Nidec Leroy-Somer has provided alternators to Yanbus power station, according to the Saudi Diesel Equipment Company
The Saudi company will be replacing DG sets for the power station’s nine gas turbine generators (GTGs), which have a total capacity of 524.6MW.
The new DG sets are supplied to replace 35-year old existing DG sets based on detailed assessment by the company responsible for the maintenance of the power station.
Saudi Diesel opted for alternators from Nidec Leroy-Somer, its trusted supplier.
The GTGs are equipped with DOL starter motors of 600kW, 4.16kV rating, and the starting current is very high– 6-times the nominal current – which means there is a huge inrush current experienced by the alternator. The company ordered two DG sets for redundancy, and reliability.
The DG set first acts as a Black Start, and is primarily responsible to start the turbines that are down or under planned maintenance shutdown. The DG set is also used to feed auxiliary loads in case the need arises – emergency loads other than the turbine load – before or after the Black Start, till such time the turbines take over the full load.
Nidec Leroy-Somer designed a medium voltage 4.16kV alternator with rated power of 4000kVA. This is a high speed alternator, IP23 rated, so there were some constraints regarding the design of the machine. An important consideration was adapting the design to the ambient temperature of 50°C with the humidity reaching 100% in consideration of the very harsh environment at the site.
Nidec Leroy-Somer also used the latest D550 digital AVR, which is ideal for parallel genset operation. The AVR also has a wide range of functionalities including online monitoring with manual and remote controls. The two alternators were designed and manufactured after thorough calculation of all electrical parameters. Once assembled, the alternators were tested and approved by Saudi Diesel along with third party inspectors.
“Any application that involves a power plant is very critical, because in case of a shutdown, the unit has to restart and come online as fast as possible, and these are very heavy turbines, each of 50MW. Also they must run to a synchronous speed before energising the equipment and connecting to the grid. That is the critical part – getting the GTGs into a synchronous speed before connecting to the grid,” said Nawar Shubber, regional sales manager at Nidec Leroy-Somer.
“Enclosures for the entire generator set, fabricated locally, contain UL-motorised louvres for totally enclosed operation during shut-down. The package is designed as a gas-tight enclosure while the fire alarm and suppression systems in these units are tested in accordance with NFPA 2001 and BS EN 15004-1,” said Kathim Alrifai, project manager at Saudi Diesel Equipment Company.
