George Charalampous discusses Alcad’s role in ensuring the Megalopolis B power station in Greece has reliable backup power. He explains how batteries have been developed to overcome the challenges of a hot climate and seismic activity
The Public Power Corporation (PPC) of Greece contacted Alcad to replace the backup batteries at Megalopolis B, a 300MW coal-fired thermal generating unit in the Peloponnese.
As the biggest energy producer and supplier in Greece, PPC has approximately 7.4 million customers and accounts for almost 85% of Greek generating capacity. This is made up from conventional thermal and hydroelectric and other renewable generators.
Megalopolis B is part of a facility with a total of 1,140MW thermal generation.
The replacement of time-served assets in plant such as Megalopolis B can be challenging, especially as new equipment is rarely a like-for-like substitution for the original. Many factors may have changed since the original installation such as building codes and minimum technical requirements.
The main priority of this replacement was to ensure that there was a safe, reliable and long-lasting backup power supply, capable of functioning in a hot and seismically active environment.
Choosing the right system
The selected battery system needed the ability to provide backup for mission critical equipment for more than eight hours. This includes switchgear, oil pumps and lighting, as well as safe shutdown of equipment and a controlled transition to backup power generation.
While there are many potential battery systems across Alcad’s battery range, the selected system comprises 680 cells in two identical arrays of MB765P batteries. Alcad took into consideration PPC’s requirements for power, voltage and duration when deciding which battery solution would be most suitable.
In order to identify the best possible size battery for Megalopolis B, Alcad used its BaSics (battery sizing and configuration system) software tool. This tool is designed to help engineers in optimising their sizing calculations. It also helps to select the correct battery for the specified application and create the optimum battery layout for the available battery room, as well as calculate the heat generated by the batteries and the ventilation required.
The MB765P batteries are ideal for providing backup power for a mix of high-power and low-power sustained loads at industrial sites. This includes power plants, substations and oil and gas facilities. Benefits include reliability and high resistance to shock and vibration, which is especially useful to withstand earthquakes.
The cells have a relatively fast recharge time due to their high chargeability. They can recover at least 80% of their capacity in 15 hours under float charge conditions after a full discharge.
A nickel technology battery system was also chosen due to the climate at Megalopolis B. Even though there is ventilation in the battery room, the temperature varies from 15°C to 30°C as there is no air conditioning. Therefore, it is vital that the chosen batteries can withstand extreme temperatures over a long life-time and operate reliably at +30°C.
Nickel technology batteries are more resilient than lead-acid in the heat. At +20°C nickel can last 20 to 30 years whereas lead-acid will only last up to 10 years. However, if the temperature reaches a constant +30°C, nickel batteries last 16 years but lead-acid only up to five. As the temperature increases the gap widens between these two technologies.
Earthquakes can be extremely disruptive in terms of power as shaking and rupturing of the ground can cause damage to structures and power generation, transmission and distribution assets, potentially leading to fire and electrical surges.
Backup batteries are vital to allow for the safe shutdown of equipment and clearing of faults. They also ensure the availability of control and monitoring equipment. Earthquakes are common in Greece, due to it being located at the intersection of several tectonic plates, so backup power is especially important.
Engineers use peak ground acceleration (PGA) as the basis of anti-seismic designs. Semicom GP Hellas, Alcad’s authorised agent in Greece, supplied a battery installation with the ability the survive an earthquake with a PGA of 0.2g. This is higher than the guidelines published by the Greek government, which state that building and structures around the town of Megalopolis should be able to withstand at least 0.16g.
Semicom GP also designed a new floor plan arrangement for the new batteries, racks and power cables, as well as supplying, installing, commissioning and testing the new battery system.
The project called for complete decommissioning and dismantling of the existing battery system and battery racks and replacement with the new battery solution. The Alcad MB batteries have high mechanical strength and robustness, with an internal steel plate structure and polypropylene outer casing. These features mean that the cells themselves are tough and robust and can withstand vibrations, shock loads and mechanical impacts. This is especially important for applications requiring earthquake proof racks, which have larger support components and additional cross-bracing compared to standard racks.
The battery room was located in the top floor of a high building without elevators. Each of the 680 new cells weighs about 40kg, so without a lift this was challenging.
The first phase involved breaking through an external wall of the battery room, and a temporary lift was then installed. The power cables were then rearranged to match the new floorplan, and the new batteries were installed, connected and commissioned. Once the installation was complete, the outer wall was replaced with new brickwork.
Semicom GP used a team of six technicians working 10-hour shifts to ensure that the work was successfully completed within the two-week time frame of PPC’s planned outage for the plant. The battery system has now been in operation for more than a year and is operating as expected, as further evidence of the performance of Alcad’s technology.
George Charalampous is Alcad’s ME area sales manager