Sparks Electrical News April 2018

MCCS AND MOTOR PROTECTION

15

CONTINUOUS MINER TRIPPING UP PRODUCTION

TALK TO THE EXPERTS WHEN SIZING TRANSFORMERS

I n a mining environment, targets need to be achieved in order to be financially viable. So, when a brand-new, state-of-the art continuous miner is working at only 30% of its capacity, it is safe to say that the environment will be tense. This was the case when NewElec was con- tacted, as the mine in Secunda had reached a critical point, and discussions were held around a very tense boardroom table as to the way forward. The continuous miner target was specified on 4-minute repetitive mining cycles. The actual performance was pinned at 30% of the specification and, further to this, losing one 270 kW water cooled cutter motor per month. The situation was clear. Motors are tripping fre- quently, failing and causing delays in produc- tion, and ultimately costing more money than they were making. As discussions continued, possible solutions were identified, one of which was designing big- ger motors to deal with the increased demand and, as such, the continuous miner manufacturer was also brought in on the discussion. The mo- tor, a soft rotor design (die cast aluminium rotor with deep bar design), was load tested under a controlled environment on a Dyno where tem- perature rise was established. NewElec proposed an evaluation period, in order to determine the cause of the problems, before designing bigger motors. The machine was originally fitted with an analogue thermal overload, with thermal memory matched to the motor. The motor would trip on average 10 times on an 8-hour shift, with an 8-min- ute cooling period after every trip. NewElec replaced the relay with the NewCode motor protection relay, for further evaluation. Upon analysing all the data available after the evaluation period, the company found that the motor was running at 110% RMS load pattern resulting in the trips occurring every 15 to 20 minutes on continuous 4-minute cycle times. NewElec advised the customer that there were two alternatives at this point, slow down the cycle times, or raise the overload trip setting to 110% rating. Generally, motors are built with an extra capacity and specific tests were car- ried out in order to prove the theory. The Con- tinuous Miner Motor Thermal overload setting was increased to 110%. The machine produced two shifts, with only one trip per shift (which took place at shift

A ccording to Ronaldo Ber- toldi, engineering manag- er at WEG Transformers Africa (WTA), a range of factors needs to be considered when correctly sizing a transformer for optimal performance in any ap- plication.

Ranked among the largest manufacturers of transformers in South Africa – and serving a range of sectors including mining, industry and agriculture – WTA is a leader in distribution transform- ers, power transformers and mini substations. “Sizing a transformer for a particular application can be done using a simple equation, but the se- lection process requires many other factors to be taken into account,” says Bertoldi. “Determining the right transformer for the job requires an in-depth assessment of the conditions under which the transformer will operate.” He emphasises the difference between the full load current required by an application, and the start-up current if there is a direct online starting process. If the motor is initiated by a direct online start, this part of the operation could require a much higher current than when it is running. Bertoldi also points out the significance of the distance between the source of the power and the equipment consuming the electricity, as there will be a voltage drop that will affect the sizing of the transformer. “Transmitting low voltage over long distances can

change, when the motor was loaded to maxi- mum before shift-end to make the machine safe and hand-over – thermal memory does not decay if the machine is switched off. This is standard in all NewElec relays, to prevent the operator from cycling power in order to gain fast thermal reset). NewElec also monitored the motors for the following 254 hours for all three shifts. The company extracted and analysed data and events and established that the cutting control system was controlling feed rates and cutting rates at 110% of motor rating. NewElec re- quested that the control system be adjusted back to the original to feed and cut of 100% of motor rating. This suggestion was not well re- ceived –as the concern was that the mine was going back to the 30% production rate – but it was allowed. The cutting control system was adjusted to feed rate at 100% cutter electrical RMS load. The customer regained the target production rate occasionally getting the 4-minute mining cycle but consistent on 5-minute cycle, and the motor ran within its 100% rating confirmed by downloading all of the detailed NewCode event history and recorded data. Ultimately the control system was set too high, and as such, the motor was overloaded, resulting in trips, and subsequent delays in starts, causing a reduction in production. So, in the end, no need to redesign and build a bigger motor, just correct the settings. By analysing data and events, NewElec can establish where the problem is, and find a solution.

also be more expensive due to the thicker cables required by the higher current,” he says. “Users can achieve amore cost effective solution inmany cases by considering a step-up, step-down configuration, where the voltage is increased to facilitate longer distances, then reduced to the requirement of the equipment at its point of location.” WTA’s years of expertise in manufacturing and repair equips it well to advise customers in the sizing and selection of the right transformer for their specific needs. Its Heidelberg facility is capable of locally manufacturing power transformers up to 40 MVA in voltages up to 132 kV as well as mini substations and ring main units. All distribution and power transformers are manufactured to SANS 780, BS 171 and IEC 60076 specifications under ISO:9001 quality standards.

Enquiries: www.zestweg.com

MASSIVE MOTORS INSTALLED BY M&C AT COBRE PANAMA

MARTHINUSEN & COUTTS, a division of ACTOM, recently executed the sub- assembly of six gearless mill drives for Minera Panamá’s remotely situated Cobre Panamá project in record time, and as a result was able to hand the machine over to the mechanical teams for professional assembly well ahead of schedule. Minera Panamá, the Panamanian subsidiary of First Quantum Minerals, is currently developing the Cobre Panamá project, located in Colón province. The mine life has been estimated at more than 30 years and will produce around 300 000 t/y copper, 100 000 oz/y gold and 2 500 t/y molybdenum. Marthinusen & Coutts has a proven track record of partnering with custom- ers on similar complex projects, while still being able to offer a cost competitive solution. Significantly, this leading repairer of rotating machinery has an es- tablished reputation as an expert in gearless mill drive refurbishment, winding termination and testing of motor segments. Projects previously successfully completed by the division include the installa- tion of six Siemens gearless mill drives at various mines in North West Zambia. Of the six ABB gearless mill drives being installed at Cobre Panamá, four will power ball mills and the other two will drive SAG mills. Importantly, these massive machines are among the largest ever installed in the world and were transported in quartered sections to site for assembly in-situ. The sheer size of the machines, with an inside diameter of 14 m, presented challenges of their own with each segment weighing approximately 80 t. Work was done on four different positions on the machines simultaneously, 3 o’clock, 6 o’clock, 9 o’clock and 12 o’clock. Commenting on the role that Marthinusen & Coutts played in this project, Divisional CEO Richard Botton said that a team of six highly competent and skilled technicians was responsible for the completion of the project within extremely tight time schedules. Work on the machines was performed back- to-back and this was accomplished using induction brazing equipment, and a bar wound winding with separate upper and lower stator bars, as opposed to set diamond lap-wound, formed type coils. “The depth of experience and technical competence within our team proved vital to the successful completion of the work, especially given the various challenges encountered on a daily basis,” he said. “The average execution per machine took just 28 days.” Botton said that working closely with the OEM – ABB – on this project, was also vital to its success. He pointed out that it is not unusual for Marthinusen & Coutts to partner with OEMs on projects such as this. Marthinusen & Coutts has an established reputation for undertaking complex projects in remote lo- cations and delivering these on time and within budget, and most importantly to the required OEM specification.

Enquiries: info@newelec.co.za

Enquiries: +27 (0)11 607 1700

SPARKS ELECTRICAL NEWS

APRIL 2018