Inside Delta Connection
Inside Delta Connection
(OP)
I have heard references to using an "Inside Delta" connection when replacing a wye delta starter with a solid state soft start. Can anyone explain what this connection is or provide links to information on it.
Thanks
Thanks





RE: Inside Delta Connection
By connecting the SCRs in series with the windings, the current controlled by the SCRs is reduced and therefore a smaller SCR can be used, or a larger motor can be used for a given soft starter size.
You must have a soft starter designed for this type of operation, many three wire units will be damaged if used inside delta and certainly will not give adequate control.
With inside delta connection, when the starter is turned off, there is still full voltage on one end of the motor windings, so a contactor must be used on the supply.
There is an app note at http://www.aucom.co.nz/technotes/me00055.pdf
Best regards,
Mark Empson
http://www.lmphotonics.com
RE: Inside Delta Connection
http://www.benshaw.com/products/lv/rsm.shtml
http://www.benshaw.com/literature/index.shtml
http://www.grossautomation.com/abb/pdf/AC1061.pdf
(ABB literature)
etc.
RE: Inside Delta Connection
RE: Inside Delta Connection
When you connect the SCRs inside the delta loop, the shape factor of the current waveform through the SCRs is considerably different from that when the SCRs are controlling line current. The conduction angle at half voltage in normal operation is in the order of 150 degrees, while the conduction angle at half voltage inside delta connection is about 90 degrees. For the same average current, the on time is much shorter so the instantaeous current is much higher leading to a higher power dissipation and therefore a higher junction temperature. It is safer to select the starter on the effective current being 2/3 rather than 1/rt3. This will ensure long term reliability similar to the normal connection.
Best regards,
Mark Empson
http://www.lmphotonics.com
RE: Inside Delta Connection
Be very carefull about using "Inside the Delta" soft starters without the isolation contactor as Marke explained. You will see in some of the website referenced that several manufacturers do not mention this issue at all, probably because it adds cost and somewhat defeats the purpose of using this technique. If there is no contactor, and one SCR shorts in the soft starter, you WILL loose the motor! The only other alternative is to have shorted SCR detection and a shunt trip mechanism on your circuit breaker feeding the motor. Even with this, post signs warning electricians that the motor leads are hot even if the starter is "off".
Marke,
Wow, I had never considered that issue about SCR sizing inside the delta but you are absolutely correct. I learn something new every day.
Infomaniac:
Not to be nit-picky, but the current is not reduced BY 58%, but TO 58%, which would be reduced BY 42%. Most of us knew what you meant, and your example was correct. I just felt compelled to clarify that for the newbies.
Subvert the dominant paradigm... Think first, then act!
RE: Inside Delta Connection
In regards to the isolation contactor, the better solution is to use a 'fault' contactor that is installed on the three 'hot' motor leads. With this type of configuration, the fault contactor is designed to open anytime the softstarter fault relay changes state due to a fault. This will de-energize the fault contactor and open the three 'hot' leads. This is very common practice (espcially in the hydraulic elevator industry where many hundreds of thousands of softstarters are being used inside the delta) that works very well. We have a lot of experience with connecting softsarters inside the delta and have no problems at all with this configuration.
RE: Inside Delta Connection
RE: Inside Delta Connection
I agree with your phase angle change inside the delta completely. That is why our softstarters are programmed to adjust the phase angle in the algorithm when it is placed inside the delta windings (there is a dip switch on the softstarter to let it know that it is being connected inside the delta windings).
In addition, most softstarters are all rated 115%-125% continuously so even if the phase angle where not considered, the softstarter would not normally have problems.
The lack of problems is evident due to increased usage by large hydraulic elevator manufacturers such as Otis, Kone, and Thyssen-Krupp. These larger manufacturers have almost entirely switched their motor control schemes to softstarters for hydraulic elevators where the softstarters are used inside the delta of the motor windings. They have been using softstarters for over a decade in this configuration and consider them superior to normal Y-D starters. The installed base is over 50,000 pieces per year.
RE: Inside Delta Connection
The important point that I was making was that several soft starter manufacturers push the inside-the-delta configuration without mentioning the fault contactor, which I think is risky at best. I wanted the uninitiated like VicP to be wary of those that hawk the cheapness of it by leaving out important components.
I agree that there is nothing wrong with the concept or success of this application from an engineering standpoint. I do, however have a problem with widespread use in an unfamiliar workplace environment, and by that I mean the general US industrial market. I believe that the success of this in the elevator industry, even in the US, is due chiefly to the fact that elevator mechanics and electricians are very familiar with Y-Delta motors and starters because that is what is commonly used in their industry. The same may also be true of the refrigeration industry and a few others, where OEMs have a specialized maintenance / service force. My caution comes from seeing many many "industrial" electricians who have been given a Y-Delta motor to replace, and did not know anything about them or how to connect them. One can argue that it should not be so, but I have seen this problem in the lumber, rock crushing, air compressor, pumping, injection molding, metal working and several other industries. As a rule, US Electricians are not experienced enough with Y-Delta because they don't run into it often enough. This may come as a shock to people in Europe and Asia where it is common, but trust me, outside of a few specialties we do not use Y-Delta very often in the US. So even if you do understand it, chances are the next guy will not, and damage to the motor, controller and machine may result. For my money, connect a full sized soft start to the motor in Delta only. It also opens up the ability to replace the motor in a hurry with a standard delt wound motor. Just my 2 cents.
Subvert the dominant paradigm... Think first, then act!
RE: Inside Delta Connection
RE: Inside Delta Connection
http://www.nsoem.com/Benshaw/literature/manuals/890001-15-xx.pdf
for more info. Certainly, a catastrophic failure can happen in the softstarters; however, it can happen in other starting arrangements too.
RE: Inside Delta Connection
I am a new member to this forum and am looking forward to communicating with you all in future. This post will be short as there is much to do and very little time to do it.
To Marke, keep up the good work. It's nice to know that there are still some people out there that understand power electronics.
To jraef and infomaniac, I find your discussions re the use of 'fault' or 'isolation' contactors very interesting. You will note with all soft starters there is a leakage current that flows even when the SCRs are in the 'off-state'. Therefore if we do as you propose and place a fault contactor in the three hot wires, every time we open this contactor we are in affect opening the output of the soft starter, causing its output voltage to become equal to the line voltage. This presents a potentially hazardous situation, hence the practice should not be adopted!!!
The best solution is to install a contactor (or motor operated circuit breaker) into the line circuit, ie not within the delta loop. Furthermore the contactor or circuit breaker should be de-energised whenever there is no need for the soft starter to control the motor. In other words the contactor should be de-energised on each stop, not just when there is a fault condition.
Inside delta or 6 wire connection is not new technology. It is also very easy to explain and apply if you know how. The 'trap' is that most 6 wire soft starters currently marketed will only operate correctly in one of the six possible connection formats. Unfortunately when these are misconnected all the good smoke tends to escape(they fail)and the user is left with an undesireable experience. I must say this is a product / technology weekness.
I have been directly involved with inside delta connected soft starters for 20 years now. To the best of my knowledge there is only one 6 wire soft starter product available on the world market that will operate in all 6 possible connections formats correctly and is automatically configurating.
I hope that you will find at least some of the above helpful to you.
Regards,
GGOSS
RE: Inside Delta Connection
RE: Inside Delta Connection
Please re-read my post.....this time carefully!
Like you, I am an advocate for 6 wire soft starter installations and have promoted this technology for 20 years. In fact as far as the Australian market is concerned, there is no-one who has done more to establish 6 wire connection as a credible alternative than I.
My comment regarding good smoke escaping relates to the many 6 wire soft starters presently on the market that will only work in one of the six possible connection formats, it has absolutely nothing to do with inside delta operation or the use of fault contactors.
On the subject of fault contactors, I would ask that you draw the electrical circuit to give yourself a full appreciation of why it is un-safe to place the fault contactor in line with the three hot wires only. You will see that this method does not provide off-state isloation. In addition, you might want to consider what would happen to the motor if the soft starter does not provide SCR failure protection and an SCR fails. In such cases the fault contactor will not open and the motor will be severly damaged.
I hope this clarifies my position.
Regards,
GGOSS
RE: Inside Delta Connection
RE: Inside Delta Connection
Done this for 20 odd years.
Mark Empson
http://www.lmphotonics.com
RE: Inside Delta Connection
RE: Inside Delta Connection
There are statutory requiremtns in certain parts of the world that demand an isolation contactor be used even for 3 wire soft starters.
Rather than continue this argument, could you refer me to a link/drawing to ensure that we are not all arguing for the same connection scheme, but have misunderstood each others posts.
Regards,
GGOSS
RE: Inside Delta Connection
In any event, we need not argue and I did not try to make it appear so. If the posts seem offensive, I assure you they are not so not hard feelings. I repsect eveyones opinions. After all, if we did not have varying opinions, then many of the engineering wonders of the world would never have existed.
In regards to a drawing, you can go to ABB's, Allen Bradleys, Siemens, or S&S web sites and search for softstarters. In the softstarter sections, just look for the models designated for hydraulic elevators and/or inside delta configurations. You will find plenty of documentation on the designs which are essentially all the same.
RE: Inside Delta Connection
No offence taken what so ever!
I have reviewed the web sites and related information and from that it appears we have in fact been communicating the same thoughts, but in 2 different languages.
In all cases, where there is a contactor installed, it is positioned in the line circuit (outside of the delta loop) hence when it is de-energised, 3-phase power is totally removed from the soft starter and the motor. To my way of thinking this is an 'isolation contactor'.
My interpretation of previous posts from other forum members was that the contactor (described as a fault contactor) could be installed within the delta loop, thus disconnecting only the three cables directly connected to the motor.
Regards,
GGOSS