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Advanced Engineering 2020

NEC, Birmingham(B40 1NT)

04/11/2020 - 05/11/2020

The UK's largest annual advanced manufacturing trade show, Advanced Engineering is your opportunity to (more)

Drives & Controls Exhibition

NEC, Birmingham(B40 1NT)

25/01/2021 - 27/01/2021

The show brings together key suppliers of state-of-the-art equipment representing the multi-tasking culture (more)

The cost of downtime is a simple equation

The cost of downtime is a simple equation When a Hull port started experiencing problems with obsolete drives, AC motors and resistors in two of its aging cranes, the situation needed addressing immediately. Peter Scott explains how the problem was solved.

The UK's leading ports group, Associated British Ports (ABP) owns and operates 21 ports around the UK and handles approximately a quarter of the country's seaborne trade. So it's no wonder that in such a buzzing environment, downtime is never an option.  With two cranes in need of urgent maintenance, the port's management was expecting a substantial bill for resolving the issue.  

The equation looked like this: a new drive for the crane, priced at over £20,000, plus a new motor, an additional £20,000, plus installation and engineering worth up to £60,000 and the additional cost of three weeks downtime. Were this not enough to furrow the brow of even the most resilient finance director, the total bill of £100,000 would be doubled, as there were two cranes on site in need of maintenance.

Unfortunately, as the cranes were over 20 years old, many of the parts needed had become obsolete and were extremely hard to source. This is when ABP Hull asked maintenance specialist CP Automation to come up with a viable solution to their troublesome equation, one that would not disrupt activity and keep maintenance expenditures down.

"We knew that the hoist drives on the two older cranes were coming to the end of their life," explains Keith Payne, electrical supervisor at ABP Hull. "In the last few years we've tried to repair and update them to the best of our capabilities, so that we could keep them going. But despite all of our predictive maintenance, there came a point when we encountered too many technical problems so we had to find a permanent solution."

Having previously worked on a similar implementation abroad, the CP Automation field maintenance team took on the challenge of fixing the Hull cranes. The solution to the product obsolescence problem came in the form of motor controllers for slip ring motors from Sprint Electric. Sprint Electric's JL/X range of slip ring motor controllers covers output currents from 100 to 1850A in either two or four quadrant mode.

A slip ring motor is a type of induction motor with a wound rotor connected to external rotor resistors via a slip ring. The motor's speed/torque characteristic is modified by resistors connected to the rotor slip rings controlled by JL/X relay output drivers. Out of the four resistor control outputs provided, only one or two would be used for applications such as slew, yaw or X/Y travel. Hoist applications however might use three or four of these outputs. For hoist applications, lowering at speeds above synchronous speed is detected and, as a result, rotor resistance is minimised for maximum regeneration into the supply. An additional digital output is provided for this purpose.

Provision is made for selection of analogue or progressive joystick switch speed demand, with two raising and two lowering speeds. Analogue outputs representing speed, torque and power are supplied in the standard configuration.

With the Sprint drives fitted, the cranes were given a new lease of life. CP Automation's solutions used a new controller and retained the existing motor, which led to a significant saving on the overall project costs. For the first crane, the total costs were significantly less than the initial budget price of changing both drive and motor, a saving of more than 60%. The second crane costs were further reduced due to the programming and design engineering done for the first crane was implemented on the second crane refit. The total bill for both cranes came in at a fraction of ABP's anticipated price.

The crane refit in Hull is a perfect example of maintenance expertise combined with speedy and committed customer service. What's more, the CP Automation team simplified an otherwise financially daunting equation: two cranes functioning at optimum performance, additional spares and support and only a few days of downtime.
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