Single phased Powerflex 525

stretch_af

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Mar 2011
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So we noticed a PF 525 with one blown fuse yesterday. It never faulted, who knows how long it ran like that. Is there a parameter that could be monitored so we would know if it were to happen again? Does DC bus voltage dip with a single phased input? Suppose I could bench check that.

Thanks
Justin
 
maybe your isn't set to fault on a output phase loss?
F021 Output Ph Loss 2 Output Phase Loss (if enabled).
Configure with A557 [Out Phas Loss En].

The drive can operate single phase. So be aware of that when configuring your drive options. I don't see a parameter for monitoring phase voltage, i know they exist in the 700 series. thought they might in 500s. I've not used 500s so hadn't looked at their params list.
 
There is nothing in A-B (6 pulse) drives that looks at the actual incoming line voltages, which makes them all suitable for using on single phase (with the proper de-rating). What the drives look at is the DC bus ripple and when excessive, they trip, then the trip tells you it was a phase loss. But if the load is light, it is the same effect as de-rating, so the drive doesn't know that it lost a phase. On a PF52x drive, the load will have to be less than about 30% of the rating of the drive, on the PF7xx drives, about 50%. So if your load was very light compared to the size of the drive, it didn't care that a fuse had blown, at least not yet. No harm, no foul.

A lot of drive mfrs are doing this now, because having a phase monitor on the front-end is basically pointless and limits your ability to sell it to people who want to use it as a phase converter.
 
Last edited:
+1 on them having no direct input phase loss fault monitoring.

For a single phase supply, the PowerFlex 4 and 520 series drives must be derated 35% on the output load but the larger 400 series drives do not support derating (Frame G & H).

For derating the 7 series drives it's the temperature of the diode/SCR (Silicon Controlled Rectifier) front end that must be kept low (25°C/77°F) to protect the bus caps from the excess bus ripple. That's why they must be further derated to 50% on the output load.

When you single phase a normally 3 phase input you essentially use 4 diodes instead of all 6, stressing the diode structure. When the dc bus drops below the ac line equivalent voltage the diodes conduct or forward bias. You also create more dc bus ripple on the dc bus using only 4 of the 6 diodes.

Just to also point out, there are single phase input supply models available which require no derating. Ideally these should be used where you know you have or want to use a single phase supply and wish to avoid derating the output load.

Regards,
George
 
So we noticed a PF 525 with one blown fuse yesterday. It never faulted, who knows how long it ran like that. Is there a parameter that could be monitored so we would know if it were to happen again? Does DC bus voltage dip with a single phased input? Suppose I could bench check that.

Thanks
Justin


Did the blown fuse cause a problem of some sort? It obviously didn't blow to 'protect' the drive .. maybe a manufacturing issue with the fuse?


I'm trying to understand why you are interested in monitoring this. If the motor is OK, and the Drive is OK, and it did not cause you any downtime ... maybe the drive and motor are a bit (33%) oversized ;) ... but where is the problem?
 
Did the blown fuse cause a problem of some sort? It obviously didn't blow to 'protect' the drive .. maybe a manufacturing issue with the fuse?

That was a separate issue with the wiring that needs to be corrected. A 3 phase 480V drive, shared it's fuses with the brake on the motor. The brake failed, shorted to ground and blew the fuse. The drive and motor ran with the brake engaged for a while. Yes, the brake needs its own fuses, I was curious if there was a way to monitor the drive more.
 
+1 on the Time Mark Phase Monitor Relay(s). I have used these on several occasions, and they work well. With the contact arrangement, you could stop the drive from running, create an alarm, or with the appropriate wiring - do both.
 
That was a separate issue with the wiring that needs to be corrected. A 3 phase 480V drive, shared it's fuses with the brake on the motor. The brake failed, shorted to ground and blew the fuse. The drive and motor ran with the brake engaged for a while. Yes, the brake needs its own fuses, I was curious if there was a way to monitor the drive more.


Why not breakers with aux contacts?
 
Originally posted by jraef:

What the drives look at is the DC bus ripple and when excessive, they trip, then the trip tells you it was a phase loss.

The problem is there are things other than phase loss that can cause bus voltage ripple high enough to trigger a phase loss diagnostic. This is one of those cases where I really wish the drive said what it really meant; there is excessive bus voltage ripple. When you see this diagnostic and the infeed circuit protection is OK it gets really confusing...unless you know what the drive REALLY means.

Keith
 
One Fault to Ruin Us All...

Hi Keith,

kamenges said:
...This is one of those cases where I really wish the drive said what it really meant...

Such features as input phase loss detection are one of many we "trade off" in choosing their "cost-effective" PowerFlex Compact Class AC drives. Once we go to the PowerFlex Architecture Class AC drives, the feature set, as we know, broadens immensely, and includes an "Input Phase Loss Fault". Still though, as you point out, they do not implement a method to detect the actual loss of a phase as in, say, measuring the voltage between input phases. They just monitor the dc bus ripple and assume that any fluctuation, beyond the Input Phase Loss Level parameter value, is likely an Input Phase Loss Fault. It definitely can be a head scratcher when you know your input phases are good. Others "things", as you eluded to, could be a fluctuating load like a pump, a bad motor bearing, under-sized dynamic brake resistor, and so on. If they monitored for actual input phase losses, and flagged this alarm for just that, then they could just say for everything else, there is "Excess DC Bus Ripple", or similar, and then you could look up what are the likely causes of that. Or ideally, have a method of detecting each of those scenarios and flagging specific faults.

But those features must be in the Master Builder™ Class AC drives, where only "The Special" can access them?

Regards,
George
 
I didn't see anyone mention overload setting, if you lost a phase the current should have went higher on other phases. And if your brake was on again current should have went higher. If overload was set properly it should detect a rise in current, in theroy 1.732 times normal current should be present on other two phases.

Also suggest above add a means to detect fuse or breakers tripping
 
AkaHammer said:
I didn't see anyone mention overload setting, if you lost a phase the current should have went higher on other phases. And if your brake was on again current should have went higher. If overload was set properly it should detect a rise in current, in theroy 1.732 times normal current should be present on other two phases.

Also suggest above add a means to detect fuse or breakers tripping

Not mentioned, no, and for good reason. What you are describing would be typical for a single-phasing issue on the motor side of a VFD (Variable Frequency Converter). The typical current imbalance one would see here on the motor leads is not relatable to the loss of a supply side phase. The Overload Fault on these drives only monitors the current in the output section and not the input section. It would or could never detect a loss or imbalance on the input supply side.

The input phases on a VFD service the full wave bridge rectifier. The rectifier section is composed of six diodes which are semiconductors designed to conduct current in one direction. The purpose of the diodes is to convert AC current to DC current to supply the DC bus. The DC current, through the bus, is then connected to a circuit of specialized transistors called insulated gate bipolar transistors (IGBT) with the motor coil connected in between them. It is the IGBT that directly controls the voltage and frequency sent to the motor coil.

When you lose an input phase on the supply side, the bridge rectifier continues to convert AC current to DC current through 4 of the diodes instead of the optimum 6 diodes. This results in DC current continuing to be supplied to the IGBT section. However, the bridge rectifier may now be under further duress and may overheat. There may also be significant DC bus ripple and the danger of overheating the DC bus capacitors. But, once the IGBT section still has sufficient current available to it, it will continue to regulate the voltage and frequency output to the motor coil. All this excess heat will continue once the load is maintained at its original current values. This will in time fatigue the drive components and likely shorten its life. This is why we derate the permissible output current where only a single phase supply is available for a normally 3 phase supply VFD i.e. less load, less heat, less stress. This single phase loss on the supply side, while potentially causing significant duress within the drive supply and power components, will not adversely affect the resultant current being produced by the IGBT output.

And again, the Overload Fault for these drives will not detect such a phase loss on the supply side as the motor side current, which the fault monitors, is continuing to be supplied and regulated by the IGBT. The very design of the bridge rectifiers for the supply section is exactly how and why we are able to run a 3 phase motor off a single phase supply without issue (once either derating is applied or a single phase supply VFD model is being used).

In short, we cannot relate the circuit-wide current characteristics we "see" in a typical direct online (DOL) starter with the current characteristics we "see" only on the output section of a VFD.

Regards,
George
 

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