The Power Management System (PMS) developed to Emirates Global Aluminium – Al Taweelah site (EGA-AT), is a complex system capable of balancing generation and load following incidents within the plant.
The PMS ensures the stability and reliability of EGA-AT plant by monitoring power flows in the interconnectors, system frequency and equipment circuit breaker status and acting according to the identified incident by reducing demand or generation.
To develop the basic design of the PMS, the static and dynamic characteristics of EGA-AT plant was modelled in Smart Flow. That includes the dynamics of potline, which is basically a DC bus behind a rectifier, but with very complex control logics. Besides that, the PMS itself was modelled including:
- Signal acquisition: measurement of voltage, current, frequency and breakers’ status signals which are used as input to the logics.
- Feedback logics: based on user-defined protection relays capable of detecting power flow or frequency violations and triggering actions like the runback of potlines, tap down or trip of rectifier transformers, or tripping of gas turbines.
- Feed forward logics: based on user-defined protection relays capable of detecting pre-coded incidents (loss of full combined cycle or loss of multiple potlines) and triggering pre-defined actions.
- Equipment protections: over-current and direct power protections were modelled using macroblocks, while over/under voltage/frequency were modelled using the existing protection relays.
- Grid MW control and isochronous load sharing: these two functionalities were added directly to the gas turbines’ governor model with the objective to control the power exchange with the grid and to control the frequency when the system is isolated from the main grid
Once the complete model was implemented, transient stability analysis were performed in batch mode to analyse the system under different network configurations facing all possible combination of incidents, resulting on more than 1000 cases. For the cases presenting stability issues or unexpected trips, the logics were adjusted and the simulations re-run until all the cases were acceptable.
The final logics were translated into a Technical Specification and shared with the Original Equipment Manufacturer to be implemented under a dedicated controller. The PMS was finally commissioned on site and it is now under operation in EGA-AT plant.