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Kirk Moss, medium voltage manager at Shaw Controls, said that the containerised solution will supply power to drive a mill on this new mine.
He said: “Containerised electrical solutions are becoming increasingly popular as these allow for speed of installation and are a particularly cost effective option for mine and plants operating in Africa.”
The custom engineered sub-station comprises a medium voltage (MV) WEG variable speed drive (VSD) and a dry type phase shift transformer driving a 2,000kW, six pole, 6.6kV squirrel cage WEG electric motor. The VSD is housed in the container while the oil cooled transformer is housed outside of it to facilitate heat dissipation.
Shaw Controls’ Johannesburg facility, which has floorspace of over 12,000m2 – Moss said that having the whole construction take place in one facility makes it easier for customers to do all quality and functional checks in one place. This solution underwent testing at Shaw Controls prior to being dispatched to site.
Moss added: “What is particularly interesting about the solution provided is that it has been specifically engineered for this particular application and utilises specialised software for frozen charge protection.”
The software, which interfaces with the VSD, allows the objective detection of a frozen charge condition by making use of torque measurements already being monitored by the VSD.
He explained: “With the addition of an encoder fitted to the electric motor, we are now able to monitor mill angle. And with the torque and angle measurements it is possible to detect if cascading has occurred within the mill.”
Another feature of this solution is the supply of a human machine interface (HMI) in the form of an interactive touch screen which has been configured to allow different levels of access. This has been done in a user friendly manner to ensure ease of use and also allow simple access to relevant data.
Moss stated that the ability to extract the most relevant data and provide this in an intuitive and simplified format allows both operational and service personnel to monitor the requisite parameters.
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This project made use of a WEG MVW01 VSD with 6.6kV output. The input solution makes use of a 36 pulse rectifier and corresponding phase shift transformer. Moss explained that this combination was selected as the best option to minimise harmonics.
The WEG MVW01 VSD range is available in 3.3kV and 6.6kV versions. This is a neutral point clamped (NPC) topology and makes use of 6.5kV IGBTs. These VSDs are engineered with few components translating into high efficiencies and optimal reliability.
Also available is the WEG MVW3000 which is available in 3.3kV and 6.6kV, and more recently in an 11kV version. This is a cascaded H-bridge (CHB) topology which makes use of low voltage IGBTs. This has low voltage power cells with built-in redundancy (optional) which allows a faulty power cell to be automatically bypassed with loss of performance.
Shaw Controls’ product line includes MV switchgear and LV withdrawable MCCs – locally manufactured products that are independently certified in accordance with the IEC 62271-200 and IEC 61439-1/2 standards. According to IEC specifications, LV covers applications up to 690V, while the MV range is from 1kV up to 52kV. All products carry ISO 9001 accreditation from Bureau Veritas.
Being part of the Zest WEG Group also allows Shaw Controls access to the substantial technical database and engineering resources of parent company WEG Brazil.
