Harmony unveiled a unique mobile emergency generator solution at its Phakisa Mine site in Welkom late last year.
At the official launch, Graham Briggs, Chief Executive Officer of Harmony, said that the investment of R60 million is testimony to Harmony’s commitment to safety at its operations.
Manufactured and supplied by Zest Energy, a Zest WEG Group company, this innovative emergency power solution comprises four trailer mounted generators which will be used as single units, in sets of two or all four together to facilitate the emergency evacuation of personnel from underground during power outages or other electrical failures. The custom engineered 2.5 MW units will service a total of thirteen Harmony operations in the Free State goldfields.
Harmony undertook an extensive investigation into the exact needs of each of the shaft operations in terms of emergency power requirements, and these differed from operation to operation. This exercise determined the specifics for each shaft and included the input of extensive data gathered through simulations as well as evacuation schedules.
Historically emergency power supply on South African mines has been done using overhead lines, however this poses the risk of security of supply and is a costly option when the maintenance, repairs and associated downtime costs are taken into account.
The other typically used option of permanent generator installations would have involved the construction of an extensive infrastructure including civils, electrical, lubrication, fuel and cooling. The costs associated with this option were considered too expensive.
The project, put out to open international tender, called for 2.5 MW units which had to be mobile and self-contained. Each generator had to have the capability to synchronise with each other and operate as either single or multiple generation units. In addition, the units had to provide sufficient power to operate the various mine winders and had to be designed to suitably handle the regenerative effects of these winders during operation.
Each unit had to generate power at 6600 Volts and had to be equipped with a medium voltage quick coupler and flexible cable to facilitate the connection of the units directly to each shaft’s electrical reticulation network. Each unit also required an adequately sized fuel storage facility to allow eight hours continuous operation at full load.
The trailer mounted units had to be capable of travelling as a normal load as per the South African Road Ordinance.
Andries ten Cate, group electrical engineer at Harmony, said that at the end of the exercise there was only one potential supplier, and this was Zest Energy.
Coenraad Vrey, managing director of Zest Energy, said that there were stringent specifications which had to be met on the project and a major advantage for all was that Zest Energy, through the Zest Group had access to various skill sets and capabilities through its holding company WEG in Brazil and other sister companies, IMS Cape, EnI Electrical and Shaw Controls.
The project presented a number of major challenges with one of the primary ones being the weight and dimensional constraints imposed by the need to engineer a truly mobile unit and this made equipment design and selection critical. The generator is powered by an MTU 20V4000G63L diesel engine with a rated capacity of 2850 kW at 1500 r.p.m.. The balance of components include a 6600 Volt WEG alternator, MV switchgear, a custom designed radiator with a mechanically driven fan and a MV cable reel with a 45 metre flexible trailing cable.
All the components are installed on a purpose built trailer with a 12 925 mm length and 2 600 mm width. The deck height is 1 150 mm. The trailer features two aluminium enclosures – a sound attenuated enclosure for the generator compartment and a separate enclosure for the switchgear and MV cable reel compartment. This dual compartment concept was designed to facilitate the ease of future maintenance.
In addition to the mobile generators, Zest Energy was also responsible for the manufacture and supply of fuel trailers for each of the four generators. These fuel trailers were fitted with double bunded fuel tanks each with a 4500 litre capacity. They are 3 998 mm long and 2 600 mm wide.
Quick and reliable electrical interfacing was a prime requisite on this project, and two standard solutions were provided. Where appropriate free standing coupler boxes or Lucy switchgear c/w coupler boxes were used. All integration stations are equipped with safety interlock systems.
“At the end of the day the project was a partnership between all stakeholders, and it was the entire team, both at Harmony and Zest, who brought it to fruition,” ten Cate said.