Ketton Cement operates a 2.7MW crusher with speed control provided by a three-section resistor, with each section dissipating 87kW of heat.
When this resistor failed one Friday, Cressall was on hand to provide prompt assistance and get the works quickly moving again.
Cressall Resistors supplied three-phase control resistors for cement crusher's 2,700kW main motor.
Ketton Cement operates a 2.7MW crusher with speed control provided by a three-section resistor, with each section dissipating 87kW of heat.
When this resistor failed one Friday, Cressall was on hand to provide prompt assistance and get the works quickly moving again.
Ketton Cement operates cement kilns at Ketton in Rutland, Ribblesdale in Lancashire and Padeswood in North Wales, and produces ground granulated blast-furnace slag (GGBS), a cement replacement in ready-mixed and precast concrete at four locations. It also produces a range of bagged cements and aggregates.
“Ketton Cement got in touch to say that the three-section speed control resistor on the main 2.7MW crusher motor had failed and asked what we could do," explained Martin Nicholls, sales director of Cressall Resistors. "The resistor operates at 2.2kV, conducting a 735A current through a resistance 0.16 ohm to dissipate 87kW of heat energy.”
Ketton Cement is the largest industrial plant in England's smallest county, with an annual output of more than one million tonnes of cement.
Originally established on this site in 1928, it is next to the quarries from which cement's raw ingredient of limestone is still taken.
This is a 24 hour a day, seven day a week operation with its huge inclined rotating kiln the major feature. Today, Ketton is one of the most efficient cement works in Europe. The loyalty of the workforce is evident in the fact that the average length of service is 18 years.
High profile successes
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 1,450˚C.
This chemically combines the stones into a hard substance called clinker, essentially changing calcium carbonate (CaCO3) to calcium oxide (CaO) which then reacts with silica (SiO2) to form calcium silicates. This is ground to a powder with about five per cent gypsum, added to control the setting time of the end-product.
Before being fed into the kiln 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 2,700kW main motor were supplied in 1985 and finally reached the end of their working life almost 30 years later.
Martin Nicholls continues: “The resistor was originally supplied in 1985 by Cutler Hammer. Luckily we had all the drawings and the right resistor material. We ordered the insulating boards from our supplier, which were delivered on Monday along with the broken resistor, which we stripped, rebuilt and returned to Ketton Cement the next day.”
Danny Osborne, maintenance engineer at Ketton Cement, adds: “We were anxious not to lose production because of the failure. Over the weekend Cressall manufactured 12 replacement Hi-Temp resistor banks to the original drawings and specifications. We stripped out the old resistors and sent them to Cressall's Dereham factory.”
Insulation boards
Cressall's supplier Presspahn, located in Bedford, also worked over the weekend, making the insulation boards which fit around the resistor banks.
These were delivered to Cressall on Monday and by Tuesday afternoon the brand-new replacements were assembled and had been collected and taken back to Ketton for fitting. The crusher was operational before Hanson's buffer stock of crushed limestone had been used up.
