The PMS issues commands to the generator governor system which balance the load between generators.

However, PMS frequency control response is slow and can have difficulty maintaining system frequency in certain circumstances. There is also a danger that the PMS could fail, leaving no automatic back-up system to take control and thus necessitating manual intervention.

The solution to the basic problem was developed by the Woodward Governor Company 30 years ago. Isoschronous Load Sharing enables generators to share load accurately whilst still maintaining the system frequency constant without the need for external PMS. In this type of system, the individual generator electronic control systems need to communicate with each other and do so by interconnections commonly referred to as system Load Sharing Lines (LSL).

The LSL has until recently been regarded as a potential problem area by many marine classification societies as the system LSLs are common to all the generator speed control systems and a fault could constitute a 'single point of failure' scenario, with the vessel experiencing a complete loss of power.

Turner Diesel has been able to eliminate the possibility of such a scenario by providing a Redundant Isoschronous Load Sharing control through implementing its own software within a Woodward 828 Digital Control System (DCS).

The 828 DCS marine control has two totally independent sets of LSL. A fault on the primary LSL immediately transfers the load sharing to the secondary lines without any disruption to the system. If a fault is detected in the secondary load share lines then a bumpless transfer over to Droop can be implemented.

It should be noted that a fault on the system LSL is an extremely rare event and is unlikely to occur even once during the lifetime of a vessel.

The Redundant Isoschronous Load Sharing system supplied by Turner Diesel thus provides users with a robust control package which complies with the safety requirements of classification societies.

The 828 DCS maintains isoschronous load sharing even with the failure of an engine speed sensor or the generator kilowatt transducer. The complete failure of an 828 DCS will not affect the ability of the other generators in the system to load share. The unit is particularly suited to retrofits and can be tailored to meet the requirements of most generator applications.

Turner Diesel can provide a complete retrofit service including the system installation and commissioning. It can also provide custom made electronic governor controls for special generator or propulsion applications, including the starting and stopping of auxiliaries and the monitoring of temperatures and pressures.

MJ Information No: 21416