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Old March 2nd, 2010, 11:52 PM   #1
knadeem
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Arrow Power Flex 700 AC, Overload

Dear All,
i have Power Flex 700 AC, i wand to know that is ther any parameter where i can set the overcurrent limit?
Because i am facing a problem of overload tripping and i want to avoid this by limiting the current.
Motor data is:
Motor Type: Induction
Motor NP Volts: 400.0 VAC
Motor NP FLA : 159.0
Motor NP Hertz: 50.0
Motor RPM: 1475.0
Motor NP Power: 90.0 KW
Motor OL HtZ: 16.7
Motor OL Factor: 1.0

Thanks in advance for ur help!
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Old March 3rd, 2010, 01:21 AM   #2
mordred
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yeah there is a parameter its maximum current usually set for 150% FLA I don't have this manual handy however perhaps its your torque requirements. Is it tripping on startup?
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Old March 3rd, 2010, 04:32 AM   #3
knadeem
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Hi Mordred
Thanks for your reply,
i am not facing the problem on start up. it is happing while running and i know at that time motor is fetching more current due to overload. But, i want to limit the current over a certon value upon which the motor could stop due to overload.this is what i want to do.
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Old March 3rd, 2010, 07:15 AM   #4
mordred
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OK there is some parqameters that can be used however there is a risk here. This sounds like its a pre installed system thats been running for a period of time so something had to have changed. I would look at monitoring loaded amps to find out if the amps are higher than the motor should be pushing. Also the usual resistance checks on the motor windings should also be looked into.
http://literature.rockwellautomation...m002_-en-p.pdf
this manual has all the parameters you will need under Motor overload factor can be checked or raised but I caution you on this for the reasons I mentioned above you could potentially burn out your motor
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Old March 3rd, 2010, 10:37 AM   #5
dondon_alba
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HiKnadeem,
Check PAR 147, 148, and 149 and make the proper calculation and make the changes. Try to monitor the running current, check your input and output voltages.
Don
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Old March 3rd, 2010, 11:28 AM   #6
mordred
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also when it faults next look at the value under 225 and 226 fault amps and fault bus voltage. It should trap how many amps is causing the fault. Also if your motor has an electronechanical brake check the wiring to the contacts and make sure its postioned correctly
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Old March 3rd, 2010, 03:00 PM   #7
DickDV
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If your motor data is entered into the drive correctly, and you have the motor overload protection turned on, then the drive will protect the motor and the shortterm overloads and overcurrent will not damage your motor.

However, you have a couple of choices usually when doing current limit in a drive/motor system. You can choose to fault the drive if the current exceeds a predetermined level. This is often called "electronic shearpin". Or, more commonly, you can choose to have the drive slow down when it hits the overcurrent point. The drive will reduce the speed reference until, if the overcurrent doesn't go away, the motor may slow all the way to stall. If the overcurrent condition is very fast, you can still fault with this configuration.

Since you have a drive capable of closed loop (vector) speed regulation and are probably using that, you can use overtorque instead of overcurrent in my examples above and the motor output will be more precisely controlled. You might want to consider that if precision is important in your situation. If you are using simple open loop V/Hz regulation, overcurrent is your only choice.
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Old March 4th, 2010, 05:04 AM   #8
knadeem
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Dear All,thaks for your help & reply!
I used the parameter #147,148 & 149. detail is as below:
P147 Current Lmt Sel => Cur Lim Val
P148 Current Lmt Val => 159 A ( Current Rating NP of Motor)
P149 Current Lmt Gain => 250 ( Default)

Before this Current Lmt value was 320, So, i changed it with Motor NP Current rating. But, After this motor speed reduced from 50HZ to 48.8 and Motor Current was also reduced from 140A to 133A. I could not understand this, as motor was running within the current limit so why its frequency reduced from 50Hz to 48.8Hz?
Is the value that i have put in P148 is wrong? anbody knows what value i should put into it?
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Old March 4th, 2010, 06:24 AM   #9
DickDV
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Those parameters look right to me except I don't understand what P149 means. We need an AB person to help on this. OkiePC, are you reading this?

I also have to wonder if you are operating in V/Hz or Vector Mode. If in Vector mode and you haven't tightened up your speed loop gains, this could happen.
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Old March 4th, 2010, 07:45 AM   #10
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Have a look on this one. You surely have a real overloading condition. You need to check mechanical loads and try to de-couple the motor. You perform the autotuning if that is a new installation or even re-tuning again.

Drive OverLoad - Drive rating of 110% for 1 minute or 150% for 3 seconds has been exceeded. Reduce load or extend Accel Time.

Excessive Load - Motor did not come up to speed in the allotted time during autotune. 1. Uncouple load from motor. 2. Repeat Autotune

Motor Overload - Internal electronic overload trip. Enable/Disable with [Fault Config 1] PAR 238 bit 3 you can enable/disable this bit. An excessive motor load exists. Reduce load so drive output current does not exceed the current set by [Motor NP FLA].

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Old March 4th, 2010, 08:27 AM   #11
dondon_alba
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PAR 149 – is the current limit gain. It sets the reponsiveness of the current limit.
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Old March 4th, 2010, 09:05 AM   #12
OkiePC
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Quote:
Originally Posted by knadeem
It is happening while running and i know at that time motor is fetching more current due to overload. But, i want to limit the current over a certon value upon which the motor could stop due to overload. this is what i want to do.
So you want the drive to limit the current to the motor to avoid the tripping you mentioned in your first post? If you do this, the drive will reduce the output frequency and slow down when you approach your current limit. If you set it too tightly, and it is actually overloaded, then you will still end up with a drive fault.

If you are trying to just make it run past a heavily loaded condition by slowing down and reducing the current, then when the load lightens up it should increase back to normal, then I think you are doing the right thing, just need to fine tune the values to get the desired result. Note that if you increase the software current limit above the motor FLA setting, and the drive runs somewhere above the FLA setting but stays below the software current limit, you may get the speed you want, but if enough time elapses, you will still get a motor overload fault.

I have not had to set up an application like this with a Powerflex, so I can't give great advice on what to set those parameters at, but I think you should experiment with the gain value and perhaps raise the current limit above what you have it set at right now.

Here's an explanation of Software Current Limit from the drive's reference manual:

Quote:
Software Current Limit - This is a software feature that selectively faults the drive or attempts to reduce current by folding back output voltage and frequency if the output current exceeds this value. The [Current Lmt Val] parameter is programmable between approximately 25% and 150% of drive rating (not the motor settings). The reaction to exceeding this value is programmable with [Shear Pin Fault]. Enabling this parameter creates an F63 “Shear Pin Fault.” Disabling this parameter causes the drive to use Volts/Hz fold back to try and reduce load.
Quote:

The frequency adjust or fold back operation consists of two modes. In the primary mode of current limit operation, motor phase current is sampled and compared to the Current Limit setting in the [Current Lmt Val]. If a current “error” exists, error is scaled by an integral gain and fed to the integrator. The output of this integrator is summed with the proportional term and the active speed mode component to adjust the output frequency and the commanded voltage. The second mode of current limit operation is invoked when a frequency limit has been reached and current limit continues to be active. At this point, a current regulator is activated to adjust the output voltage to limit the current. When the current limit condition ceases or the output voltage of the current regulator attempts to exceed the open loop voltage commands, control is transferred to the primary current limit mode or normal ramp operation.
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Last edited by OkiePC; March 4th, 2010 at 09:14 AM.
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Old March 6th, 2010, 05:13 AM   #13
knadeem
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Thanks all of you and specially OKiePC for his valuable input.
now, i am holidays and i will go back to plant on Monday, i will do as OKiePC said to fine tune it and then i will come back to you.

Thanks again for all to support.
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Old March 7th, 2010, 10:08 PM   #14
Gene Bond
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This is very commonly used for pumps, where the flow may exceed the design HP under certain conditions, so the current limit is usually set to 100% of motor FLA. Quite often, the FLA is set to 1.15xFLA, so the service factor can be used as well.

The cause is simply rounding errors and unknown mechanical design specs when the pump is selected. As usual, the electrical engineers have to bail out the mechanical engineers!
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