Робочий зошит 
з англійської мови за професійним спрямуванням 
"Electrician. Workbook"

 Інтегрований урок 

Англійська мова за професійним спрямуванням та Електротехніка  

Тема: "Будова силових трансформаторів / Сonstruction of power transformers"

Інтегрований урок.pdf by Oлена Скачко

 CONSTRUSTION OF THE TRANSFORMER. 3D VIDEO ANIMATION.

 Electricity Matching Game

https://learningapps.org/15621379 

 The electrician's tools

https://learningapps.org/13377470 

Vocabulary - Electricity 

https://learningapps.org/10793964 

Energy

RECTIFIER

A rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction. The reverse operation is performed by the inverter.

The process is known as rectification, since it "straightens" the direction of current. Physically, rectifiers take a number of forms, including vacuum tube diodes, wet chemical cells, mercury-arc valves, stacks of copper and selenium oxide plates, semiconductor diodes, silicon-controlled rectifiers and other silicon-based semiconductor switches. Historically, even synchronous electromechanical switches and motors have been used. Early radio receivers, called crystal radios, used a "cat's whisker" of fine wire pressing on a crystal of galena (lead sulfide) to serve as a point-contact rectifier or "crystal detector".

Rectifiers have many uses, but are often found serving as components of DC power supplies and high-voltage direct current power transmission systems. Rectification may serve in roles other than to generate direct current for use as a source of power. As noted, detectors of radio signals serve as rectifiers. In gas heating systems flame rectification is used to detect presence of a flame.

Depending on the type of alternating current supply and the arrangement of the rectifier circuit, the output voltage may require additional smoothing to produce a uniform steady voltage. Many applications of rectifiers, such as power supplies for radio, television and computer equipment, require a steady constant DC voltage (as would be produced by a battery). In these applications the output of the rectifier is smoothed by an electronic filter, which may be a capacitor, choke, or set of capacitors, chokes and resistors, possibly followed by a voltage regulator to produce a steady voltage.

More complex circuitry that performs the opposite function, that is converting DC to AC, is called an inverter.

INVERTER

A power inverter, or inverter, is a power electronic device or circuitry that changes direct current (DC) to alternating current (AC).[1] The resulting AC frequency obtained depends on the particular device employed. Inverters do the opposite of “converters” which were originally large electromechanical devices converting AC to DC.[2]

The input voltage, output voltage and frequency, and overall power handling depend on the design of the specific device or circuitry. The inverter does not produce any power; the power is provided by the DC source.

A power inverter can be entirely electronic or may be a combination of mechanical effects (such as a rotary apparatus) and electronic circuitry. Static inverters do not use moving parts in the conversion process.

Power inverters are primarily used in electrical power applications where high currents and voltages are present; circuits that perform the same function for electronic signals, which usually have very low currents and voltages, are called oscillators. Circuits that perform the opposite function, converting AC to DC, are called rectifiers.

 THYRISTORS

Click on this link to find more information about Thyristors.

 TRANSISTORS

A transistor is a semiconductor device used to amplify or switch electronic signals and electrical power. Transistors are one of the basic building blocks of modern electronics. 

It is composed of semiconductor material usually with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals controls the current through another pair of terminals. Because the controlled (output) power can be higher than the controlling (input) power, a transistor can amplify a signal. Today, some transistors are packaged individually, but many more are found embedded in integrated circuits.

Most transistors are made from very pure silicon, and some from germanium, but certain other semiconductor materials are sometimes used. A transistor may have only one kind of charge carrier, in a field-effect transistor, or may have two kinds of charge carriers in bipolar junction transistor devices. Compared with the vacuum tube, transistors are generally smaller and require less power to operate. Certain vacuum tubes have advantages over transistors at very high operating frequencies or high operating voltages. Many types of transistors are made to standardized specifications by multiple manufacturers.

Transistor classification

Transistors fall intotwo main classes – bipolar and field effect. They are also classified according to the semiconductor material employed – silicon or germanium, and to their field of application (for exam-ple, general purpose, switching, high frequency, and so on). 

 SEMICONDUCTOR DIODES

A diode is defined as a two-terminal electronic component that only conducts current in one direction (so long as it is operated within a specified voltage level). An ideal diode will have zero resistance in one direction, and infinite resistance in the reverse direction.

Although in the real world, diodes can not achieve zero or infinite resistance. Instead, a diode will have negligible resistance in one direction (to allow current flow), and very high resistance in the reverse direction (to prevent current flow). A diode is effectively like a valve for an electrical circuit.

HOW TRANSFORMERS WORK

 

 OHMMETERS

The instrument, which is used to measure the value of resistance between any two points in an electric circuit is called ohmmeter. It can also be used to find the value of an unknown resistor. The units of resistance are ohm and the measuring instrument is meter. So, the word “ohmmeter” is obtained by combining the words “ohm” and “meter”.

Types of Ohmmeters

Following are the two types of ohmmeters.

• Series Ohmmeter
• Shunt Ohmmeter

Now, let us discuss about these two types of ohmmeters one by one.

 Active, Reactive and Apparent Power

Active Power

Definition: The power which is actually consumed or utilised in an AC Circuit is called True power or Active power or Real power. It is measured in kilowatt (kW) or MW. It is the actual outcomes of the electrical system which runs the electric circuits or load.

Reactive Power

Definition: The power which flows back and forth that means it moves in both the directions in the circuit or reacts upon itself, is called Reactive Power. The reactive power is measured in kilo volt-ampere reactive (kVAR) or MVAR.

Apparent Power

Definition: The product of root mean square (RMS) value of voltage and current is known as Apparent Power. This power is measured in kVA or MVA.

It has been seen that power is consumed only in resistance. A pure inductor and a pure capacitor do not consume any power since in a half cycle whatever power is received from the source by these components, the same power is returned to the source. This power which returns and flows in both the direction in the circuit, is called Reactive power. This reactive power does not perform any useful work in the circuit.

In a purely resistive circuit, the current is in phase with the applied voltage, whereas in a purely inductive and capacitive circuit the current is 90 degrees out of phase, i.e., if the inductive load is connected in the circuit the current lags voltage by 90 degrees and if the capacitive load is connected the current leads the voltage by 90 degrees.

Hence, from all the above discussion, it is concluded that the current in phase with the voltage produces true or active power, whereas, the current 90 degrees out of phase with the voltage contributes to reactive power in the circuit.

Therefore,

True power = voltage x current in phase with the voltage

Reactive power = voltage x current out of phase with the voltage

Active component of the current

The current component, which is in phase with the circuit voltage and contributes to the active or true power of the circuit, is called an active component or watt-full component or in-phase component of the current.

Reactive component of the current

The current component, which is in quadrature or 90 degrees out of phase to the circuit voltage and contributes to the reactive power of the circuit, is called a reactive component of the current.

VOLTMETER

Definition: The instrument which measures the voltage or potential difference in volts is known as the voltmeter. It works on the principle that the torque is generated by the current which induces because of measurand voltage and this torque deflects the pointer of the instrument. The deflection of the pointer is directly proportional to the potential difference between the points. The voltmeter is always connected in parallel with the circuit.

Symbolic Representation of voltmeter

The voltmeter is represented by the alphabet V inside the circle along with the two terminals.

Why is Voltmeter connected in Parallel?

The voltmeter constructs in such a manner that their internal resistance always remains high. If it connects in series with the circuit, it minimises the current which flows because of the measurand voltage. Thus, disturb the reading of the voltmeter.

AMMETERS

Definition: The Ammeter is a measuring instrument used to find the strength of current flowing around an electrical circuit when connected in series with the part of the circuit being measured.

The ideal ammeter has zero internal resistance. But practically the ammeter has small internal resistance. The measuring range of the ammeter depends on the value of resistance.

Symbolic Representation

The capital alphabet A represents the ammeter in the circuit.

 Three Phase Wyes and Deltas

Three phase voltages can be generated and transformed as either a Wye or a Delta. Wye and Delta refer to the connections between the single phase windings which connect to create three phase voltages. Notice the polarity of each winding at the connection points. In a Wye all the ends or 2's are connected together while the beginnings or l's are connected to the three phase power source, Ll, L2, and L3. In a Delta the end (2) of one winding is connected to the beginning (1) of .another winding. Three phase power is connected to each of these 1, 2 junction points.

 Star or Wye (Y) Connection

In this method of interconnection, the similar ends say, ‘star’ ends of three coils (it could be ‘finishing’ ends also) are joined together at point N. 

Delta (Δ) or Mesh Connection

In this form, of interconnection the dissimilar ends of the three phase winding are joined together i.e. the ‘starting’ end of one phase is joined to the ‘finishing’ end of the other phase and so on. In other words, the three windings are joined in series to form a closed mesh.

3-PHASE POWER

   

Most power is distributed in the form of 3-phase AC. Basically, instead of just one coil turning in agenerator, there are three coils, spaced 120 degrees apart.

As the coils turn through the magnetic field, power is sent out on three lines. Three current and voltage sine waves are generated, 120 degrees out of phase with each other. Each sine wave represents the current or voltage on one of the phases.

Three-phase electricity powers large industrial loads more efficiently than single phase electricity. When single-phase electricity is needed, it is available between any two phases, or, in some systems, between one of the phases and ground.

 POWER IN AC CIRCUITS

Power is dissipated in AC resistive circuits the same way as in DC resistive circuits. Power is measured in watts and is equal to the current times the voltage in the circuit.

The power consumed by the resistor in an AC circuit varies with the amount of current flowing through it and the voltage applied across it. 

The relationship of power, current, and voltage in resistive AC circuit.

Picture shows the relationship of power, current, and voltage. The power curve does not fall below the reference line because the power is dissipated in the form of heat. It does not matter in which direction the current is flowing, as power is assumed to have a positive value.

Power varies between the peak value and 0. Midway between peak value and 0 is the average power consumed by the circuit. In an AC circuit, the average power is the power consumed. This can be determined by multiplying the effective voltage value by the effective current value. This is expressed as

P=IE