 hours turns into years!! I have had numerous threats giving me 24 hours to remove my web site or appear in court. Never happened yet.

Best regards,

#20 mariomaggi

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Posted 26 August 2007 - 08:27 AM

Quazi,
I think that the voltage regulators on 750 kVA generators were not suitable to manage non-sinusoidal voltages, as happens during startings with soft starters. Probably such electronic regulators try to increase voltage for short times over the voltage rating of thyristors.
Do you checked the voltage rating of such thyristors, or do you have the part number?

Regards
Mario



Mario Maggi - Italy - http://www.evlist.ithttps://www.axu.it





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