Electric Motor using at escalator overspeed

[Leendabests]

Dear All,

I have one case where there is an escalator speed up while going down when loads of people on the escalator. The electric motor that has been used is 4 pole. My question, how the motor can ran overrated rpm? The motor still in the good condition.

Thank you. Hope to hear from you guys soon.

 

[waross]

The slip frequency of standard induction motors is around 2% to 3%. If the over speed is more than about 55 or 6% there may be something wrong.
Possible causes:
The escalator is overloaded.
Belts are slipping.
The motor is a special design with a greater than normal slip frequency.
How much overspeed?
What is the current relative to rated current when the escalator is overhauling.

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

 

[Leendabests]

Yes... when there are load of people at the slipped escalator but not overloaded... there are 2 escalators side by side.. the other one working in good condition with the same capacity as the slipped one. They are using Ac motor coupled with gearbox. It happen once in a while but still danger to the users. I can say more than 10% overspeed.

 

[ozmosis]

I'm surprised at an escalator over speeding and not overloading. Usually there is very accurate monitoring on these applications and 10% over speed is very unusual I would say.
Bill, have you seen an escalator with belts? I haven't, usually chains from g/box. That's not to say hey don't have belts but that type of load is typically not using them.

 

[Leendabests]

The escalator will trip if it is overload. The overspeed.. is it related to slip frequency? what causes the slip frequency can occur?

 

[waross]

Example: An induction motor with a synchronous speed of 1800 RPM has a rated speed of 1760 RPM. That is a slip of 40 RPM. That is a slip of 2.22% or 1.33 Hz
At synchronous speed PLUS the slip speed or slip frequency a motor will generally regenerate close to full load current.
Is this a VFD driven motor with a problem in the regeneration circuit or possibly some poor settings?

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

 

[Leendabests]

What cause to the motor slip more than 10%? Is it related to the electromagnetic, impedance, resistance, torque? The slipped happen once in awhile not everytime its running.

 

[mikekilroy]

PERHAPS IT IS time to tell us how the motor is powered: across the line? vfd? etc..

there are settings in some vfds that allow them to speed up if overrun load on them to prevent over voltage errors; might be yours is set like this (wrong for elevator).

 

[Leendabests]

The motor is directly powered from supply. No vdf connected to the motor.

 

[waross]

The problem may be in the supply and/or wiring, in the motor or a mechanical problem.
Check your contactor and wiring for loose or corroded connections. Evidence of heat will be an indication. The motor may appear good, but there may be a problem with the rotor. A growler test may be indicated.
Mechanical. There can't be any mechanical slippage, right? I have seen issues where a coupling was slipping on a shaft and throwing the machine timing out. Couldn't happen, right? I had to paint a line across the coupling to demonstrate to the mechanical guys that what couldn't happen was happening.
Do you have a spare, good motor? Change out the motor. If the problem goes away it is a motor issue. If not, then check the supply (unbalanced currents may or may not be an indicator. If the supply looks good then look for a mechanical issue.

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