I. Electrotechnical fundamentals (i) circuits and their physical volume
1. Circuits
The closed path through which the current passes is called the circuit. The circuit is formed for a certain need by a combination of electrical equipment or circuit elements。
The role of circuits: to achieve transmission, distribution and conversion of electricity。
2. Components of circuits
Power: devices providing electricity
Intermediate: the role of transmission, distribution and control of electricity
Load: a device to extract electrical energy。
3. Basic physical volume of circuits
(1) electricity
Electricity generation: the current is formed by a structured and directed movement of charge (with electric particles)。
The direction of currents: the customary direction of positive charge movements is the direction of currents
The size of the current is indicated by current intensity i: i = q/t
The amount of electricity per second through the transect of the conductor is 1 cologne (c) and the current is 1 ampere。
The international unit for currents is amber, and smaller units include milligrams and microbes。
(2) electricity
Physically, voltage is defined as the power of the field to move the unit positive charge from one point of the field to another。
For engineering applications, electrical voltage in circuits is the underlying cause of current generation. In numerical terms, the voltage equals the difference between two points of the grid。
The international unit of voltage is volt, and the usual units are millivols and kv。
In the technical fundamentals analysis of electricians, the positive direction of the voltage is usually stated to be a high-level point to a low-level, so the voltage is also referred to as voltage reduction。
(3) electricity
The transfer of the unit positive charge from the negative pole to the positive pole of the power is called the power dynamics of the power。
Electric dynamics measure the physical volume of power transformation energy power。
(4) electrical resistance
The barrier to currents presented by the conduit is called electrical resistance。
R = old l / s
R - retardation
L-conductor length (m)
S-conductor interdiction area (m2)
Electro-resistance rate of the old-conductor (m)
The electrical resistance size of the vector is associated with temperature。
The resistance temperature factor for copper is 0. 047°c。
An increase of 0. 47c/o in electrical resistance at 1°c
(5) electricity
The conversion of electricity is carried out in the process of current operation. Thus, the amount of electricity consumed by current operation can be measured by electricity。
Electricity (or electricity) is also commonly used as a measure in daily production and life: 1 degree = 1 kw. H = 1 kv. A. H
The concept of 1 degree electricity: 1 hour heating of 1,000 w electric furnaces; 10 hours lighting of 100 w electric lights; 25 hours lighting of 40 w electrical lights。
Note: 1 degrees = 1 kw • h = 3,600,000 j
(6) electricity
In electrical technology, currents are referred to as power in units of time。
International unit: u [v], i [a], electro-p watt
1 kw = 1000 w
Normally, the actual power of electrical appliances is not equal to the rated power. When the actual power is less than the rated power, the real power of the appliances in use does not reach the rated value and when the actual power is greater than the rated power, the appliances are vulnerable to damage。
Thermal effects of currents
Electricity heats through the conductor, a phenomenon known as the heat effect of the current。
Experimental evidence: the heat generated by the current through the conductor is proportional to the level of the current strength, and to the conductor's resistance and utilisation time, which is called the jj。
Q= i2rt
Q-choose from current overconductors
I - electricity flow through the conductor amber (a)
T-hours of electrotime
Pure electrical resistance circuit w=q=i2rt
(ii) basic laws of the circuit
Part of the circuit om law
The experimental conclusions of german scientist om in 1827: in a circuit that does not contain a power source, the current through the conductor is proportional to both ends of the conductor's voltage and inversely to the resistance of the conductor。
2. Full circuit om law
The currents of the entire circuit are inversely proportional to the electrical dynamics of the power supply, and the resistance of the entire circuit is called the full circuit orm law。
3. Serial and combined resistance applications
(1) blocked circuits
Several of the resistors were connected in a sequential manner, and there was no connection between them. Interdiction circuit characteristics:
I1 = i2 = i3
The total voltage at both ends of 2 circuits equals the sum of the resistance voltage: u=u1+u2+u3
3 total electrical resistance equals the sum of the resistance: r=r1+r2+r3
The two end of the chain of resistance is proportional to its resistance value。
(2) interrupted and connected circuits
In the circuits, several end-of-blocks are connected together at one point on the circuit, and their other end is connected together at another point on the circuit. And connect the circuits to features:
1 equals the same voltage at both ends of the circuit and equals the voltage at both ends of the circuit: u=u1=u2=u3=un
The total current of 2 circuits is equal to the sum of the combined resistance: i=i1+i2+i3+in
3 and the total resistance of the circuits is equal to the countdown of the resistance
(3) interrupted circuits
Interruptive elements in circuits are linked and combined and are referred to as hybrids。
4. Practical applications of chained resistance
(b) the use of several chains of electrical resistance to obtain greater resistance
(c) the use of several electrical resistances to form sub-pressurers
(b) limit and regulate current sizes using chained resistance methods
The scale of electrons measured by the meter is expanded by a cascade method。
