Good day,
I have two gas engine generators rated at 5,200kW each, running parallel to the grid.
In parallel mode, both are running in droop mode 5% with kW output control. DCS controls the load sharing between the two generators by sending the kW setpoint to each generator, and the engine control system adjusts the droop curve accordingly.
In Island mode, there is no control from DCS. Both engines change the operation mode to droop mode 5% with speed control. There is provision for speed raise/lower command from DCS at engine control system, but it was not configured.
There is no communication between both engines. The engines are not aware of individual generation and the total house load.
Until recently, the islanding process happened during both generators running at equal load. For example, house load is at 5MW; each engine runs at 2.4MW while importing 200kW from the grid.
When island, each engine takes the load from the grid equally. Due to the stable house load (electrolyzer plant), the generators can maintain the frequency with no intervention from the operator, operating in the droop mode.
However, recently, the grid connection was lost during the generator start-up. During this time, the load sharing was at 75% on generator 1, 25% on generator 2. After one hour without intervention from the operator, the generator trip due to underfrequency. Based on the 1s trending data, it was +/- 2% fluctuation. (maybe higher in finer resolution, as the underfrequency setting is at 5%). The typical island operation with 50/50 load sharing has only +/- 0.5% frequency fluctuation.
Does the imbalance load sharing prior islanding contribute to this frequency instability? In my understanding, the droop curves are different due to the load during the islanding.
How do the engines react from the additional load released by the grid? Are they going to share the load in 75/25 manner?
I tried to visualize this problem with the tandem bicycle analogy, this time it is an e-bike.
With full loaded rack, both riders cycle the same cadence/rpm of the electric motor. Rider 1 inputs more power (75%), while rider 2 inputs 25%. Once the electric motor goes off, I couldn't visualise how the riders cadence will be.
Thanks!
I have two gas engine generators rated at 5,200kW each, running parallel to the grid.
In parallel mode, both are running in droop mode 5% with kW output control. DCS controls the load sharing between the two generators by sending the kW setpoint to each generator, and the engine control system adjusts the droop curve accordingly.
In Island mode, there is no control from DCS. Both engines change the operation mode to droop mode 5% with speed control. There is provision for speed raise/lower command from DCS at engine control system, but it was not configured.
There is no communication between both engines. The engines are not aware of individual generation and the total house load.
Until recently, the islanding process happened during both generators running at equal load. For example, house load is at 5MW; each engine runs at 2.4MW while importing 200kW from the grid.
When island, each engine takes the load from the grid equally. Due to the stable house load (electrolyzer plant), the generators can maintain the frequency with no intervention from the operator, operating in the droop mode.
However, recently, the grid connection was lost during the generator start-up. During this time, the load sharing was at 75% on generator 1, 25% on generator 2. After one hour without intervention from the operator, the generator trip due to underfrequency. Based on the 1s trending data, it was +/- 2% fluctuation. (maybe higher in finer resolution, as the underfrequency setting is at 5%). The typical island operation with 50/50 load sharing has only +/- 0.5% frequency fluctuation.
Does the imbalance load sharing prior islanding contribute to this frequency instability? In my understanding, the droop curves are different due to the load during the islanding.
How do the engines react from the additional load released by the grid? Are they going to share the load in 75/25 manner?
I tried to visualize this problem with the tandem bicycle analogy, this time it is an e-bike.
With full loaded rack, both riders cycle the same cadence/rpm of the electric motor. Rider 1 inputs more power (75%), while rider 2 inputs 25%. Once the electric motor goes off, I couldn't visualise how the riders cadence will be.
Thanks!