Synchronous motor controllers 1

[Thedroid]

We have 5 1250hp 4160v synchronous motors at the plant. They are controlled by a GE Multilin SPM, a GE Multilin SR469 and also a Motortronics MVC Plus soft start. I'm wondering if the SR469 is neccesary in this type of setup. The MVC seems to have the neccesary protection, and already provides most of the protection. I'm trying to figure out exactly what each unit is protecting, but the prints leave alot to be desired. Does anyone have any ideas why we would need the extra relay? I'm trying to find a sequence of operation, and also have been going through the prints and settings trying to identify the trips and controls.

The control system seems overly complex, and luckily we have not had any trouble yet. The starters are about 2 yrs old and I'd like to get real familiar with them before we have trouble. The equipment they drive is critical, and there will be lots of pressure in the event of a breakdown.

 

[jraef]

Most of the functions of the 469 are indeed included in the MVC controller. The reason why the 469s are there is usually a function of a bidding process in which noboby wants to bother with any investigating or comparison.

That said, there are a few differences, most of which are never used by anyone. But just in case you do, here they are:

The 469 is capable of waveform capture and storage for future retrieval by some sort of higher level system. Not terribly useful, but there you go.

The 469 can take in up to 2 external analog inputs for things such a vibration sensors etc., the MVC cannot. However, for far less than the $7k cost of a 469, you can use separate analog limit alarm relays and trip the digital inputs.

The 469 can drive up to 4 external analog outputs, the MVC cannot. Again, external analog sensors are less expensive if that is an issue.

The 469 is capable of accepting 3 additional CTs if you want to do differential protection. Not usually done in motors below 2500HP though.




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[Thedroid]

Hmm after reading your post I'm guessing that the 469's are being used for their analog outputs. The control room monitors current, voltage, KW demand, field amps and maybe even a few others. All of the units are hooked up to the analog boards and also through modbus. I'll check the manual to see if some of these features can be read from the Modbus.

 

[Thedroid]

I also need to find some more prints, so I can identify which unit is providing each analog signal now.

 

[Thedroid]

Doesn't look like the MVC is going to provide the required outputs to the control room. It has two analog outputs, but the options are limited on what they can be set to read. The manual I have doesn't go into any detail on whats available through modbus.

 

[jraef]

Pretty much everything is available on the Comm port. I have a Modbus Map somewhere, it's a little old but that info would not have changed. I'll post it if I find it.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[oldfieldguy]

If anything is superfluous in the line-up, it'd be the SPM. The 469 provides power factor elements that provide the protection needed for synchronous motors, assuming your motor is brushless, therefore not requiring sensing for a field application relay.

The 469 provides a lot of control and data acquisition capabilities that the MVC lacks. It is a good choice for a control and data platform.

Look at your control elementary diagram and see where the output relays of each device are used. This may give you an idea of what the designers were trying to accomplish. I have seen a Multilin relay installed with NO protective function at all. The client liked his old protection, but he wanted the metering functions provided by the Multilin.

old field guy

 

[Thedroid]

That's what I'm in the process of doing now. The prints from motortronics look pretty good, they just don't show any of the plc inputs or outputs, and they don't show how the 469 is connected into the system. Our in house prints show the plc inputs and outputs, but all of the ice cubes and tdr's are called different names.

I'm still digging for as much info as I can get. There at least 10 different schematics for each mill.