ACTOM Distribution Transformers has successfully achieved the SA Bureau of Standards’ new SANS 780: 2019 Edition 5 standard for single-phase 16kVA to 3.15MVA distribution transformers after having a sample unit undergo a series of tests at the SABS’ National Electrical Test Facility (NETFA) recently.
The new standard represents a significant advance as it demands lower no-load and load losses than required under the SANS 780: 2009 Edition 4 standard that formerly applied to this range.
Junior Projects Engineer Augustine Baloyi conducts a routine test on a 200kVA 11kV/420V transformer under the supervision of Chief of Test Harness Mashicila in Distribution Transformers’ test facility.
The transformers to which the newly-introduced standard applies are extensively used in the local market by Eskom, municipalities and electrical contractors.
The sample transformer that was put through the required tests at NETFA during July and August this year was a 200kVA 11000/420V oil immersed unit.
Distribution Transformers decided to provide a sample from the lower end of the range for testing to ensure that the fullest possible battery of tests could be performed by NETFA on the unit, thereby enabling the division to assure its customers that all the requirements applicable in terms of the new standard have been met.
The above table shows the old vs new required losses for a 200kVA transformer.
After a pre-test inspection and full routine tests monitored by a NETFA engineer were carried out on the sample unit at Distribution Transformers’ own test facility in Knights, Germiston, the following tests were performed on the unit by NETFA:
l Temperature rise test at the NETFA High Current lab.
l Short circuit withstand test at the NETFA High Current lab.
l Lightning impulse test at the NETFA High Voltage Lab.
Following the successful outcome of the NETFA tests, a post-test inspection for mechanical deformation of the windings and full routine tests were conducted at Distribution Transformers’ facility, again monitored by a NETFA engineer.
“The reduction in losses will further assist our strained electricity generation sector,” commented Lee Mbenge, Distribution Transformers’ Projects Manager.
“The SANS type and special testing is onerous on the transformer, especially when it comes to demonstrating the ability to withstand short circuit by testing, whereby 115% of Un is used to calculate the short circuit currents, the total change in inductance does not exceed 4.0% per phase and the successive shorts can be repeated until there is less than 0.25% change,” Lee concluded.