Motor jogging factor. 2

[beyond86]

Gents, I have some problems with understanding information from datasheet of induction motor. I hope you will help me.
I have induction motor 10MW. I found followed information in datasheet:
Safe stall time:
a) @ 100% V 9 sec (hot), 14 sec (cold)
b) @ 77 V 15.2 sec (hot), 23.6 sec (cold)
c) Cooling down time: 1800 sec (to allow one restart)
d) Jogging factor: 2 hot, 2 cold
So, my questions are:
1. How much times I can restart motor immediately after stop?
2. What is jogging factor means? (Is it means that I can restart motor 2 times from hot\cold?)

Currently, I want to allow restart motor once and after inhibit restart during 1800 sec.

 

[beyond86]

In attached file you can find full datasheet.

 

[LionelHutz]

After cold start wait 1800 seconds (30 minutes) then you can start one more time. After that I don't know when you can start again unless that the datasheet gives another number since I didn't look at it.

 

[beyond86]

LionelHutz, please clarify your answer. Why after cold but not hot?
What is jogging factor means?

 

[edison123]

A nice explainer.

https://instrumentationtools.com/motor-jogging/

What does your 10 MW motor drive? Such large motors are not frequently started and stopped due to high thermal time constant.

Muthu

http://www.edison.co.in

 

[LionelHutz]

I've never seen a definition for jogging factor and I've never seen jogging factor used before on a datasheet so I have no clue what that could mean. Ask the manufacturer.

 

[beyond86]

A nice explainer.

Yes, I saw it, but the article didn't clear my understanding.
The motor drives compressor (boil of gas at LNG plant).
According to process, after stop we have only 15 minutes to restart the motor, if not we must perform preparation of process which takes more than one hour.
So I try to understand, can I immediately restart the motor after stop.
My concern about this:
c) Cooling down time: 1800 sec (to allow one restart)
As I understood, I can make one restart after stop, and if this restart doesn't success, protection device will inhibit followed restart during 1800 sec.

 

[edison123]

Most motors are rated S1 duty which is continuous duty. If you want frequent starts and stops, google motor duty cycles or talk to the OEM. At this level of power, it will not be a run of the mill motor.

Muthu

http://www.edison.co.in

 

[electricpete]

Agreed, at this size things tend to be motor-specific and there doesn't appear to be much more that can be guessed from this info provided.

Contacting the motor manufacturer for clarification is good advice.

I will mention it may also be productive to contact the customer who purchased the motor. The reason is that the data sheet states "to be completed by the supplier" and as such I suspect the blank data sheets (and the associated definitions) may have been part of the purchase specification.

=====================================
(2B)+(2B)' ?

 

[beyond86]

LionelHutz, please explain this:

After cold start wait 1800 seconds (30 minutes) then you can start one more time.

Why did you decide like that?

 

[LionelHutz]

First start is assumed to be a cold start so cold start then cool down for 30min before doing one re-start. Also, the data says "to allow one re-start". If that was the cooling down time after a hot start then you could re-start every 30 minutes.

 

[beyond86]

LionelHutz, thanks!

 

[Gr8blu]

beyond86 You need to look at the IEEE, NEMA, and IEC definitions of "cold" vs "hot" starts and what - exactly - that entails.

COLD START: ALL PARTS OF MACHINE ARE AT AMBIENT TEMPERATURE
HOT START : WHENEVER ANY PART OF MACHINE IS NOT AT AMBIENT TEMPERATURE

When a machine attempts to start the FIRST time, it is effectively at the same temperature as the surrounding medium (usually air). This is considered a "cold" start. During the start attempt, machine windings and other components will generate heat or become warmer due to simple proximity to a heat generator. The design of the machine (in terms of thermal mass and torque generation), coupled with the load characteristic (inertia, torque required to accelerate, acceleration time), determine how much heat is generated by a given attempt.

The "default" sequence is 2 cold, 1 hot. This means one attempt from ambient, plus one immediately afterward OR one attempt after the machine has reached a steady-state operating temperature below the maximum allowable temperature rise. Some designs use a 3 cold / 2 hot sequence ... which effectively means components don't get as hot during a given acceleration attempt.

The "start sequence" instruction from the manufacturer usually includes some sort of discussion regarding how long a dwell time is necessary after a "hot" start the next attempt can be made. The duration has to do with whether the machine's rotor is spinning at or near running speed, thus moving air within the machine enclosure. For most machines with a rotor turning at or near operating speed, the dwell time is 20-30 minutes. For machines where the rotor is at standstill (i.e., the machine stalled and never got turning in the first place), the dwell time is typically 45-60 minutes.

Further to your initial discussion, I also see you want to perhaps start the motor in a (relative) hurry after a shutdown, presumably to limit difficulties with the driven load (compressor) such as condensation. In this case, you'd also need to know how long the motor takes to spin down to zero speed when connected to the load (should be on the order of seconds, if not tens of seconds) AND whether the machine can be restarted "on the fly". There is a very short period of time where you can reclose the breaker and "catch" the motor ... for something in this power/speed range, that is likely to be under six seconds. If you cannot reclose successfully in less than that period, you will have to wait until the unit comes to a complete stop. If the machine has reached steady state operating temperature before the event, you would have one less than the listed number of "hot" start attempts to try without waiting for the defined dwell time.

Lastly - there is often one other line to the starting discussion. That is the MAX Number of start attempts allowed in a 24-hour period. Typically, this is SIX. In case you're interested, that comes from the wear and tear associated with the start itself. Most machines are designed to handle one start per day, five days a week, fifty weeks a year, for twenty years (i.e., 5000 starts). If you actually tried to operate at 6/day, your machine life expectancy would be about 27 months.

Converting energy to motion for more than half a century

 

[edison123]

Gr8blu

Is that 5000 starts @ 1 start/day=20 years and 6 starts/day=27 months empirical or theoretical ?

Muthu

http://www.edison.co.in

 

[LionelHutz]

My experience would say that's just a theory.

 

[Gr8blu]

edison123 The physics and materials properties of the machine components and how they react (individually and jointly) to thermal and mechanical stresses from a start attempt are well understood by the equipment designers (i.e., motor OEMs). Everything has a fatigue cycle limitation - including mechanical fits and electrical contacts such as the bar-to-ring joint on a squirrel cage induction machine (or synchronous rotor). The 5000-start limit is a mathematical approximation, but empirically valid. Think of it as being the same as an L10 life for a bearing: 90 percent of bearings will reach the L10 life limit; some may last considerably longer under optimum operating conditions.

Also consider that most general-purpose industrial machines were originally intended to be "turned on and forgotten" - which means at best a once-per-day start. In many cases, the process would operate several days continuously with a few "down days" every once in a while.

OEMs also recognize that initial commissioning of a process encompasses several unknowns, and that the number of attempts during this period will therefore be considerably more than the norm. This is where the "max number per day" comes in, and why relay manufacturers use a "thermal model" approach to shave a few minutes here and there off the dwell times.

Is the 27 months empirical? No. It is obtained by dividing the known "start life" value of 5000 by the number of starts per day (in this case, 6) to obtain a probable number of days before the likelihood of damage to the equipment becomes highly probable.

Converting energy to motion for more than half a century

 

[edison123]

Thanks, Gr8blu.

I often tell my clients 20-25 years is the insulation life. This info on frequent starts reducing the life drastically by nearly 90% will jolt them into taking care of their machines better.

Muthu

http://www.edison.co.in