1336 Force Bus Voltage Problems

[The Plc Kid]

I am having issues with a 1336 Force AC Drive that the bus voltage is going too low when increasing speed.

Currently i can only run at about 50-60% motor rated rpm and if we go higher the bus voltage drops down to around 400 and we lose the drive enable.

This is a common dc bus application and i do not see the bus voltage drop with my meter connected but i do see it drop on the drive HIM.

The dc bus inductor http://literature.rockwellautomation.com/idc/groups/literature/documents/tg/1336t-tg002_-en-p.pdf pdf page 107 seems to be getting really hot also. What is the dc bus inductor? It really looks like an internal brake resistor the way it is connected?

This system is common dc bus with 1 common rectifier and about 12 drives the drive in question is 100 HP and the system has a ab dc bus chopper module connected to a larger braking resistor outside the cabinet to shed excess bus voltage. If this dc bus inductor is acting like a brake module then it should not even be there?

Drive part # is 1336T-R100-AN-GT2EN Series D

Any Ideas?

 

[The Plc Kid]

This http://samplecode.rockwellautomation.com/idc/groups/literature/documents/in/1336s-in046_-en-p.pdf also has some info on the dc bus inductor but it still looks like a brake module to me or works with a brake?

 

[Gil47]

Wild guesses

Make sure all 3 phase to the common rectifier are drawing current.

If the Inductor is getting hot could it be that you have a large AC component on the DC bus line.
Is 1 phase of the drive giving a continuous DC or continuous half wave DC to a motor lead.

 

[rdrast]

The inductor isn't a brake module, it's, well, and inductor. It shouldn't be very large, but it does provide some impedance in the DC line if it's the one I'm thinking of.

Where did you measure the buss voltage? Measuring it on the actual common buss might not give you the right reading. Measure it directly on the DC Buss bars in the affected drive. A loose connection, a bit of corrosion, anything like that can cause a problem when the current demand peaks.

I'd say take an infrared snapshot, but the incident is probably too short to make much of a temperature rise.

 

[DickDV]

Since this is a common bus configuration, you don't have to be concerned about input phase loading or the condition of the input rectifier.

If the bus choke is getting too hot, I would first measure the DC current flowing into the problem drive bus. If this is too high, the choke will overheat. If not too high, I suspect the choke is bad. If the current is too high and the drive output to the motor is not being overloaded, I would suspect the bus capacitors. If these are failing and conducting current, they should also be getting hot.

This is an interesting problem and I'd sure like to know what ends up being the problem.

One last thought. Grounds on the output can cause the DC bus current to run high as well. It depends on what kind of ground reference the bus power supply has.

 

[The Plc Kid]

The precharge board had a dmaged resistor on it. The signal from the bus passes through the precharge board to the gate driver board and is then reduced to a lower signal 5 volt max i think which is sent to the main control board and then scaled to give the bus voltage to the drives processor.

This was losing voltage as the drive speed increased and the bus voltage changed. This is also why it read low on the HIM but not on my meter.

The bus voltage was not going that low the drive just thought it was and it was reacting correctly.

This was a hard find. Thanks for the help everyone.

 

[sthompson]

The precharge board had a dmaged resistor on it. The signal from the bus passes through the precharge board to the gate driver board and is then reduced to a lower signal 5 volt max i think which is sent to the main control board and then scaled to give the bus voltage to the drives processor.

This was losing voltage as the drive speed increased and the bus voltage changed. This is also why it read low on the HIM but not on my meter.

The bus voltage was not going that low the drive just thought it was and it was reacting correctly.

This was a hard find. Thanks for the help everyone.

It is always nice when someone gets back to the list with the outcome for a problem they posted on. Congratulations on sorting it out.

Stu.....

 

[DickDV]

And I second the congratulations! I've never intended to be a component level troubleshooter on drives rather attempting to be an application and startup specialist. But, inevitably, you have to dig in once in a while. So, this problem interested me and I really appreciate the followup.

Thanks again, PLC Kid.