Hoist motor load test failure 3

[mohamedmoheb]

Dears,

i have a single jip machine and i face a problem with it.the drum winch motor is working properly when there is no load & when i test it with load the motor is not moving correctly.

Site conditions:
380V 60Hz

Motor conditions:
3phase motor @50Hz : 230/400V D/S - 4.87/2.81A D/S - 1.10KW - 1395r.p.m
@60Hz : 265/480V D/S - 4.87/2.81A D/S - 1.27KW - 1675r.p.m

please advice where i can expect the failure?? and what will be suggestions.

thank you

 

[jraef]

You have the wrong motor. The V/Hz ratio of the motor design must match that of your power supply yours does not. You must either change the motor, or you must use something like a VFD. But using a VFD on a hoist motor is not something to be undertaken by amateurs, it requires specific experience in doing that. My suggestion is to replace the motor with one from a local supplier that has motors designed for use in a 380V 60 Hz environment. That V/Hz combination is common in Brazil and as such, Weg provides motors that would likely work, I would suggest contacting a local Weg distributor wherever you are.

"Will work for (the memory of) salami"

 

[mohamedmoheb]

thanks for your reply.
i want to clarify from you what will happen if i change the motor power wiring from star to delta, because i think if the supply power not enough, i may use delta wiring to reduce power required to run the motor.

 

[jraef]

The hoist was ordered with the wrong motor for your available supply. You cannot change the design rating of the motor by the way it is connected, but that problem will be masked by a much bigger problem if you try what you are thinking of.

If you change the motor connection from Star (380V) to Delta (220V), and then connect it to your 380V supply, you will be applying 1.732x as much voltage as the windings are designed for. The motor will produce a potentially very destructive initial torque surge, followed immediately by saturation, which will severely over heat it and likely destroy it in short order. It will run WORSE than it does now.

The two suggestions I already made are your only viable options in my opinion. Most likely someone is not going to like it because of the cost, but the truth hurts sometimes. Someone should have paid more attention to details before purchasing it.

"Will work for (the memory of) salami"

 

[electricpete]

Site conditions:
380V 60Hz

Motor conditions:
..@60Hz : 265/480V D/S

what will happen if i change the motor power wiring from star to delta,

jraef was definitely right as usual. The motor won't match the supply in either configuration.

In star it is designed for 480V @60hz and you're giving it 380V@60hz. Torque vs speed curve is reduced by approx (380/480)^2. You don't way what failure you are having, but I imagine it may stall and trip. If you make it to full speed, current for a given horsepower would be higher by approx 480/300 and motor should be derated.

In delta, you would be giving it too much voltage. You would have torque capability to accelerate and run the load, but the core would be over-excited. You would have high/non-sinusoidal magnetizing current and increase in core heating. The motor might overheat and fail even at currents below the overload setting.



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

 

[waross]

You may try a pair of 480V;120V Boost rated transformers in an open delta auto-transformer configuration. That should boost the 380 Volts up to 475 Volts. A pair of 500 VA transformers should suffice.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[zlatkodo]

You need to rewind motor from 400 V, 50 Hz to 380 V, 60 Hz.

 

[eng2waleed2mouhammed]

hi mohamed
i think zlatkodo is right you should rewind the motor from 400v at 50 hz to 380 at 60 hz.

 

[waross]

Small transformers are much cheaper than rewinding.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[mohamedmoheb]

Zlatkodo & Waleed,
actually i cannot make any change in the motor of my machine. i can only use transformer to solve this problem,but i need to know should i use transformer for this motor only or for the full machine?.

for information this motor is part of BMU Machine which consist of Motors for different functions as Slewing motors, Travelling motors, pump motors and lifting motors. all of these motors are working properly with 60hz except the drum winch motor that i mention about it before.

 

[eng2waleed2mouhammed]

mohamedmoheb
if the other motors work well with the supply you have , you need to use the transformer only for the motor you have problem with.
good luck

 

[waross]

Good practice is to supply all the motors with the correct voltage.
Transformer sizing:
Add the currents of all motors.
This current must flow through the 120 Volt windings of the transformers.
Multiply the current by 120 Volts to get the VA required to supply the whole machine.
Buy two of the next larger standard size transformers.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[electricpete]

but i need to know should i use transformer for this motor only or for the full machine?.

It seems to me with one motor misapplied, we here on the board have no idea whether other motors on the machine are similarly misapplied or not. You might want to look at the other nameplates to answer this question for yourself.

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

 

[jraef]

I doubt all the other motors are working properly, but you have just not yet experienced the failure, maybe because they are running under very light loads and/or very short duty cycles and/or have VFDs on them already, for example the traverse and slew control motors. We will have to assume that your "pump" is not a centrifugal pump, otherwise the 20% increase in speed would result in an increase in LOAD on the motor of 172%, unless you have some other mechanical means of reducing the excess flow. A little research on what a "BMU machine" is (Building Maintenance Unit) and I can imagine it is a hydraulic pump which would most likely be a positive displacement gear pump. So depending on the design of the hydraulic system, the increased speed may possibly result in higher pressures. This may or may not be the case, but give the potential for life-safety of this machine working properly, I for one would certainly investigate that THOROUGHLY.

Your drum motor in question is designed to accept a V/Hz ratio of 8:1, your site has a V/Hz ratio of 6.33:1, so your motor (in Star) is being under excited and you have lost significant torque. Your motor PEAK torque, which is quite often needed in hoists, will be reduced to roughly 63% of the motor's design rated peak torque, that is a very serious problem on a hoisting application. So in order for that motor to produce designed torque at 60Hz, you must give it 475V as waross explained (a third option that I failed to think of by the way, kudos Bill).

Assuming that ALL of your motors are rated for 50Hz and getting 60Hz, you will have a similar issue throughout this system and I would suggest either boosting the voltage to 475 for any of them in such a condition, or replacing them with properly rated motors.

"Will work for (the memory of) salami"

 

[ters]

You actually may never solve your problems if the machine is designed for 50Hz. Whatever you do along the lines other posters proposed, all your motors will still run 20% faster at 60Hz. So if machine design is such that some of its rotating functions cannot be accelerated for 20%, then there is practically no electrical fix for your problems.

 

[waross]

According to the original post, the motor is dual rated for 50/60 Hz. If that information is correct, that leaves only the voltage issue.

Bill
--------------------
"Why not the best?"
Jimmy Carter