ABB Protection Relay Modbus Communication Problems 1

[cdevine]

We are having a problem with the loss of modbus communications between ABB protection relays and our ControLogix PLC.

We have several (approx 25) 11kV and 3.3kV switchboards comprising ABB protection relays (approx 120 x REF610, 15 x RET541, 15 x REX521). The relays communicate via Modbus RTU to a Prosoft Modbus card (MVI56-MCM) located in Allen Bradley ControLogix Racks. There is no more than 8 relays on an segment so multiple relays, Prosoft cards and ControLogix Racks are involved.

Communications is stable to all nodes for an extended period (days) and then one relay will not respond. The failed relay is random and does not appear to be coincident with large motor starts or other electrical noise. Response is identified by looking at the receive packet counter in RSLogix for the failed node and recognising that it does not increment. The master continues polling adjacenet nodes successfully. Power cycling the failed relay reestablishes communications to the relay.

Cable segments are Unitronic Comms cables with a characteristic impedance of 100-120 Ohms.

Has anyone had similar problems with the ABB relays on Modbus? What can I do to be 100% sure it is the relays that are the problem?

Chris Devine

http://www.icande.com.au,

http://www.redbusbar.com

 

[dpc]

We've had problems with ABB recloser controls with similar comm issues. You should contact ABB and see if there is a firmware upgrade. I have found it is very difficult to get ABB to admit there is an issue (with anything - no matter what product), but if you are persistent and get the right person, you might actually get some assistance.

The symptoms you are describing do seem to point to the ABB relays as the root source of the problem.

 

[slavag]

Hi.
What is BR: 9600 or 19200? what is connection of shield of RS485 twisted pair.

Dave, those relays RET and REX with same version about 2-3 years, btw, not possible provide upgrade FW, only replace relays or communication card in REF610 or RER133 card for the RET541. REF610 with same version about one years.

Best Regards.
Good Luck.
Slava

 

[cdevine]

Thanks for your responses.

It is interesting that other ABB relays have communication issues as well. I did like the thought of the firmware upgrade but it sounds as though it is not possible.

Baud Rate is 9600. Shield is continuous and earthed at Prosoft card end only. Terminating resistors (120 Ohm) are installed at bus end nodes only.

The installation is less than 12 months old.



Chris Devine

http://www.icande.com.au,

http://www.redbusbar.com

 

[slavag]

Hi.
From my point of view don't think about FW upgrade. Not needed.
BR 9600 is good, about shield..Im not sure if it's right connection ( if I remeber right, you have earthed every part of RS485 bus, but in one side only). I have check it. Could you please ( of course if it's possible) send to Forum communication connection diagramm, I try check it and will back to you up to end of this week.
Good Luck.
Slava

 

[slavag]

Hi Chris.
Please find attached data about RE_610 relays connection.
In additional.
REX521 RS485 dosen't include grounding point on teh relay plug, that means, you have connect
RE_610 X5.5/6 to REX521 X3.1/9
RE_610 X5.5/7 to REX521 X3.1/10

RET54x with RER133 it's other story, please find in the ABB library manual of RER133, it's special connection of first RER133 and others.
Hope that help.
Good Luck.
Slava

 

[cdevine]

Thanks Slava for following through with this.

Given that your suggestions are focussed on cable and earthing arrangements, is this communication lockup something you have experienced before due to incorrect cabling arrangements?

In my experience incorrect cabling has caused either no communications or communication that has failed due to noise but self heals.

Your thoughts? Thanks.

Chris

Chris Devine

http://www.icande.com.au,

http://www.redbusbar.com

 

[slavag]

Hi.
We haven't a big experience with RS485 bus, usually with protective relay we use star connection with FO.
For ABB relay is owner SPA protocol ( start or loop).
But we see problems with RS485 bus becouse not "xmmm.. correct" connection of bus. From time to time,one of devices was "freeze" in HMI and only restart of device was help.
Intuitivy, Im always start debuging from communication connection and not from devices, but..before about one year we was connected RS485 bus with meters and fault in one of them make same problem, like to your. From other hand, you have few buses, that means it's some systematic problem.
Need think, I try found additional info.
Best Regards.
Slava

 

[dpc]

One thing to verify is the termination impedance of the RS485 circuit. The ABB devices we had each had its own termination resistor, which we had to physical remove when we had multiple devices in parallel.

But I don't think this would cause the lock-up you are seeing. Just a lot of comm errors.

"An 'expert' is someone who has made every possible mistake in a very narrow field of study." -- Edward Teller