Motor frequent start alarm
Motor frequent start alarm
(OP)
I have a 13years MV induction motor(8-poles) driving a reciprocating nitrogen compressor. The HP nitrogen are stored in "bullets" for safety purging/inerting system and pressurising cooling water system, both are for plant emergency shutdowns or trips.
Leaks in N2 or cooling water systems lead to HP N2 quickly depleted. During the early years of our plant, the N2 compressor started twice per day. When there is a leak, the compressor may be auto-started 5 to 8 times a day and this frequent starts went on without detection until I accidently discovered it last year from the process pressure trends.
The motor manufacturer specifies on its nameplate max no. of starts of 1000 times per year, which is about 3 times per day or at 8 hours intervals.
My question may be weird but this is what I am thinking now. I am thinking of finding a "frequent start alarm" that can installed on the motor starter. Do you think whether there is such device exist?
Leaks in N2 or cooling water systems lead to HP N2 quickly depleted. During the early years of our plant, the N2 compressor started twice per day. When there is a leak, the compressor may be auto-started 5 to 8 times a day and this frequent starts went on without detection until I accidently discovered it last year from the process pressure trends.
The motor manufacturer specifies on its nameplate max no. of starts of 1000 times per year, which is about 3 times per day or at 8 hours intervals.
My question may be weird but this is what I am thinking now. I am thinking of finding a "frequent start alarm" that can installed on the motor starter. Do you think whether there is such device exist?





RE: Motor frequent start alarm
"Most people stop working when they find a job"
RE: Motor frequent start alarm
Depending on the frequency of your pumping cycles when suppliing a leak, you may be able to use a similar scheme to reduce your starts.
Yours
RE: Motor frequent start alarm
The cheapest method would be to search out a specialized timer called a "Short-Cycle" timer. They are designed to do just that function in a round about way.
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: Motor frequent start alarm
Jraef's suggestion for a more sophisticated motor protection relay from GE or Schneider would be a better investment considering the size of this motor.
You could also put a gas meter with a pulse output onto the low side of the air compressor or better yet a high pressure gas meter with pulser in between your storage tanks and your process. You could then use a counter that sets off an alarm if nitrogen usage is too high.
RE: Motor frequent start alarm
The HP Nitrogen system is critical for integrity of the plant, we do not want to leave the N2 pressure to drop below the safety level.
As for jraef's advise, I will look for more information about modern digital MPR to see if it can provide a separate output as an alarm but not to inhibit re-starting of the motor.
RE: Motor frequent start alarm
RE: Motor frequent start alarm
"Most people stop working when they find a job"
RE: Motor frequent start alarm
A timer free running that gets reset at each start that is set to the minimum time between starts you want to allow.
A counter that counts up at each start. This counter is reset by the above timer reaching it's setpoint.
A logic block that looks for the counter to exceed a set value. This block would toggle an output.
You could then stick in some latching relay logic and a reset button or whatever else you'd want to make it suitable to your application.
Basically, the logic would allow the number of starts per x time to be exceeded until you reach the counter check and then you'd get an output. For example, you could set the timer to 40min and the counter check to 3. Then, the third time in a row that the motor is started with less than 40 minutes between the starts the counter would hit 3 and give you an ouput. If the starts are more than 40 minutes apart then the counter keeps getting reset to 0 and would never reach 3.
Telemecancique Zelio or Moeller Easy are models of these types of relays. You just program them right from the display on the relay.
I believe this will cover what you want. I'm sure there are other ways to do it but I personally think the price and simplicity of these programmable relays is hard to beat.
RE: Motor frequent start alarm
Here are the ones I have used at one time or another, they all can be programmed as I mentioned above.
GE/Multilin link, US
Hint, don't bother with the 239 and 269, they are both obsolete.
Areva Micom P24x relay link
Schweitzer SEL-701 link
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: Motor frequent start alarm
When the system leaks, the compressor starts more often. They have little counters which could be hooked to your aux contacts on your starter/contactor. You can program in the number of counts before an alarm is sounded. Some of them have a RTC so you can cause a reset of the count after X days or hours. They can also be provided with contacts to initiate some other function (alarm light). This would be very cheap to do. However, given the size (and cost) of this motor, it would probably be best to put on some protective relaying outside of the standard stuff like overload and single phase protection as suggested. These relays would give you the functionality you need. If you want a counter or something check out Red Lion Controls or some other manufacturer of process controls.
RE: Motor frequent start alarm
RE: Motor frequent start alarm
LionelHutz & jraef's ideas is definitely workable.
I will also looking into setting this alarm from the DCS (or the Safeguarding system), where the motor Start & Stop commands are initiated.