Softstarter "inside delta" connection. Why only for some kind of softstarters ?

Softstarter "inside delta" connection. Why only for some kind of softstarters ?

Electrical topic:

I am pondering which softstarter for a relatively large motor.
Maybe I can install the softstarter inside the delta as opposed to in the line. This reduces the current by a factor 0.58.

However, on page 46 in this handbook it says that only few softstarters can be connected inside the delta, but does not describe the reason.
http://www.scribd.com/doc/7271011/Soft-Starter-Handbook

And if I check some Siemens softstarters, the series 3RW30 and 3RW40 the inside delta connection is not mentioned.
For the 3RW44 series the inside delta connection is mentioned.

Anyone knows why some softstarters can be used inside the delta, and some not ?

"inside delta" connection

Inside delta operation requires extra circuitry to calculate proper firing angle. They also have SCR / IGBT's with a wider firing angle range. Hope this helps. I will try to post a article on my blog. http://www.plc-electrical-industrial-help.blogspot.com/ Thanks.

Remember also that you need both ends of all the motor coils to do this. So, a three lead or nine lead motor is not a candidate.

As a general rule I discourage doing inside delta in favor of conventional motor lead connections to simplify troubleshooting and wiring between the motor and the starter.

Softstarters are rather cheap anyway. Why press your luck?

Dont understand the "firing angle" explanation, but I guess it means there is an explanation.
The link does not lead to something.

Because of the size of the motor it will be six leads any way we do it.
It is for Taiwan, so 3x220V --> Bigger Softstarter. It is also a class 20 start, so that means a relatively big softstarter too.
The motor is In 500A @ Un 220V. That becomes 290A if the softstarter is in the delta.
I need to save the space, the expense, and also since we are thinking about omitting the bypass to minimize the dissipated heat in the panel.

One other reason some softstarters cannot be used inside delta is due to them being only "two legged" softstarts. One of the phases passes straight thru.

At your size tho, I don't think you will run into that. And with those high currents, I suppose the savings is significant.

Your comment about the bypass I don't understand. Unbypassed SCR's generate heat, bypassed SCR's don't. Maybe you were saying that the extra heat was ok in view of the savings eliminating the bypass.

DickDV said:

Your comment about the bypass I don't understand. Unbypassed SCR's generate heat, bypassed SCR's don't. Maybe you were saying that the extra heat was ok in view of the savings eliminating the bypass.

Click to expand...

It is a question of an existing panel size where the bigger softstarter has to be squezed in. Omitting the bypass generates another problem though. Without a bypass there will be more dissipated heat in the panel, and more so if the current is 500A in stead of 290A. And the panel has to be in a warm location (Taiwan). So it may mean we have to add panel cooling just because of the softstarter.

Did a bit of Googling:
Information from Danfoss about why you can't use the full 1.73 ratio for reduced sizing of the Softstart, see page 3.
http://danfoss.tpu.ru/files/MCD-3007.pdf

And found this discussion from 2007 on another forum, one of the participants has a strangely familiar name:
http://www.eng-tips.com/viewthread.cfm?qid=177014&page=1

Bryan

Thanks Bryan.

The Danfoss manual was interesting.
Since a regular 3-phased softstarter has to be modified with a kit in order for it to be capable of "inside the delta" I guess it is not to be taken lightly.

All the other warnings are already heeded.
We will be using a contactor in the line, and there will be fast semiconductor fuses, and we are reading the ratings from the manufacturers specs, rather than estimating it by ourselves.

The AB SMC Flex can also perform this inside delta configuration however as you should note for delta an isolating contractor is required since the delta terminals of the drive directly connect one end of each winding to the Smart Starter's supply.

http://literature.rockwellautomation.com/idc/groups/literature/documents/um/150-um008_-en-p.pdf

I am getting it now.

Why "low-cost" 2-phase softstarters cannot be used for "inside the delta" connection:
When the 2-phase softstarter is connected in line with the motor, the 3rd phase is regulated because it is interconnected with the 2 phases that are regulated with SCR's. This works with the motor in both star and delta connection, because the current flows via the 2 regulated phases.
If the 2-phase softstarter is connected inside the delta, one phase is not regulated at all. If the motor is up and running 100% it would be OK. But when the motor is to start or stop regulated, it will not work. At standstill, the one unregulated phase still has full voltage over the winding.

With 3-phase softstarters it may or may not work:
The problem may be that the motor current is measured in only 2 of the phases.
The softstarter calculates the SCR trigger point based on the shape of the motor current curve. Because in a regular inline connection the phases are interconnected, the unmeasured phase current can be deduced from the two other phases. With an inside the delta connection, the 3 phases are not directly interconnected and the unmeasured phase's current shape cannot be calculated accurately enough for the trigger time to be correct. So for a 3-phase softstarter one must check that it is specifically designed for "inside the delta".

Okay, I think my application is a suitable reason to extend this thread.

I have a new project involving a frozen block grinder (80lb blocks of beef) with a 200HP motor. The OEM wires the motor delta, but they want too much for a control$ package, so I have a price list put together for what I think I need to use an SMC-Flex, but now my concerns turn to inside the delta wiring.

Can I use the SMC-Flex soft starter for "outside" delta motor wiring as long as it is sized correctly? EDIT:found answer for this part In Bryan's 2nd link above.

I don't have the full nameplate data but I spoke to people in engineering for the supplier of the machine, and they told me they wire it delta, and gave me the RPM and FLA, said they wire it Delta with the soft starter they offer and quoted us for wye-delta contactor starter package which we won't purchase. So, I assume, (for now, until I get the whole part number) that FLA number I wrote down at work is for delta operation.

I must keep an existing disconnect out on the floor at the machine and the existing wiring from the 300HP system that is being removed, so would my disconnect need to be 6-poles in order to make the equipment safe for washdown if I used inside the delta wiring?

I should probably just call RAM after searching here for SMC Flex, I found my comments about my last experience with them...my all A/B system is up to $12k already...that's just for parts, not installation labor.

Please advise on the outside the delta sizing, and comment on the use of isolation contactors and semiconductor fuses...I think I will be doing a redesign over the weekend.

I want to use the SMC-Flex and add a 20-comm-d to be able to give the SCADA programmer all the data he needs to measure (count) product through this machine and report faults, but I would consider advice for other mfgs that offer d-net.

Thanks,
Paul

try on Zener soft stater ..www.zener.co.au..

why not look at the weg 06 softstarter range thet are suitable for inside delta and have inbuilt bypass contactor

I have decided that I will use outside the delta wiring so that I can keep the $10k disconnect from the older larger HP machine. I also am leaning toward not using a line side isoltion contactor, but I have been contemplating using a load side contactor tied to the safety circuit. I have not done enough investigation to determine if this is acceptable or not.

And, I am still trying to decide what type of branch circuit protection to use on the line side of the soft starter.

Okay, for this somewhat expensive controller, I want semi-conductor fuses.

Simple, right? Just look them up in the SMC Flex book, but, due to past experiences and the rather demanding load of the machine, we are leaning towards oversizing the controller which leads to a bit of detective work for me to figure out the fusing.

I ran the SMC Flex SCCR Wizard and it spit out some part numbers for me.

I need help understanding part of its results from folks more experienced with sizing these things.

Okay, google may have come through for me with the fuse part number:
http://www.mgl.com.hk/mgl/documents/Ferraz_PDF/D-SCAC/PC3xaR69VAmBlade.pdf

Boss was shocked at the price difference between A/D and A/B for the isolation contactor, made him scared of the cheap fuji, so he wants A/B for the contactor and probably the fusible disconnect too.

The first contactor I selected was over $3000 from A/B, but today I used the config tools for a safety contactor and found one rated for 300 amps for about $1900 before discount.

I am not sure 300A is large enough to meet code and whether I am allowed to use the fact that it will be interlocked with the SMC in properly sizing it.

Too bad A/D does not make larger size fusible disconnect switches. The A/B unit I selected is $2743 before discount.

The motor FLA is 226, so we might be way overkill, but as long as I get the fusing right, I'd rather have too much umph in the starter than not enough to let this big machine grind up large hard frozen blocks of beef. I have read one mention of oversizing the soft starter causing a problem, so if I am setting myself up for an uh-oh, please let me know. With the programmability of the SMC Flex, I do believe I can tell the 250HP controller that the motor FLA is 226 and be alright.

Again, this will be a line connected motor, not inside the delta.

Thoughts and advice welcome, please.
TIA,
Paul