Motor Starts per/hour
Motor Starts per/hour
(OP)
Hi Guys, what is the norm for Starts per/hour for large LV motors 600kW 690Volt 50Hz either DOL or VSD's is there any literature available on this subject.
When was the last time you drove down the highway without seeing a commercial truck hauling goods?
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RE: Motor Starts per/hour
Typical for that large a motor is a loooooOOOOOOOOOoong time between starts, likely no more than once maybe twice and hour with the requirement of x running minutes after a start required.
No doubt someone will chime in on some lit.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Motor Starts per/hour
Now, if the motor is already available at site, search for the motor data sheet. If not readily available, request the motor supplier.
For VFD driven motors, the permissible no. of starts may be relatively more compared to DOL started motor, due to the lower starting current or absence of starting inrush current.
RE: Motor Starts per/hour
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Motor Starts per/hour
RE: Motor Starts per/hour
Dave
RE: Motor Starts per/hour
CR
"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]
RE: Motor Starts per/hour
Note I used the phrase "equally-spaced starts per hour". Site operations usually interpret four starts per hour to mean "four consecutive start attempts, then report the dead motor to maintenance". Modern protection relays prevent that kind of stuff, but old electro-mechanical schemes don't. If you have the capability, a DCS historian is very much your ally when it comes to determining what happened to your motor.
RE: Motor Starts per/hour
The number of allowable starts per hour doesns't tell the whole story.
Also the motor design is important. Any-one who remembers the old "U" frame motors will remember the great reduction in the allowable locked rotor time and allowable starts per hour of the "T" frame motors.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Motor Starts per/hour
As a general guide, for NEMA frame motors, MG-10 gives some recommended limits for DOL starting which is repeated here:
https://www.joliettech.com/easa-electrical-enginee...
For each speed and horsepower rating (up to 250hp), it gives recommendations for:
A = Maximum number of starts per hour.
B = Maximum product of starts per hour times load Wk2 [in units lbm-ft^2]
C = Minimum rest or off time in seconds between starts.
We choose whichever is lower from column A or B depending on Wk2. For low-inertia loads the column A limit is followed. For high inertia loads the starting frequency is reduced below the column A value based on column B.
I've always been annoyed that they bothered to list a minimum rest time between starts (column C) but not a minimum run time between starts. It gives the [false] impression that running time after start is irrelevant. But actually for the first few minutes immediately after start, running is much more effective at removing the starting heat than resting.
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(2B)+(2B)' ?
RE: Motor Starts per/hour
Before the "U" frame motors were the NEMA frame motors.
If you find an old text that lists comparative frame sizes between NEMA frame, "U" frame and "T" frames you will see that between the NEMA frames and the "T" frames the HP has about doubled for a given physical size of frame.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Motor Starts per/hour
Thank you all for contribution I finally got confirmation from manufacturer on permissible DOL starts/per hour ( client specification calls for 6 x hour )
The temperature in Mozambique between September and April is around 45 deg C with 80% humidity. Its a coal conveyor drive, the clients 6 starts/per hour seem extreme to me. I have attached Manufacturers DATA sheet.
RE: Motor Starts per/hour
RE: Motor Starts per/hour
16 seconds Locked Rotor. Wow. I've seen motors with 1sec LR limits.
10,000lbs, what a beast.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Motor Starts per/hour
"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington
RE: Motor Starts per/hour
RE: Motor Starts per/hour
RE: Motor Starts per/hour
For reduced voltage starting, I use the I^2t to compare the start to the motor rating.
RE: Motor Starts per/hour
voltage sags / flicker on the rest of the system
Your facility may have issues with starts occurring too often, if it affects other equipment or even causes nuisance light flickers.
Your utility likely has quality standards that dictate a minimum interval of time for energy inrush events (large motor starts).