electrical field

Electrical Engineering | Development of Electrical Engineeirng

Soon after FARADAY’s discovery of electromagnetic induction, the first hand-powered generator was built by PIXII in 1832. However, the first generators were useless for practical use.
The discovery of the dynamo-electric principle by SIEMENS in 1867 was of decisive importance for practical application. This enabled powerful dynamo machines to be built.
In 1881 EDISON presented the first usable incandescent lamp and in 1882 the world’s first power station went online in New York. The first power station in Europe was built in Berlin’s Friedrichstrasse in 1884.

The first generators

Soon after MICHAEL FARADAY’s discovery of electromagnetic induction and the law of induction in 1831, the first devices were built that took advantage of this discovery. This z. B. rotated coils in front of stationary permanent magnets or permanent magnets in front of stationary coils. HIPPOLYTE PIXII, the mechanic from AMPÈRE, built the first hand-operated generator in 1832. In this generator, a horseshoe magnet was turned in front of two coils with a hand crank.

The first generators were of little practical importance. Above all, their performance was too poor for practical applications. The magnetic fields for induction were mostly generated by permanent magnets, which were relatively weak and whose strength was reduced by the constant vibrations of the generators.

Generator by H. PIXII, the AMPÈRE mechanic

A new technical principle

To obtain stronger magnetic fields and greater power from the generators, electromagnets were needed. However, these had to be generated by batteries or a second generator. There was also talk of external excitation of the electromagnets. Overall, this was very complex, and so such arrangements were mainly used in research laboratories.

For the broad application of electromagnetic induction, an invention by the technician and entrepreneur WERNER VON SIEMENS (1816-1892) was of decisive importance. SIEMENS discovered the dynamo-electric principle in 1866and presented this to the Berlin Academy of Sciences on January 17, 1867. He realized that the iron core of an electromagnet retains a residual magnetic field after switching off the current. This magnetic field is sufficient to induce a small voltage in a generator. This voltage can be used to operate the electromagnet and to strengthen the magnetic field. This induces a greater voltage. So the magnetic field of the electromagnet and the induced voltage swing each other up to the full power of the generator.
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WERNER VON SIEMENS with his first dynamo machine (1867)

SIEMENS called these generators, which excite their own magnetic field, dynamo machines. With this invention from Siemens, power generators could be built. A new branch of technology, electrical engineering, emerged. In 1878 Siemens & Halske was already producing 25 dynamo machines per week.

Old dynamo machine (around 1900)

Wide use of electrical energy

The further development of electrical engineering took place very quickly and is characterized by the widespread use of electrical energy in all areas of life.
So gradually electric motors for drives began to gain acceptance. In 1879 the first electric train was presented at the trade exhibition in Lichterfelde. It was the forerunner of the electric tram. The first electric elevator could be seen in Mannheim in 1881. In 1882 the first electric mine train ran in a mine in Zeukerode near Dresden and the ancestor of all-electric cars rolled over Berlin’s Kurfürstendamm.

Advances have also been made in lighting technology. In 1881 the American inventor THOMAS ALVA EDISON (1847-1931) presented a usable electric light bulb and a model of a lighting system for residential areas at an exhibition in Paris. In 1882, EDISON set up the world’s first power station in New York and a DC power network for incandescent lamps. In 1884 the first electric motors were connected to the grid.

Also in 1884, the Deutsche Edison-Gesellschaft, later the Allgemeine Elektrizitäts-Gesellschaft (AEG), and the Siemens & Halske company built Europe’s first power station at Friedrichstrasse 55 in Berlin. Two restaurants and a few shops were illuminated with four steam engines, seven dynamo machines and 100 kW power.
The first system for the remote transmission of electrical energy in Germany has put into operation in 1891 from Lauffen to Frankfurt / Main over 175 km.

Electrical engineering and energy supply in Berlin

In the 19th century, Berlin was the centre of the development of electrical engineering. In 1880 the engineer EMIL RATHENAU acquired the EDISON patents for Germany and in 1883 founded the “Deutsche Edison-Gesellschaft”, today’s AEG. This quickly developed into the largest incandescent lamp manufacturer in Europe. As early as 1884 300,000 lamps were produced, in 1891 there were more than a million.

The first “block station” with an output of 100 kW was built in 1884. The electrical engineering generated there was used to illuminate the Café Bauer Unter den Linden and several neighbouring shops. More small power plants were built in quick succession. In 1896, 166,182 incandescent lamps and 8,216 arc lamps were supplied centrally with electrical energy in Berlin. At that time, every single lamp, every machine was recorded and registered individually.

But the need for electrical energy for motors also grew steadily. While the proportion of “power” in Berlin was only 50% in 1898, by 1900 it had grown to 75%. After all, the need for drive energy increased faster than the output of the power plants. In 1906, the Berliner Elektrizitätswerke only allowed the connection of an electric motor with the consent of a power cut from 4 p.m. to 10 p.m. in winter.
In particular, the generation of direct current in central stations with voltages of 110, 220 and 440 V. It was increasingly difficult to supply the newly emerging industrial companies on the outskirts of the city. The maintenance of the generators was laborious and dangerous. A worker who had to adjust the brushes of the commutator on such a generator according to the current consumption decided: “I am a father of a family and, in the face of my conscience, I cannot take responsibility for doing service on the commutator.”
G. FERRARIS in Turin and N. TESLA in New York had already dealt with the technical application of single- and two-phase alternating currents in the 1880s. Generators, motors and transformers were tried and tested in practice and introduced. They were much lighter and safer to use than DC machines. Nevertheless, alternating current was not given a chance because the motors did not start under load.
The engineers HASELWANDER from Siemens and the Russian V. DOLIVO-DOBROWOLSKY (AEG) found a solution by introducing a three-phase alternating current. The v. Dolivo-Dobrowolsky was also the initiator of the first three-phase long-distance transmission over 175 km from Lauffen to Frankfurt / Main, which caused a sensation at the Electrotechnical Exhibition in Frankfurt in 1891. This made it possible to transmit electrical energy over long distances without any problems, “a thousand horsepowers were able to be guided through a keyhole, the thin wire”, as a French writer enthusiastically written.

In Berlin, three-phase power stations were built in Oberschöneweide (1897) and Moabit (1900), soon afterwards others, which, however, found it difficult to meet the rapidly increasing demand from industry and households. This was only possible with the construction of new large power plants such as the Klingenberg power plant and the expansion of electricity networks for the long-distance transmission of electrical energy.

Electrical work

The electrical work indicates how much electrical energy is converted into other forms of energy.
Formula symbol: W
Units: one watt-second (1st W.⋅ s), one joule (1 J)
Electrical work has to be done to move a charged body in an electrical field.
The electrical work indicates how much electrical energy is converted into other forms of energy.
Formula symbol: W
Units: one watt-second (1st W.⋅ s), one joule (1 J)
Electrical work has to be done to move a charged body in an electrical field. The work to move such a body is equal to the product of its charge and the voltage between the starting point and the endpoint:
W.= Q ⋅ U
Another equation is used for calculations in a circuit. The work in the electrical circuit is equal to the product of the electrical power and the time during which the power is expended:
W.= P⋅ t
Both calculation equations can be converted into one another.
In general, if you apply a force F to move a body along the path s, you do work on this body. Two differently charged bodies attract each other. If you want to pull them apart, you have to apply a force to move one of these bodies in the electrical field of the other body. With this shift,

electrical work
electrical work

The electrical work in a plate capacitor

In some cases, the equation for electrical work is particularly easy to derive. This is possible if the force and the displacement path are directed in the same way. In addition, it is necessary that the electric field strength is constant over the entire path and thus the force is also constant. These conditions are very well met within a plate capacitor. The aim is to calculate the W= FD that has to be done to move a charged test specimen between two plates of a plate capacitor, the distance between which is d. Under the conditions mentioned, the following applies to this work:
W.= Fs
The force on a test specimen inside a plate capacitor is the product of its electrical charge and the electrical field strength in the capacitor:
F.= Q ⋅ E
This results in the following for the electrical:
W.= Q ⋅ E⋅ d
The following applies to the electric field strength E between the capacitor plates:
E.=Ud( U voltage between the plates)
If one uses this equation to replace the electric field strength E in the calculation formula for the electric work, the overall result is:
W.= Q ⋅ U
 
The electrical work in a current-carrying conductor
One can imagine a straight piece of a conductor like a plate capacitor with tiny plate surfaces. Since an electrical voltage is applied to a line wire and electrical charges flow in the conductor – that is, they are “shifted” – the voltage source performs electrical work on the charge carriers. This work is necessary, for example, to overcome the line resistance. Since it is not possible to “count” all charge carriers individually in a live conductor, the equation obtained using the plate capacitor is converted for calculations in electrical circuits.
The total charge flowing through a piece of the conductor is the product of the current I and time:
Q = I⋅ t
The following then applies to w=fd
W.= Q ⋅ U= I.⋅ t ⋅ U= P⋅ t
Electrical work is the product of electrical power and time. This equation applies provided that the power converted in the circuit is constant.
Note for calculations of electrical work
As a rule, either the power or voltage and current strength are specified on electrical components. For example, every light bulb is provided with a power rating. If you want to calculate the electrical work of an incandescent lamp, you only have to multiply this power figure by its operating time. A 100 W lamp that has been in operation for 12 hours, therefore, has an electrical work of
W.= P.⋅ t = 100 W ⋅ 12 H = 1200 W ⋅ h = 1.2 kW ⋅ h

performed.

What is an Ammeter

Ammeters are measuring devices that can be used to measure the electrical current in a circuit. They are available in many different designs. Effects of the electric current are used in ammeters of various types.
Ammeter, also current strength or ammeter called, measuring instruments, with which one can measure the electric current in a circuit are. They are available in many different designs. Different effects of the electric current are used in ammeters of different designs.
Ammeters must always be connected in series with the electrical device or component on which the amperage is to be measured. This is necessary so that the current flows through them, the strength of which is to be measured (Fig. 2).
As a flow meter using, Moving Coil. They differ in their structure and in their mode of operation.

Circuit of an ammeter

Moving coil measuring devices

In moving-coil measuring devices, a rotatably mounted small coil is in the magnetic field of a permanent magnet. A pointer is connected to this coil. If a current flows through the small coil, it becomes a magnet itself and interacts with the magnetic field of the permanent magnet. The greater the current through the coil, the stronger the resulting magnetic field and the stronger the deflection of the coil and thus the pointer (Fig. 3). The magnetic effect of the electric current is used.

Moving coil measuring mechanism

Moving iron gauges

Moving iron gauges, also known as soft iron gauges, have a fixed iron plate in a coil and a rotatable iron plate connected to the axis and the pointer (Fig. 4). If current flows through the coil, the two iron sheets are magnetized in the same direction and repel each other. The repulsion and thus the deflection of the pointer is greater, the greater the current through the coil. The magnetic effect of the electric current is used.

Moving iron measuring mechanism

Hot-wire gauges

In hot-wire meters, a pointer is connected to a thin platinum wire that is firmly stretched between two connections (Fig. 5). If a current flows through this wire, it heats up and expands. This expansion is transferred to a pointer. The greater the current that flows through the wire, the greater the expansion. So the thermal effect of the electric current is used.

Multimeters

Nowadays, multimeters are mostly used to measure voltage or current. Multiple measuring devices are often moving-coil measuring devices in which the measuring range can be changed and which are suitable for measuring direct current as well as measuring alternating current.
If you use a multimeter to measure the current, you should follow the steps below:

  • Set the type of current (direct current or alternating current) on the measuring device that is present in the circuit!
  • Set the largest measuring range for the amperage on the measuring device! This is especially necessary if you do not know how big the current is.
  • Connect the measuring device in series to the electrical device in the circuit in which the current is to be measured! With direct current, make sure that the negative pole of the electrical source is connected to the negative pole of the measuring device and the positive pole of the electrical source is connected to the positive pole of the measuring device.
  • After closing the circuit, switch the measuring range down so that the last third of the scale can be read as far as possible. Then the measurement error is due to the measuring device being the smallest.
  • Read the amperage! Please note that the set measuring range indicates the maximum value on the scale!
Hot-wire measuring mechanism
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