VARC – experimental verification

Experimental results – mechanical parts

The actuator arrangement with the vacuum interrupter has been tested in the laboratory. A picture of this prototype is shown below. The total weight of the Thomson armature disk, the pulling rod, the over-travel mechanism and the moving contact in this case was 3.5 kg.

Example recordings are shown below to illustrate the OPEN operation. The diagram to the left shows that the capacitors was pre-charged to around 300 V and was fully discharged in approximately one millisecond. This gave rise to a current current in the coil, which peaked at about 3.2 kA after approximately 0.8 ms.

The right diagram shows the speed of the Thomson disk and the positions for the Thomson disk and the moving contact. The diagram shows that the speed of the actuator reaches a speed of approximately 3 m/s in less than 2 ms and that the speed then decreases. The position of the moving contact has changed 6 mm in 3 ms. The movement of the contact is somewhat delayed relative the movement of the Thomson armature disk due to the action of the over-travel mechanism.

A high-speed camera was used to observe the movements in the Thomson actuator. The experiments were repeated and it was found that the position was reproduced with a good repeatability. The observed standard deviation was about 0.1 mm.

Experimental activities and results – module prototype

The power electronic converter, the resonant circuit and the MOV was implemented for testing interruption of 10 kA peak with 40 kV transient inception voltage (TIV), i.e. the protective voltage of the MOV. The equipment was tested together with the fast-acting circuit-breaker prototype. The prototype is shown in the photo below.

The complete module prototype with the MOV stack, resonant capacitors and inductors ,and electronics (from the front to the back)

Recorded diagrams from an test performed at KEMA in June 2018 appear below. The upper diagram shows the voltage between the vacuum interrupter terminals together with the output voltage from the converter. The relation between the MOV protection voltage and the converter voltage demonstrates that few semiconductors performing repetitive switching operations can create sufficient amplitude of the oscillating current to create the required zero-crossings of the current passing through the vacuum interrupter. The lower diagram shows that the fault current to be interrupted is created by discharging a capacitor through an inductor through the vacuum interrupter. It also shows the oscillating current that is excited by the VSC so that the zero-crossing occurs at the peak of the “line” current. The time required to reach the desired oscillating current amplitude in this case was 0.4 ms, which is far shorter that the time to achieve sufficient contact gap even with a extremely fast actuator. The total time from trip command given to the circuit-breaker until current interruption occurred was 2.8 ms in this experiment.

The video below illustrates the complete operating principle.

On-going development

SCiBreak presently is in the process of developing a current-interrupting module capable of interrupting a peak current 10 kA against the transient inception voltage (TIV) 40 kV. The TIV is determined by the protective voltage (voltage at high current) of the MOV. The operating time should be less than 3 ms.