OPERATIONS MANAGEMENT
Schematic shows an HPGR system
The industry is caught between a rock and a hard place
(MV) variable speed drives (VSDs), which are already renowned for their energy saving qualities. However, it would be prudent to carefully consider the optimal design of the complete VSD system,
especially the choice between air-cooled and water-cooled drives. Especially because the latter boasts additional energy and cost benefi ts. Let’s consider air-cooled drives fi rst. An air-cooled MV drive setup comprises the VSDs and integrated transformer, together with upstream switchgear, often all housed in an electrical room, otherwise known as an ‘E-room’. All the heat losses from the equipment into the E-room must be handled by a large heating ventilation and air-conditioning (HVAC) system, with a considerable impact on both upfront investment and operating costs, including energy usage and maintenance. T is comes with a relatively large installation footprint on sites where space can sometimes be at a premium. In general, the effi ciency of this approach is typically lower than 96.5%.
Furthermore, with the arrangement described above (an air-cooled MV drive with integrated transformer), a separate, external step-down transformer is needed from the 33kV grid supply to the motor voltage of 11.6kV or 3.3kV. T is incurs further energy losses of 1% while adding further to the fi nancial burden. In contrast, a growing number of mining
sites are adopting water-cooled drives paired with an external ONAN- (oil natural and air natural) cooled transformer. Only the VSD panel has to be installed in the E-room, which is therefore much smaller. No step-down transformer is required. Direct connection at 33kV means that just a single, external transformer is used, which also acts as the converter transformer. T e cooling water for the drive is usually supplied by the plant’s common water system. If this is not available, then a closed-circuit cooling system is created using a chiller or fi n-fan heat exchanger. Even in this case, the energy losses are much lower than when using an HVAC system to cool the air in the E-room. In some cases, it might be possible to recover heat from the cooling circuit for use in other parts of the process to further boost the overall system effi ciency. Water-cooled drive systems achieve
Optimal VSD design improves the energy effi ciency of equipment
an effi ciency of greater than 97.5% T at means they will have energy losses of some two percent lower than the equivalent air-cooled drive system. And because water-cooled drives generally run cooler than air-cooled versions there is less stress on their critical electronic components. T is helps ensure a longer service life.
www.engineerlive.com 21
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52
