In this article Paul Brickman of Crestchic, the leading global manufacturer of loadbanks used for power testing in the marine sector, looks at how the market and its needs are changing.
Meeting the power needs of ‘super vessels’
In recent times we have witnessed a massive growth in the size of seagoing vessels for transportation of products, leisure and oil & gas exploration & production. As these vessels continue to grow in size, their power needs grow too, as does the complexity of on-board systems. Modern sea vessels often contain complex propulsion, production and environmental support systems which must operate reliably for long periods of time, often hundreds, if not thousands of miles offshore. Ensuring the availability of power for these systems is a critical function to guarantee vital services can run uninterrupted, making pre-launch reliable testing of power supplies of particular importance.
In the 1940s the world moved on from colonialism to globalisation. This movement was accompanied by rapidly growing trade and the need for effective means of transport which was the first driving-force in the development of sea vessels. Fast forward 70 years and we now have different driving-forces in the growth and development of these vessels. For example the reason behind the recent increase of the size of container ships is economy of scale. Fitting more products on container ships and making less journeys will inevitably save money. One of the world’s largest container ships, the MSC Zoe,is 1,297ft (396m) long and can carry over 19,000 20ft equivalent units “TEU” or shipping containers as most people know them. Simply put, it is a lot cheaper to transport cargo if you move large quantities at a time.
As ships continue to grow in size and complexity, the power systems will continue to develop and the need for testing will remain an absolute necessity.
Any offshore power generation unit is a complex system, or series of systems, working together to perform several functions at once, and at the system’s heart is the generator or gen-set. This could consist of several gas turbines and/or diesel generators. However, various discrete systems and components complete the total package, such as alternators, regulators, transformers and switchgear.
These additional components typically come from various manufacturers, and are usually designed to interface with a number of makes, models, and sizes of generators. As with any other mechanical or electrical components, all are potentially subject to failure, and have varying maintenance needs, at the very least requiring regular testing and servicing.
Ship categories and their power needs
Ships can fall into a number of categories, all with different uses and power needs. Cruise ships, for example,require massive electrical installations in order to power the shopping malls, entertainment centres, bars and restaurants on-board. One of the largest cruise ships in the world, the Allure of the Seas by Royal Caribbean, is 1,187ft (362m) long. Setting a new world record for the most passengers able to be accommodated, the ship can hold 6,360 passengers, 2,200 crew members and features 25 restaurants and 24 passenger lifts.
Military vessels, in comparison, also have high power needs in order to run complex propulsion, life support and weapon systems. Failure of these systems in operation may have a devastating impact so it is extremely important to perform rigorous testing.
Other types of ships include car and passenger ferries, oil tankers, nuclear ships and fishing vessels, all with specific power requirements. These systems must be able to operate at full power even in the harshest conditions, with all components working together to do their individual jobs
The issues created by increased vessel size
Operating these huge vessels requires complex electrical systems which need to be correctly and thoroughly tested. However, the stresses introduced by this level of operation cannot be simulated by discrete tests of a system’s numerous individual components: automatic transfer switches, switchgear, load-sharing centres, voltage regulators, alternators, electrical cabling and connectors, ventilation, cooling systems and fuel systems.
While the generators may have been tested at the factory, the variables of their interaction with other parallel-connected power generation units, load profile, ambient temperature, humidity, fuel, exhaust and cooling systems can be significantly affected by the installation.
A system-wide test is therefore the only way to ensure the individual components of any power generation system will work together harmoniously, whether for continuous production demands, or in emergency power outage situations.
Main engines and generators on board these vessels require a constant and reliable electricity supply to keep them going. Pumps driven electrically take in cold water from the ocean to cool engines, and also convey fuel from fuel tanks to the engine. Electrical power is vital for many operational functions – without it, ships literally come to a halt.
Large equipment such as propulsion motors and bow thrusters, requires electricity of high voltage. As for smaller machinery (cabin lights, galley equipment), the electricity goes through transformer and is thus stepped down into lower voltage. Large cables snake through the whole ship to distribute electrical power. They carry power from generators to switchboards, through passageways, public rooms, and crew and passenger cabins.
The correct and comprehensive testing of these systems at the commissioning stage is vital to ensure trouble-free propulsion, production, efficient power generation and the safety of personnel.
R+R – the role of resistive and reactive testing
A resistive-reactive load test of an installation’s power system can accurately simulate the system’s response to a changing load pattern and power factor (pf) demands, such as would be encountered during real world running conditions or in the event of standby genset having to operate.
Resistive-reactive load banks are used to test the engine/turbine generator set at its rated pf. In most cases this is 0.8 pf. The reactive component of the load will have a current that “lags” the voltage. The resulting power is described in two terms, the kW, or real power, and the kVA or apparent power. The combination of resistive and reactive current in the load will allow for the full kVA rating of the generator windings to be tested. Even though the genset is producing more kVA, it is actually not producing more kW. The “real” power (kW) required from the engine/turbine is essentially the same.
The inductive loads developed during reactive testing illustrate how any given system will handle the voltage drop in its regulator, paramount when paralleling generators. The test will also verify that this regulator is working properly. If not, its magnetic field could collapse, rendering the generator useless and preventing other generators in the system from operating efficiently in parallel. Resistive-reactive testing can also reveal additional stresses (and help predict pending failures) of a system’s switchgear, alternators, and other systems that resistive-only testing cannot.
It is clear that a procedure involving reactive as well as resistive testing is far more comprehensive and thorough than a resistive-only test, more accurately replicating the conditions likely to be faced in a real conditions, and so more readily identifying any potential source of a problem. Carefully managed reactive-resistive testing is therefore the only way to guarantee the operation of full-time or emergency power systems.
Commissioning aside, which is invariably performed onshore, loadbanks have other uses on large vessels. Permanently installed loadbanks allow for comprehensive testing to be integrated into the maintenance procedures of emergency systems in particular. Oversized generators can be cleared of any carbon build-up with regular sessions of full load application, ensuring reliable performance when called upon for particular production cycles or an emergency.
What does the future hold ?
The need for testing these systems is supported by the American Bureau of Shipping (ABS), a classification society, with a mission to promote the security of life, property and the natural environment, primarily through the development and verification of standards for the design, construction and operational maintenance of marine-related facilities.
All major ship classification companies will have a close eye on competent testing more so then ever before with the recent growth in the industry. Through all levels of the shipbuilding journey from the ship owner, the ship builder and the ship insurer all parties must insure power on the ship has been tested adequately to avoid a disaster.
Founded in 1983, Crestchic is one of the world’s leading specialist manufacturers of loadbanks which are used in the testing of power supplies in the most demanding climactic and environmental conditions across seven continents. Operating from locations in the UK, North America, China, Singapore, Netherlands, France, Germany and UAE, the company is at the forefront of innovation and design, with thriving sales and rental operations and a loyal and growing customer base worldwide. For further information call +44 (0)1283 531645.