Electrical power, designated in the diagrams by the letter P, is a physical quantity that characterizes the rate of conversion or transmission of electricity. The standard concept is the effort to move an electric charge along a route from point F1 to point F2.
The electrical power of a device is a key parameter that determines the potential for its operation in the electrical network. Used to calculate circuits and operating modes of equipment to ensure the safety of electrical networks. The greater the power of the device, the faster they perform the desired action.
Formulas for calculating voltage, current, power, resistance Source amperof.ru
Electrical current through voltage and current
Since the potential difference calculated by the formula (F1-F2) determines the voltage (U), it is easy to conclude that the relationship established by Ohm’s law cannot be used. Electrical power (P) is also qualified by the current strength (I) on a specific section of the line. Final expression: P = U x I.
What is the load determined in terms of current and resistance?
Through a simple conversion, the electrical energy consumption is determined using the following formula: P = I2 x R. This shows the dependence of the power on the nominal value of the resistor connected to the line of the network element. For a complete circuit, the source resistance (internal) and the conductance of the connection point are indicated.
We use an electric meter
The third method is that almost all metering devices are equipped with a light indicator; the number of flashes means some kind of power consumption imp/kW.
We disconnect all consumers in the apartment, leaving only the device of interest connected. Within 15 minutes, we count the pulses and multiply by four (to get the number per hour). Having found out the figure, divide it by imp/kW and find out the power of the unit.
You can also record the meter reading and turn on the electrical appliance whose consumption we are trying to determine for some time, preferably for an hour. We record new readings, subtract the old ones from them, and as a result we find out the approximate power.
An electronic meter allows you to view all parameters in real time: current, electricity consumption, network voltage, by going through the menu of the metering device. We talked about how to take readings from an electric meter in the corresponding article!
An analogue of an electric meter can be a household wattmeter, with which you can quickly and accurately determine the power consumption of electricity by the device. The video below clearly demonstrates the operation of this device:
What is it and how to calculate the load
Electric current load is a quantity characterizing its properties. Shows how much energy is consumed by electrical appliances. The current power is measured using a special device - a wattmeter.
If you connect a meter in series, you can check the current strength. When connecting in parallel, the voltage is determined. The amount of circuit consumption is calculated using the formulas: P = I x U or P = U2/ R = I2 x R.
The electrical load is equal to the voltage across the consumer multiplied by the amount of current flowing through it.
P = U x I
The formula indicates which measurements determine this parameter. If the load is active, it is measured in Watts, the reactive unit of electrical power is VA.
Reactive unit of electrical power - VA Source infourok.ru
Current measuring instruments
Electrical measuring instruments are a special type of devices that are used to measure many electrical quantities. These include:
- AC ammeter;
- AC voltmeter;
- Ohmmeter;
- Multimeter;
- Frequency meter;
- Electric meters.
Ammeter
To determine the current strength in an electrical circuit, you need to use an ammeter. This device is connected to the circuit in series and, due to its negligible internal resistance, does not affect its state. The ammeter scale is graduated in amperes.
In a classic device, a measured current passes through an electromagnetic coil, which creates a magnetic field that causes the magnetic needle to deflect. The deflection angle is directly proportional to the measured current.
Classic ammeter
An electrodynamic ammeter has a more complex operating principle. It contains two coils: one is movable, the other stands still. They can be connected to each other in series or in parallel. When current passes through the coils, their magnetic fields begin to interact, which as a result causes the moving coil with an arrow attached to it to deviate by a certain angle proportional to the magnitude of the current being measured.
Voltmeter
A voltmeter is used to determine the voltage (potential difference) across a section of the circuit. The device must be connected parallel to the circuit and have high internal resistance. Then only hundredths of the current will enter the device.
School voltmeter
The principle of operation is that inside the voltmeter there is a coil and a series-connected resistor with a resistance of at least 1 kOhm, on which the volt scale is calibrated. The most interesting thing is that the resistor actually registers the current strength. However, the divisions are selected in such a way that the readings correspond to the voltage value.
Ohmmeter
This device is used to determine electrically active resistance. The principle of operation is to change the measured resistance into a voltage directly dependent on it thanks to an operational amplifier. The desired object must be connected to a feedback circuit or to an amplifier.
If the ohmmeter is electronic, then it will work on the principle of measuring the current flowing through the required resistance at a constant potential difference. All elements are connected in series. In this case, the current strength will have the following dependence:
I = U/(r0 + rx),
where U is the emf of the source, r0 is the resistance of the ammeter, rx is the desired resistance. According to this dependence, resistance is determined.
Electronic ohmmeter
Multimeter
The devices given as an example are used today only in schools for physics lessons. Multimeters were invented for professional tasks. The most common device includes simultaneously the functions of an ammeter, voltmeter and ohmmeter. The device can be either easily portable or huge stationary with a large number of possibilities. The name “multimeter” was first applied specifically to a digital meter. Analog devices are more often called “avometer”, “tester” or simply “Tseshka”.
Universal multimeter
The work of current is a complex but very important topic in electrodynamics. Without knowing it, you will not be able to solve even the simplest problems. Even electricians use job finding formulas to make the necessary calculations.
How to determine the maximum current load
The useful power shows the maximum value in a situation where the load resistance R is compared with the same parameter inside the source - r.
R = r.
P max = E2 / 4r, where E is the driving force of the current source.
To calculate the maximum current load for an electrical device, you need to know the rated load parameter and the AC input voltage. The technical data sheet of the device, manual or emblem contains the first indicator.
For example, when the appliance rating (P) is 12 W, the maximum current consumption at AC voltage will be for:
- 120 V – I = 12/120 = 0.100 A or 100 mA.
- 220 V – I = 12 / 220 = 0.055A or 55 mA.
If necessary, the amount of electricity consumed is expressed through a complex value. For this purpose, basic relationships are used, impedance is used instead of resistance.
Efficiency
When performing necessary (useful) work, for example, mechanical work, it is necessary to perform a larger amount of work, since in reality there are resistance forces and part of the energy is subject to dissipation (dissipation). The efficiency of work is determined using the efficiency factor ($\eta $), while:
\[\eta =\frac{P_p}{P}\left(5\right),\]
where $P_p$ is useful power; $P$ is the consumed power. From expression (5) it follows that the useful power can be found as:
\[P_p=\eta P\ \left(6\right).\]
Electrical Appliances Parameters
Every modern apartment must be equipped with electrical appliances. To connect them to the network, it is necessary to draw up a schematic diagram where the loads connected to individual lines will be distributed in coordination with each other. It is necessary to build in a circuit breaker based on the PUE to prevent emergency situations.
First, the electrical wiring parameters are clarified. Then they are checked according to the group diagram for connecting to the network of household electrical appliances.
Standard characteristics of electrical power consumption (W):
- desktop computer – 170-1,250;
- LCD TV – 120 – 265;
- laptop – 40-280;
- air conditioning – 1,200 – 2,500;
- iron – 450-1850.
To protect the network, you need an automatic machine; we choose it taking into account all the significant factors.
Automatic switch for protecting the electrical network Source vmasshtabe.ru
It is important to pay attention to loads that have increased reactive energy parameters.
Selection of circuit breaker rating
Current source efficiency
To solve practical problems when connecting several consumers to a standard 220 V home network, the total current strength in individual lines is calculated.
Calculation procedure for one household air conditioner:
- power consumption – 1,250 W;
- cosϕ – 0.75;
- I = 1,250/ (220 * 0.75) = 7.58 A.
Other consumers make calculations in a similar way. Less powerful devices are combined into a unit for connection to one line. Make the necessary adjustments taking into account placement in order to economically use cable products. A suitable machine is selected from the standard model range in the higher side of the nominal value (with a reserve of current strength).
Next, check the compliance of the conductors. The cross-sectional area is calculated using the well-known geometric formula:
S = ¼ * π * d2.
Next, according to the table from the PUE, select the appropriate option. For the example presented above, when connecting only one air conditioner, it is enough to use a copper conductor with a cross-sectional area of 1.5 mm square. This is enough for long-term transmission of current up to 19 A.
What is it measured in?
The unit of measurement of electrical power is W for Russia. By international standards - W. This is the energy provided per unit of time. One W is equal to a joule per second (J/s). Moreover, a joule is a unit of electrical power, a second is a unit of time.
For small values, multiple prefixes are used: “milli-”, “micro-”, for large values - “mega-”. For example: 5,800 W = 5.8 kilowatts = 5.8 kW.
When you multiply 1 Kilowatt by 1 hour, you get a Kilowatt-hour (kW x h). This is a unit of measurement of the amount of electricity provided to subscribers. It is used by energy enterprises that own the appropriate equipment (generators and transformer substations). They generate and convert the produced electricity, which is then distributed to consumers.
In the same way, the energy capacity of batteries is measured in units of ampere hours (Ah). Portable types of energy storage batteries are measured in milliampere hours (mAh).
The energy in batteries is measured in milliamp hours (mAh). Source listtopa.ru
For the unit of measurement Watt, according to international standards, the letter designation W is allocated after James Watt. He was the first to use the term “horsepower,” which today is an obsolete unit of the W parameter.
Energy conversion indicators:
- horsepower (HP) - 746 W;
- kilo Watts (kW) – 1×1000 W;
- megawatts (MW) −1×1000000 W;
- gigawatt (GW) – 1×1000000000 W.
Today, "horsepower" is used to indicate the second measure of engine power in vehicles.
We use an electric meter
The third method is that almost all metering devices are equipped with a light indicator; the number of flashes means some kind of power consumption imp/kW.
We disconnect all consumers in the apartment, leaving only the device of interest connected. Within 15 minutes, we count the pulses and multiply by four (to get the number per hour). Having found out the figure, divide it by imp/kW and find out the power of the unit.
You can also record the meter reading and turn on the electrical appliance whose consumption we are trying to determine for some time, preferably for an hour. We record new readings, subtract the old ones from them, and as a result we find out the approximate power.
What determines the load of electric current?
Existing electrical wiring lines experience resistance during the movement of electrons, which characterizes voltage loss. Circuits where an alternating current source is present have one feature - the key role here is played by a sinusoidal oscillation of electrical indicators.
Sinusoidal oscillation of electrical indicators. Source urpsvet.ru
The following information will allow you to select the best calculation method based on actual network conditions.
Instantaneous electrical power: calculating the value
This indicator establishes the instantaneous values of the measured data. The key definition is considered taking into account the fact that a single simple charge (q) moves in a certain time Δt. To perform a specific action, the energy of electric current PF1-F2 = U/ Δt or (U/ Δt) x q = U x (q/ Δt) is expended. The formula takes into account the movement of q over the period Δt. Since the current, according to the classical definition, is equal to the charge moving from F1 to F2 (I = q/ Δt), the final expression is derived: PF1-F2 = U x I.
Conditionally assuming that the time period is very short, we obtain the instantaneous power for part of the electrical circuit P(t) = U(t) x I(t). The same conclusions can be drawn taking into account the corresponding resistance parameter: P (t) = (I (t))2 x R = (U(t))2/ R.
Electrical power: DC circuit
The previously mentioned formulas are shown without correction factors. They are used to calculate a circuit connected to a direct current source. Using an ordinary device - a multimeter, with the switch in the correct position, the resistance of the load connected to the network is set.
With its help, the load resistance is set. Source hammer-shop.ru
Looking at your passport
The first way is to look at the passport of the electrical appliance. All factory units are supplied with a label on the body, instructions and a passport with a guarantee. These booklets indicate the scope of application, operating conditions, and technical data.
Above is a small fragment of passport data, or rather a table with data on the model range of convector heaters. Column No. 1 indicates the current passing through the device, the second column indicates how much electricity the device consumes when one heating element and two are turned on. Using the heater as an example, you can easily find out the power consumption of the device using the passport. In a similar way, you can determine how much a TV or even an LED lamp consumes.
Electrical power: AC circuit
For such lines, it is unacceptable to use formulas that determine instantaneous parameters, since the final indicator changes from a minimum value to a maximum value with the network frequency. A typical single-phase 220 V network is characterized by a 50 Hz sinusoidal signal. It is allowed to use the simple formula P = U x I when connecting devices with resistive parameters:
- Heating elements of washing machines;
- spirals of infrared heaters;
- incandescent light bulbs.
Using this formula, the load is set.
Units of measurement and designation
The unit of power in the International System of Units (SI) is the watt. In this case, the Russian designation: W , international: W ). 1 W = 1 J/s. From the formula P = U*I it follows that: 1 watt = 1 volt * 1 ampere, or 1 W = 1 VA.
There are also power units that are multiples of watts: hectawatt (gW), kilowatt (kW), megawatt (MW). In other words, 1 GW = 100 W, 1 kW = 1000 W, 1 MW = 1,000,000 W.
The units of power used in electrical engineering are multiples of the watt: microwatt (µW), milliwatt (mW), hectowatt (gW), kilowatt (kW) and megawatt (MW). In other words, 1 µW = 1*10-6 W, 1 mW = 1*10-3 W, 1 gW = 1*102 W, 1 kW = 1*103 W, 1 MW = 1*106 W.
Each electrical appliance has a certain power (indicated on the device). Here are typical wattage ratings for some electrical appliances.
| Device | Power, W |
| TV in standby mode | 0,5 |
| Flashlight lamp | About 1 |
| Incandescent lamps | 25-150 |
| Fridge | 160 |
| Electric heater | 500-2000 |
| Vacuum cleaner | Up to 1300-1800 |
| Electric kettle | Around 2000 |
| Iron | 1200-2200 |
| Washing machine | Up to 2300 |
Previously, the unit of measurement used to denote power was horsepower (hp), which is still known today. Convert from horsepower to watts using the expression: 1 hp. = 735.5 W.
Energy can be of two types: reactive and active.
Active is the true electrical power that produces real work in the load, W shows this parameter. It converts energy into mechanical, thermal and other forms.
If you turn on a powerful unit or capacitor, the voltage inside the network drops. Such loads create an oscillating circuit that receives energy from the power source. In this situation, only P act components perform useful functions. The active indicator is calculated in the following way:
- U x I – direct current (alternating current with a resistive load);
- U x I x cos fi – for a single-phase 220 V line;
- U x √3 x cos fi = U x 1.7321 x cos fi – 3-phase network, U x √3 x 380V.
There are other types of energy, but more on that later.
Active and passive energy Source ppt-online.org
Reactive power
This indicator shows the loads that are created in devices due to fluctuations in the energy of the electromagnetic field.
Reactive power, regardless of the absence of useful work, must be taken into account to correctly evaluate key network data. Cables and wires, when current passes through them in any direction, heat up. This happens quite cyclically. Energy effects at high intensity:
- damage cable cores and protective insulation;
- contribute to the occurrence of a short circuit;
- destroy the windings of transformers and drives.
Reactive power is expressed as VA (volt-amperes) and is calculated by multiplying the voltage by the current and the shear angle:
P r = U x I x sin fi.
When connecting a load with capacitive parameters, the value becomes negative, when inductive it becomes positive. Since the characteristics of the magnetic field change, the unit of measurement for reactive power is VA.
If the parameters of total electrical power are shown as vectors, a triangle appears. The length of its sides will be equal to the amount of electricity consumed by a particular component. The angle between the apparent power (Pap) and the active power (ϕ) is used for calculations. The total value is determined by the expression: P total = √((P act)2 + (P react)2).
Negative influence of reactive load
Three-phase network power calculation
If we represent the powers in the form of vectors, then the vectors P and Q in sum will give the total power. It is equal to:
S = √ (P2 + Q2).
Total S graph
The formulas for P and Q are:
- P = U*I*sinφ (for a single-phase network) and P = √3* U*I*sinφ (for a three-phase network);
- Q = U*I* cosφ (for a 220 V network) and Q = √3*U*I* cosφ (for a 380 V line).
For your information. Calculations for a three-phase network are correct for symmetrically loaded phases. Otherwise, the powers of all phases are summed up.
The smaller the angle φ between vectors S and P, the higher the power factor cosφ. Complete coincidence of vectors is prevented by Q. The load on power lines and power supply system equipment increases with a large angle value. Overheating of wires and wear of power system equipment occurs.
In practice, the main consumers of manufacturing enterprises are transformers, electric motors and long-distance cables. Therefore, IN is in the lead there, consuming Q. There is an overconsumption of consumed energy, for which enterprises are punished with fines.
Reactive power (RP) carries with it the following disadvantages:
- does not perform useful work;
- causes unnecessary energy consumption and unexpected overload of electrical equipment;
- may cause an emergency.
To compensate for PM, it is necessary to include capacitive elements in parallel with such consumers. For this purpose, Q compensation devices are built. They can be capacitor or inductive, depending on what type of reactive load predominates. Capacitor units, including capacitor batteries, are placed both at power substations and in separate blocks. Such compensation replenishes the reactive component of the energy consumed from the supplier.
Complete condenser unit KKU
What is power in electricity
Voltage is the work done to move a unit of charge. Current is the number of coulombs moved in 1 second. When multiplying the first parameter by the second, the total amount of work done in 1 second is obtained.
The strength of electricity is a numerical current meter that characterizes its energy qualities. The power indicator equally depends on voltage and current strength. How is current power measured? To measure this parameter, a Wattmeter is used; the unit of measurement is designated in the same way - W (Watt).
By using the dependence of the power parameter on current and voltage, specialists can transmit electricity over long distances. For these purposes, energy is converted at step-down and step-up transformer substations (transformer substations).
Types of capacities
Power is a measured physical quantity that is equal to the rate of change with the conversion, transmission or consumption of system energy. According to a narrower concept, this is an indicator that is equal to the ratio of time spent on work to the period itself spent on work. In mechanics it is designated by the symbol N. In electrical engineering the letter P is used. You can often also see the symbol W, from the word watt.
AC power is the product of current, voltage and cosine of the phase shift. In this case, only the active and reactive varieties can be easily counted. You can find out the full power value through the vector dependence of these indicators and area.
Main power types.
Electrical power and inactive power
Equipment certificates contain active load - power factor, which is an important characteristic. It shows how efficiently a household appliance consumes electricity.
Fig.8
This is a number from −1 to 1, it is never equal to one. This coefficient depends on the type of load: C, L or R. The first 2 negatively affect PF = cos φ of the system. If its parameter is large, the current consumed by the devices increases. Many power loads are inductive, causing the current to lag behind the voltage.
Inactive energy arises in electrical AC circuits of alternating current networks. It is calculated simply: the square root of the sum (Pa2 + Pr2). If the reactive load is zero, then the passive load is equal to the modulus |Pa|.
The presence of nonlinear current distortions in electrical networks is caused by non-compliance with the direction that occurs between U/I, since the energy has a pulsed nature. In nonlinear modes, the apparent current power (EP) increases. Such a load is inactive and consumes Pr and current distortion energy. The unit of measurement is the same as regular power W.
Looking at your passport
The first way is to look at the passport of the electrical appliance. All factory units are supplied with a label on the body, instructions and a passport with a guarantee. These booklets indicate the scope of application, operating conditions, and technical data.
Above is a small fragment of passport data, or rather a table with data on the model range of convector heaters. Column No. 1 indicates the current passing through the device, the second column indicates how much electricity the device consumes when one heating element and two are turned on. Using the heater as an example, you can easily find out the power consumption of the device using the passport. In a similar way, you can determine how much a TV or even an LED lamp consumes.
