Natural natural sources from which energy is drawn to prepare it in the right forms for various technological processes are called energy resources. There are the following types of basic energy resources: a chemical energy of the fuel; b atomic energy; to water power ie hydraulic; r radiation energy of the sun; d wind power. e energy of ebbs and flows; Well geothermal energy. Primary energy source or energy resource coal gas oil uranium concentrate hydropower solar...
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Lecture number 1.
Basic definitions
Power system (power system)consists of power stations, electrical networks and consumers of electricity, interconnected and connected by a common mode and common control of this mode.
Electrical power (electrical) system- this is a set of electrical parts of the power plant, electrical networks and consumers of electricity, i.e. it is part of the energy system, with the exception of heat networks and heat consumers.
Electrical network- a set of electrical installations for the distribution of electrical energy, consisting of substations, switchgears, overhead and cable power lines.
Electrical substations- an electrical installation designed to convert electricity from one voltage or frequency to another voltage or frequency.
Characteristics of power systems
The frequency at all points of electrically connected networks is the same
Equality of consumed and generated capacities
The voltage at different network nodes is not the same
Benefits of interconnecting power systems
Improving the reliability of power supply
Improving the sustainability of power systems
Improving the technical and economic indicators of energy systems
Stable power quality
Reducing the required power reserve
The loading conditions of the units are improved due to the leveling of the load schedule and the reduction of the maximum load of the power system.
There is an opportunity for a more complete use of the generating capacities of ES, due to the difference in their geographical position in latitude and longitude.
The operational management of power systems is carried out by their dispatch services, which establish, on the basis of appropriate calculations, the optimal mode of operation of power plants and networks of various voltages.
Energy sources
There are renewable and non-renewable energy sources.
Natural (natural) sources from which energy is drawn to prepare it in the right forms for various technological processes are called energy resources.
There are the following types of main energy resources:
a) the chemical energy of the fuel;
b) atomic energy;
c) water energy (i.e. hydraulic);
d) solar radiation energy;
e) wind energy.
f) tidal energy;
g) geothermal energy.
The primary energy source or energy resource (coal, gas, oil, uranium concentrate, hydropower, solar energy, etc.) enters one or another energy converter, the output of which is either electrical energy or electrical and thermal energy. If thermal energy is not generated, then it is necessary to use an additional energy converter from electrical to thermal (dashed lines in Fig. 1.1).
The largest part of the electrical energy consumed in our country is obtained by burning fuels extracted from the bowels of the earth - coal, gas, fuel oil (a product of oil refining). When they are burned, the chemical energy of the fuels is converted into thermal energy.
Power plants that convert the thermal energy obtained by burning fuel into mechanical energy, and this latter into electrical energy, are called thermal power plants (TPPs).
Power plants that operate with the highest possible load for a significant part of the year are called base, power plants that are used only during part of the year to cover the "peak" load are called peak.
ES classification:
Electrical part of ES
Power stations (PS) are complex technological complexes with a total number of main and auxiliary equipment. The main equipment is used for the production, conversion, transmission and distribution of electricity, the auxiliary equipment is used to perform auxiliary functions (measurement, signaling, control, protection and automation, etc.). We will show the mutual connection of various equipment on a simplified circuit diagram of the ES with the generator voltage busbars (see Fig. 1).
Rice. one
The electricity generated by the generator is supplied to the SS busbars and then distributed between the auxiliary needs of the SN, the load of the generator voltage NG and the power system. Separate elements in fig. 1 are intended for:
1. Q switches - for switching on and off the circuit in normal and emergency modes.
2. QS disconnectors - to relieve voltage from de-energized parts of the electrical installation and to create a visible open circuit, which is necessary during repair work. Disconnectors, as a rule, are repair, and not operational elements.
3. SS busbars - for receiving electricity from sources and distributing it among consumers.
4. Relay protection devices RZ - to detect the fact and location of damage in the electrical installation and to issue a command to turn off the damaged element.
5. Automation devices A - for automatically turning on or switching circuits and devices, as well as for automatically regulating the operating modes of electrical installation elements.
6. IP measuring instruments - to control the operation of the main equipment of the power plant and the quality of energy, as well as to account for the generated and supplied electricity.
7. Measuring current transformers TA and voltage TV .
Test questions:
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Electric energy of a system of charges.
Field work during dielectric polarization.
Electric field energy.
Like any matter, the electric field has energy. Energy is a function of state, and the state of the field is given by the intensity. Whence it follows that the energy of the electric field is a single-valued function of the intensity. Since it is extremely important to introduce the concept of energy concentration in the field. The measure of the field energy concentration is its density:
Let's find an expression for. For this, we consider the field of a flat capacitor, assuming that it is everywhere homogeneous. An electric field in any capacitor arises during its charging, which can be represented as a transfer of charges from one plate to another (see figure). Elementary work ͵ expended on charge transfer is equal to:
where a is the complete work:
which goes to increase the field energy:
Considering that (there was no electric field), for the energy of the electric field of the capacitor we obtain:
In the case of a flat capacitor:
since, - the volume of the capacitor, equal to the volume of the field. Τᴀᴋᴎᴍ ᴏϬᴩᴀᴈᴏᴍ, the energy density of the electric field is:
This formula is valid only in the case of an isotropic dielectric.
The energy density of the electric field is proportional to the square of the intensity. This formula, although obtained for a uniform field, is true for any electric field. In the general case, the field energy can be calculated by the formula:
The expression includes the permittivity. This means that the energy density in a dielectric is greater than in a vacuum. This is due to the fact that when creating a field in a dielectric, additional work is performed connected with the polarization of the dielectric. Let us substitute the value of the electric induction vector into the expression for the energy density:
The first term is related to the energy of the field in vacuum, the second is related to the work expended on the polarization of a unit volume of the dielectric.
The elementary work spent by the field on the increment of the polarization vector is equal to.
The work of polarization per unit volume of a dielectric is:
because that is what we wanted to prove.
Consider a system of two point charges (see figure) according to the principle of superposition at any point in space:
Electric field energy density
The first and third terms are associated with the electric fields of charges and, respectively, and the second term reflects the electrical energy associated with the interaction of charges:
The self-energy of the charges is positive, and the interaction energy can be both positive and negative.
Unlike a vector, the energy of an electric field is not an additive quantity. The interaction energy can be represented by a simpler relation. For two point charges, the interaction energy is:
which can be represented as the sum:
where is the potential of the charge field at the location of the charge, and is the potential of the charge field at the location of the charge.
Generalizing the result obtained to a system of an arbitrary number of charges, we obtain:
where is the charge of the system, is the potential created at the location of the charge, all the rest system charges.
If the charges are distributed continuously with the bulk density, the sum should be replaced by the volume integral:
where is the potential created by all the charges of the system in the volume element. The resulting expression matches total electrical energy systems.
The area of the economy that covers the resources, extraction, transformation and use of various types of energy.
Energy can be represented by the following interconnected blocks:
1. Natural energy resources and extractive enterprises;
2. Processing enterprises and transportation of finished fuel;
3. Generation and transmission of electrical and thermal energy;
4. Consumers of energy, raw materials and products.
Brief content of the blocks:
1) Natural resources are divided into:
renewable (solar, biomass, hydro resources);
non-renewable (coal, oil);
2) Mining enterprises (mines, mines, gas rigs);
3) Fuel processing enterprises (enrichment, distillation, fuel purification);
4) Transportation of fuel (railway, tankers);
5) Generation of electrical and thermal energy (CHP, NPP, HPP);
6) Transmission of electrical and thermal energy (electric networks, pipelines);
7) Consumers of energy, heat (power and industrial processes, heating).
The part of the energy sector concerned with obtaining large amounts of electricity, transmitting it over a distance and distributing it among consumers, its development is carried out at the expense of electric power systems.
This is a set of interconnected power plants, electrical and thermal systems, as well as consumers of electrical and thermal energy, united by the unity of the process of production, transmission and consumption of electricity.
Electric power system: CHP - combined heat and power plant, NPP - nuclear power plant, CPP - condensing power plant, 1-6 - consumers of electricity CHP
Scheme of a thermal condensing power plant
Electrical system (electrical system, ES)- the electrical part of the electric power system.
The diagram is shown in a single-line image, i.e. one line means three phases.
Technological process in the power system
A technological process is a process of converting a primary energy resource (fossil fuel, hydropower, nuclear fuel) into final products (electricity, thermal energy). The parameters and indicators of the technological process determine the efficiency of production.
Schematically, the technological process is shown in the figure, which shows that there are several stages of energy conversion.
Scheme of the technological process in the power system: K - boiler, T - turbine, G - generator, T - transformer, power lines - power lines
In boiler K, the energy of fuel combustion is converted into heat. The boiler is a steam generator. In a turbine, thermal energy is converted into mechanical energy. The generator converts mechanical energy into electrical energy. The voltage of electrical energy in the process of its transmission through power lines from the station to the consumer is transformed, which ensures the efficiency of transmission.
The efficiency of the technological process depends on all these links. Consequently, there is a set of regime tasks associated with the operation of boilers, turbines of thermal power plants, turbines of hydroelectric power plants, nuclear reactors, electrical equipment (generators, transformers, power lines, etc.). It is necessary to choose the composition of the operating equipment, the mode of its loading and use, to comply with all restrictions.
electrical installation- an installation in which electricity is produced, generated or consumed, distributed. Can be: open or closed (indoors).
power station- a complex technological complex on which the energy of a natural source is converted into the energy of electric current or heat.
It should be noted that power plants (especially thermal, coal-fired) are the main sources of environmental pollution by energy.
electrical substation- an electrical installation designed to convert electricity from one voltage to another at the same frequency.
Power transmission (power line)- the structure consists of elevated power transmission line substations and step-down substations (a system of wires, cables, supports) designed to transfer electricity from the source to the consumer.
Electricity of the net- a set of power transmission lines and substations, i.e. devices that connect the power supply to the .
Consider a system of two point charges (see figure) according to the principle of superposition at any point in space:
.
Electric field energy density
The first and third terms are related to the electric fields of the charges 
And 
respectively, and the second term reflects the electrical energy associated with the interaction of charges:
Self-energy of charges positive value 
, and the interaction energy can be both positive and negative 
.
Unlike the vector 
the energy of the electric field is not an additive quantity. The interaction energy can be represented by a simpler relation. For two point charges, the interaction energy is:
,
which can be represented as the sum:
where 
- charge field potential 
at the location of the charge 
, but 
- charge field potential 
at the location of the charge 
.
Generalizing the result obtained to a system of an arbitrary number of charges, we obtain:
,
where 
-
system charge, 
- potential created at the location 
charge, everyone else system charges.
If the charges are distributed continuously with bulk density 
, the sum should be replaced by a volume integral:
,
where 
- the potential created by all the charges of the system in the volume element 
. The resulting expression matches total electrical energy systems.
A charged metal sphere in a homogeneous dielectric.
In this example, we will find out why the electric forces in a dielectric are less than in vacuum and calculate the electric energy of such a ball.
H 
the field strength in the dielectric is less than the field strength in vacuum in 
once 
.
This is due to the polarization of the dielectric and the appearance of a bound charge near the surface of the conductor. 
the opposite sign of the charge of the conductor 
(see picture). Related charges 
screen the field of free charges 
, reducing it everywhere. The electric field strength in the dielectric is equal to the sum 
, where 
- field strength of free charges, 
- field strength of bound charges. Given that 
, we find:
→
→
→ 
→
→
.
Dividing by the surface area of the conductor, we find the relationship between the surface density of bound charges 
and surface density of free charges 
:
.
The resulting ratio is suitable for a conductor of any configuration in a homogeneous dielectric.
Let's find the energy of the electric field of the ball in the dielectric:
It is taken into account here that 
, and the elementary volume, taking into account the spherical symmetry of the field, is chosen in the form of a spherical layer. 
is the capacity of the ball.
Since the dependence of the electric field strength inside and outside the ball on the distance to the center of the ball r is described by different functions:
energy calculation is reduced to the sum of two integrals:
.
Note that bound charges arise on the surface and in the volume of the dielectric sphere:
,
,
where 
is the volume density of free charges in the sphere.
Prove it yourself using links 
,
and the Gauss theorem 
.
The self-energy of each shell are equal respectively (see example 1.):
,
,
and the shell interaction energy:
.
The total energy of the system is:
.
If the shells are charged with equal charges of opposite sign 
(spherical capacitor), the total energy will be equal to:
where 
is the capacitance of a spherical capacitor.
The voltage applied to the capacitor is:
,
where 
And 
- electric field strength in layers.
Electrical induction in layers:
- surface density of free charges on the capacitor plates.
Given the connection 
from the definition of capacity, we get:
.
The resulting formula is easily generalized to the case of a multilayer dielectric:
.
· The potential of an electric field is a quantity equal to the ratio of the potential energy of a point positive charge placed at a given point of the field to this charge
or the potential of the electric field is a quantity equal to the ratio of the work of the field forces to move a point positive charge from a given point of the field to infinity to this charge:
The potential of the electric field at infinity is conditionally taken equal to zero.
Note that when a charge moves in an electric field, the work A v.s external forces is equal in absolute value to the work A s.p. field strength and is opposite to it in sign:
A v.s = – A d.s.
· Electric field potential created by a point charge Q on distance r from the charge
· The potential of the electric field created by a metallic, charge-carrying Q sphere with radius R, on distance r from the center of the sphere:
inside the sphere ( r<R) ;
on the surface of a sphere ( r=R) ;
out of scope (r>R) .
In all the formulas given for the potential of a charged sphere, e is the permittivity of a homogeneous infinite dielectric surrounding the sphere.
· The potential of the electric field created by the system P point charges, at a given point, in accordance with the principle of superposition of electric fields, is equal to the algebraic sum of potentials j1, j2, ... , j n, created by individual point charges Q1, Q2, ..., Qn:
· Energy W interactions of a system of point charges Q1, Q2, ..., Qn is determined by the work that this system of charges can do when they are removed relative to each other to infinity, and is expressed by the formula
where is the potential of the field created by all P- 1 charges (excluding i th) at the point where the charge is located Q i .
· The potential is related to the electric field strength by the relation
In the case of an electric field with spherical symmetry, this relationship is expressed by the formula
or in scalar form
and in the case of a homogeneous field, i.e., a field whose intensity at each point is the same both in absolute value and in direction
where j1 And j2- potentials of points of two equipotential surfaces; d- the distance between these surfaces along the electrical field line.
· Work done by an electric field when moving a point charge Q from one point of the field, which has the potential j1, to another one that has the potential j2
A=Q ∙(j1 – j2), or
where El- the projection of the tension vector on the direction of movement; dl- movement.
In the case of a homogeneous field, the last formula takes the form
A=Q∙E∙l∙cosa,
where l- movement; a- the angle between the directions of the vector and displacement .
A dipole is a system of two point electric charges of equal size and opposite in sign, the distance l between which there is much less distance r from the center of the dipole to the observation points.
The vector drawn from the negative charge of the dipole to its positive charge is called the arm of the dipole.
The product of the charge | Q| dipole on its shoulder is called the electric moment of the dipole:
Dipole field strength
where R is the electric moment of the dipole; r- the module of the radius-vector drawn from the center of the dipole to the point, the field strength in which we are interested; α is the angle between the radius vector and the dipole arm.
Dipole field potential
The mechanical moment acting on a dipole with an electric moment , placed in a uniform electric field with intensity
or M=p∙E∙ sin,
where α is the angle between the directions of the vectors and .
In an inhomogeneous electric field, in addition to the mechanical moment (pair of forces), some other force acts on the dipole. In the case of a field with symmetry about the axis X, the force is expressed by the ratio
where is the partial derivative of the field strength, characterizing the degree of field inhomogeneity in the direction of the axis X.
With force F x is positive. This means that under the action of its dipole is drawn into the region of a strong field.
Potential energy of a dipole in an electric field
