Power measurement. In DC circuits, power is measured with an electro- or ferrodynamic wattmeter. Power can also be calculated by multiplying the current and voltage values measured with an ammeter and a voltmeter.
In single-phase current circuits, power measurement can be carried out with an electrodynamic, ferrodynamic or induction wattmeter. Wattmeter 4 (Fig. 336) has two coils: current 2, which is connected to the circuit in series, and voltage 3, which is connected to the circuit in parallel.
The wattmeter is a device that requires the correct polarity when switched on, therefore its generator clamps (the clamps to which the conductors coming from the source 1 side are connected) are denoted with asterisks.
To expand the measurement limits of wattmeters, their current coils are connected to the circuit using shunts or measuring current transformers, and voltage coils are connected through additional resistors or measuring voltage transformers.
Measurement electrical energy. Measurement method... To account for electrical energy received by consumers or given away by current sources, electricity meters are used. The electricity meter is similar in principle to a wattmeter. However, unlike wattmeters, instead of a spiral spring, which creates a counter-torque, the meters provide a device similar to an electromagnetic damper, which creates a braking force proportional to the speed of rotation of the moving system. Therefore, when the device is connected to an electrical circuit, the resulting torque will cause not a deflection of the moving system by a certain angle, but its rotation with a certain frequency.
The number of revolutions of the moving part of the device will be proportional to the product of power electric current for the time during which it acts, that is, the amount of electrical energy passing through the device. The number of revolutions of the counter is fixed by a counter mechanism. The gear ratio of this mechanism is chosen so that, according to the counter readings, it would be possible to count not the revolutions, but directly the electrical energy in kilowatt-hours.
The most widespread are ferrodynamic and induction meters; the former are used in DC circuits, the latter in circuits alternating current... Electricity meters include electrical circuits DC and AC as well as wattmeters.
Ferrodynamic counter(fig. 337) set on e. p. from. direct current. It has two coils: a fixed 4 and a movable 6. The fixed current coil 4 is divided into two parts, which cover the ferromagnetic core 5 (usually of permalloy). The latter makes it possible to create a strong magnetic field and significant torque in the device, which ensures the normal operation of the counter under conditions of shaking and vibrations. The use of permalloy helps to reduce the error of the counting mechanism 2 from the hysteresis of the magnetic system (it has a very narrow hysteresis loop).
To reduce the influence of external magnetic fields on the meter readings, the magnetic fluxes of the individual parts of the current coil are mutually opposite direction(astatic system). In this case, the external field, weakening the flux of one part, accordingly enhances the flux of the other part and has a generally small effect on the resulting torque generated by the device. The moving coil 6 of the counter (voltage coil) is located on an armature made in the form of a disk made of insulating material or in the form of an aluminum bowl. The coil consists of separate sections connected to the plates of the collector 7 (these connections are not shown in Fig. 337), along which brushes made of thin silver plates slide.
The ferrodynamic meter works principally as a DC motor, the armature winding of which is connected in parallel, and the excitation winding - in series with the electricity consumer. The armature rotates in an air gap between the poles of the core. The braking torque is created as a result of the interaction of the flow of a permanent magnet 1 with eddy currents arising in the aluminum disk 3 during its rotation.
To compensate for the influence of the friction torque and thereby reduce the errors of the device in ferrodynamic meters, a compensation coil is installed or a petal made of permalloy is placed in the magnetic field of a stationary (current) coil, which has a high magnetic permeability at low field strength. At light loads, this lobe amplifies the magnetic flux of the current coil, which leads to an increase in torque and friction compensation. With increasing load, the induction magnetic field the coil increases, the petal is saturated and its compensating effect ceases to increase.
When the meter is running on e. p. from. strong shocks and impacts are possible, in which the brushes can bounce off the collector plates. This will create sparks under the brushes. To prevent it, a capacitor C and a resistor R1 are included between the brushes. Compensation of the temperature error is carried out using a thermistor RT (semiconductor device, the resistance of which depends on temperature). It is connected together with an additional resistor R2 in parallel with the moving coil. To reduce the impact of shaking and vibrations on the operation of meters, they are installed on e. p. from. on rubber-metal shock absorbers.
Induction counter has two electromagnets (Fig. 338, a), between which an aluminum disk 7 is located. disk (as in a conventional induction measuring mechanism, see § 99).
In an induction meter, the torque M must be proportional to the power P = UIcos ?. For this, the coil 6 of one of the electromagnets (current) is connected in series with the load 5, and the coil 2 of the other (voltage coil) is connected in parallel with the load. In this case, the magnetic flux F1 will be proportional to the current I in the load circuit, and the flux F2 will be proportional to the voltage U applied to the load. To ensure the required phase angle? between the flows F1 and F2 (so that sin? = cos?), a magnetic shunt 3 is provided in the electromagnet of the voltage coil, through which part of the flow F2 is closed
in addition to the disk 7. The phase angle between the flows F1 and F2 is precisely regulated by changing the position of the metal shield 1 located in the path of the flow branching through the magnetic shunt 3.
The braking torque is generated in the same way as in a ferrodynamic meter. The frictional moment is compensated by creating a slight asymmetry in the magnetic circuit of one of the electromagnets using a steel screw.
To prevent the armature from rotating in the absence of a load under the action of the force created by the friction compensating device, a steel brake hook is attached to the meter axis. This hook is attracted to the brake magnet 4, thereby preventing the movable system from rotating without load.
When the meter is operating under load, the brake hook has practically no effect on its readings.
In order for the counter disk to rotate in the required direction, it is necessary to observe a certain order of connecting the wires to its terminals. The load clamps of the device, to which the wires coming from the consumer are connected, are denoted by the letters I (Fig. 338, b), the generator clamps, to which the wires from the current source or from the AC network are connected, by the letters D.
Quite often, it becomes necessary to measure the power consumed from the network, or generated into the network. This is necessary to account for the consumed or generated energy, as well as to ensure the normal operation of the power system (avoidance of overloads). Power can be measured in several ways - direct and indirect. For direct measurement, a wattmeter is used, and for indirect measurement, an ammeter and a voltmeter.
DC power measurement
Due to the absence of a reactive and active component in DC circuits, a wattmeter is used very rarely to measure power. As a rule, the amount of consumed or delivered energy is measured by an indirect method, with the help of measuring the current I in the circuit, and with the help of measuring the voltage U of the load. After that, applying a simple formula P = UI and get the power value.
To reduce due to influences internal resistance devices, devices can be connected according to various schemes, namely, with a relatively low load resistance R, the following switching scheme is used:
And with a large value of R, such a scheme:
Power measurement in single-phase AC circuits
The main difference between AC circuits and DC networks, perhaps, is that there are several capacities in alternating voltage - . The full is often measured by the same indirect method using an ammeter and a voltmeter and its value is S = UI.
The measurement of active P = UIcosφ and reactive Q = UIsinφ is performed by a direct method, using a wattmeter. To measure, the wattmeter is connected to the circuit according to the following scheme:
Where the current winding must be connected in series with the load R n, and, accordingly, the voltage winding is parallel to the load.
Measurement of reactive power in single-phase networks is not performed. Such experiments are often performed only in laboratories, where wattmeters are switched on according to special schemes.
Power measurement in three-phase AC circuits
As in single-phase networks, also in three-phase networks, the total energy of the network can be measured indirectly, that is, using a voltmeter and ammeter according to the schemes shown above. If the load of the three-phase circuit is symmetrical, then you can apply the following formula:
U l - line voltage, I - phase current.
If the phase load is not symmetrical, then the powers of each of the phases are summed up:
When measuring active energy in a four-wire circuit using three wattmeters as shown below:
The total energy consumed from the network will be the sum of the readings of the wattmeters:
The method of measuring with two wattmeters is no less widespread (applicable only for three-wire circuits):
The sum of their readings can be expressed by the following expression:
With symmetrical load, the same formula applies as for total energy:
Where φ is the shift between current and voltage (phase shift angle).
The reactive component is measured according to the same scheme (see figure c)) and in this case it will be equal to the difference between the algebraic indicators of the devices:
If the network is not symmetrical, then two or three wattmeters are used to measure the reactive component, which are connected according to different schemes.
Active and reactive power measurement process
Measure the active power of the alternating voltage circuit. They are connected in the same way as wattmeters. Reactive energy accounting for single-phase consumers is not kept in our country. Its accounting is carried out in three-phase circuits of large industrial enterprises that consume large amounts of electricity. Active energy meters are marked with CA, reactive CP. Electronic electricity meters are also widely used.
All users of electrical appliances, before purchasing a new device, want to know how to calculate the power consumption. This is necessary in order to plan the load on the home power grid or a specific power source. Also power - the most important indicator for a rough calculation of energy costs.
Power formula
The first thing you need to pay attention to is the passport data of the devices. The power consumption in watts can also be indicated on various plates attached to the devices.
Often the power indicator is indicated in volt-amperes (V * A). This usually happens when the energy consumed by the device has a reactive component. Then the total power of the electrical device is indicated, and it is measured in volt-amperes.
But this information is not always available. Then a simple formula and measuring instruments come to the rescue.
The main formula used to calculate the power consumption:
P = I * U, that is, you need to multiply voltage and current.
If there is no power in the passport data of the electrical appliance, but the current is indicated, then it can be recognized by this formula. Suppose the device takes a current of 1 A and operates from a 220 V. Then P = U * I = 1 * 220 = 220 W.
Power measurement with instruments
If this is an ordinary household appliance plugged into an outlet, then the supply voltage electrical network known - 220 V. When connected to other power sources, their voltage is taken.
The amperage can be measured:
- clamp meter;
- using a tester.
With the help of a clamp meter, measurements are easier, since they are carried out in a non-contact way on one wire suitable for the load.
There are two methods for measuring power with a multimeter:
- Turn it on in the current measurement mode in series with the electrical appliance and then calculate the power using the formula. This method is not always suitable, since it may not be possible to break the power supply circuit of the device to connect the multimeter;
- Connect a multimeter to the device in resistance measurement mode and then determine the current using the formula I = U / R, knowing the voltage. Then calculate the power.
Important! If the current strength of household electrical appliances is measured, then the tester is set to measure alternating current.
Power meter
The problem of accurately calculating the power consumption of a TV or computer display comes down to the build quality of the screen, energy-saving features and the patterns of equipment use by a particular user. Good way find out exactly the consumption of a specific electrical appliance - use a special wattmeter to measure the power of household devices.
This meter is an inexpensive but safe and effective means of determining power consumption. The wattmeter is plugged directly into an outlet, and then an electrical appliance is connected to its outlet.
Power measurement with an electric meter
In order to find out the power of the electrical appliance, using the meter, you need to disconnect all other devices from the network and look at the meter:
- there is electronic devices metering, which immediately show what the power consumption is. To do this, you just need to use the appropriate buttons, having found the active power;
- In other electricity meters, the blinking indicator allows you to count the number of pulses. For example, having counted them in 1 minute, you need to multiply the resulting figure by 60 (you get the number of pulses per hour). The imp / kW * h value (3200 or other figure) must be indicated on the device. Now the number of pulses per hour is divided by imp / kW * h, and the power of the electrical appliance is obtained;
- If an induction meter is installed, the power is calculated in several steps.
Calculation of power consumption using an induction meter:
- you need to find a number on the counter display indicating the number of revolutions of the disk made per 1 kWh;
- using a stopwatch, count how many rotations the disc will make in 15 seconds (you can take another time interval);
- calculate the power by the formula P = (3600 x N x 1000) / (15 x n), where n is the coefficient found on the counter, N is the number of disk rotations counted, 15 is the time interval in seconds, which can be represented by another digit.
Example. In 15 seconds, the disc made 5 rotations. The transmission ratio of the electric meter is 1200. Then the power will be equal to:
P = (3600 x 5 x 1000) / (15 x 1200) = 1000 W.
Obviously, it is almost impossible to measure the power of devices designed for low consumption using an induction meter. Measurement error is too large. If the disc rotates very slowly, it is impossible to correctly account for a fraction of the revolution. On an electronic meter, the result will be slightly more accurate.
There are calculators in the network for calculating power, where in the corresponding windows you need to enter the values of currents and voltages and get the calculated power value. Sometimes in the calculator field it is enough to indicate the name of the electrical appliance. Another option is to use tables that show the average values of power consumption for various electrical appliances.
Consumed energy
Energy consumption is closely related to power. It is calculated based on the power of the device multiplied by its operating time. This is exactly the indicator by which consumer electricity costs are judged. The exact value of the consumed power in the entire apartment or house for a certain period of time will be indicated by the meter data. In order to think over ways to reduce this consumption, measurements of the power of specific electrical appliances are used.
Energy saving methods:
- If possible, try not to use old models of refrigerators, televisions and other household electrical appliances, which are designed for significantly higher consumption;
- Replace incandescent bulbs with fluorescent ones, or even better - with LED ones. For comparison: an average incandescent lamp consumes 60 W, a fluorescent lamp - 15 W, and an LED lamp - only 8 W. When using 5 lamps different types within 3 hours a day, the daily consumption is obtained: incandescent lamps - 0.900 kWh, fluorescent lamps - 0.225 kWh, LED lamps - 0.120 kWh. Significant savings;
Important! Low power energy saving lamps does not mean poor lighting. Their brightness practically corresponds to more powerful analogs of incandescent lamps.
- Most TV and computer displays consume between 0.1 and 3 watts of electricity, even while in sleep mode. Therefore, it is important to disconnect them from the mains when the devices are not used for a long time.
Methods for calculating power using measurements with a tester will give approximate values due to insufficient consideration of the reactive power indicator in AC power grids. The most accurate is the measurement of power consumption with a wattmeter for domestic use.
Video
20 , 11:39
As each of us probably knows, human sensory abilities have a wide range. Some people see very well, others not very well. Some have excellent hearing, while others are deaf. The same applies to energy sensitivity.
All things are made of vibrational energy. Some people perfectly understand the energy that surrounds them, and they can easily tell when there is a lot or little. They can easily sense the "good" and "bad" vibrations.
Not all energy-sensitive people have all of the following characteristics all the time, but if you notice even a few of them, you are most likely quite sensitive to vibrational energy.
Strong human energy
1. You know how to deeply empathize with other people
Often a person with a strong energy can be seen where someone is offended or in upset feelings. Energy-sensitive people are often the first "recipients" of information about someone else's problem. At the same time, the victim always wants to hold the hand of such a person, hug him and cry to him.
Energy-sensitive people are very sensitive to the emotions of others (and sometimes physical pain), so they easily understand and empathize with those who are suffering.
2. Emotional roller coaster
The presence of a keen sense of vibrational energy often means that when a person feels "high" energies around him, he is on an emotional lift and vice versa. Have a few options at hand in case of an emotional downturn.
3. Dependency
Being sensitive to energy, such a person feels much more than other people. To escape the feeling of low vibrational energy, often such people can use alcohol or some other relaxing means to reduce the intensity of the negative energy sensations.
These people may be prone to other types of addictions, such as eating, gambling, or shopping.
Man and his energy
People with strong energy often understand very well the motives of people's behavior, in some cases they catch and feel right on the go when someone wants to say something, good or bad, it does not matter.
This is a very useful feature, since no one can use such a person for their own purposes.
5. People with strong energy are most often introverts.
Not all sensitive people are introverts, but many are. The process of feeling the emotions and feelings of other people is very exhausting mentally, therefore, energy-sensitive people often need rest and recovery after such "sessions".
They are often after prolonged social interactions may feel drained.
6. A person can see signs
People with strong energies are much more likely to understand the signs that the Universe sends them. They are more likely to find meaning in events and circumstances that most other people would consider coincidental.
Human energy
As we can see, strong energy is a double-edged sword. Focusing on vibrational energy allows for a deeper understanding of the universe, but on the other hand, it can also lead to some heightened stimulation and cause a lot of problems if left unattended.
If you think you have a strong energy and are energetically sensitive, there are a number of things you can do to properly use your gift and not drain so much.
First of all, the first thing that can help you to strengthen your vibration "receivers" or better feel the vibration of the environment is meditation or yoga for mental and physical lifting. It's also a good idea to clean up your home and workspace regularly.
Be mindful of the people you surround yourself with and stay away from toxic individuals, events and circumstances, especially when you are feeling overwhelmed. It is very important to work on self-acceptance and learn to love yourself and your gift.
If you came to this world as a person sensitive to the perception of energy, then some responsibilities automatically fall on you. However, the constant influx of energy from the environment can be overwhelming and painful.
But if you learn to manage your gift, amazing things will begin to happen. Reading energy from people and being able to empathize with others will be a huge benefit.
Energy-sensitive people have the power to push the world for positive change, and they also have the ability to become the world's greatest leaders, healers and teachers.
Now let's look at what types of energy for people exist today.
Energy of the human body
1) People are energy mirrors
If energy is directed at such a person, no matter positive or negative, it will always return to the one who directs it. That is, a person-mirror reflects energy.
These properties of energy inherent in certain people can and should be used, and with a high degree of efficiency, in order to protect oneself from negative energy, and first of all, from its purposeful flows.
People - mirrors perfectly feel the people around them, so if they have to reflect negative energy, being near its carrier, they immediately understand who is in front of them and try not to enter into any contacts with this person.
True, it should be added that the carrier of negative energy himself, at a subconscious level, tries not to meet with such "mirrors", because getting back his own negative will not affect him the best way, up to the development of various diseases or, at least, ailments.
And vice versa, for a carrier of positive energy, contact with people-mirrors is always pleasant, because the reflected positive returns to its owner, charging him with another portion of positive emotions.
As for the person-mirror himself, after he quickly realized that he has a carrier of positive energy in front of him, in the future he will only be glad to communicate with such a person and will maintain warm relations with him.
2) People are energy leeches
There are a lot of people with such energy, and each of us almost daily encounters and communicates with them. These can be work colleagues, relatives, or good acquaintances.
In essence, energy leeches are the same as energy vampires. That is, these are people who are experiencing problems with replenishing their energy reserves, and the easiest way for them to do this is to stick to another person, taking away energy from him, and with it life force.
Such people are persistent and aggressive, they emit negativity, and they have an inherent method of siphoning energy from others, which is quite simple. They create a conflict situation, start a quarrel or dispute, and sometimes they can even humiliate a person when other methods do not help.
After what happened, their well-being significantly improves, vigor comes to them, and they feel a surge of strength, because they have drunk enough energy from a person to feed themselves. A person - a donor who has been exposed to an energy leech, on the contrary, feels empty, depressed, and sometimes he may even have physical ailments.
In order for the leech to feel well, there must always be donors around it, and they themselves strive to keep such people in their field of vision, to whose energy field one can stick.
The impact of energy on humans
3) People are energy walls
A person - an energy wall - is a person with a very strong energy. Often you can hear about such people that they are impenetrable. All troubles, if any, appear on their way of life, fly away from them literally like from a concrete wall.
However, there is a negative side to interacting with such people. Negative energy directed at them naturally bounces off and does not always return to the one who directed it. If at the moment there are other people near the “wall”, then the negative can go to them.
4) People are energy sticklers
These people, from the very moment they meet them, begin to pour out a huge amount of negative energy on the interlocutor. Moreover, without waiting for the question, they immediately spread all the negative that they have accumulated.
Sticking, like a leech, does not take energy directly. Such a person also tries to settle in the living space of others and stay in it for a long time. Stickers are people with very bad and low energy, they constantly impose themselves, they always want to be around, they constantly call their "victims", look for meetings, ask for advice, etc.
But if later some difficulties arise in their life, then they are very fond of blaming those who were around for all the negative that is happening. Thus, adherents do not create conflict situations like leeches, but receive their portion of someone else's energy with the help of moral support, sympathy and advice.
That is, by imposing themselves on the people around them, as well as forcing them to communicate in indirect ways, the sticklers feed on the energy of these people. But it should be added that people communicating with them do not suffer, as from contact with energy vampires.
Energy man
5) People are energy absorbers
In this capacity, sinks can be both donors and recipients. These people are very sensitive, their energy-information exchange is always accelerated. They like to get into someone else's life, showing a pronounced desire to help and influencing someone else's energy.
There are two types of absorbers: the first absorb both positive and negative energy, they like to be offended for no reason, but they quickly forget the offense; the latter take a lot of negative energy, while giving a lot of positive, they are sensitive to the problems of people, positively influencing the biofields of others, but they themselves suffer.
6) People are energy samoyeds
These people are always fixated on their experiences. Samoyeds are withdrawn and consciously do not want to communicate with others. They do not know how to properly redistribute energy, so they accumulate a lot of negativity in themselves.
7) People are energy plants
People - plants give energy, that is, they are real energy donors. Excessive curiosity is inherent in this type of people. This feature brings them a lot of trouble, because it causes displeasure and anger of the people around them.
8) People - energy filters
A human filter has a strong energy, capable of passing a huge amount of positive and negative energy through itself. All information absorbed by such a person in a modified form returns to its source, but carries a different charge.
Everything negative remains on the filter, to which the positive is added. "Filters" are often successful natural-born diplomats, peacemakers, psychologists.
9) People are energy intermediaries
Energy exchange works great for intermediaries. They perfectly accept energy, but it is extremely difficult for them to resist the effects of negative energy. For example, someone shared negative information with the mediator and gave him negative energy. The intermediary cannot cope with it, so it passes the information on.
A similar situation occurs with positive information. This type of people is one of the most common.
An electrical product, in accordance with its purpose, consumes (generates) active energy consumed to perform useful work... With constant voltage, current and power factor, the amount of consumed (generated) energy is determined by the ratio Wp = UItcosφ = Pt
where P = UIcos φ is the active power of the product; t is the duration of work.
The unit of energy in SI is the joule (J). In practice, the non-systemic unit of measurement Watt x hour (W x h) is still used. The relationship between these units is as follows: 1 Wh = 3.6 kJ or 1 W s = 1 J.
In periodic current circuits, the amount of consumed or generated energy is measured by induction or electronic e electric meters.
Structurally, an induction meter is a microelectric motor, each rotor revolution of which corresponds to a certain amount of electrical energy. The ratio between the counter readings and the number of revolutions made by the engine is called the gear ratio and is indicated on the dashboard: 1 kW x h = N disk revolutions. According to the gear ratio, the counter constant C = 1 / N, kW x h / rev is determined; C = 1000-3600 / N W x s / rev.
In SI, the counter constant is expressed in joules, since the number of revolutions is a dimensionless quantity. Active energy meters are produced for both single-phase and three- and four-wire three-phase networks.
Fig. one . Scheme for connecting meters to a single-phase network: a - direct, b - a series of measuring transformers
A single-phase meter (Fig. 1, a) of electrical energy has two windings: current and voltage and can be connected to the network according to schemes similar to those for switching on single-phase wattmeters. To eliminate errors when turning on the meter, and, consequently, energy metering errors, it is recommended in all cases to use the meter switching circuit indicated on the cover covering its outputs.
It should be noted that when the direction of the current in one of the meter windings changes, the disk begins to rotate in the other direction. Therefore, the current winding of the device and the voltage winding should be switched on so that when the receiver consumes energy, the counter disk rotates in the direction indicated by the arrow.
The current output, indicated by the letter G, is always connected from the supply side, and the second output of the current circuit, indicated by the letter I. In addition, the output of the voltage winding, unipolar with the output Г of the current winding, is also connected from the supply side.
When turning on the meters through measuring current transformers, it is necessary to simultaneously take into account the polarity of the windings of the current transformers and voltage transformers (Fig. 1, b).
Meters are produced both for use with any current transformers and voltage transformers - universal, in symbol which the letter U is added, and for use with transformers, the nominal transformation ratios of which are indicated on their plate.
Example 1 . A universal meter with parameters Uп = 100 V and I = 5 A is used with a current transformer with a primary current of 400 A and a secondary current of 5 A, and a voltage transformer with a primary voltage of 3000 V and a secondary voltage of 100 V.
Determine the constant of the circuit, by which the meter readings must be multiplied to find the amount of energy consumed.
The circuit constant is found as the product of the current transformer transformation ratio by the voltage transformer transformation ratio: D = kti x ktu = (400 x 3000) / (5 x 100) = 2400.
Like wattmeters, meters can be used with different measuring transducers, but in this case it is necessary to recalculate the readings.
Example 2 . A meter designed for use with a current transformer having a transformation ratio kti1 = 400/5 and a voltage transformer with a transformation ratio ktu1 = 6000/100 is used in an energy metering circuit with other transformers having such transformation ratios: kti2 = 100/5 and ktu2 = 35000/100. Determine the constant of the circuit by which the meter readings must be multiplied.
The circuit constant D = (kti2 x ktu2) / (kti1 x ktu1) = (100 x 35,000) / (400 x 6000) = 35/24 = 1.4583.
Three-phase meters, designed to measure energy in three-wire networks, are structurally two combined single-phase meters (Figure 2, a, b). They have two current windings and two voltage windings. Usually such counters are called two-element counters.
All that has been said above about the need to observe the polarity of the windings of the device and the windings of the measuring transformers used with it in the switching circuits of single-phase meters, fully applies to switching circuits, three-phase meters.
To distinguish the elements from each other in three-phase meters, the outputs are additionally designated by numbers, simultaneously indicating the sequence of the phases of the supply network connected to the outputs. Thus, phase L1 (A) is connected to the terminals marked with numbers 1, 2, 3, phase L2 (B) is connected to terminals 4, 5, and phase L3 (C) is connected to terminals 7, 8, 9.
The definition of meter readings included with transformers is discussed in examples 1 and 2 and is fully applicable to three-phase meters. Note that the number 3, standing on the meter panel in front of the transformation ratio as a multiplier, speaks only of the need to use three transformers and, therefore, when determining permanent scheme not taken into account.
Example 3. Determine the circuit constant for a universal three-phase meter used with current and voltage transformers, 3 x 800 A / 5 and 3 x 15000 V / 100 (the form of the record specifically repeats the record on the dashboard).
Determine the constant of the circuit: D = kti x ktu = (800 x 1500) / (5-100) = 24000
Fig. 2. Schemes for connecting three-phase meters to a three-wire network: a - direct for measuring active (device P11) and reactive (device P1 2) energy, b - through current transformers for measuring active energy
It is known that when changing at different currents I can be obtained the same value of active power UIcosφ, and hence the active component of the current Ia = Icosφ.
An increase in power factor leads to a decrease in the current I for a given active power and therefore improves the utilization of transmission lines and other equipment. With a decrease in the power factor at constant active power, it is required to increase the current I consumed by the product, which leads to an increase in losses in the transmission line and other equipment.
Therefore, products with a low power factor consume additional energy Δ Wp from the source, which is necessary to cover losses corresponding to the increased current value. This additional energy is proportional to the reactive power of the product and, provided that the values of current, voltage and power factor are constant over time, it can be found by the relationship Δ Wp = kWq = kUIsinφ, where Wq = UIsinφ is reactive energy (conventional concept).
The proportionality between the reactive energy of an electrical product and the energy generated additionally at the station is maintained even when the voltage, current and power factor change over time. In practice, reactive energy is measured by an off-system unit (var x h and its derivatives - kvar x h, Mvar x h, etc.) using special meters, which are structurally completely similar to active energy meters and differ only in the winding switching circuits (see Fig. 2, a, device P12).
All calculations related to the determination of the reactive energy measured by the meters are similar to the above calculations for active energy meters.
It should be noted that the energy consumed in the voltage winding (see Fig. 1, 2) is not taken into account by the meter, and all costs are borne by the electricity producer, and the energy consumed by the current circuit of the device is taken into account by the meter, i.e. in this case, it is charged to the consumer.
In addition to energy, some other load characteristics can be determined using electricity meters. For example, according to the readings of the reactive and active energy meters, it is possible to determine the value of the weighted average load tgφ: tgφ = Wq / Wp, where e Wz is the amount of energy taken into account by the active energy meter for a given period of time, Wq is the same, but taken into account by the reactive energy meter for the same period of time. Knowing tgφ, cosφ is found from trigonometric tables.
If both meters have the same gear ratio and circuit constant D, the load tgφ can be found for of this moment... For this, for the same time interval t = (30 - 60) s, the number of revolutions nq of the reactive energy meter and the number of revolutions np of the active energy meter are counted simultaneously. Then tgφ = nq / np.
With a sufficiently constant load, it is possible to determine its active power from the readings of the active energy meter.
Example 4. An active energy meter with a gear ratio of 1 kW x h = 2500 rpm is included in the secondary winding of the transformer. The meter windings are connected via current transformers with kti = 100/5 and voltage transformers with ktu = 400/100. For 50 seconds, the disc made 15 revolutions. Determine the active power.
Constant circuit D = (400 x 100) / (5 x 100) = 80. Considering the gear ratio, the counter constant C = 3600 / N = 3600/2500 = 1.44 kW x s / rev. Taking into account the constant scheme C "= CD = 1.44 x 80 = 11 5.2 kW x s / rev.
So and m thus, n revolutions d of the claim correspond to the energy consumption Wp = C "n = 115.2 [15 = 1728 kW x s. Therefore, the load power P = Wp / t = 17.28 / 50 = 34.56 kW.