A charging resistor is put in place for impulse testing
The recent installation of an impulse voltage generator at a local transformer manufacturing facility in Heidelberg is a substantial investment that the company hopes will provide an important service, especially for its larger customers.
An impulse generator produces short, high-voltage surges to test the strength of electric power equipment against lightning and switching surges. It comprises multiple capacitors that are first charged in parallel through charging resistors by a high-voltage, direct-current source. These are then connected in series and discharged through a test object by a simultaneous spark-over of the spark gaps.
The specialised equipment will allow in-house testing of transformers at Zest WEG’s manufacturing facility and aims to save time and money for its customers.
The company explains that impulse testing is important to establish whether transformers can withstand waves on the network induced by lightning faults and whether the transformer’s insulation is capable of withstanding such faults. This is especially important in South Africa, where lightning flash density is high.
Where the transformer size is larger than the 72.5 kV voltage class, impulse testing is a routine test according to IEC 60076-3 standards. Customers have an option to do an impulse test in lower voltage classes as a type test.
The company notes that major energy utilities often require suppliers to have this testing capability and that the impulse voltage generator will allow it to expand its range of transformers up to 50 MVA, 132 kV units. Impulse testing had previously been outsourced by the company, which added to the lead time for completing units.
Impulse tests are also required by the global IEC 60076 series of standards, which include full wave lightning impulse tests for line terminals and chopped wave lightning impulse tests for line terminals for power and distribution transformers.
The impulse generator will also allow Zest WEG’s transformer facility to test its own product prototypes, which are developed with the technical support and shared resources of its research and development facilities in Brazil.