Electricity transmission and distribution systems are a very complex chain of several components. Such chain is built from the elements that directly influence the transmitted electricity, such as transformer, circuit breakers and other types of switches, busbar systems, conductors, insulation components, etc.
Besides these components, the power system features the equipment that improves the quality of electricity and safety of the system in general. Amongst the parts that need to be tested, reactors are key. Even in the era when powerful computers and simulation tools are available, testing of electromechanical components still plays a crucial role in quality verification, which is necessary to guarantee their safety and, as a consequence, the resilience of the entire power grid.
In this respect, in their facilities in Prague (Czech Republic), experts from KEMA Labs (the CESI Testing, Inspection and Certification Division) recently tested two types of starting reactors according to IEC 60076-6 and GOST 14794-79. Starting reactors are used to control starting current of electrical machines as synchronous and asynchronous motors. Starting current may be equal to 5 to 6 even 10 times of the rated current. Thus, starting reactor must withstand series of temporary overloading. Such tests are, therefore, crucial to avoid safety and productivity issues that could massively affect the resilience of the customer’s power grid.
In particular, KEMA Labs Prague has successfully conducted temperature rise tests of two three-phase current-limiting dry-type reactors with natural air cooling and vertical arrangement of phases for our customer KPM LLC, Russia. Such tests are very important, as they guarantee service continuity and resilience to components, which are subjected to extremely harsh operating elements.
After completing tests at rated currents 630 A and 1,600 A, the reactors were supplemented by special overload modes up to 1.6 times the rated current. In order to obtain such parameters, the equipment of both high-voltage and high-power laboratory had to be combined for the tests. Due to the size of test circuit, the test object had to be placed in such a way that all circuit elements, including auxiliary switches, disconnectors, busbar systems etc., were able to carry out continuous currents up to 2,560 A.
The key condition for trouble-free compensation of reactive power is the symmetry of three-phase connection, which is not simple in case of vertically arranged three-phase reactors, as their mutual inductance plays important role here. In this case, circuits must be symmetrized, which is possible by adding other passive elements, able to carry continuous currents to the circuit. Another option is possible by using three single-phase independently regulated sources capable of delivering required power. In terms of required parameters, both options were used in this test.
Another challenge the KEMA Labs experts faced and overcame consisted of the measurement of temperatures at potential and measurement of temperatures exceeding 180 °C with regards to fixation of thermocouples. This was achieved by data loggers operating in a special mode, using insulating thermometers powered by their own batteries. Additionally, a thermal camera was used to monitor temperatures and possible hot spots.
All technical challenges were overcome, and both cases resulted in valuable and recognized KEMA Type Test Certificate Of Temperature Rise Performance according to IEC 60076-6.
Read more about such tests here.