Circuit breakers are ubiquitous wherever there are electrical circuits that need protection against excess current caused by an overload or short circuit. They range in size and capacity from devices the size of a fingernail used for semiconductor protection to devices as large as a truck designed to protect the high voltage circuits that supply power to cities.
Electrical power is, in most cases, not produced at the same location as it is consumed. The power grid connects power plants with end users and transports the electrical energy from production to consumers.
The power grid is organized into different voltage levels from a few hundred volts (LV), to several 10 kV (MV) up to several 100 kV (HV), depending on the amount of power transportation capacity needed.
The different voltage levels are interconnected by substations which contain voltage transformers, circuit breakers, surge arrestors, isolators etc. as well as other measurement equipment and switchgear.
To ensure reliability and safety of switchgear and circuit breakers, testing against applicable standards must be done in both R&D facilities for development purposes as well as at independent test houses for certification.
Because of its importance in the economy of a country, a set of strict regulations of how these apparatus should behave, and how they need to be tested, has been defined. The “Short-Circuit Testing Liaison (STL)” has created an internationally accepted report called “Harmonization of Data Processing Methods for High Power Laboratories”. This standard describes a set of rules on where and how to measure values in the digitized information.
HV Impulse Testing
Most of the power grids worldwide are built by power lines on masts. They are highly exposed to lightning strikes with the risk of damage on the components in a substation. Damage to one or several of the elements may result in partial loss of the power distribution capability, unsatisfied consumers and high cost for repair. Performing Lightning Impulse testing on transformers, surge arrestors, isolators and switchgear is an important part of the quality proving process and documents the components withstand capabilities.
Current Zero Testing
Current zero (CZ) refers to the interruption phenomena in high power circuit-breakers. Many, if not all circuit-breakers in commercial use today are working based on contacts moving away from each other, thus creating an electrical arc between the contacts. The current zero phenomena is an indicator for the pressure, temperature, ion density, plasma flow, etc. Current zero measurements are used to understand the phenomena of the arc and to identify the dominant parameters for a successful interruption of the current.