Advice 1: What is ampere

The unit "ampere" is used to measure the strength of an electric current all over the world. But few people think about for what reason this unit got its name.
What is ampere
The name of the unit of current "ampere" received from the surname of the French physicist Henri-Marie (in another transcription - andré-Marie) Ampsand who lived in the period from 1775 to 1836. The main sphere of his activity was the study of electromagnetic phenomena, while he established, in particular, that the strength of the magnetic field generated by the conductor with current depends on the strength of this current, not voltage. For this reason, it is named after the unit of current strength, and not any other electrical values.Other areas of physics Henri Amps little interest. Nevertheless, it was he who coined the term "Cybernetics, not Norbert Wiener, who only gave him a new value. The term "kinematics" refers to the field of physics, which in all secondary schools studied even earlier electromagnetic phenomena, Ampere also invented. He also studied botany and even philosophy.If placed in parallel in a vacuum two infinitely thin wire, place them at a distance of exactly one meter from each other and pass through each of them a current of one ampere, they will interact with the power of two by ten to the minus seventh Newtons. Thus, through each one of them will be 6,2415093 ten to the eighteenth degree of electrons per second.Amper linked to other units of measure: volt, Ohm and watt. If the conductor resistance of one Ohm voltage is applied in one volt through it flows a current of one ampere. In this case, it will stand out in the heat one watt of power.If to measure length and weight in different countries use different units, the volts, amperes, ohms and watts adopted as official units, respectively, voltage, current, resistance and power in all countries without exception.

Advice 2: What are stray currents

Stray currents – electrical currents in the ground that appear when you use it as a conducting medium. Under their action occurs the corrosion of metallic objects in the ground or come in contact with it. As a rule, these objects are a shell of electric cables, various building structures and pipelines.
What are stray currents
Stray currents typical for electrified railway and tram tracks, which are serviced improperly or accidental leakage from power lines. Sometimes such currents is called zero current, which exist in the grounded metal structures.

Sources of stray currents.



Sources of currents in the earth are underground, tram, electrified with direct current suburban rail transport. The wires in these types of transport are connected with a plus power source and a minus, with a return conductor rail tracks.
Products humus, alkali, lime, sour marshy soils containing lime, slag, ash creates conditions for intensive soil corrosion of the shells of metal.


Because of poor isolation of the roadway from the ground, a large resistance of track, as well as violations of the joints of the rail, part of the current passes to the negative pole of the power source via earth. Meeting on the way the metal sheath of cables, pipelines and other underground structures, currents pass through these conduits and returning to the earth to get to minus traction substation.

Throughout this chain the path of the electric current there is a phenomenon of electrolysis. Where the metallic sheath of the cables and track are the electrodes (anode and cathode) and the damp soil containing large amounts of salts and acid – electrolytic environment (electrolyte). And if you move to DC current through the electrolyte, the electrode with higher potential dissolves.
Electrolysis – the process of separating components of substances in solution, by passing electric current through it.


Scientists have calculated that the magnitude of stray current in one ampere, in one year destroyed 33 pounds of lead, 3.95 kg aluminum and 9 pounds of iron. The strongest destruction of exposed lead sheath on the cable lines.

Prevention of stray currents



To protect underground structures and metal sheaths of cables from corrosion stray currents take special measures:
- as far as possible to reduce the resistance of the rail by welding of joints of rail and isolate the rail from the ground.
- to reduce the voltage drop in the rails using special line of the cable connecting different points of the rail with the negative bus of the substation.

These methods achieve significant unloading rail network and reduce the number of stray currents.

Advice 3: What is the ampere force

The ampere force is called the force with which the magnetic field acts on a current-carrying conductor placed in it. Its direction can be determined using the left hand rule, and the rule of clockwise.
What is the ampere force
Instruction
1
If in a magnetic field to put metal conductor, then it will be a force from this field, ampere force. The current in the metal is the directional movement of many electrons, each of which acts the Lorentz force. The forces acting on the free electrons have the same magnitude and the same direction. Add up with each other, they give a net force of ampere.
2
The force got its name after a French physicist and scientist Andre Marie ampere, who in 1820 experimentally studied the effect of magnetic field on current-carrying conductor. Changing the shape of conductors and their location in the magnetic field, Ampere determined the force acting on the parts of the conductor.
3
Power module ampere proportional to the length of the conductor, the current in it and the module of magnetic field induction. It also depends on the orientation of the conductor in a magnetic field, in other words, from the angle that forms the direction of the current relative to the magnetic field induction vector.
4
If the induction at all points of the conductor are identical and the magnetic field is homogeneous, then the power module ampere is equal to the product of the current in the conductor, the module of magnetic induction in which it is located, length of the conductor and the sine of the angle between directions of current and magnetic field induction vector. This formula is true for the conductor of any length, as long as it is entirely in a uniform magnetic field.
5
In order to know the direction of the force of the ampere, you can use the left-hand rule: if you put your left hand so that four fingers indicated the direction of the current, while the field lines would be in the palm of the hand, the direction of the force amp will show bent 90° thumb.
6
Since the product of the module of magnetic field induction vector of the sine of the angle is a module of the components of the induction vector which is directed perpendicular to the conductor, the orientation of the palm can be determined by this component. Component perpendicular to the surface of the conductor must enter the open palm of his left hand.
7
To determine the direction of the force of the ampere there is another way, it is called the rule of clockwise. The ampere force is directed in the direction from which the shortest rotation current to the field visible in a counterclockwise direction.
8
Power amps can be demonstrated on the example of parallel currents. Two parallel wires will repel if the currents in them are in opposite direction to each other, and attracted to, if the directions of the currents are the same.

Advice 4: What is the ammeter

Ammeter - instrument for measuring current in electrical circuits. According to the principle of ammeters are magnetoelectric, electromagnetic, thermoelectric, electrodynamic and others.
Ammeter AC
The device which measure the power flowing in the circuit current is called the ammeter. Because the values, which gives the device (amperage) depends on the resistance of the elements inside the ammeter, it should be very low.
The internal structure of the ammeter depends on the purpose of use, type of current and the operating principle.
There are ammeters, which react not by resistance of the conductor and emitted by the heat or magnetic waves.


Moving coil ammeters




Devices that respond to magnetic phenomena (magneto) is used to measure currents of very small values in circuits with DC. Inside them there is nothing superfluous, except for the coil connected to her pointer and scale with tick marks.


Electromagnetic ammeters




Unlike magneto, they can be applied for networks with alternating current, often in chains for industrial use with a frequency of fifty Hertz. Electromagnetic ammeter can be used for measurements in circuits with a large current.


Thermoelectric ammeters




Used for measuring AC current with high frequency. Inside the device installed a heating element (the conductor with a high resistance) thermocouple. Due to the flowing current heats the conductor, and a thermocouple records the value. Due to the heat rejected frame with the arrow at a certain angle.


Electrodynamic ammeters




Can be used not only to measure DC current, but AC. Due to the features of the device, it can be applied in such networks, where frequency is two hundred Hertz.
Electrodynamic ammeter is mainly used as a check meter to check the devices.
They react strongly to third-party magnetic fields and on overload. Because of this, as the meters are rarely used.


Ferrodinamicheskoy




Very reliable devices, which have high strength and little exposed to magnetic fields that occur not in the device. Such ammeters are installed in automatic control systems as the recorders.

It so happens that the scale of the instrument is insufficient and it is necessary to increase the values that should be measured. To achieve this, use the bypass (conductor with high resistance joined in parallel with the device). For example, to set the value of one hundred amperes, and the unit is only rated for ten, then attach the shunt, whose resistance value nine times lower than that of the device.
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