From erecting skyscrapers and loading cargo at ports to maintaining power plants and assembling aircraft, cranes are crucial for operations that require robust and reliable lifting solutions. As the construction industry continues building upwards — with 600 more skyscrapers in the pipeline for London alone — cranes will be key to realising future industry projects.

A crucial control system

At the heart of crane operations is a control system, which is responsible for managing the various movements and functions of the crane. These systems include both mechanical controls, like gears and pulleys, and electrical controls, such as motor drives and braking systems. The primary objective of a crane control system is to ensure that the crane operates efficiently and safely — whether that’s lifting a beam into place on a skyscraper or positioning a delicate component in a manufacturing process.

Motor control systems in cranes play a crucial role in managing the speed, torque and direction of the crane’s movements. They enable operators to have precise control over the crane's actions, from the gentle lifting of a load to the exact positioning of materials.

Advanced control systems also include features for monitoring and adjusting performance in real-time, which helps to maintain the operational efficiency and safety of the crane. By integrating these controls, cranes can achieve higher productivity, reduced operational costs and improved safety.

The role of motors

Motors are the powerhouses behind the various functions of a crane, driving the mechanisms that lift, lower and move loads. In crane systems, motors are used to control different parts, including the hoist, trolley and the crane's overall movement on its tracks or rails. Each motor's performance must be precisely managed to ensure that the crane can handle heavy loads safely and efficiently. Several advanced motor control technologies are required to provide the necessary regulation and coordination for optimal crane operation.

Variable frequency drives (VFDs) are one critical component in crane motor control systems. They adjust the frequency of the electrical power supplied to the motors, allowing for precise control of motor speed and torque. This is essential for the smooth lifting and lowering of loads, as well as for finetuning the crane's movements. By optimising motor performance, VFDs help reduce energy consumption and mechanical stress, extending the life of the crane's components and enhancing overall efficiency.

Dynamic braking systems are another essential, allowing for rapid deceleration and stopping of the crane's movements. This capability is critical for ensuring safety and preventing accidents, especially in emergency situations where quick response times are necessary. Dynamic braking systems help manage the kinetic energy generated by the crane's movements, converting it into heat and dissipating it safely, which prevents potential hazards associated with uncontrolled load movement.

Resistor reliability

Resistors play a vital role in a crane’s dynamic braking system, by managing power dissipation and ensuring safe and efficient operations. In crane applications, resistors are used in various ways to enhance the performance and reliability of the control systems.

When a crane slows down or stops, the kinetic energy from the moving parts is converted into electrical energy, which needs to be dissipated to prevent damage or overheating. Resistors absorb this energy and convert it into heat, allowing for controlled and safe deceleration. This is crucial for maintaining the stability and safety of the crane, especially when handling heavy loads or during emergency stops.

Cressall Resistors is a leader in power resistor solutions, offers a range of products specifically designed for crane motor control systems. Its dynamic braking resistors are designed specifically for high-power applications, to operate efficiently in demanding and harsh environments often encountered in crane operations.

Motor control systems are the backbone of efficient, safe crane operations. By integrating these technologies, and the resistors that safeguard the systems, cranes can achieve superior performance, reliability and safety, elevating efficiency across many industries.

Mike Torbitt is managing director of Cressall

www.cressall.com

I joined Cressall Resistors full-time in 2009, after completing two summer placements with the company during my university studies. Back then, the existing standard product range catered for most applications. Five years later, the R&D demands have skyrocketed. To respond to the industry need, many manufacturers find themselves investing in their research, design and test capabilities.

Manufacturers with constant R&D investments have a higher chance of succeeding in the global market. To attain the best professional advantage, investment in R&D comes hand in hand with processes such as market development and new business processes.

Manufacturers should be firm about what they plan to accomplish with their business. The most successful businesses are always innovating. They are always finding new ways to build up their competitive advantages. R&D is necessary in boosting the vision and objectives of a business, so companies should never be reluctant to take action toward innovation.

Cressall’s testing facility, for example, provides the means to carry out impulse tests of up to 400,000 Volts. This facility is allowing us to explore the limits of existing designs. We can make refinements to designs and change the materials we sue to extend the limits of the technology we have already developed. 

There is a solid relationship between the amount of effort put into research and development, and the way a company performs. Companies that use R&D investment as the main driver for progress are inclined to achieve better outcomes for investors and overall be more innovative than their competitors.

Cressall has recently invested in a temperature regulated water circulation system that can be used for developing our water cooled resistors. The continued success of the water cooled EV2 resistor has merited investment for further development. We have a development program in place which is based on feedback from the market place. As a result we are looking to create smaller designs with lower pressure drops as well as reducing cost.

R&D is recognised as an important factor in economic growth and balance. R&D can easily lead to highly valued technologies, strategies and designs for your company that could be the origin of potential value when considering sustaining a competitive advantage.

Qualified R&D projects allow manufacturers to defray relevant costs with the help of the Research and Development Relief for Corporation Tax. This option allows a business to reduce its tax bill. Small to medium size businesses also get tax credits in cash disbursed by HM Revenue and Customs.

Many of the products Cressall manufactures are made in small batches for specific customer requirements. The ability to develop, manufacture and support bespoke solutions benefits Cressall in the market. However, the conditions are more competitive than ever and to ensure our solutions are price competitive, we have to be able to explore through simulation and testing all design possibilities.

Developing our in-house R&D capability allows Cressall to adapt its product range, meaning that when a customer gives us their product specifications, it's likely that we already have a close fit.

Plant managers across the UK have struggled for years to replace damaged power resistors for one reason or another. Often, the original supplier no longer exists in the UK market, or does not supply resistors any longer, so managers are forced to look for the required components elsewhere. Whether the application is crane control, pumps, fans or compressors, replacement resistors are still needed for legacy systems.

Ketton Cement in Rutland, is part of the Hanson Group which is one of the UK’s largest suppliers of heavy building materials to the construction industry.

Cement is made by crushing and heating limestone or chalk with small amounts of other natural materials, such as clay or shale, in a rotating kiln to a temperature of 1450°C. This chemically combines the stones into a hard substance called clinker, essentially changing calcium carbonate to calcium oxide, which then reacts with silica to form calcium silicates. This is ground to a powder with about 5% gypsum, added to control the setting time of the end-product. 

Before being fed into the kiln to begin the process of making cement, the limestone is broken up into small stones by a giant rock crusher with a capacity of 1.6 million tonnes a year. The 258kW three-phase control resistors for the crusher's 2700kW main motor were supplied in 1985 and finally reached the end of their working life almost 30 years later. 

The resistor operates at 2.2kV, conducting a 735A current through a resistance 0.16 ohm to dissipate 87kW of heat energy. When this resistor failed one Friday, Cressall was on hand to provide prompt assistance and get the works quickly moving again.

The resistor was originally supplied by Cutler Hammer. Luckily Ketton Cement had all the original drawings and even more fortunately, some of the right resistor material was at hand. Cressall ordered the insulating boards from its supplier, who delivered them swiftly. Cressall’s engineers also got hold of the broken resistor, which they stripped, rebuilt and returned to Ketton Cement the next day. 

In the case of like-for-like replacements, intellectual property is always a caustic issue. With over a century of experience in the UK resistor market, Cressall Resistors owns the intellectual rights for many of the power resistors designed and manufactured in the UK. This enables the company to undertake virtually any maintenance or refurbishment project requiring resistor technology. 

 

New resistors may be needed when motors are being repaired or rewound. Cressall has the knowledge, experience and range of resistor technologies to produce cost-effective designs for new or replacement motor control applications, particularly for customers with legacy systems for which the original equipment supplier no longer exists or has ceased manufacture. 

It’s always easier to manufacture a replacement resistor if the original design is available. When this is not the case, the manufacturer’s expertise and experience comes in. Cressall has the details of almost every resistor manufactured by other British suppliers such as GEC, Eaton Cutler-Hammer and TPR since 1950, so it is usually possible to produce replacements for older resistors when needed. 

Over that fateful weekend Cressall manufactured 12 like-for-like replacement Hi-Temp resistor banks to the original drawings and specifications. In the end, the crusher was operational before Hanson's buffer stock of crushed limestone had been used up.

If a customer cannot supply the remnants for any reason, a good resistor supplier should be able to work from photographs and a description, or even just the rating plate details of the motors involved. Although it may not be possible to produce a carbon copy, it is normally feasible to produce resistors that are functionally identical in terms of electrical and thermal performance, as well as physical size. The resistor itself may be different, but the laws of thermodynamics remain the same. 

Training included environmental health and safety, line management and sustainable business improvements. The last of these involved the delivery of the Sustainable Improvement Programme course, a Level 4 NVQ qualification in Business Improvement Techniques.

Focus Management for Business secured funding support to minimise the cost of the training programmes and the company is now engaged in the next phase of their business improvement techniques programme.