High-Power Testing Laboratory

Star-delta tap-changing (SLG)

The generator is connected to the transformers and the power supply fed directly to the high-power testing laboratory by means of a 20 kV bus bar run. Starting from the star-delta tap-changing operation at the generator terminals, each of the two winding systems is run into the safety-switch compartments. The bus bar run consists of an insulated aluminum tubular system. In each phase of the two winding branches, a combination of two circuit-breakers assumes the role of safety switch. A modified SF6 circuit-breaker 3 AS1 (up to 80 kA at 19 kV) has been used as the primary-current breaker (safety switches), while a 3 AF vacuum circuit-breaker serves as the residual-current breaker.

Safety switch

In the subsequent transformer undervoltage switchover, the two generator systems can be connected in parallel and then run along the underground bus bar directly into the test laboratories for testing the switching capacity without the transformers being interposed. As of the transformer switchover, the bus bars are run uninsulated on supports. The two generators can also feed in in parallel. If the circuit contains three single-phase transformers, each phase of a generator system is connected to the appropriate terminals of the low-voltage windings. Switchover takes place by means of straps.

Making switch

The making switches are tripped with the generator voltage. The system can be switched on simultaneously or time-graded, whereby exact connection is specified for each desired instant. Located behind the safety switches are the making switches. These are single-pole, oil-insulated devices developed specifically for this purpose in the high-power testing laboratory at the Siemens Energy Schaltwerk. The operating of this type of making switch is 5 ± 0.1 ms and the maximum permissible peak short-current circuit 230 kA.

Current-limiting reactor

The high-current bus bar runs from the making switches (which are located in separate compartments) to the reactor compartments of the two generator windings, in which there are two tappable coils for each phase. Each of these coils has twelve taps that enable very finely stepped current grading by connecting various coils in parallel and series.

The high voltage and high current are distributed to the three high-power testing laboratories by an aluminum-tube, duplicate bus bar system – rated for 150 kV and a short-circuit current of 170 kA - and located between the machine room and the test laboratory.
Located next to one another in the tension section laboratories are two bus bar systems, each of which is assigned a specific impulse transformer set and consequently one of the two independently usable short-circuit generators. Both bus bar systems are connected to the three-phase test-laboratory feeds located on the lower level via motorized linear-travel disconnectors. These allow variable connection to the individual test laboratories and therefore the necessary degree of flexibility in operation. If the two bus bar systems are connected in parallel, the total current of the two systems is available in the test laboratories. When required, the generator of the medium voltage test laboratory can be coupled to the bus bar systems via the overhead-line system to increase the testing power or to obtain other combined testing possibilities regarding switching capacity.
The disconnectors of the tension section laboratory can be remotely controlled by means of a mimic diagram with position indicator located in the control room. This ensures quick switching and a clear visual overview of the momentary operating state of the high-voltage circuit.

A digital transient measuring system is used to record the measured values of the switching capacity. This comprises two systems of identical design, which can be operated independently of one another. In turn, each system is equipped with 20 channels with a sampling rate of 100 MSamples and a 14 bit resolution and switchable time-bases.
The data of the switching capacity tests are transferred from the test to the transient recorder in the control room via a fiber-optic links with (in part) up to 120m long glasfiber cables.