The Beginning

Introduction

In the beginning of electrical power supply (1880-1890) the importance of switching devices was minor. Small units for illumination of a house and commercial building had been put into operation. Knife switches, strip fuses and a simple bulb for supervision of voltage were sufficient for dynamos with a power of 15...25 kW.

Edison,T.A. started running the first central station and first public electric utility in New York (Pearl Street) on September 4th, 1882. At first he used three and later six 150 kW, 110 VDC, 1200 rpm "Jumbo Generators" (due to their large size). He developed a complicated lighting system with lines, distribution boards, fuses, breakers and metering devices. The first public power station in Germany with six steam machines (150 HP each) and 12 dynamos with a total power of 540 kW (110 VDC with two-wire connection) was put into operation on May10th,1885 (Berlin, Markgrafenstrasse 44).

The first switching devices were more or less provisional ones due to lack of experience and limited knowledge. They have were in an empirically-manual manner and were suitable for single tasks. Such an example was the "general interrupter" in the Berlin power station which would enable an emergency cutout of the whole grid. Figure 2 shows such a makeshift construction (nominal current approximately 2000 A and 2x110 VDC. Unlocking the four clamps lets the copper ear plate fall down and interrupt the circuit.

At this time DC was mostly used. Due to this and the inductance of the machines the control and extinguishing of the lightning arc when switch off occurred, was difficult even at low voltages (65...110 VDC). Developing motors and generators was a challenging task anyway- so nobody was really interested in the so called "auxiliary devices" - low voltage circuit breakers. The initial switching devices originated from laboratories (mercury bowls) or from the telegraph industry (switches and push buttons). Because these devices did not meet heavy-current requirements, engineers avoided them or tried to reduce the breaking capacity with de-excitation of generators.

At the time of introduction of alternating current, oil was estimated as the optimal extinguishing agent. The pioneer of alternating current, Ferranti, was the first at using oil for that purpose. He plunged the agile part of the Ferranti-oil-fuse (1894) into the oil after opening the contact. The first high-voltage device working completely in oil was developed by C.L.E. Brown (one of the founders of Brown, Boveri & Cie) in Baden/Switzerland in 1897. He proposed at the headquarters Porta Volta in Milan to put an air-circuit breaker (5 kV) in a barrel of oil for testing purposes. This was successful, and a new 16-kV-breaker was developed in the same year for Paderno (with an oil hutch made of glass). Later, steel plate hutches were used.

One could now protect the generator by switching it off with a circuit breaker and de-exciting it in case of a certain smell, electrical arc, or loud noises. Previously, this was not possible due to the long reaction time (Figure 3).