Halloween Kinda Thing?????

We had a recent post about a 3-Phase Motor that reversed direction, apparently, on it's own. It wasn't connected to a drive.

Now, I had a situation today that was kinda similar, but it does have a drive. I only post this to show that it is possible (Murphy?).

I have a drive that is configured to run in Forward ONLY at one of two constant speeds. The speed is selected by a selector switch. The drive goes FAST, or SLOW, or STOP.

The drive drives a motor to an auger. Sometimes the auger is over-loaded. The drive has always tried to maintain speed until it tripped out on over-current caused by excessive material loading. It has operated as expected for about a year.

Today, I saw the auger get over-loaded with wet material (it is supposed to be dry). The drive slowed down from 1200-RPM to 0-RPM without tripping....

AND THEN IT REVERSED DIRECTION

and ran in reverse at 200-RPM for about 5-Seconds then stopped and tried to go FORWARD AGAIN at 1200-RPM 'til it slowed down to 0-RPM and so on.

It could be an interesting "feature" in some applications, but could be disasterous in others!

Just wanted to indicate that weird stuff can happen with drives.

I guess that's why they sell overspeed and underspeed monitoring relays!...

beerchug

-Eric

What type of drive? I have an AB 1305 and noticed that one of the fuse indicators on the power feed was lit. When checked, sure enough, the fuse was blown! NO indication from the drive that anything was wrong. In the manual it says that it checks for phase to phase shorts and phase to ground shorts but nothing about a completely missing phase.

In my case, the motor never reversed but I suppose this type of thing might be able to cause reversing.???

ndzied1 said:

I suppose this type of thing might be able to cause reversing.???

Click to expand...

Doubtful... A lot of AC drives are designed to use single OR three-phase power, you just have to size them correctly based on what type your using.

Remember that they just convert the incoming AC to DC, so they don't care if the third wire is connected or not. With 3-phase, you can drive a larger motor.

You have just discovered a good reason NOT to use fuses for circuit protection. If your drive was protected by a circuit breaker, an overload on one line would have opened all three!

I always use circuit breakers rather than fuses on every piece of equipment we build. Sure, they cost a lot more, but it's well worth it...

The main reason it that, 9 times out of 10, the customer doesn't have the correct replacement fuse on hand (or worse, doesn't even know there ARE different types of fuses!), so they stick any old thing in there to get the machine running again...

Spooky things are bound to happen!...

beerchug

-Eric

The phase to phase shorts and phase to ground shorts the drive looks for is on the load side, a nice safety feature so you don't take out the drive when then the motor goes.

You said the fuses were on the line side. I know the ab 160 drives can run with a certain phase missing. I belive that phase is L3. Because the drive takes the incoming power and converts it on to a single dc bus and the output wave is created by chopping the bus voltage apart to supply the output. But the drive uses only 2 phases for its internal control voltage so if that third leg is missing it doesn't know the difference. As long as the other 2 legs can handle the increased amp draw.

With that being said yes you can run a 480 3-phase motor from a single phase supply.

Drewcrew6

Doubtful... A lot of AC drives are designed to use single OR three-phase power, you just have to size them correctly based on what type your using.

Click to expand...

I guess that's why my degree says Mechanical Engineering and not Electrical

I always use circuit breakers rather than fuses on every piece of equipment we build. Sure, they cost a lot more, but it's well worth it...

Click to expand...

Unfortunately, I don't get to make that decision. banghead

Phase to phase

As far as my concerns, most of our new ABB AC drive and Siemens Simovert Master Drives has a parameter settings for the phase to phase connections.

Speaking of weird stuff with motors and drives we have an oven line that uses 4 AC TECH drives for the conveyors and 3 AC TECH drives for the blowers. Once all of the conveyor drives simultaneously changed their freqs to 45HZ. They were changed back to their previous freqs and a few minuets later two of them (on opposite ends) went to 35HZ. A few days later the 3 blower drives simultaneously changed their freqs to 15HZ. The only connection any of these drives have in common is the power feed. No problems since.
Spooky anit it?

For a second, I though Terry was back, until I realized the thread is 8 months old.

You too?...

I though the same thing!...

Too bad, we could really use one of his analogies (involving beer of course!) over in the current Indirect Addressing thread... :nodi:

beerchug

-Eric