setting up a GE AF-600 VFD

Hey guys,

Today I've had some VFD faults occur with some pumps as I've been doing some testing. I'm trying to figure out the cause and think I might have found it, but I'm looking for a sanity check.

The VFDs I'm working with are GE AF-600 models. The fault code I'm getting when the pumps are at 100% speed is "Output Frequency at Maximum Limit". If I back the speed down a bit, the fault goes away.

I went through the parameters for the motor; motor voltage is 460V, current is 18.5A, horsepower is 15, all that looks good. The odd thing is the "base speed" setting, though. Right now the base speed on both VFDs is set to 1728 RPM. I don't exactly know where that number came from, I'm not the one who set up the VFD. If I check the nameplate on the motor itself, there's an HP field that says 1175. On the bottom half of the nameplate under a big title of "Inverter Duty" it states that the Hz range of the pump is 6-60 and the RPM is 120-1200.

I'm thinking in the VFD, my min speed should be 6 Hz instead of 0, and the base speed shouldn't be 1728 RPM, it should be 1175 or maybe 1200. Does this sound reasonable to anyone? Am I way off base?

Thanks!

UPDATE: drive two's max frequency is set to 120Hz, while drive one's max frequency is 60Hz. Base frequency of both pumps is 60Hz. drive two isn't having issues at full speed, so is that 120Hz setting correct in this application? Should I make max frequency a slightly higher number rather than double the base frequency?

Depending on the system capabilities your 'UPDATE' is how I would handle this. By increasing the Max freq. to something that you know the system can safely handle.

I'm thinking in the VFD, my min speed should be 6 Hz instead of 0, and the base speed shouldn't be 1728 RPM, it should be 1175 or maybe 1200. Does this sound reasonable to anyone? Am I way off base?

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This too is a reasonable assumption but if left as is likely will not cause any issues.

RussB said:

Depending on the system capabilities your 'UPDATE' is how I would handle this. By increasing the Max freq. to something that you know the system can safely handle.

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Thanks for the sanity check!

Someone entered the motor nameplate info into the drive incorrectly. You have a 6 pole motor, someone told the drive it is a 4 pole motor. The drive will actually measure the motor speed, or at least the slip. So it is detecting that something isn't right with this, either the motor is spinning faster than the drive is telling it to at 60Hz, or maybe the slip is not what it thinks it should be when the drive puts out 60Hz, because the actual motor does not have the correct characteristics of what the drive thinks a 4 pole motor should have.

Your drive should be programmed for the actual nameplate data of the motor it is connected to. As to the max speed, understand that when you over speed a motor with a VFD, torque begins to drop precipitously once you go over base speed. So at 120Hz, a motor designed for 60Hz will have less than half of the available torque it did at 60Hz. In theory the HP remains the same but in practice, the losses in the motor increase, which robs you of useable power.

In a centrifugal pump, the other side of that coin is that if the pump was designed for a flow value at 1175 RPM, and you increase the speed to increase the flow, the HORSEPOWER required by that pump increases at the CUBE if the speed change. So for example if you run that pump which was designed to use 15HP at 1178RPM and increase the speed to 1728 RPM , the speed is increased by 147% of base design speed, so the HP required by the pump at that speed will be approximately 45HP. The actual motor HP stayed roughly the same but a little less from losses, so is now woefully inadequate and it will overload.

What we don't know here is whether all of this was understood and thought of when the entire system was designed, but the evidence, being they didn't set up the drive correctly, would indicate someone had no idea what they were doing here. I'd be VERY careful with any ASSumptions from here on out.

jraef said:

Someone entered the motor nameplate info into the drive incorrectly. You have a 6 pole motor, someone told the drive it is a 4 pole motor.

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Yeah I'm not sure who set up the VFDs, I think they may have just used whatever "default" values were in their head from other projects as opposed to actually checking the nameplate; there were lots of odd settings for overcurrent and max freq, when the settings were below the nameplate's rated values.

The drive will actually measure the motor speed, or at least the slip. So it is detecting that something isn't right with this, either the motor is spinning faster than the drive is telling it to at 60Hz, or maybe the slip is not what it thinks it should be when the drive puts out 60Hz, because the actual motor does not have the correct characteristics of what the drive thinks a 4 pole motor should have.

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I think this is definitely part of it. Also, the max freq warning is set to 60Hz, and if the motor is spinning at 60Hz, well, that'll cause a warning and then eventually a VFD fault.

Your drive should be programmed for the actual nameplate data of the motor it is connected to.

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I've gone through and checked all the values and made some adjustments. I think I'm going to have to go through the rest of the VFDs for other pumps and make sure they're set up correctly.

As to the max speed, understand that when you over speed a motor with a VFD, torque begins to drop precipitously once you go over base speed. So at 120Hz, a motor designed for 60Hz will have less than half of the available torque it did at 60Hz. In theory the HP remains the same but in practice, the losses in the motor increase, which robs you of useable power.

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Yeah, I did some Google research and found some great graphs that describe base speed and what happens if you overspeed. Here we will never run the pumps over 60Hz, so nothing exotic or complex going on.

What we don't know here is whether all of this was understood and thought of when the entire system was designed, but the evidence, being they didn't set up the drive correctly, would indicate someone had no idea what they were doing here. I'd be VERY careful with any ASSumptions from here on out b

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I can definitely say that the guy who I think set up the VFDs is a bit...well, he's definitely a character, lol. Long story short, what this means is that I'm going to have to go through all the VFDs and make sure the nameplate info is correct, especially the base speed, and make sure that the warnings are set correctly. Now that I'm thinking about it, this sort of stuff isn't surprising coming from the guy who set them up.

Thanks for all the great info.

I definitely agree that the programming for all of the drives that this person has set up should be checked. Some of the illogical settings you have reported make it reasonable to assume that the original programmer did not know what he was doing.

For reasons of safety as well as protection of the motors and loads, check them out.