Sasol Mining – part of South African integrated energy and chemical company Sasol – undertakes the company’s coal mining operations. Sasol Mining operates six coal mines that supply approximately 40 million tons of thermal coal feedstock per annum. At the company’s largest colliery, the Syferfontein mine in the Secunda area, Sasol Mining identified that the ventilation shaft was not sufficient to ensure the required aeration of the mining district. To ensure uninterrupted power supply to a new ventilation shaft, a new substation was needed.
In underground mining, ventilation systems are of paramount importance to ensure safe working conditions for people. Ventilation systems provide clean air, dilute and remove dust together with natural and machine exhaust gases, and provide cooling for personnel and machinery. Ventilation systems need to run continuously 24 hours a day, throughout the year, which means uninterrupted power supply is a key requirement. The energy demand is significant, and ventilation systems are currently the largest consumers of power in underground mines, accounting for as much as 50% of energy use.
For the new substation that feeds the new ventilation shaft, Sasol Mining chose a protection and control solution with ABB’s Relion relays from the product family’s 615 and 620 series, and the all-in-one protection relay REX640 to be installed in the medium-voltage switchgear. This is Sasol Mining’s first installation with ABB’s Relion protection and control relays.
“A key consideration for us, when deciding in favour of the Relion relays, was that they offered all the functionality we need,” said Divesh Ramasur, senior electrical engineer at Sasol Mining. “They are also flexible and offer extensive event and fault recording capabilities.”
Sasol Mining chose these protection and control relays because they offer the necessary circuit breaker control functions, and embed arc flash protection for increased safety. They also have simpler GOOSE (Generic Object-Oriented Substation Event) protocol utilisation and all have a R/L (remote/local) switch available on the relay faceplate for easier operation. Furthermore, the customer chose Relion 620 series relays for motor protection. These relays offer stall protection functionality and thermal overload protection which takes into account the actual starting time of the motor.
The installation of Relion relays has resulted in cost reduction and a smaller switchgear footprint. “With REX640 we can use only one relay for transformer protection, whereas earlier we had to use many different relays to achieve the same level of protection,” said Ramasur. “The REX640 relay has many protection functions available for transformer protection, such as low-impedance differential protection, low-impedance restricted earth-fault protection, sensitive earth fault protection, and tap changer control, all integrated into the relay. On top of that it has many binary inputs and outputs, and the relay can incorporate many analog inputs.”
As a result, the footprint of the switchgear was reduced, as there was no longer the need to install three different relays to obtain the same functionality. The smaller footprint was also achieved thanks to the built-in R/L switch and master trip relay, which meant there was no longer a need to install separate switches on the switchgear panel. The cost reduction, thanks to using REX640, was about 25%.
Ramasur also found the configurable LEDs on the relays to be of great help in finding faults quickly. He explained: “A great benefit comes from the 11 configurable LEDs and even 33 configurable LEDs for the REX640. They can be used to indicate which function operated, making it faster for the operator to find the fault.” What’s more, with the Relion 615 series (REF615) and 620 series (REM620) protection relays in the substation, the customer estimates that total costs were reduced by 10%.
On top of mining, Sasol is also involved in energy, chemicals and synthetic fuels. ABB and Sasol have a long business relationship and Sasol has previously used Relion relays at its Secunda and Sasolburg petrochemical plants, proving their suitability for operation in harsh environments. To further ensure optimal performance, Sasol Mining chose an additional layer of protection by way of conformal coating on the relays. Adding a conformal coating to the printed wired boards (PWBs) protects the electronic circuits in particularly demanding environmental conditions, such as in underground mining.
ABB’s scope of work was to supply, install and commission the equipment. Commissioning of the protection relays took place in June 2020.
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