VFD Internal Fault Protection

[mull982]

Do most newer drives provide some sort of internal method for detecting faults on the drives secondary? For instance if there is a fault on the load side side of the drive, will the drive be capable of tripping itself protecting both the drive and the motor? Is this typically just an overcurrent setting in the drive that may or may not be adjustable?

Is the drive capable of distinguishing between a phase fault and a ground fault on the secondary? I've seen some drives with a ground fault indication?

Now on the line side of the drive there is usuall fuses or a breaker. I saw a post recently discussing line fueses on a drive, and it appears that for a fault on the input side of the drive the drive cannot protect itself, and in most cases neither can the fuses, and usually the drive is ruined.

 

[Besoeker]

Do most newer drives provide some sort of internal method for detecting faults on the drives secondary? For instance if there is a fault on the load side side of the drive, will the drive be capable of tripping itself protecting both the drive and the motor? Is this typically just an overcurrent setting in the drive that may or may not be adjustable?
Is the drive capable of distinguishing between a phase fault and a ground fault on the secondary? I've seen some drives with a ground fault indication?

Most of the drives I've dealt with have built in motor protection and algorithms to predict motor thermal performance. They also have output earth fault protection, input phase loss, output phase loss, drive over temperature, inputs for motor thermistors etc.
The drive inverter IGBTs usually have de-sat protection which is not user adjustable. This looks at the voltage across the IGBT and, if it gets too high, the gate drive is suppressed. This is local to the device and independent of any control loops. If it all works as intended, the output stages should be pretty much bullet proof. And, in fairness, reliability is usually very good.

Now on the line side of the drive there is usuall fuses or a breaker. I saw a post recently discussing line fueses on a drive, and it appears that for a fault on the input side of the drive the drive cannot protect itself, and in most cases neither can the fuses, and usually the drive is ruined.

The input circuit for most inverters is a diode rectifier. It is entirely possible to fit fuses with a lower i^2t than the diodes and that would protect the diodes in the event of them seeing prospective fault current.
Our experience is that such faults are so infrequent that we have long since dispensed with semiconductor fuses at the input.

Just my take.

 

[mull982]

Most of the drives I've dealt with have built in motor protection and algorithms to predict motor thermal performance. They also have output earth fault protection, input phase loss, output phase loss, drive over temperature, inputs for motor thermistors etc.
The drive inverter IGBTs usually have de-sat protection which is not user adjustable. This looks at the voltage across the IGBT and, if it gets too high, the gate drive is suppressed. This is local to the device and independent of any control loops. If it all works as intended, the output stages should be pretty much bullet proof. And, in fairness, reliability is usually very good.

How does the drive recognize a ground fault on the secondary? Zero sequence sensing of some sort?

Also for a L-L fault with high current magnitude, will the drive trip on some level programmed in the drive?

 

[Besoeker]

How does the drive recognize a ground fault on the secondary? Zero sequence sensing of some sort?

I don't know how the various manufacturers do it.
Output line current is generally monitored in each phase so I suppose it wouldn't be too difficult sum them.

Also for a L-L fault with high current magnitude, will the drive trip on some level programmed in the drive?

On the drives we make a direct line to line fault on the output (actually at the output) shuts off the output IGBTs on de-sat. This directly shuts off the gate drive.

 

[kwired]

Do most newer drives provide some sort of internal method for detecting faults on the drives secondary? For instance if there is a fault on the load side side of the drive, will the drive be capable of tripping itself protecting both the drive and the motor? Is this typically just an overcurrent setting in the drive that may or may not be adjustable?

Is the drive capable of distinguishing between a phase fault and a ground fault on the secondary? I've seen some drives with a ground fault indication?

Now on the line side of the drive there is usuall fuses or a breaker. I saw a post recently discussing line fueses on a drive, and it appears that for a fault on the input side of the drive the drive cannot protect itself, and in most cases neither can the fuses, and usually the drive is ruined.

proper overcurrent protection on the supply side can minimize additional damage done by a fault but remember if there was a fault within the drive but before the monitored output there is most likely damaged equipment within the drive anyhow. Most likely the rectifier(s).