IEC Duty Motors for Crane applications 1

[NickParker]

Can S1 duty IEC Motor be used in place of S4 duty motor for crane application? Have a proposal from vendor; The motors are for overhead Cantilever crane 16t.

All the motors are of S1 duty (Slewing, Hoisting, Travelling Motors).

 

[che12345]

Dear Mr. NickParker (Electrical)(OP)16 Jan 23 13:05
"....Can S1 duty IEC Motor be used in place of S4 duty motor for crane application? Have a proposal from vendor; The motors are for overhead Cantilever crane 16t.....All the motors are of S1 duty (Slewing, Hoisting, Travelling Motors)...."
1. I take it to mean that the vendor is proposing (with the same kW rating) S1 duty motor in replace of the S4 motor.
2. Refer to IEC:
(a) the S4 duty cycle resembles that of a crane operation cycle, i.e. Start - load - off say within minutes. Stop for some minutes and repeat the start cycle. The off time is usually > the run time. However, there can be numerous start-run-stop in an hour.
(b) the S1 duty does NOT indicate the Start but with continuous loading for long hours to stop.
(c) it is the responsibility of the purchaser to declare the duty (e.g. S!....S10)
3. If above 2 (c) information is NOT available or contracture agreed upon; a S1 duty motor of the same kW rating would be fine as a replacement of a S4 duty motor.
Che Kuan Yau (Singapore)

 

[NickParker]

3. If above 2 (c) information is NOT available or contracture agreed upon; a S1 duty motor of the same kW rating would be fine as a replacement of a S4 duty motor.

Does that mean S1 duty can be used in lieu of S4 for any crane application and there will not be any issue. If S1 can be used, why do other duty motors (S2, S3..) exist? Just curious!

 

[edison123]

No, it would not be fine. S1 duty motor will fail on S4 duty. Unless all these motors are VFD operated.

Muthu

http://www.edison.co.in

 

[edison123]

I have a 60 ton EOT with all 3 motors S1 duty rated but all VFD operated. So the stator currents never exceed the rated.

Muthu

http://www.edison.co.in

 

[Gr8blu]

NickParker: Why do ratings other than S1 exist? Think of it like a percentage load (over the long haul). An S1 duty is continuous - which means there is no "off" period where the motor can cool down. So the design has to be very thermally robust - which in turn means a fair bit of mass and/or surface area to dissipate the heat. As the duty cycle starts to have longer "off" periods (S2 shorter than S3 shorter than S4, etc.) the ability for the machine to run into a short time overload increases - or in other words, the designer can get by with a bit less mass and/or surface area for the same power output. The exception to this is probably S10, which is based on a very high peak / irregular loading cycle. In this case, the machine rating has to be enough for the WORST CASE AVERAGE rating over a rolling 5 minute window. Why 5 minutes? Because that represents the (typical) length of time for the main winding (stator, in AC or armature in DC) to reach a stable operating temperature. As an example: a steel mill I once designed a machine for indicated the machine should be rated for 6000 HP. This was because they took the average power load over the entire rolling cycle (roughly 38 minutes). However, when applying the 5-minute average, I found that the amount of work done in the first 6 minutes meant that the machine was delivering an average loading of 11500 HP (during that particular period; it was much lower during the remaining 32 minutes of the complete cycle). So the machine was designed to handle 11500 HP continuously (as a thermal rating) but only had a 6000 HP nameplate - which is what the user wanted. For reference - the application was a steckle mill, where the same machine/set of rolls acts as both rougher and finishing stand.

Converting energy to motion for more than half a century

 

[che12345]

@ NickParker (Electrical)(OP)17 Jan 23 10:27
" #1. .....3. If above 2 (c) information is NOT available or contracture agreed upon; a S1 duty motor of the same kW rating would be fine as a replacement of a S4 duty motor.....#2. Does that mean S1 duty can be used in lieu of S4 for any crane application and there will not be any issue. #3. If S1 can be used, why do other duty motors (S2, S3..) exist? Just curious! "
1. Yes. See IEC S1 duty does NOT show the starting period, while S4 duty shows the starting and the running period. For S1 duty, the starting period say not exceeding 30s is negligible to the running time say 8-10h.
1.1 The load (kW) profile of S! duty would be >> than S4 duty for the same duration, say within 1h as a unit time. Therefore, a S! duty motor of the same kW rating would be fine for S4 duty.
2. S1....S9 load profile are illustrated in IEC standard. Where the load does NOT requires S1 duty, a suitable S1....S9 may be chosen; at a lower cost and size/weight etc.....
Che Kuan Yau (Singapore)

 

[che12345]

@ Mr. edison123 (Electrical)17 Jan 23 13:41
".....No, it would not be fine. S1 duty motor will fail on S4 duty. Unless all these motors are VFD operated."
I am of the opinion (per IEC) that:
1. (a) S1 duty does NOT show the starting period, while S4 duty shows the starting and the running period. For S1 duty, the starting period say not exceeding 30s is negligible to the running time say 8-10h.
(b) for S4 duty, the running period say 10 times the starting period say 10s , and off for say >>> run period. However, it is expected to start again after a long off period, say within 1h.
(c) The load (kW) profile of S! duty would be >> than S4 duty for the same duration, say within 1h as a unit time. Therefore, a S! duty motor of the same kW rating would be fine for S4 duty.
2. It depends on numerous factors, but as an indication; S1 duty motor can handle 1.15 time the load operating with S4 duty.
BTW Attention: This 1.15 time capability is NOT the same as the "service factor 1.15" which is a "fictitious" term coined up by the US manufacturers (NEMA). The tern is NOT recognized by the IEC, an international community.
3. The S1...S9 duty definition is independent of the use of VFD, soft starting, DOL, SD, AT .... etc as the starting period is << to running time. It is understood that starting surge would be 6-10 times the running current but of short period say NOT exceeding 30s.
Che Kuan Yau (Singapore)

 

[edison123]

che

AC1 vs AC4 contactors. Think on those lines.

There is a sound reason for these motor duty ratings. Your theory of S1 duty motor is enough for all motor applications is plain wrong.

Muthu

http://www.edison.co.in

 

[che12345]

@ Dear Mr. edison123 (Electrical)18 Jan 23 08:57
".....AC1 vs AC4 contactors. Think on those lines....There is a sound reason for these motor duty ratings. Your theory of S1 duty motor is enough for all motor applications is plain wrong. "
1. I fully agreed with you that there is a need of AC1...AC4 ...for contactors, dependent on the switching application. Where AC4 is > AC1 etc.
Please see my earlier post dated 17 Jan 23 23:24.
" The same is also S1....S9 load profile are illustrated in IEC standard. Where the load does NOT requires S1 duty, a suitable S2....S9 may be chosen; at a lower cost and size/weight etc....."
2. I am of the opinion that S1 > S2....S9. Therefore, a S1 duty motor (of the same kW rating ) would be fine for S2---S9 duty application.
Che Kuan Yau (Singapore)

 

[che12345]

@ edison123 (Electrical)18 Jan 23 08:57
"....che....AC1 vs AC4 contactors. Think on those lines. There is a sound reason for these motor duty ratings. Your theory of S1 duty motor is enough for all motor applications is plain wrong " .
1. I look into the IEC standard and arrived at the opinion based on the following stated in the IEC document:
(a) S1 Continuous running duty,
(b) S2....S9 are various forms of intermittent, periodic duty including starting,
(c) S4 for intermittent period duty with starting e.g. S4 25% J[sub][/sub] = xyz...
2. Based on above 1 , it is clear that S1> S2....S9, onerously.
3. If a S1 duty motor is unable to fulfill a S2...S9 duty load, the S1 motor is under-sized. BTW: There is NO duty more onerous than S1. Excluding S10 .
4. It is my opinion that a S1 duty motor with the same kW would be fine for any S2...S9 duty load.
Che Kuan Yau (Singapore)

 

[davidbeach]

Continuous running means thermal equilibrium. If the cooling is adequate all is well and the motor never overheats. Starting is a process of dumping a lot of heat into the rotor in a quick hurry and then hoping it runs long enough so that there's enough cooling to get back to a reasonable heat level. That's why motors can run continuously but have a limited number of allowable starts during a period of time. I don't know the IEC ratings, but if you took a motor that was rated for two starts per hour, aka a continuous duty motor, and started it 20 times an hour it wouldn't last long, even if it only ran for 20 minutes per hour. What ever the standard you need a motor that can take the required number of starts.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[edison123]

che


Learn about I[sup]2[/sup]t, thermal equilibrium and no. of hot starts allowed for S1 duty motors before making such bold claims.

Again, there is a reason for standards mentioning so many duty cycles and OEM's asking for duty cycles for each application.

Muthu

http://www.edison.co.in

 

[che12345]

@ Mr. edison123 (Electrical)19 Jan 23 06:43
" #1. ....Learn about I2t, thermal equilibrium and no. of hot starts allowed for S1 duty motors before making such bold claims."
Referring to IEC standard, no. of hot starts allowed for S1 duty motors is irrelevant on the "duty " . The document shows the duty, NOT the number of starts permitted etc.

"#2. ... there is a reason for standards mentioning so many duty cycles and OEM's asking for duty cycles for each application ".
IEC document does NOT mention " so many duty cycles " . It differentiates different duty, NOT the duty cycles. A motor may be subjected to say S4 duty ten cycles say in an hour; and to same S4 duty , but say five cycles for the same period of time. Both are subjected to the same S4 duty, but with different number of cycles within the same time. Obviously, the former is more onerous than the latter.
This example illustrates the difference between "duty" and "duty cycle". Where the term "duty" has nothing to do with "duty cycle". For a load, the duty say S1...S9 does NOT change, but the number of cycle can be different drastically !.

3. It is obvious that both "duty" and " number of cycle" are relevant on the motor sizing.
Che Kuan Yau (Singapore)

 

[Gr8blu]

All -
Some perhaps relevant motor design history is in order.

In the early days, machines were expected to operate in a thermally-acceptable fashion at power loads up to the listed nameplate value. This worked just fine when the driven loads were primarily fans, pumps, short-run conveyors, and small compressors. The next step was to apply these same machines to industrial processes such as paper-making and metal rolling. All of a sudden, it became imperative to have enough "stock" on hand to see a company through a outage event (regardless whether it was planned or unplanned). To that end, the users asked the manufacturers to produce some equipment with some "extra" thermal capability. The result was the "service factor". The intent of this additional capacity was to enable the user to accomplish one of two things: either overload the machine for a few days before a planned outage so that there was extra "stock" on hand to meet demand, and/or to run at overload for a few days after the outage (planned or unplanned) to make up the "stock" shortfall. It was never intended to be a way to operate above nameplate on a continuous basis instead of uprating the capacity (or initially under-sizing the capacity) of the equipment to run the process.

However, that is indeed one of the things the term has become synonymous with. The other is that the longevity of the equipment can be reliably traced to the thermal stress on the winding(s). The thought process became something like "if we build in extra thermal margin, we're going to have extra life because we won't be pushing the machine as hard, so we won't need to upgrade/replace it for another 20 years". Hence the progression toward machines with a non-unity service factor being restricted to unity (or very slightly above unity) loading over the long term.

I partially agree with che: the IEC world does not CURRENTLY accept the concept of a non-unity service factor (or capability). However, this was not always the case, for the reasons given in the opening paragraph. As to the term "duty": IEC defines it as the following.

Duty is defined as being the load condition the machine is subject to, including (if applicable) the periods of starting, electrical braking, operating with no load, and rest, as well as their duration and sequence in time.

The key thing to remember here is that ALL these things must be taken into account in the machine design. An S1 duty with a minimal start/brake capability over the life of the machine may not be as robust when applied to an application with another duty (e.g. S4) compared to one that has been specifically designed to meet that S4 duty - which happens to have similar "continuous" loading and increased starting/braking cycles. The differences in design may be related process-imposed thermal, electrical, environmental, and/or mechanical stress.

Converting energy to motion for more than half a century

 

[edison123]

che - In what world?

With all due respect, I know you are an expert in switchgears but motors and transformers is another field altogether.

I service, repair and rewind all types of motors and I can confirm a 10 HP S4 duty motor is a different beast when compared to a 10 HP S1 duty motor, both in design and construction.

Muthu

http://www.edison.co.in

 

[che12345]

@ Mr. edison123 (Electrical)21 Jan 23 04:20
"....#1. (no. of hot starts allowed for S1 duty motors is irrelevant on the "duty ")
My opinion is based on the the IEC standard :
(a) definition of "Duty" has nothing to do with "number of starts". Load A has the loading characteristic/profile of say S4. It does NOT change with time i.e. every time it stsrts, it takes say 10s , load for say 50s , then off. The off duration is dependent on the next cycle. The next cycle may vary say 5s, 5min, 5h etc. i.e. the NEXT " starts" . Note: the "duty" is the same i.e. starts for 5s, load for 50s, then stop. Irrespective of number of cycle per hour etc.....
(b) S! "duty" is more onerous than S4.

#2. che - In what world?
In the IEC world. According to IEC standard.

#3. I service, repair and rewind all types of motors and I can confirm a 10 HP S4 duty motor is a different beast when compared to a 10 HP S1 duty motor, both in design and construction.
The "duty" has nothing to do with the kW rating. Any say 1.., 10... 100...kW motor can be rated S1 duty or S2....S9 with qualifying conditions. .
A S1 "duty" motor (with the same kW rating) would be fine for say S4 duty load, with the same number of starts.
Che Kuan Yau (Singapore)

 

[FacEngrPE]

I live in the NEMA / NEC world, but have encountered cranes built in the IEC world. I see the situation this way.

In the US the CMAA standards need to be used to match a crane duty to the design margin needed for motor selection. In the IEC world there are similar standards for selecting the motor duty class and design margin.

Comparison of Standards - Comparison of FEM, HMI, & CMAA Classifications Class I - Locations The ISO column here is most likely ISO 4301-1:2016 Cranes — Classification See the complete list of ISO Crane Standards here

https://www.iso.org/ics/53.020.20/x/

IEC 60034-1 (Rotating electrical machines) defines several duty characteristics, explanation here. it does not tell you how to apply the motor to a crane, that is in ISO 4301.

The proposed change from S4 to S1 might or might not work depending on the duty the crane encounters. As there has been a past motor failure, I am inclined to think the S-1 motor would have a significantly shortened service life or might turn out to be completely unsuitable.

 

[che12345]

@ FacEngrPE (Mechanical)
"....The proposed change from S4 to S1 might or might not work depending on the duty the crane encounters. As there has been a past motor failure, I am inclined to think the S-1 motor would have a significantly shortened service life or might turn out to be completely unsuitable."
1. I wish to point out that per IEC:
(a) " duty " i.e. S1....S9, where S1 is more onerous than S2>S3>S4>S5..... The "duty " has nothing to do with the "number of cycles" per unit time.
(b) " duty " S1 ....S9 show the loading patent i.e. start-load-rest; next cycle, stat-load rest ....
(c) " duty " has nothing to do with kW rating. Any kW motor can be rated with duty S1, or S2....S9 . Where S1 is more onerous i.e. S1> S2> S3>...S9.
2. " duty " has nothing to do with the "pull-up torque", "starting current surge value" and the "rotor moment of initial" , etc...which are important factors for a crane motor .
3. A S1 duty motor with the same kW, same data as above 2, same operational condition (cycle) as above 1, would be fine to replace a S4 duty motor.
Che Kuan Yau (Singapore)

 

[FacEngrPE]

Che

My caution is due to having run into some cases where thermal performance is the more critical part of the motor selection. The same situation Gr8blu describes.

Mostly - lower duty cranes usually have more idle time in their operating cycle. That can make thermal performance less important. For port and mill cranes, more care is required.