Hi everyone,


I’m looking for some expert advice on a reactive load sharing and excitation issue we are experiencing with one of our marine generators.


System Setup:


• Application: Marine Genset (Caterpillar 3516B)


• AVR: Leroy-Somer R630


• PMS / Synchronization: SYMAP (running in Symmetric load sharing mode for both kW and kVAR).


• Busbar Voltage: 460V (60Hz)


Problem Description:


When this specific generator is synchronized and running in parallel with other gensets (ton the 460V busbar, it intermittently absorbs reactive power (negative kVAR / capacitive). Eventually, the SYMAP system trips the generator breaker, giving an "Excitation Fault" alarm (likely due to reverse kVAR / severe under-excitation). The issue is intermittent and usually happens when there are load fluctuations on the vessel.


Key Symptoms & Observations:


1. The Flashing LED: While running in parallel and taking negative kVAR, the pid iexc min LED on the R630 AVR flashes continuously.


2. Voltage Discrepancy: The main busbar operates at 460V. However, I noticed that the off-grid (no-load) voltage of this specific generator seems to be around 457V.


3. Hardware Condition: Because the pid iexc min LED is flashing, it indicates that the AVR is actively trying to reduce the excitation current to its absolute minimum limit. This leads me to believe that the rotating diodes, exciter, and main field are healthy, and the AVR is intentionally suppressing the field.


Current Hypothesis:


Because the generator's baseline voltage is set lower (457V) than the busbar (460V), the AVR "sees" the 460V upon synchronization as an overvoltage. It then aggressively reduces the excitation current to lower the voltage, hitting its minimum limit (iexc min). This intentional under-excitation causes the generator to absorb kVAR from the stronger generators on the bus, eventually leading to the SYMAP trip.


My Planned Action:


I am planning to take the generator off-grid (no-load) and adjust the baseline voltage to match the 460V busbar using the voltage setting potentiometer (P1/P5 depending on the exact R630 configuration), and slightly check the excitation ceiling limit (P4) to ensure it's not choking the AVR during high inductive demands.


Questions for the Experts:


1. Does my diagnosis regarding the pid iexc min flashing and the voltage discrepancy sound correct?


2. Are there any specific parameters or PID settings (like P7) on the R630, or within the SYMAP logic, that I should be double-checking before performing this mechanical adjustment?


3. Could there be any other hidden causes for this specific AVR behavior during parallel operation?



Note: the low KVAR on this generator was observed a long time ago but no trips happened, but during the past year we faced trips due to “Excitation fault” and no rewind nor any major maintenance were conducted.

Note 2: regarding adjusting AVR potentiometers, I would like to know which ones are to be adjusted when the generator on-load and parallel, and which ones are to be adjusted when generator is running off-load?
and which ones are NOT to be adjusted when generator is running in parallel?

Any insights or similar experiences would be highly appreciated.

Thanks in advance!

 

Hi

Could you tell us how many DG are installed and operated ?

Also is SYMAP used as Digital Protection device and PMS?

What is controls philosophy used here ? Is that island mode controls scheme and Droop control ?

Thx for your reply with these clarifications we would be able to support remotely

Regards,
James

 

There should be a controls philosophy as Load sharing control with Symap as PMS?? right?

I saw that you mentioned Load sharing mode with Sympa


I had a read on Leroy somer AVR R630 you should be able to set the right configuration for parallel operation mode

 

Hi

Could you tell us how many DG are installed and operated ?

6 gensets, 3 online and 3 standby.

Also is SYMAP used as Digital Protection device and PMS?

Yes

What is controls philosophy used here ? Is that island mode controls scheme and Droop control ?

Thx for your reply with these clarifications we would be able to support remotely

Regards,
James

Hi, thanks for the great question. To clarify the control philosophy and architecture of our system:


1. Grid Type (Island Mode): Yes, the system operates entirely in Island Mode. It is an isolated marine vessel (barge) power plant, so the generators are responsible for establishing and maintaining the grid voltage and frequency without any connection to a shore/utility grid.


2. Control Philosophy (Active Load Sharing over Droop):


The underlying primary control at the generator level relies on Droop Control:


• Reactive Power (kVAR): Managed by quadrature droop on the Leroy-Somer R630 AVR (adjusted via potentiometer P1).


• Active Power (kW): Managed by speed droop on the engine governors.


However, the overall control scheme is an Active / Isochronous Load Sharing system managed by the PMS (SYMAP).


• The SYMAP operates in Symmetric (SYMM) Mode for both kW and kVAR sharing.


• It acts as the secondary controller, continuously monitoring the busbar and individual generator outputs. It sends correction signals (bias/pulses) to the AVRs and Governors to compensate for the droop, thereby keeping the busbar strictly at nominal values (460V and 60Hz) while forcing proportional active and reactive load sharing among the connected gensets.


So essentially, the AVR's local droop provides the baseline stability for paralleling, but SYMAP is actively correcting it to maintain rigid bus parameters.

 

Hi
Thank you for these clarifications.

When did the problem started?was the Genset operating correctly before this issue..

 

Did you reviewed the Installation & Maintenance manual from Leroy Somer ( Nidec)?

The manual show how to get the Generator /AVR connected together and also how to get the setting right

 

Good evening

Is that possible for you to get some trends on this event issue...?