electrical motor winding protection.

[Mlmlzx]

Dear sirs,
Is it possible to protect winding of motor by using limiting switch? I frequently have a problem of motor winding failure. The motor is used for pumping water from underground tank to almost 15 metres above. From there, water is distributed to each floor.

Regards,

 

[che12345]

Dear Mr. Mlmlzx (Electrical)(OP)29 Mar 22 02:23
"....#1. Is it possible to protect winding of motor by using limiting switch? #2. I frequently have a problem of motor winding failure. The motor is used for ...."
#1. What do you mean by " limiting switch " ? Yes, if you mean by (limiting the water flow) by say a valve in order to limit the [motor from over-loading]. Or, limit the (frequency) of the motor [start and stop]. etc., etc.
#2. Ask the rewinding workshop for advice on what is the (main or frequent cause) of the [winding failure], e.g. a) all three-phase winding evenly over-heated, b) short across from only one winding to frame/earth, c) short across two windings, etc., etc.
#3. if the motor is operated by VFD:. a) what is the cable length from VFD to the motor, b) is VFD cable been used? c) any problem on bearing current? etc., etc.
#4. If the motor is not operated by VFD: a) too long starting time, b) too frequent start stop, c) what is the motor rated current (A) against the full-load running current (A), e) what is the thermal over-load setting (A) ? f) whether the voltage and frequency are within limits, are all the three-phase voltage and current balance? etc., etc.
#5. Protect the motor from rain, direct sun light exposure, sand storm and flood.
Che Kuan Yau (Singapore)

 

[Mlmlzx]

the motor is for residential purposes only, is single phase, and no vfd. Can a bimetallic strip be used to protect the winding from getting damaged due to heat (caused by jammed rotary ie not rotating when started).

regards,

 

[che12345]

Dear Mr. Mlmlzx (Electrical)(OP)6 Apr 22 02:57
"...the moto is single phase, and no vfd. Can a bimetallic strip be used to protect the winding from getting damaged due to heat (caused by jammed rotary ie not rotating when started)".
1. Yes.
The " bi-metallic strip" is the thermal over-load installed in the starter, in series with the motor winding. The thermal over-load works on the [current] drawn by the motor. There are other types, e.g. embedded/attached on the winding that works on the [heat/temperature] etc., etc.
2. For thermal over-loads, it is important: a) to set the current (A) max = motor name-plate current rating (A). Can be lower if the load is light, but DO NOT exceed. b) select the tripping characteristic Class 10A or 10 type would generally be suitable.
Che Kuan Yau (Singapore)

 

[RRaghunath]

Mlmlzx,
If your purpose is to disconnect the motor power supply when the motor starts under 'rotor locked' condition, a switch like that senses 'rotor locked' status can be used to switch off the motor. However, you need to add some delay to allow motor to pick up speed. The switch can be one that senses rotor movement/speed or flow switch that senses water flow in the pump discharge.
Bimetal overload relay also can help though this may take a little longer to operate (but may be good enough for a small motor).
There are MPCBs which are similar to MCBs but meant for motors specifically (and include motor protection elements) can be a good choice that is simple as well.

 

[FacEngrPE]

Frequent winding failure is unusual for a motor operating within it's nameplate rating.
Things to check -
[ul]
[li]Motor current, If all three phases are equal and higher than nameplate current your flow rate is likely too high. To verify throttle the flow, the amps should drop. A possible long term fix is to trim your pump impeller.[/li]
[li]Unbalanced Motor Current, particularly in combination with unbalanced voltage, indicates a need for electrical troubleshooting. Link to Fluke discussion on unbalanced. The problem may be elsewhere in your power supply system.[/li]
[li]Motor wound incorrectly, this becomes more likely each time the motor is rewound unless the shop keeps the winding diagram from the first time they encountered the motor. If you find evidence of incorrect winding, it might be time to replace the motor.[/li]
[/ul]

 

[crshears]

Looks like overthinking may have begun here; OPr has followed up and stated motor is single phase residential with no VFD.

What type of motor is this? Motors this small are commonly split-phase start with a centrifugal starting switch; if the switch contacts fail to close reliably upon motor shutdown, failure to rotate will ensue on subsequent motor start-up attempt.

Remember: supplying more information yields better answers.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[FacEngrPE]

As this is a single phase motor, my comments about unbalanced do not apply. I was a bit hasty in my response.

Overloading from pumping too much water is easy to check for, so I still recommend it. Pump affinity laws tell us that power increases with water flow faster than with pressure increase, so throttling the discharge while monitoring current is a good test.

And as crshears states failure of starting circuit components is a frequent cause of single phase motors. The troubleshooting needed is dependent on the starting circuit used.

Figuring out what is causing your motor to have a short life will benefit you more than adding more motor protection.