motor rotor speed lower than pump speed
motor rotor speed lower than pump speed
(OP)
Hi experts,
Can a motor with 10HP, rotor speed of 1765 rpm having synchronous speed of 1800 rpm drive a centrifugal pump with 1770 rpm and rated power of 7.3HP? Motor rotor speed is less than pump speed but can the motor accelerate the pump to its rated speed? Or motor rotor speed and pump speed
should be the same? to meet the pump requirements at that pump's rated speed. Thanks in advance
Can a motor with 10HP, rotor speed of 1765 rpm having synchronous speed of 1800 rpm drive a centrifugal pump with 1770 rpm and rated power of 7.3HP? Motor rotor speed is less than pump speed but can the motor accelerate the pump to its rated speed? Or motor rotor speed and pump speed
should be the same? to meet the pump requirements at that pump's rated speed. Thanks in advance





RE: motor rotor speed lower than pump speed
Yes
Yes. This depends on how the motor starts, i.e. DOL our some sort of soft start is what affects the ability to start. Most pumps like to start against a closed valve, but it's not vital.
They are the same within normal limits. This sounds like a 60htz, 4 pole motor. You will find the variance on incoming frequency gives you more change in rpm than this and the pump will not be affected by this very minor gap in rpm.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: motor rotor speed lower than pump speed
If the pump curve is drawn at 1770 rpm and the motor speed at the fullload motor speed is 1765 rpm then the flow and head would be slightly lower but hardly noticeable on a pump of this size. However, at the duty point of the pump system the motor speed could well be above 1765 rpm but would have to be measured to confirm this.
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: motor rotor speed lower than pump speed
That's +/- 17.5 rpm based on 1750rpm, so 5 rpm is negligible.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: motor rotor speed lower than pump speed
1800 is the no load speed
it slows down a bit when the pump is loaded
Approximate Electrical Motor Speed (RPM)
........Speed with-----Synchronous Speed with
......... Rated Load ..... No Load
Poles.....60 hz 50 hz ... 60 hz 50 hz
2........3450 2850......3600 3000
4........1725 1425.....1800 1500
6........1140 950....... 1200 1000
8.........850 700 ........ 900 750
Independent events are seldomly independent.
RE: motor rotor speed lower than pump speed
The pump curves are usually drawn or published with speed between 1750 to 1780 for 4 pole 60Hz operation.
Induction motor speed varies with the load.
Even for the same power supply frequency and No of pole, the full load speed varies with the size of the motor.
The larger kW motor will have speed closer to the synchronous speed and vise vesa.
For induction motor,the No load speed will still be below the synchronous speed by a few RPM.
RE: motor rotor speed lower than pump speed
Slip is basically the difference between synchronous speed and the nameplate rated speed when under full load (current).
Your nameplate will show a slip speed that equates to the rated current that, given you are on the rated voltage, will deliver the nameplate power for the motor.
The closer the rotor speed to synchronous, the less load/current is used. If an IM is operating DOL and operates at a slower rated rotor speed than the nameplate, it will be drawing excess current and going into overload. Not good if operating like this for long periods of time and your safety overloads should protect the motor from overheating.
RE: motor rotor speed lower than pump speed
RE: motor rotor speed lower than pump speed
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: motor rotor speed lower than pump speed
You are talking about a -2% deviation as slip speed from synchronous and, unless you have an additional device that is uncontrolled, I cannot see why this is being requested unless it is a safety function to feedback that the motor is actually running when commanded and, for example, a belt has not broken between motor and pump.
However, this would be a comparator rather than actual measurement of speed and again, usually this is load being measured (or no load in this case).
RE: motor rotor speed lower than pump speed
=====================================
(2B)+(2B)' ?