I have a problem with a O&K escalator. The Ac drive is a Telemecanique 40 horsepower drive with a braking resistor. The problem is that when the escalator is running in the down direction with a full load of people the ac drive faults out with a overspeed speed fault. The escalator has two motors and the drive has a braking resistor. Isn't it the duty of the A.C drive to control the speed of the escalator under load. Any comments or suggestions will be greatly appreciated.

is there a drive for each motor? Are the motors properly phased with each other? a little more info please.

Ok, with the motors generally up the top and the direction going down the esc will have the biggest load trying to pull the motor speed off its s curve at the bottom generally at full load. If the esc is reversed it actually has a diminishing load going towards the motors, so its not surprising its only in the down direction. Is the speed reference via an encoder or vector control? Check these connections, check your dynamic breaking resistor.

There is only one Ac drive controlling both motors, there is a motor on the left and on the right of the gearbox. The motors are in phase with each other, one motor spins forward and the other in reverse, they are properly phased. The Ac drive was swapped with the escalator next to it and the same fault occurs. The Ac drive is in vector control mode and does not get a reference from a encoder. There are four braking resistors wired in series parallel. I will get the specifications of the resistors "wattage and ohms" and post it later on today if I get a chance.

Thanks.

I think vector control uses the stator current and rotor speed to control the motor, or motors. You may want to go through the parameters, some may have reverted to default for one reason or another. the slip parameter is one to look at. also you must be pulling too many amps with a full load. Can you you clamp an amp meter while your running on each motor separately?

When you swapped the drive, did you also swap the resistors? When the load is negative, the load driving the machine, the braking resistors bleed off the excessive current and voltage. This slows the machine and controls the current.When the load is positive, the machine pulling the load, the braking resistors aren't being used. This keeps the DC buss at a constant voltage. Sounds like one of the braking resistors is open.

Exactly. Also if you have swapped to drives it may be just be the drive that is faulty. I would however check all the setting with the other esc and make sure they are the same, and check the dynamic braking resistors are all ok. Your not even using the slow down part of the s curve which is where the braking resistors are really used, so that's where to chopping of the output occurs as Johnny has posted.

The drive was swapped with the unit next to it but not the resistors. There are four resistors that total up to 27 Ohms, the resistors read the same as the other unit, I've checked all of the parameters and they seem to be okay. The escalator does not get a full load every day where I can check the amperage draw of the motors. I'm leaning towards the resistors not being able to bleed off the the excessive voltage and current. I will try to go there soon and check on a couple of more settings on the drive itself. I would like to replace the drive with a re-gen drive.

If you have swapped the drive to the next esc and it faults the same it appears to me that you have transferred the fault next door. If the fault is exactly the same, then to me it cant be the resistors, motors(differing resistance) etc just the drive. So I would get the drive checked for that bleed off and try to get a new drive. You could swap the drive and leave them in place to see if the other drive effects the original esc for further proof if it doesn't fault out.

The drive was swapped and the same escalator that runs in the down direction still faults out with a over speed fault telling me that it has something to do with the resistots, motors, etc.

I am not very informed about escalators so help me out here, how is the speed determined? Is there an encoder in the motor? Or does it use some other means of sensing positions and getting a speed? Just reading through the thread, and all that you have swapped with known goods, makes me wonder...

Check with drive manufacturer, maybe 27 ohms isnt the right value. You would never know it on the up unit, there is never an overhauling load.

Ah well yes I agree with this. Check all the motor resistances, current readings with a tong tester in situ of you can, and rotate the fly wheel with it off to see if you have a bearing faulty.

Thanks for all of the input, I know that this is a late post by I ending up replacing the drive with a regenetive drive and it has solved the issue.

Thank you