MechChem Africa

Greenergi (Pty) Ltd, the sole distributor of cast resin transformers (CRTs) from Trafo Elettro Italy, has established a relationship with Martec – now part of the Pragma Group – to take this dry-type transformer technology further. MechChem Africa talks to Mervyn Low, the company’s MD.

Greenergi cast resin transformers CRTA dry-type transformer, says Low, has no oil in it, which has a number of benefits. “There are several types of dry-type transformers. The first-ever transformers were open wound transformers where the coils were visible and these were air-cooled. One of the major drawbacks of this type of transformer is that the coils are not kept structurally rigid in fault conditions. Currents passing through a transformer coil produce forces – (Fleming’s left hand rule – and if these currents are excessive, such as in short circuit conditions, then the transformers are subjected to very large radial and axial forces, which very likely will damage the coils,” he tells MechChem Africa.

“Mechanically, it is very important to keep a transformer’s coils as rigid as possible and prevent any movement of the windings, which is where cast resin type transformers come in,” he continues.

Describing the construction of a typical cast resin transformer, he says that, instead of rolling transformer wire onto a cotton-reel- like core, “we use flat foil windings like those on a roll of paper towel or an old-fashioned film reel. Usually the windings are made from aluminium foil but copper is also used. Separating the winding is a double layer of insulating film. For the HV coil for cast resin transformers we connect ten or more of these pancake coils in series and stack them in columns to form the complete coil. Comparedto conventionally wound transformers, this pancake/foil coil construction reduces inter- turn stresses with the benefit of increased resistance to high-voltage impulses, ” Low says.

“The high voltage (HV) coils and the low voltage coils (LV) are nested in the same column on a common core, with an air gap between them for cooling. For transformer with higher power ratings, the LV coils are manufactured with gaps in the LV winding itself to promote airflow for better cooling. The cast resin HV coils, due to their construction, have the benefit of significantly reduced partial discharge – typically less than 10 pC (picocoulomb),” he explains.

“For three-phase cast resin transformers, we use an EI-core with the I forming the yoke across the top to close the magnetic flux circuit. Mechanically, the construction is very simple and this enables us to make these transformers robust and reliable,” he adds.

But it is the construction and materials used that make this technology electrically efficient and safe.

Describing the material used for the cores, Low says they are made from grain oriented silicon steel (GOSS), which ...

Read more... Click to download and read pdf

BANNER 8

Contact MechChem Africa

Title: Editor
Name: Peter Middleton
Email: mechchemafrica@crown.co.za or peterm@crown.co.za
Phone: +27 11 622 4770
Fax: +27 11 615 6108

Title: Editor
Name: Glynnis Koch
Email: mechchemafrica@crown.co.za
Phone: +27 11 622 4770
Fax: +27 11 615 6108

Title: Advertising Manager
Name: Brenda Karathanasis
Email: brendak@crown.co.za
Phone: +27 11 622-4770
Fax: +27 11 615-6108

saiw logo block

sassda logo block

saiche logo block

 
Full Name*
Invalid Input

Company Name*
Invalid Input

Your Email*
Invalid Input

Phone*
Invalid Input

Postal Address 1*
Invalid Input

Postal Address 2*
Invalid Input

Postal Code*
Invalid Input

Street Address 1
Invalid Input

Street Address 2
Invalid Input

Postal Code
Invalid Input

Town / City*
Invalid Input

Country*
Invalid Input

Magazine

Invalid Input

Invalid Input