We have a Sinus Penta VFD that's running a brake dyno that we use for testing brakes for racing. 125HP motor connected to about 1200lbs of counter weight. Our cycle is speed up, motor off, brake with our attached caliper down to preset rpm, release, then ramp back up.

The problem is that we are getting a voltage spike to the dc bus on our ramp up. Right before the max speed.

We have installed a brake resistor and changed the parameters as per instruction from the technician in Italy. It's still overvolting. It's like it's not throwing the voltage to our resistor at all. We have a line reactor hopefully coming on Monday. Our building is an old textile factory with 600v service, that is actually about 622. We hope to drop it to about 590 and clean up any noise in the supply.

We've tried everything from changing accel/deccel ramps and running on speed control vs torque. We even changed the rubber coupling from the motor in the chance that it was worn out.

We have been dead in the water for a week and are losing money daily. Is there anyone here who has extensive knowledge with VFD's used to run brake dynos? Specifically, the Sinus Penta sold by Teco Westinghouse. We have talked with every local rep/tech that claims to know our problem but how we are using this drive is uncommon. And because of our voltage, we ordered the drive from Canada in hopes to save money as to not need a transformer to drop the voltage.

Any help would be greatly appreciated.

Jake

 

You have not specified the details mentioned below
1. your system is 600V DC or AC?
2. the VFD input is 600V?

The spike you are getting in the input terminal? or VFDs DC bus? and the details of spikes.

plz reply with the ans.

Additionally,
during ramp up the IGBTs inside VFD circuit gets fired with high frequency in the range of 10-20KHz, this leads to very high dV/dt and dI/dt (rate of change of voltage and current).
This leads to generation of voltage spikes.

Plz contact your VFD supplier and confirm from them the snubber circuit in the VFD is healthy or not, this circuit is responsible to minimize the spikes.

If necessary you can engage additional electric filters (made of resistance, capacitance and inductance) to suppress the spikes.

In the market you will also get VFD harmonic filters which are not very much costly.

You can design of your own filter also, these are basically capacitance with some added resistance (design calculation procedure may be Googled).

If you still want a further solution, plz email me with your system line diagram, VFD & motor details and spike details to [email protected].

 

Just letting you know that I emailed you with my response.

>If you still want a further solution, plz email me with your
>system line diagram, VFD & motor details and spike details
>to [email protected].

 

Hi MBM8000,

I am not familiar with the Sinus Penta VFD - I am familiar with several different VFDs and DC bus over voltage.

It is pretty common to have DC bus over voltage when you don't have some form of load to absorb the inertia from the rotating mass and you ask the VFD to stop the drive.

Basically:

* You get your load up to speed and ask the VFD to "stop"

* Your VFD is trying to ramp & stop the rotating mass - it will attempt to out-perform your caliper (or depending on your ramp, drive the load while you are braking with the caliper)

* You generate DC

* You charge the VFD capacitor bank and trip with DC bus OV

For a typical application - i.e.; centrifugal/cast fan or blower spinning in air, large rotating mass and no process load - I'd fit a braking resistor.

In your case a resistor bank is bad.

You don't want the resistor bank to stop the load - you want to test
your brakes.
I suspect your resistor bank is not working OR configured properly anyway - you should not be getting DC bus over voltage if it was correctly sized and the VFD correctly configured - is it getting hot?

REGARDLESS
The VFDs we use have an internal parameter call "Coast-to-stop" - this prevents the VFD from attempting to brake the load. When you ask the VFD to stop - it ceases all output instantly. You need to find the equivalent parameter on the Sinus Penta VFD and enable it.

Alternately once the VFD is at speed and could try dropping the mains supply to the VFD. This is ugly but should do same thing (unless it can powers itself from the DC bus ...)

ALTERNATE
Use a mechanical coupling to disconnect the load once you are at speed. This will give you a better test of your caliper anyway as you will not have the motor coupled. You can then focus on getting the VFD brake sorted to stop the motor rotating mass as a separate issue.

Regards,
PB

 

You must detect DC bus voltage on brake resistor when it connected to DC bus for short time. It maybe before reaching max speed when deceleration phase occurs really. If not, you must check with Sinus which overvoltage will lead to braking operation? What are power and resistance of used braking resistor?

 

I do know something about the Sinus Penta drives. They are made by Elletronica Santerno in Italy and are a pretty good drive. I have to assume you are using the Sinus 5T/6T because that is the only version that is rated for 600V operation. The 5T is rated for 600V, +10,-15% so it is good for 510-660VAC input. The 6T is actually capable of 690V, so I don't think that dropping the voltage to 590V is going to help if that's what you have.

If you only have the Sinus 4T, that's the first problem, that drive is only good for 500VAC, plus 10%, so 550V max. If that's what Teco sold you, they have made a mistake.

Please confirm which drive you have, because it makes a LOT of difference. The 5T/6T version is capable of Line Regeneration, which would make it perfect for your project, but you may not have set it up correctly.

 

Thanks for the response. My boss may chime in with his own response using this shared login. But for now, I'll clear up a couple of things if needed.

The supply is 600V AC. (nominal ~620)
The motor is 125 Hp. 575Vac.
We are installing a line reactor tomorrow before the drive to drop our incoming to ~590Vac and to hopefully clean up any harmonic issues.

The hardest part to understand for us is that we have been operating for 7 months with no issue. Nothing in our setup/parameters has changed. Then out of the blue, about a week ago, this fault is constant.
We did as per instruction from the manufacturer run a diode test on the terminals leading to our resistor. It checked out good. I'm assuming this was to verify that the igbt is working properly? The resistor is built for 29,700 watts 8.4ohms.

At this point, I'm not sure if we have a "coast to stop" parameter in our drive. I would think it would have been mentioned already.

Thanks again for the reply.

 

Thanks for your response.

We have the 5t drive.

In fact today, we had our rep from Italy logging in and he actually changed the value of our drive to the 6t. (using password protected service level) Along with numerous other changes. After we lost internet connection, (and he had to attend to family matters being several hours ahead of our Eastern US time) we tried running tests and noticed the dc bus voltage going over 1000 Vdc. We stopped in fear of hurting the drive. Although it never did over volt.
We did however make some changes in the code that talks to modbus based on his parameter changes. We ran a few cycles tonight before leaving work and managed to not over voltage. We are not sure about the changes made in the parameters though. And our rpms are going well beyond what we want as our cycles are very specific.

We hope to hear more from them tomorrow. Our line reactor was delayed due to shipping problems and I plan on picking it up tomorrow. Again, we don't know if it will help solve our problem but we know that it is at least a good device to have installed.

Not to sound like a broken record, but the biggest quandary in this whole mess is that we've ran for several months with no problem. Out of the blue, non stop over volt faults.

Thanks again for your input. We hope to update tomorrow with more information.

 

Does the motor have an encoder for speed feedback? We had a drive from a different manufacturer that suddenly started getting overvoltage faults. The problem was the encoder getting flaky so the drive thought the motor was overspeeding and tried to slow it down. Replacing the encoder fixed it.

To rule out phantom trips, we put a power analyzer on the DC bus and watched the voltage. It wasn't "swelling", but spiking. As soon as we identified the spikes, their tech support immediately said it was the encoder, which it was.

 

> ... we tried running tests and noticed the dc bus voltage going
> over 1000 Vdc. We stopped in fear of hurting the drive. Although it
> never did over volt. ...

Not surprising if the voltage rating was changed to 690V. The DC bus NOMINAL voltage on a 690V supply would be around 973VDC, Over Voltage Trip limits are typically somewhere around 1100VDC for that class.

The real question is why the DC bus is rising on you, when it was not doing that before. Only two things can make the bus rise; A Line Voltage issue and a Load Regeneration issue. It HAS to be one of those.

The issue of the encoder problem is one potential that could lead to a load regen related cause. But if you have no encoder, that could not be it. If however you are using Sensorless Vector Control, a similar issue can be created by severe electrical noise on the output side of the drive. With SVC control, the motor position feedback is derived from the current signature of the output to the motor. As the rotor bars pass through the stator field, they create miniscule distortions in the current waveform that are sensed, tracked and monitored by the vector algorithm in the CPU and used to indicate rotor speed error so that it can compensate. So similar to the defective encoder issue, if there is noise imposed on the output conductors from some outside source, that noise might be getting interpreted by the VFD as the motor turning faster than it is telling it to. The drive then responds by trying to back off the output frequency, which puts the load into regen mode. Since it was working earlier, look for something that has been added near by, some wiring that has been changed, a broken shield connection on the output cables, something like that.

What can make it change on the line side is someone having installed Power Factor Correction Capacitors somewhere in the facility. Under the right set of circumstances, the PFC caps can resonate with the VFD caps on the DC bus and cause the DC bus to rise. Line noise from severe notching (usually caused by large SCR power controls) can also cause the rectifier to over react and raise the DC bus (too complicated to explain here). So there too, look for something new that has been added to the facility.