Rear Admiral JS Mann, NM, VSM (Retd), Distinguished Member, SAMDeS
Preamble
Electrically driven ships are not new, both AC and DC powered ships using conventional power trains were in vogue since beginning of the last century. However , the advancement of technology in the field of high powered solid state switching devices and multi megawatt variable speed drives has brought a revolution in the field of marine electric propulsion. Though it found its place in merchant marine first with the introduction of hybrid drives using a combination of diesel and electric including Power Take-Off (PTO) and Power Take In (PTI) configuration using shaft generators and now with podded propulsors.
Navies around the world initially limited its use to auxiliary and amphibious ships, but the trend has seen a sea change in the recent past with the technology maturing and becoming more and more reliable, cost-effective and energy-efficient. Today, combatant warships such as Queen Elizabeth Class Aircraft Carriers, LPDs as well as front line warships such as F-125, Type 45 frigates, French FREMM class frigates, USS Zumwalt class Destroyers, Korean Daegu Class Frigates (FFX-II), are installed with state of the art electric propulsion systems to leverage the distinct benefits of electric drives.
Why Electric Propulsion?
Modern war at sea will be determined by navies that can use stealth ( both in terms of radar and IR signature) effectively, endure longer and be more resilient. The Navy’s pressing demands for dynamic response in speed, torque, ultra-quiet operation, and minimum mechanical vibrations have necessitated consideration of electric propulsion as the future at sea. The inception and growth of the Electric Propulsion Technology in surface combatants necessitate its evaluation and a road map for its induction into the country simultaneously paving the path of self-reliance through Atma Nirbhar Bharat initiatives in which our PSUs like BHEL and HAL and private players like L&T, Siemens, etc and can play a vital role. Considering the Indian Navy’s Perspective plan for Shipbuilding, it is time that we deep dive into the selection of various combinations as per role and operational requirements and find the indigenous solution for it.
Options Available
Though the concept is primarily based on employing either partial or fully integrated electrical power systems catering to both propulsion as well as ship’s systems including power weapons and sensors. With the dispensation of gearboxes and lengthy shafts with multiple supports, a more space-saving, flexible configuration can be evolved. It can either be a pure fully integrated electric propulsion ( IEP/ IFEP) which uses common electric generation sources with multiple bus bars feeding to both propulsion as well as onboard consumers including weapons and sensors or use a combination of electric with conventional/mechanical / waterjet propulsion drives. For example, Royal Navy Type 23 ASW frigates have CODLAG type of arrangement comprising of twin shaft and each shaft driven by gas turbine (for boost mode) and an electric motor (for silent and cruise mode) which have been operating successfully. In hybrid-electric propulsion, the Electric drive operated on economical prime movers such as DGs or low power (LP) GTGs, are normally employed to optimize overall energy efficiency and radiated noise levels and cost of operation of the propulsion plant during slow and quiet operations whereas the conventional (mechanical) drive operated on high-speed diesel (HSDs) or high power (HP) GTGs, is used to get boost speeds with fuel economy at higher speed operations. Thus, such an arrangement accrues benefits of both types of propulsion systems to suit the modern ship’s diversified operating profile. Indian initiative of BHEL/ GE in indigenizing the electric propulsion package for marine applications, we are sure that future platforms can benefit immensely from it.
Technologies Required
The success of this program depends on the indigenous development of high capacity permanent magnet propulsion motors of around 25 MW range with a tightly integrated Variable Frequency Drive capable of giving above 95% efficiency. It is pertinent to note that PM motor built by DRS Technologies for Zumwalt class destroyers uses 36.5 MW pm motors with 98% efficiency. The Koreans are using a 1.7 MW HED Propulsion system with Active Font End (AFE) rectification to meet the input power quality requirements without the need for bulky phase-shifting input transformers for their Daegu class frigates. We need to identify an optimum building block for it and an equivalent of LM 2500 GT (22 to 34MW) may be the ideal choice around which complete architecture can be evolved.
Conclusion
Considering the futuristic technologies which are environment friendly, provide stealth, reliability, extended endurance, ease of operation and maintainability in naval operations, electrical propulsion is the only solution.
In our quest for Atma Nirbhar Bharat we need to identify the needed technologies and with the strength of our PSUs and private partners, we should develop these modules within India in a time-bound manner and it should form the backbone of our future indigenous ship construction programs.
SAMDeS intends to hold an international ‘physical’ conference on “Electrifying the Indian Navy” in Early November 2022. Watch this space for more information.