Collins Walker Limited is a world force in the manufacture of electric steam and hot water boilers. It is one of the few companies in its field which design and manufacture the whole boiler system in-house, including the pressure vessels, cabinets and controls. Supplying both immersion and electrode systems, Collins Walker customize each boiler to exactly meet the client’s needs, and the company exports over 50% of its production.

The electrode boilers are more robust than immersion types, in part because they don’t use heating elements and the switching needed to control them. They are more tolerant of current and voltage fluctuations, and so are popular in places like Africa and the Middle East where power supplies are not as reliable as those in the UK.

Immersion boilers and relay contactors

Since the company was set up in 1972, its immersion boilers have used relay contactors to control the switching of power to the elements. On larger boilers, this can amount
to a bank of up to 60 contactors. With their associated wiring, contactors can be a source of faults, and require regular maintenance.

Although having multiple contactors gives some degree of control by staging the switching,
the boiler and the electrical supply can still be subject to power surges. With larger boilers rated at thousands of kilowatts, even Collins Walker’s power station customers are concerned about the huge draw when boilers are switched on.
The heating elements themselves suffer thermal shock each time the power is switched,
and this leads to element failures.

Looking for an alternative

As part of its product development, Collins Walker has been working on ways to improve the reliability of components, reduce the need for maintenance,
and improve the energy efficiency of their boilers.

Due to the continual switching, contactors wear out and need replacedment. As the larger boilers can have up to 60 stages, each with their own contactor, maintenance can become a significant time and cost factor. As contactors on have two states, on and off, the elements they control are subject to a thermal shock as the power goes from off to full on, and back again.

Finding a solution to the problems caused by the switching had become an increasingly urgent task. By replacing the relay contactors with a thyristor controller, Collins Walker has found it can address all these problems, and improve energy efficiency by giving much finer control of the power being applied to the boilers.

Thyristor control

Although thyristors are more expensive, one can replace many contactors. Particularly in large boilers with many stages, there is a saving in manufacturing time and cost as the wiring is significantly reduced.

The most important advantage of thyristor control is their ability to gradually apply power to the elements in the boiler, virtually eliminating the problem of thermal shock, and extending the life of the heating elements.

Without the physical contacts found in contactors, a thyristor controller doesn’t wear out with the continual switching.

Choosing CD Automation

There are a number of potential suppliers of thyristor controllers, and Collins Walker needed to choose the right one to gain the maximum benefit from the change in switching specification for its boilers.

With the two main contenders offering units with broadly similar benefits for the boilers, Collins Walker, needed to understand the factors which might affect the production side of the equation.

One company produces very sophisticated thyristor controllers. However, from Collins Walker’s perspective, there is far too much functionality built in to these. Much of this was of no practical use to the company, and meant the units are very complicated to set up. In fact, this process is so complex, an engineer from the supplier is needed to set up each thyristor during production of the boiler. This complicates production scheduling for Collins Walker, and can result in delays if the engineer needs to come out again.

CD Automation’s thyristor controller has been designed for ease of installation, and Collins Walker is able to configure and set them up in house. Chris Goddard of Collins Walker says of the CD Automation units,

“They are simple to set up, controllable, and cost effective.”

This was the key consideration in the final choice of CD Automation’s thyristor controllers.

Working with CD Automation

Collins Walker has been impressed with the availability, knowledge and enthusiasm of the staff at CD Automation. Chris Goddard comments,

“They’re very good, actually. When ever you ring them, they’re always there to answer the phone.”

During the installation of the first CD Automation thyristor controller, Collins Walker staff asked them lots of questions, and were sometimes on the phone with them for over an hour. CD Automation did not spare any effort in ensuring Collins Walker were able to successfully install the first thyristor controller themselves. Chris Goddard summed them up:

“So, I’m quite impressed with them.”

Thyristor control

Collins Walker now use CD Automation’s thyristor controllers on all but the smallest boilers – those less than 100 kW which only have one of two contactors.

The controllers are programmed to bring in the power gradually, for example starting at 10% for a few seconds before moving on to 20%, and so on. The power is also reduced gradually, smoothing the whole process of switching the power on and off.

The thyristor is attached to a PLC (Programmable Logic Controller), forming part of a PID Loop (Proportional Integral Derivative). This is a specialised feedback system which helps to anticipate the lag in the system, so the switch on or off occurs just before it’s needed. This prevents thermal overshoot, where the elements are still supplying heat after the set temperature has been reached and the power switched off, making the boiler more energy efficient. This is only possible with thyristor control as a PID Loop cannot be implemented on a boiler using contactors.

The outcome for Collins Walker

Using the CD Automations thyristors, Collins Walker is able to maintain complete control of its boiler production, and is producing a product which requires less maintenance and is more energy efficient.

The maintenance and energy savings are passed on to Collins Walker’s customers, improving their ability to win contracts for the supply of robust, reliable and efficient boilers.

Learn more on thyristors or scr power controller.

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