11. Short-Circuit Performance Tests

The interruption and switching tests are normally carried out in a high-power test laboratories of either manufacturers (often they have an accredited laboratory) or in third-party testing facilities depending on users’ requests. Apart from custom-designed special equipment, the aim is the development of products that will be ultimately submitted to a type-test report in accordance with international and national standards. Research and development test requirements can vary depending on the stage of development, but the final aim is usually a design capable to withstand the standardized stresses of the standards in order to obtain a type-test report.

The acceptance tests are carried out to verify the performance of withstanding non-standardized stresses that may occur under special conditions of power networks or under special environment and operation conditions requested by a user. Regarding short-circuit interruption tests, examples are TRVs beyond the standardized limits (e.g., in the application of series compensated capacitors, series current-limiting reactors, or filter banks in converter stations) or other special conditions (e.g., exceptional short-line fault conditions, missing current zeros, high DC time constants, etc.). Usually, equipment has already been type-tested before being subjected to the additional acceptance tests. The user of switchgear proposes the test requirements based upon his knowledge of abnormal conditions in his power system. Manufacturer’s and independent laboratories often perform such tests.

Type tests are aimed to demonstrate the capability of a single sample of a batch of identical products to conform to a certain standard. Once this has been demonstrated, a type-test certificate is issued by a certification authority. A certificate contains a record of a series of type tests carried out strictly in accordance with a recognized standard. It is a proof that the component tested has fulfilled all the requirements of a recognized standard. If the equipment tested has fulfilled the requirements of this standard, the relevant ratings assigned by the manufacturer are endorsed by the certifying authority. The certificate is applicable only to equipment of a design identical to the tested one. The certifying authority is responsible for the validity and the contents of the certificate.

The responsibility for conformity of any apparatus has the same designation as the one tested rests with the manufacturer. The certificate contains the essential drawings and a description of the equipment tested.

Type tests are carried out in independent, duly accredited test laboratories. Several of these in the world apply the rules of the short-circuit testing liaison (STL), an organization of test laboratories and authorities looking after a uniform interpretation of standards throughout the world by providing practical guidelines (STL 2011a). STL, a purely technical institute, makes use of the competence and expertise of its members to provide these guidelines. This voluntary society also defines the test report templates to assure that equipment users can easily compare the results of the different member laboratories. The society also defines rules and procedures to assure the quality of the test results and certified products.

Five categories of tests are distinguished by STL to verify (STL 2011b):

STL members issue certificates on these five items related to the specified rated values, except for the mechanical performance, for which there is no rating defined.

By the repetition of the type test duties after a period of time, usually after 5 years, assurance can be obtained that the manufacturing quality of the circuit breaker or switchgear, quality of material, and workmanship is maintained.