How to lower the voltage in a DC circuit. High or high voltage. How to lower the voltage in the network

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High and high voltage. Causes

How can a high or increased voltage appear in our electrical networks? voltage. As a rule, low-quality Electricity of the net or network failures. The disadvantages of networks include: outdated networks, low-quality network maintenance, a high percentage of depreciation of electrical equipment, inefficient planning of transmission lines and distribution stations, and an uncontrolled increase in the number of consumers. This results in hundreds of thousands of consumers receiving high or overvoltage. The voltage value in such networks can reach 260, 280, 300 and even 380 Volts.

One of the reasons for the increased, oddly enough, may be the reduced voltage of consumers located far from transformer substation. In this case, electricians often deliberately increase the output voltage of the electrical substation in order to achieve satisfactory current indicators for the last consumers in the transmission line. As a result, the voltage in the first line will be increased. For the same reason, one can observe increased tension in holiday villages. Here, the change in current parameters is associated with seasonality and frequency of current consumption. In summer, we observe an increase in electricity consumption. During this season, there are a lot of people in the dachas, they use a large amount of energy, and in winter the current consumption drops sharply. Consumption in summer cottages grows on weekends, and falls on weekdays. As a result, we have a picture of uneven energy consumption. In this case, if you set the output voltage at the substation (and they are usually not of sufficient power) to normal (220 Volts), then in the summer and on the output the voltage will drop sharply and will be reduced. Therefore, electricians initially set up the transformer for increased voltage. As a result, in winter and on working days, the voltage in the settlements is high or increased.

The second large group of reasons for the appearance of high voltage is phase imbalances when consumers are connected. It often happens that consumers are connected randomly, without a preliminary plan and project. Or in the course of project implementation or development of settlements there is a change in the value of consumption in different phases of the transmission line. This can lead to the fact that on one phase the voltage will be reduced, and on the other phase it will be increased.

The third group of causes of increased voltage in the network is accidents on power lines and internal lines. Two main reasons should be distinguished here - a zero break and the ingress of high voltage current into ordinary networks. The second case is a rarity, it happens in cities in a strong wind, hurricane. It happens that the power line of an electric transport (tram or trolley bus) falls into the lines of city networks during a break. In this case, both 300 and 400 volts can get into the network.
Now let's consider what happens when the "zero" disappears in the internal house networks. This case happens quite often. If two phases are used in one entrance of the house, then when zero disappears (for example, there is no contact at zero), the voltage value changes on different phases. In the phase where now the load in the apartments is less, the voltage will be overestimated, in the second phase it will be underestimated. Moreover, the voltage is distributed inversely with the load. So if in one phase the load at this moment is 10 times greater than in the other, then we can get 30 Volts (low voltage) in the first phase, and 300 Volts (high voltage) in the second phase. Which will lead to the combustion of electrical appliances, and possibly a fire.

What is dangerous high and high voltage

High voltage is dangerous for electrical appliances. A significant increase in voltage can lead to the combustion of devices, their overheating, additional wear. Electronic equipment and electromechanical devices are especially critical to high voltage.

Increased voltage can lead to a fire in the house, causing great damage.

If you are tired of constantly changing burnt out lamps, use one of the tips below. But in all cases, success is achieved by a significant reduction in stress.

In the daytime and especially at night, the voltage in the network often reaches 230-240V, which leads to accelerated burnout of the filaments of electric lamps. It is estimated that a voltage increase of only 4% compared to the nominal one (that is, from 220 to 228V) reduces the life of electric lamps by 40%, and with an increased "power" of 6%, this period is reduced by more than half.

At the same time, reducing the voltage on the lamps by only 8% (up to 200-202V) increases the "experience" of their work by 3.5 times, at 195V it increases by almost 5 times. Of course, with a decrease in voltage, the brightness of the glow also decreases, but in many cases, in particular in office premises and in public places, this circumstance is not so important.

How to reduce the voltage on electric lamps? There are two easy ways.

The first- turn on two lamps in series (Fig. 1). And what kind of lamp to take as an additional one? It can be the same as the main one. But then both lamps will shine weakly. It is best to select a lamp so that the power of the lamps differs by 1.5-2 times, for example, 40 and 75 W, 60 and 100 W, etc. Then a lamp of lower power will glow brightly enough, and a more powerful one will be weaker, acting as a kind of ballast that extinguishes excess voltage (Fig. 2.).

At first glance, there is no gain, because you have to use two lamps at once instead of one. But this is what the simplest calculation shows; the voltage drop across the lamps when connected in series is distributed inversely with their power. Therefore, at a mains voltage of 220V (let's take a pair of 40 and 75 W lamps), the voltage on a 40-watt lamp will be about 145V, and on its 75-watt "partner" - a little more than 75V.

Since the durability depends on the magnitude of the voltage, it is clear that it will be necessary to change mainly a lamp of lower power. And that, as practice shows, in the worst case, serves for at least a year. Under normal conditions, from 5 to 8 lamps have to be changed during the same time (meaning daily work for 12 hours). As you can see, the savings are quite tangible.

Another way-sequential inclusion of a lamp and a semiconductor diode. Due to its small dimensions, it can be installed in the switch cone between the terminal and one of the supply wires. With this option, a barely noticeable flicker of the lamps occurs (due to half-wave rectification alternating current), and the average voltage across them is about 155V.

Now about the choice of the type of diode. It must have a certain margin for permissible current and be designed for a voltage of at least 400V. Of the miniature diodes, the KD150 and KD209 series meet this requirement.

However, KD105 brand diodes should be used with lamps whose power does not exceed 40W, and KD209 diodes (with any letter index) should be used in conjunction with 75-watt lighting fixtures.

Of course, you can use more powerful diodes of other types, but then they will have to be installed outside the switch. Properly selected diode lasts almost unlimited time.

Now let's look at another question. What if the house has a general switch for the entire entrance? In this case, one high power diode is installed.

It is mounted on a metal corner, screwed to the wall next to the switch with screws, and covered with a casing with ventilation holes.
Recommended types of diodes: KD202M, N, R or S, KD203, D232-D234, D246-248 with any letter index.

When choosing the type of diode, remember that its maximum allowable operating current (indicated in the passport of the semiconductor device) must be 20-25% higher than the total current consumed simultaneously by all the lamps related to this switch. If the diode allows the current of all the bulbs (it is easy to calculate by dividing the total power of all the bulbs by the mains voltage of 220V) should not exceed 4A.

And the last thing: when connecting an additional lamp or diode, do not forget that you are dealing with high voltage posing a danger to your life. Therefore, be sure to de-energize the line, and only then get to work. All the best.

When it comes to reducing the voltage in the network, then finding the problem is more difficult, since it depends on the type of electricity consumer used. There are two main types of consumers: resistance and motor.

As for the consumer of the resistance type, then for them the voltage drop is directly proportional to the drop in the consumed current (s-n Ohm l \u003d U / R). For fuses, low current does not pose any danger. If we take a resistance that consumes 300 W (Fig. 55.2) at 240 V, then at a voltage of 24 V it will consume only 3 W.

As for the type of engine, it is first necessary to distinguish them by the action of a larger moment of resistance (Fig. 55.3). So, you can compare piston (larger moment of resistance? And drive motors (smaller moment of resistance?.

Regarding centrifugal fans, they are between these two categories. Mostly, their characteristics do not withstand a significant drop in supply voltage, and therefore they are classified as devices with a large moment of resistance.

Recall that the ability of the motor to drive the device (shaft torque) depends on the square of the supply voltage. That is, if it is designed to operate on a 220 V supply, and the voltage drops to 110 V, then the torque will decrease by 4 times (Fig. 55.4). If the moment of resistance is too high when the voltage drops, the motor will stop. In this case, the current consumed by the motor will be equal to the starting current, which it will consume during a forced stop. At this moment, only the built-in protection (thermal relay) can save it from severe overheating, which will quickly turn off the power.

When the drive torque is low, lowering the voltage will cause the rotation speed to decrease because the motor has less available power. This property is widely used in most multi-speed motors that rotate air conditioner fans (Fig. 55.5). When switching to BS (high speed), the resistance is short-circuited and the motor is powered from 220 V. Its rotation speed is nominal.

When switching to MC (low speed), the resistance is connected in series with the motor winding, due to which the voltage across it decreases. Accordingly, the torque on the shaft also decreases, so the fan starts to rotate at a reduced speed. The current consumption becomes smaller. This property is widely used in the manufacture of electronic speed controllers (based on thyristors), which are used to control the condensation pressure by changing the speed of rotation of fans in air condensers (Fig. 55.6).

These regulators, called current converters or gates, function like other limiting regulators, working on the principle of "cutting off" the frequency of the alternating current amplitude.

In the first position, the pressure is high and the speed controller completely skips the mains half cycles. At the motor terminals, the voltage (shaded area) corresponds to the mains supply, and it starts to rotate at maximum speed, while consuming the rated current.

In the second position, the condensing pressure begins to decrease. It enters the regulator, cutting off a part of each half-cycle entering the engine input. The voltage at the motor terminals decreases, along with the speed and current draw.

In the third position, the tension is too weak. Since the motor torque is less than the fan resistance torque, it stops and starts to heat up. Thus, the speed controllers are mainly adjusted to the limit permissible value minimum speed.

In addition, the “cut-off” method can be applied to single-phase motors when they are used for drives with low resistance torque. As for three-phase motors (used to drive machines with high resistance), it is recommended to use multi-speed motors, motors direct current or frequency converters.

AT Everyday life We often have to deal with voltage drops. It can be caused by a momentary shutdown or a sudden drop in current. In order to limit the voltage drop, it is necessary to correctly select the cross-section of the supply wires. But in some cases, a decrease in the voltage level is not due to a decrease in power in the supply wires.

For example, let's take a 24 V electromagnet coil that controls a small contactor (Fig. 55.7). When the electromagnet is triggered, it consumes a current equal to 3 A, and when held, it is 0.3 A (10 times less). In other words, the connected electromagnet draws a current equal to ten times the holding current. Although the turn-on time is short (20 ms), this factor can have an effect in large command circuits with a large number of contactors and relays.

In the presented diagram (Fig. 55.8), 20 contactors are installed - C1-C20. As soon as the current is turned off, they are all in standby mode, and when turned on, they work simultaneously. When activated, each contactor consumes 3 A, which means that a current of 3 × 20 = 60 A will flow through the secondary winding of the transformer. If the resistance of the secondary winding is 0.3 Ohm, then the voltage drop on it when the contactors are activated will be 0.3 × 60=18 V. Since the voltage of the contactors reaches only 6 V, they will not be able to work (Fig. 55.9).

In this case, the transformer, together with the wiring, will overheat greatly, and the contactors themselves will hum. And this will continue until the circuit breaker trips or the fuse blows.

If the resistance of the secondary winding of the transformer is 0.2 Ohm, then when the contactors are turned on, the voltage in it will be 0.2 × 60 = 12 V. In this case, the contactors will be powered from 12 V, instead of 24 V, and there is no chance that they will turn on. Their work will be similar to kA in the previous example, since the voltage in the network is abnormally high.

Difficulties with resistance secondary winding are explained by the significant open-circuit voltage at the output of the transformer, in contrast to the voltage under load. As the current draw increases, the output voltage decreases.

As an example, consider a 220/24 transformer (Fig. 55.10) with a power of 120 VA connected to a 220 V network. If the transformer produces a current of 5 A, then the output voltage will be 24 V (24 × 5 \u003d 120 VA). But when the current consumption drops to 1 A, the output voltage becomes large, for example, 27 V. This is provoked by the resistance of the secondary winding wire.

As soon as the current starts to decrease, the output voltage rises. And the reverse situation: as soon as the consumed current becomes more than 5 A, the output voltage decreases to 24 V, as a result of which the transformer overheats.

If the transformer is of low power, then certain difficulties may arise, so the selection of the power of the transformer should not be neglected.