Electricity + Control March 2018

A large WEG power transformer in the Brazilian testing facility, illustrating the potential physical size of the larger units.

der ISO 9001 [4] quality standards. WTA also offers extensive maintenance and repair services, includ- ing the repair and rewinding of transformers up to 100 MVA and 132 kV, and mini-substations up to 1 600 kVA and 33 kV. It can also repair medium voltage switchgear in-house and on site, as well as replace leaking gaskets, neoprene cone rubbers, bushings, inspection covers on on-load tap chang- ers, conservators and valves. The modern facilities allow sandblasting and spray-painting of transform- ers and components. The company can supply, install and test protec- tive relays, silica gel and breathers and can conduct infrared surveys to detect potential faults. Manufac- turing capacity includes the vacuum treatment and drying of cores, and the complete testing of units to SABS, IEC and BS standards.To do this,WTA has three test bays capable of testing 100 MVA 132 kV units (IEC and BS), 10 MVA 66 kV units (IEC and BS) and 3 150 kVA 33 kV units (SANS 780 [1]). All distribution and power transformers are manufactured to SANS 780 [1], BS 171 [2] and IEC 60076 [3] specifications under ISO:9001 [4] quality standards. References [1] SANS 780. 2009 (Edition 4): Distribution Trans- formers. [2] BS 171. 1970. Specification for Power Trans- formers. [3] IEC 60076. 2015. Power Transformers. [4] ISO 9001. 2015. Sets out the criteria for a quali- ty management system.

there is a controlled environment; where this is not the case, then a tamper-proof solution is vital. He also emphasises the differences between inland and coastal conditions that impact upon transformer selection – introducing a corrosive en- vironment and variation in ambient temperatures. This will affect the material used to manufacture the transformer and the final finish that we apply. In coastal areas, we usually supply 3CR12 stainless steel for the enclosure where the corrosion levels are high. Where corrosion is expected to be less, there is the option of zinc-spraying where a layer of zinc is coated onto a mild steel enclosure. The modern polyurethane paints also provide a very ef- fective coating, which can last for over a decade. Inland installations are usually done with mild steel. The ambient temperature is a significant factor, even within South Africa’s temperature ranges. WTA designs and manufactures according to SANS 780 [1] quality standard, which allows a maximum ‘rise’ of 65°C – from the losses in the transformer that are dissipated as heat – plus the ambient tem- perature. According to the standard, the combina- tion of the two should not exceed 95 to 100°. While temperatures in Gauteng may only reach around 35°C maximums, there are other parts of the country where 45°C temperatures are not un- common. This means that in these very hot areas, we must design the transformer with sufficient cooling to allow a rise of only 50°C – so that the total is not more than 95°C. AboutWTA WTA’s years of expertise in manufacturing and re- pair equips it well to advise customers in the siz- ing 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 [1], BS 171 [2] and IEC 60076 [3] specifications un-

A transformer will usually feed a range of equipment so it is important to know about the starting sequence – does the user start up the equipment all at once, or one at a time?

Ronaldo Bertoldi is the Engineering Manager at WEG Transformers Africa (WTA). Enquiries: Tel. +27 (0) 11 723 6000 or email marketing@zestweg.com

Electricity + Control

MARCH 2018

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