The most important task of equipment statistics is to measure the power of plant engines. Engine power is called its ability to perform certain work per unit of time (second). The basic unit of power is the kilowatt (kW). Since a plant's power equipment may include motors whose power is expressed in different units, the total power of all motors is expressed in kilowatts. To do this, use the following constant relationships:

Engine power can be characterized from different points of view.

Depending on the design of the engine, power is distinguished between theoretical, indicator and effective (real).

Theoretical power(#) is determined by calculations based on the assumption that there are no mechanical losses (from friction) and thermal losses (from radiation) in the engine. Theoretical power can be calculated for any engines.

Power indicator(#/s) - engine power taking into account thermal, but excluding mechanical losses. Measured M.nd on the part of the engine where radiation losses end.

The third type of design capacity is effective power (G This is the actual power, taking into account thermal and mechanical losses. Measured at the engine working shaft.

Depending on the intensity of engine operation, its power can change, therefore, there are such power with load: normal (economic), maximum long and maximum short time.

Power is normal(L/^g) is the power at which the engine most economically consumes fuel and energy per unit of force, that is, it has the highest efficiency (efficiency). When the load deviates up or down from normal efficiency. decreases.

In general, in order to obtain the maximum amount of energy when operating power devices, a maximum load mode is established for them, in which the engine can operate for an indefinitely long period without damage to its condition. The power characteristic of the maximum load of most power engines is called maximum duration (Mmt()-

Maximum short-term power (No.) is the maximum load of the engine for which it can operate for a short time without an accident, usually no more than 30 minutes.

All three types of load power are potential, since they determine not the actual, but the possible load. To fully characterize the power of an engine, its power, by design and by load, should be taken into account simultaneously. As a rule, this will be the maximum continuous effective power.

To characterize engine power according to operational purpose They distinguish between connected power, installed, available, peak, reserve, average actual and average annual.

Connected capacity (Mprisd) is the power of all receivers connected to the power plant, including the power of the electric motors of someone else's current for subscribers and the electric motors of their own current.

Large power plants provide electricity to subscribers with different load schedules. For example, in the morning the energy demand for production and urban transport (trams, trolleybuses) sharply increases, but for lighting decreases; In the evening hours, the work of some enterprises stops, but the need for entertainment venues for electrical energy increases sharply. Due to the frequent connection of subscribers to the station, the connected power is usually 2-2.5 times greater than the station capacity. So, a station with a capacity of 30 thousand kW can serve subscribers whose current receiver power is 60 thousand kW or more.

Power installed(l/) is the total maximum continuous effective power of the installed engines (for a power plant - the power of electric generators).

Since some of the engines undergoing repair and awaiting repair cannot be used, great importance acquires available power (Мяві)- the total power of all devices, minus those that are under repair or awaiting repair.

For a certain period, for example per day, month or quarter, it is important to determine the maximum load, which is called peak power of the ShA.

The difference between available and peak power is called reserve power. It consists of two parts that have different economic significance: the power of backup engines, intended to replace those that are running in the event of an accident, and the underload of engines operating during rush hour.

For many practical calculations it is determined average actual power L. It is calculated for an individual engine by dividing the energy generated during the period in kilowatt-hours by the actual operating time in hours, that is

To calculate the average actual power of several engines that work together, the energy they produce must be divided by the operating time of all engines, reduced by the time they work together. Thus, the formula for the average actual power of two engines operating together in one or another combination will have the form

Example 7.1

Calculate the average actual power of two engines, of which the first worked from 6 to 16 hours and produced 630 kW x hour of energy, and the second worked from 8 to 23 hours and produced 715 kW x hour of energy.

Total amount of energy produced: 630 + 715 = 1345 kW x h.

Total engine operating time: (16-6) + (23-8) = 25 hours.

Time for the engines to work together: (16-8) = 8 hours.

In addition to the average actual power, calculate average annual power (M), which shows how many kilowatt-hours of energy are produced per hour on average per year.

To do this, the energy produced is divided by the number of lesson hours - 8760. is always less than and their ratio A^UL^ characterizes the degree of engine utilization over time over an annual period.

Enterprises have engines installed that perform various functions: primary engines produce mechanical energy, and secondary engines transform mechanical energy. energy into electrical(electric generators) or electrical into mechanical and thermal (electric motors and electrical devices).

If, to determine the total power of an enterprise, the power of the primary and secondary engines is added, then a repeated count will be allowed; In addition, the total power calculation should only include the power that is used in the production process. Consequently, the power of the engines installed at the power station of the enterprise, the energy of which is supplied to the side, should not be taken into account when determining the energy capacity of a certain enterprise, since it will be taken into account at the enterprises that consume energy.

Rice. 7.1. V

From Fig. 7.1 shows that prime movers can directly drive working machines or transmit mechanical energy to electric generators to transform it into electrical energy; The electricity from your own electric generators can be used both to power electric motors and electric devices of your own and mixed current, and to meet the economic needs of the enterprise. Part of the electricity can be released to the side. At the same time, energy received from outside ensures the operation of electric motors and electric devices of foreign and mixed current. The power of direct primary engines and the power of transport engines are taken into account independently. By summing the powers of the primary and secondary engines, we will allow double counting. Therefore, the calculation formula is applied energy capacity of the enterprise, which completely eliminates double counting:

The total power of prime movers No.) also takes into account the power of direct-acting motors and those used in factory vehicles.

Formula 7.3 not only eliminates the repeated calculation of power, but also distinguishes between the power of a mechanical and electric drive.

The power of the mechanical drive is equal to the difference between the power of all primary engines of the enterprise and the power of that part of them that serves electric generators (Mpd-M^^^^). This the difference is the power of the prime movers directly connected to the working machines (using a transmission or gear system).

The power of an electric drive is defined as the sum of the powers of electric motors and electrical devices, that is, secondary engines that directly serve the production process.

Sometimes, when calculating the energy power of an enterprise, the power of the primary engines servicing electric generators Gp.d.obs.el.gen)> unknown. To determine it, you need to multiply the power of electric generators by a factor of 1.04. The origin of this coefficient is as follows: the average efficiency of electric generators is taken to be 0.96, which means that the power of the prime movers that serve them can be obtained by dividing the power of the prime movers by 0.96 or multiplying by = 1.04. 0.96

For determining the amount of energy consumed by the enterprise, use a formula similar to that used to calculate the total power:

Example 7.2

Calculate the potential and average actual capacity of the enterprise, knowing that the enterprise worked for 200 hours and little his The following power equipment is at our disposal:

^^=400+50+350 0.736+100 0.736 - 250-1.04 + 220 + 600 = І34І.2l5zh.

To calculate If it is necessary to determine the energy consumed by the enterprise:

Yeschipr = 80000 + 42000 o 0.736+10000 - 0.736 - 48000 o 1.04 + 42000 + 90000 = 200352 kW.

The concept of power (M) is associated with the productivity of a particular mechanism, machine or engine. M can be defined as the amount of work done per unit of time. That is, M is equal to the ratio of work to the time spent on its completion. In the generally accepted international system of units (SI), the common unit of measurement M is the watt. Along with this, horsepower (hp) still remains an alternative indicator for M. In many countries around the world, it is customary to measure the M of internal combustion engines in hp, and the M of electric motors in watts.

Varieties of EIM

As the scientific and technological progress A large number of different units of power measurement (PMU) appeared. Among them, the ones in demand today are W, kgsm/s, erg/s and hp. In order to avoid confusion when moving from one measurement system to another, the following EIM table was compiled, in which real power is measured.

Tables of relationships between EIM

EIM	W	kgsm/s	erg/s	hp
1 W	1	0,102	10^7	1.36 x 10^-3
1 kiloW	10^3	102	10^10	1,36
1 megaW	10^6	102 x 10^3	10^13	1.36 x 10^3
1 kgcm per second	9,81	1	9.81 x 10^7	1.36 x 10^-2
1 erg per second	10^-7	1.02 x 10^-8	1	1.36 x 10^-10
1 hp	735,5	75	7.355 x 10^9	1

Measurement of M in mechanics

All bodies in the real world are set in motion by a force applied to them. The effect on the body of one or more vectors is called mechanical work (P). For example, the traction force of a car sets it in motion. This thereby accomplishes mechanical R.

From a scientific point of view, P is a physical quantity “A”, determined by the product of the magnitude of the force “F”, the distance of movement of the body “S” and the cosine of the angle between the vectors of these two quantities.

The work formula looks like this:

A = F x S x cos (F, S).

M "N" in this case will be determined by the ratio of the amount of work to the time period "t" during which the forces acted on the body. Therefore, the formula defining M will be:

Mechanical M engine

The physical quantity M in mechanics characterizes the capabilities of various engines. In cars, the M of the engine is determined by the volume of the liquid fuel combustion chambers. M of a motor is work (the amount of energy generated) per unit of time. During its operation, the engine converts one type of energy into another potential. In this case, the motor converts thermal energy from fuel combustion into kinetic energy of rotational motion.

It is important to know! The main indicator of the M engine is the maximum torque.

It is the torque that creates the traction force of the motor. The higher this indicator, the greater the M of the unit.

In our country, M power units are calculated in horsepower. All over the world there is a trend of calculating M in W. Now it's already power characteristic indicated in the documentation in two dimensions at once in hp. and kilowatts. In what unit to measure M is determined by the manufacturer of power electrical and mechanical installations.

M electricity

Electrical M is characterized by the rate of conversion of electrical energy into mechanical, thermal or light energy. According to the International SI System, a watt is an EIM in which the total power of electricity is measured.

that is, the product of force vectors and speed of movement is power. How is it measured? According to the international SI system, the unit of measurement for this quantity is 1 Watt.

Watt and other power units

Watt means power, where one joule of work is done in one second. The last unit was named after the Englishman J. Watt, who invented and built the first steam engine. But he used another quantity - horsepower, which is still used today. One horsepower is approximately equal to 735.5 watts.

Thus, in addition to Watts, power is measured in metric horsepower. And for a very small value, Erg is also used, equal to ten to the minus seventh power of Watt. It is also possible to measure in one unit of mass/force/meters per second, which is equal to 9.81 Watts.

Engine power

This value is one of the most important in any motor, which comes in a wide range of power. For example, an electric razor has hundredths of a kilowatt, and a spaceship rocket has millions.

Different loads require different power to maintain a certain speed. For example, a car will become heavier if more cargo is placed in it. Then the friction force on the road will increase. Therefore, to maintain the same speed as in an unloaded state, more power will be required. Accordingly, the engine will consume more fuel. All drivers know this fact.

But at high speeds, the inertia of the machine is also important, which is directly proportional to its mass. Experienced drivers who are aware of this fact find the best combination of fuel and speed when driving so that less gasoline is consumed.

Current power

How is current power measured? In the same SI unit. It can be measured by direct or indirect methods.

The first method is implemented using a wattmeter, which consumes significant energy and heavily loads the current source. It can be used to measure ten watts or more. The indirect method is used when it is necessary to measure small values. The instruments for this are an ammeter and a voltmeter connected to the consumer. The formula in this case will look like this:

With a known load resistance, we measure the current flowing through it and find the power as follows:

P = I 2 ∙ R n.

Using the formula P = I 2 /R n, the current power can also be calculated.

How it is measured in a three-phase current network is also no secret. For this, an already familiar device is used - a wattmeter. Moreover, the problem of how electrical power is measured can be solved using one, two or even three devices. For example, a four-wire installation would require three devices. And for a three-wire with an asymmetric load - two.

Power- a physical quantity equal in the general case to the rate of change, transformation, transmission or consumption of system energy. In a narrower sense, power is equal to the ratio of the work performed in a certain period of time to this period of time.

Distinguish between average power over a period of time

and instantaneous power in this moment time:

The integral of instantaneous power over a period of time is equal to the total transferred energy during this time:

Units. The International System of Units (SI) unit of power is the watt, equal to one joule divided by a second. mechanical work electrical power

Another common, but now outdated, unit of power measurement is horsepower. In its recommendations, the International Organization of Legal Metrology (OIML) lists horsepower as a unit of measurement “which should be phased out as soon as possible where it is currently used and which should not be introduced if it is not in use.”

Relationships between power units (see Appendix 9).

Mechanical power. If a force acts on a moving body, then this force does work. Power in this case is equal to the scalar product of the force vector and the velocity vector with which the body moves:

Where F- force, v- speed, - angle between the vector of speed and force.

A special case of power during rotational motion:

M- torque, - angular velocity, - pi, n- rotation speed (revolutions per minute, rpm).

Electric power

Mechanical power. Power characterizes the speed at which work is done.

Power (N) is a physical quantity equal to the ratio of work A to the time period t during which this work was performed.

Power shows how much work is done per unit of time.

In the International System (SI), the unit of power is called the Watt (W) in honor of the English inventor James Watt (Watt), who built the first steam engine.

[N]= W = J/s

• 1 W = 1 J / 1s
• 1 Watt is equal to the power of a force that does 1 J of work in 1 second or when a load weighing 100 g is raised to a height of 1 m in 1 second.

James Watt himself (1736-1819) used another unit of power - horsepower (1 hp), which he introduced in order to compare the performance of a steam engine and a horse.

1hp = 735 W.

However, the power of one average horse is about 1/2 hp, although horses are different.

“Living engines” can briefly increase their power several times.

A horse can increase its power when running and jumping up to tenfold or more.

Making a jump to a height of 1 m, a horse weighing 500 kg develops a power equal to 5,000 W = 6.8 hp.

It is believed that the average power of a person during quiet walking is approximately 0.1 hp. i.e. 70-90W.

When running and jumping, a person can develop power many times greater.

It turns out that the most powerful source of mechanical energy is a firearm!

Using a cannon, you can throw a cannonball weighing 900 kg at a speed of 500 m/s, developing about 110,000,000 J of work in 0.01 seconds. This work is equivalent to lifting 75 tons of cargo to the top of the Cheops pyramid (height 150 m).

The power of the cannon shot will be 11,000,000,000 W = 15,000,000 hp.

The force of tension in a person's muscles is approximately equal to the force of gravity acting on him.

this formula is valid for uniform motion with constant speed and in the case of variable motion for average speed.

From these formulas it is clear that at constant engine power, the speed of movement is inversely proportional to the traction force and vice versa.

This is the basis for the operating principle of the gearbox (gearbox) of various vehicles.

Electric power. Electrical power is a physical quantity that characterizes the speed of transmission or conversion of electrical energy. When studying AC networks, in addition to instantaneous power corresponding to the general physical definition, the concepts active power, equal to the average value of instantaneous reactive power over the period, which corresponds to energy circulating without dissipation from source to consumer and back, and total power, calculated as the product effective values current and voltage without taking into account phase shift.

U is the work performed when moving one coulomb, and the current I is the number of coulombs passing in 1 second. Therefore, the product of current and voltage shows full time job, performed in 1 second, that is, electrical power or electric current power.

Analyzing the above formula, we can draw a very simple conclusion: since the electrical power “P” equally depends on the current “I” and on the voltage “U”, then, therefore, the same electrical power can be obtained either with a high current and a low current voltage, or, conversely, at high voltage and low current (This is used when transmitting electricity over long distances from power plants to places of consumption, through transformer conversion at step-up and step-down power substations).

Active electrical power (this is power that is irrevocably converted into other types of energy - thermal, light, mechanical, etc.) has its own unit of measurement - W (Watt). It is equal to 1 volt times 1 ampere. In everyday life and in production, it is more convenient to measure power in kW (kilowatts, 1 kW = 1000 W). Power plants already use larger units - mW (megawatts, 1 mW = 1000 kW = 1,000,000 W).

Reactive electrical power is a quantity that characterizes this type electrical load, which are created in devices (electrical equipment) by energy fluctuations (inductive and capacitive) of the electromagnetic field. For conventional alternating current, it is equal to the product of the operating current I and the voltage drop U by the sine of the phase angle between them:

Q = U*I*sin(angle).

Reactive power has its own unit of measurement called VAR (volt-ampere reactive). Denoted by the letter "Q".

Power density. Specific power is the ratio of engine power to its mass or other parameter.

Vehicle power density. In relation to cars, specific power is the maximum engine power divided by the entire mass of the car. The power of a piston engine divided by the displacement of the engine is called liter power. For example, the liter power of gasoline engines is 30...45 kW/l, and for diesel engines without turbocharging - 10...15 kW/l.

An increase in the specific power of the engine ultimately leads to a reduction in fuel consumption, since there is no need to transport a heavy engine. This is achieved through light alloys, improved design and boosting (increasing speed and compression ratio, using turbocharging, etc.). But this dependence is not always observed. In particular, heavier diesel engines can be more economical, as the efficiency of a modern turbocharged diesel reaches up to 50%

In the literature, using this term, the inverse value kg/hp is often given. or kg/kW.

Specific power of tanks. The power, reliability and other parameters of tank engines were constantly growing and improving. If on early models were actually content with automobile engines, then with the increase in the mass of tanks in the 1920s-1940s. Adapted aircraft engines, and later specially designed tank diesel (multi-fuel) engines, became widespread. To ensure acceptable driving performance of a tank, its specific power (the ratio of engine power to the combat weight of the tank) must be at least 18-20 hp. With. /T. Specific power of some modern tanks (see Appendix 10).

Active power. Active power is the average value of instantaneous alternating current power over a period:

Active power is a quantity that characterizes the process of converting electricity into some other type of energy. In other words, electrical power, as it were, shows the rate of electricity consumption. This is the power for which we pay money, which is counted by the meter.

Active power can be determined using the following formula:

The power characteristics of the load can be precisely specified by one single parameter (active power in W) only for the case direct current, since in a DC circuit there is only one type of resistance - active resistance.

The power characteristics of the load for the case of alternating current cannot be accurately specified by one single parameter, since there are two different types resistance - active and reactive. Therefore, only two parameters: active power and reactive power accurately characterize the load.

The operating principles of active and reactive resistance are completely different. Active resistance - irreversibly converts electrical energy into other types of energy (thermal, light, etc.) - examples: incandescent lamp, electric heater.

Reactance - alternately stores energy and then releases it back into the network - examples: capacitor, inductor.

Active power (dissipated through active resistance) is measured in watts, and reactive power (circulating through reactance) is measured in vars; Also, to characterize the load power, two more parameters are used: apparent power and power factor. All these 4 parameters:

Active power: designation P, unit: Watt.

Reactive power: designation Q, unit of measurement: VAR (Volt Ampere reactive).

Apparent power: designation S, unit: VA (Volt Ampere).

Power factor: designation k or cosФ, unit of measurement: dimensionless quantity.

These parameters are related by the following relations:

S*S=P*P+Q*Q, cosФ=k=P/S.

CosФ is also called power factor.

Therefore, in electrical engineering, any two of these parameters are specified to characterize power, since the rest can be found from these two.

It's the same with power supplies. Their power (load capacity) is characterized by one parameter for DC power supplies - active power (W), and two parameters for sources. AC power supply. Typically these two parameters are apparent power (VA) and active power (W).

Most office and household appliances are active (no or little reactance), so their power is indicated in Watts. In this case, when calculating the load, the value is used UPS power in Watts. If the load is computers with power supplies (PSUs) without input power factor correction (APFC), laser printer, refrigerator, air conditioner, electric motor (for example, a submersible pump or a motor as part of a machine), fluorescent ballast lamps, etc. - all outputs are used in the calculation. UPS data: kVA, kW, overload characteristics, etc.

Reactive power. Reactive power, methods and types (means) of reactive power compensation.

Reactive power is the part of the total power expended on electromagnetic processes in a load that has capacitive and inductive components. Doesn't perform useful work, causes additional heating of the conductors and requires the use of an energy source of increased power.

Reactive power refers to technical losses in electrical networks according to Order of the Ministry of Industry and Energy of the Russian Federation No. 267 dated October 4, 2005.

Under normal operating conditions, all consumers of electrical energy whose mode is accompanied by the constant occurrence of electromagnetic fields (electric motors, welding equipment, fluorescent lamps and much more) load the network with both active and reactive components of the total power consumption. This reactive component of power (hereinafter referred to as reactive power) is necessary for the operation of equipment containing significant inductances and at the same time can be considered as an unwanted additional load on the network.

With significant consumption of reactive power, the voltage in the network decreases. In power systems that are deficient in active power, the voltage level is usually lower than the nominal one. Insufficient active power to complete the balance is transferred to such systems from neighboring power systems that have excess generated power. Typically, power systems are deficient in active power and deficient in reactive power. However, it is more efficient not to transfer the missing reactive power from neighboring power systems, but to generate it in compensating devices installed in the given power system. Unlike active power, reactive power can be generated not only by generators, but also by compensating devices - capacitors, synchronous compensators or static reactive power sources, which can be installed at substations of the electrical network.

Reactive power compensation, currently, is an important factor in solving the issue of energy saving and reducing loads on the power grid. According to estimates of domestic and leading foreign experts, the share of energy resources, and in particular electricity, occupies a significant amount in the cost of production. This is a strong enough argument to seriously approach the analysis and audit of an enterprise’s energy consumption, the development of a methodology and the search for means to compensate for reactive power.

Reactive power compensation. Reactive power compensation means. The inductive reactive load created by electrical consumers can be counteracted with a capacitive load by connecting a precisely sized capacitor. This reduces the reactive power consumed from the network and is called power factor correction or reactive power compensation.

Advantages of using capacitor units as a means of reactive power compensation:

• · low specific losses of active power (the own losses of modern low-voltage cosine capacitors do not exceed 0.5 W per 1000 VAr);
• · no rotating parts;
• · simple installation and operation (no foundation required);
• · relatively low capital investments;
• · the ability to select any required compensation power;
• · Possibility of installation and connection at any point in the electrical network;
• · no noise during operation;
• · low operating costs.

Depending on the connection of the capacitor unit, the following types of compensation are possible:

• 1. Individual or constant compensation, in which inductive reactive power is compensated directly at the point of its occurrence, which leads to unloading of the supply wires (for individual consumers operating in continuous mode with constant or relatively high power - asynchronous motors, transformers, welding machines, discharge lamps, etc.).
• 2. Group compensation, in which, similar to individual compensation for several simultaneously operating inductive consumers, a common one is connected permanent capacitor(for electric motors located close to each other, groups of discharge lamps). Here the supply line is also unloaded, but only before distribution to individual consumers.
• 3. Centralized compensation, in which a certain number of capacitors are connected to the main or group distribution cabinet. Such compensation is usually used in large electrical systems with variable loads. Such a capacitor installation is controlled by an electronic regulator - a controller that constantly analyzes the consumption of reactive power from the network. Such regulators turn on or off capacitors, with the help of which the instantaneous reactive power of the total load is compensated and, thus, the total power consumed from the network is reduced.