How to reduce the voltage in a DC circuit. High or increased voltage. How to reduce network voltage

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High and increased voltage. Causes

How high or increased voltage levels may appear in our electrical networks voltage. As a rule, poor quality can lead to an increase in voltage Electricity of the net or network failures. Disadvantages of networks include: outdated networks, low-quality network maintenance, high percentage of depreciation of electrical equipment, ineffective planning of transmission lines and distribution stations, uncontrolled growth in the number of consumers. This results in hundreds of thousands of consumers receiving high or increased voltage. 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 readings for the last consumers in the transmission line. As a result, the first ones in the line will have increased voltage. For the same reason, one can observe increased tension in holiday villages. Here, changes in current parameters are associated with seasonality and frequency of current consumption. In the summer we see an increase in electricity consumption. During this season, there are many people at their dachas; they use a large amount of energy, and in winter, current consumption drops sharply. On weekends, consumption in summer cottages increases, and on weekdays it decreases. 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 weekends the voltage will drop sharply and will be reduced. Therefore, electricians initially set the transformer to higher voltage. As a result, in winter and on weekdays, tension in villages is high or increased.

The second large group of reasons for the appearance of high voltage is phase imbalances when connecting consumers. It often happens that connecting consumers occurs chaotically, without a preliminary plan and project. Or during the implementation of a project or development of settlements, the consumption value changes at different phases of the transmission line. This can lead to the voltage being low in one phase and high in the other phase.

The third group of causes of increased voltage in the network are accidents on power lines and internal lines. Here we should highlight two main reasons - a break in the zero and the entry of high voltage current into ordinary networks. The second case is rare; it happens in cities during strong winds or hurricanes. It happens that the power line of an electric transport (tram or trolleybus) ends up on a city network line when it breaks. In this case, both 300 and 400 Volts can enter the network.
Now let’s look at what happens when the “zero” disappears in internal home networks. This case happens quite often. If two phases are used in one entrance of a house, then when zero is lost (for example, there is no contact at zero), the voltage value changes in different phases. In the phase where the load in the apartments is now less, the voltage will be overestimated, in the second phase it will be underestimated. Moreover, the voltage is distributed inversely proportional to the load. So if on one phase the load at this very moment is 10 times greater than on 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 burning of electrical appliances and possibly a fire.

Why is high and increased voltage dangerous?

High voltage is dangerous for electrical appliances. A significant increase in voltage can lead to burnout of devices, overheating, and 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're tired of constantly changing burnt-out lamps, use one of the tips below. But in all cases, success is achieved through a significant reduction in tension.

During the day 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 an increase in voltage by only 4% compared to the nominal (that is, from 220 to 228V) reduces the service life of electric lamps by 40%, and with an increased “power” of 6%, this life is reduced by more than half.

At the same time, reducing the voltage on the lamps by only 8% (to 200-202V) increases the “experience” of their operation by 3.5 times; at 195V it increases 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 areas, this circumstance is not so important.

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

First- turn on two lamps in series (Figure 1). What kind of lamp should I 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 the lamp of lower power will glow quite brightly, and the more powerful one will glow weaker, acting as a kind of ballast that dampens excess voltage (Fig. 2.).

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

Since longevity depends on the voltage, it is clear that you will mainly have to change the lamp of lower power. And even that, as practice shows, in the worst case, lasts at least a year. Under normal conditions, during the same time it is necessary to change from 5 to 8 lamps (this means daily operation for 12 hours). As you can see, the savings are quite significant.

Another method - sequential connection of a lamp and a semiconductor diode. Due to its small size, 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 choosing the type of diode. It must have a certain allowable current reserve and be designed for a voltage of at least 400V. Of the miniature diodes, the KD150 and KD209 series meet this requirement.

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

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

Now let's look at one more question. What should you do if the house has a common switch for the entire entrance? In this case, install one high-power diode.

It is mounted on a metal corner, screwed with screws to the wall next to the switch, 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 permissible operating current (indicated in the passport of the semiconductor device) should be 20-25% higher than the total current consumed simultaneously by all lamps related to this switch. If the diode allows the current of all lamps (it is easy to calculate by dividing the total power of all lamps by the network voltage of 220V) it should not exceed 4A.

And lastly: 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 turn off the power to the line, and only then get to work. All the best.

If we are talking about 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 resistance type consumer, for them the voltage decrease is directly proportional to the drop in current consumption (Ohm value l = U / R). For fuses, low current does not pose any danger. If we take a resistor 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, we can compare piston (higher moment of resistance?) and drive engines (lower moment of resistance?.

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

Let us 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 power supply, and the voltage drops to 110 V, then the torque will decrease by 4 times (Fig. 55.4). If the resistance torque 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.

If the torque of the driven device is low, a decrease in voltage will lead to a decrease in rotation speed, since the motor has less available power. This property is widely used in most multi-speed motors that rotate air conditioning 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 MS (low speed), a resistance is connected in series with the motor winding, which causes the voltage across it to decrease. Accordingly, the torque on the shaft decreases, so the fan begins to rotate at a reduced speed. The current consumption becomes less. This property is widely used in the manufacture of electronic speed controllers (based on thyristors), which serve to regulate condensation pressure by changing the rotation speed of fans in air-cooled condensers (Fig. 55.6).

These regulators, called current converters or valves, function like other limiting regulators, working on the principle of “cutting” the amplitude frequency of alternating current.

In the first position, the pressure is high and the speed regulator completely skips half-cycles of the network. At the motor terminals, the voltage (shaded area) corresponds to the mains power, and it begins to rotate at maximum speed, while consuming the rated current.

In the second position, the condensation pressure begins to decrease. Enters into the regulator, cutting off part of each half-cycle supplied to the motor input. The voltage at the motor terminals decreases along with the speed and current consumption.

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

In addition, the shearing method can be used in 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.

IN Everyday life We often have to deal with voltage drops. It can be caused by a short-term shutdown or a sharp 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, the decrease in 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 of 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 hold-mode current. Although the on-time is short (20 ms), this factor can have an impact in large command circuits with many 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 fire simultaneously. When triggered, 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 across it when the contactors are triggered 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 along 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 operation will be similar to kA in the previous example, since the voltage in the network is abnormally high.

Difficulty 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 current consumption 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 = 120 VA). But when the current consumption decreases to 1 A, the output voltage becomes high, for example, 27 V. This is caused by the influence of the resistance of the secondary winding wire.

As soon as the current begins to decrease, the output voltage increases. And the opposite situation: as soon as the current consumption 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 small power, then certain difficulties may arise, so you should not neglect the selection of the transformer power.