Network filter

A surge protector is a device designed to suppress interference at the edge of the supply network and equipment. Various kinds of perturbations easily distort the form of voltage, as a result it ceases to meet the requirements of the standard or carries a danger to consumers. This term is often used in relation to computer extenders, falling under the definition.

The voltage form of the

industrial network The strictest requirements are imposed on frequency. Deviation from the norm does not exceed 0.2 Hz. The relative value is less than 1%.Prescribed in GOST 54149 and the requirements for single voltage surges. Instability interferes with the proper operation of the equipment, can lead to the failure of a number of devices. A colorful example is the electronic unit of a washing machine, the cost of which is such that often the repair of equipment becomes impractical. Not surprisingly, the input filter is certainly worth a surge protector.

The classic type of filter

It is a mistake to think that the purpose of this small element is solely to protect equipment stuffing. The network filter also prevents the network from interfering with it. Not without reason, in the old manuals for electric tools, it was highly recommended that all digital equipment be turned off from the sockets during the period of work, even if the power filter is always included in any drill. Interference from the work of the collector engine is so great that there is a sense once again to be safe.

In the simplest case, flicker( flicker) of lighting devices leads to nervous system disorders. For digital electronics, harsh emissions are dangerous. The network filter is a device for suppressing all frequencies except 50 Hz. The only device unable to cope with a large range of trouble.

Frequency response of the

network filter Let's consider how the surge protector performs its own duties. To build the devices used reactive elements:

  1. Capacities( capacitors).
  2. Inductance.

The indicated components are characterized by frequency selectivity. Inductances become low-pass filters and capacitances become high. In the first case, slow voltage changes occur at the output, in the second case they are fast. It seems enough to put the choke at the entrance to the technique to get rid of trouble, but the situation is more complicated. The characteristic will be too flat, and the mass of harmful signals will pass through the circuit.

In practice, the surge protector is built on the basis of resonant circuits that selectively pass frequencies of 50 to 60 Hz and suppress those lying above and below the specified range. This allows you to protect equipment from unwanted exposure. Each resonant circuit includes inductance and capacitance simultaneously. The combination of properties gives a specific quality: at the resonant frequency, the system shows zero resistance. Therefore, the requirements of the standards are so stringent( deviation less than 1%).

The meaning of the amplitude-frequency characteristic is to demonstrate how much of the signal spectrum will be output. Professionals on schedule immediately say what happens in the end. The higher the curve rises above the horizontal axis, the better the corresponding frequencies travel to the output. The frequency response of the mains filter is an equilateral bell with a crown located in the region of 50 Hz.

Amplitude-Frequency Response explains the variety of network filter circuit diagrams that exist on the market. In each case, try the minimum cost to achieve the desired result. To explain the difficulties, let us see how, for example, a switching power supply works.

Highest harmonics in digital technology, their filtering

Personal computers use switching power supplies, as in most devices. The essence of the action of devices is reduced to rectifying the input current and further cutting it into bundles of high-frequency pulses. Such a signal detects a complex spectrum, part of it passes to the input of the device( plug).

By definition, a 50 Hz network frequency consists of a single harmonic. On the graph, this is simply a vertical line with an amplitude of 311 V. The value is obtained if the square root of two is multiplied by 220 V( the effective value of the voltage in the network).In fact, distortions lead to a spectrum of complex shape. A network filter by definition must pass an extremely useful signal. This is the only line on the 50 Hz graph.

Filter with European connectors

Such a network filter is impossible to build today, the characteristic of the device is represented with vertical slopes and an extremely narrow strip. It has already been said that in each case, choosing a schematic diagram, the designer tries to solve the problem with minimal expenses. In developed countries, it is known that with an abundance in the share of non-linear load consumers( over 15%), to which computer system blocks belong, a number of situations arise:

  1. Overheating and destruction of neutral conductors. In theory, according to Kirchhoff's law, the current in the serial is the same, in practice it is different. Reactive elements store power, and at a particular point in time they give it unevenly. Due to this, the power peaks in the neutral wires exceed phase by 1.5 times or more. As a result, isolation suffers, the vein is capable of burning. Readers have already guessed why computer network filters, commonly called rats, are required.
  2. Even the vanishing of the case of the system unit does not always eliminate the problems of the biting computer. Sometimes a person does not know that it is impossible to touch an iron helper and grounded objects at the same time. It is possible to get an electric shock. The power supply filter of the power supply unit is designed so that the harmonics direct the housing. Therefore, the equipment will certainly be plugged into a properly equipped outlet. Often in homes, the TN-C-S or TN-C electricity supply system. In this case, the passage of harmonics into the network will cause an unpleasant effect( but not so painful as with the absence of zeroing).
  3. It has been established that a switching power supply causes flattening of the peaks of the feeding sinusoid for other consumers. If you take computer equipment, it leads to a number of negative effects.

Surge protectors have an off-on button.

  1. First, by reducing the amplitude of the voltage, the heat release in active resistances increases. This directly follows from the Joule-Lenz law, which states that the effect depends on the square of the current. And the current, of course, increases when the voltage drops, the switching power supply ensures that the power( the product of current and voltage) remains the same.
  2. Secondly, resistance to voltage dips is reduced. The switching power supply continues to operate after the phase disappears. It is easier to see the example of speakers, which are still half a second to continue playing, being disconnected from the outlet. The effect is due to the energy stored in the input capacitors, depending on the voltage amplitude( flattened tops lower).

Other adverse effects are known. For example, harmonics of increased frequency negatively affect the operation of transformers due to surface currents and proximity effect. Tesla found that electrical oscillations above 700 Hz do not cause harm to humans. Explanation - the high-frequency current flows only over the surface, disrupting the transmission of the magnetic field in the transformer. The proximity effect is manifested in the occurrence of interference in the wiring due to the re-radiation of energy.

Everything described requires the use of network and intermediate filters. In electronics, between cascades include at least separation capacitors for DC isolation. For professionals, surge protectors are considered only an example in the complex means of dealing with harmonics. Due to the flatness of the amplitude-frequency characteristics of the individual spectral components freely pass, although weakened.

Using the

filter For example, the use of external network filters for computers( rats) is considered a de facto standard and is designed to protect not so much office equipment as wires and other consumers. Similar to say about the electric tool, washing machines. Collector engines are highly sparkling, surge protectors protect the network itself from exiting unnecessary interference.

Filter Design

They told about the household tool, it is known that, as a rule, there are no inductances there, and above it was said that filters are built on the basis of resonant circuits, where elements are required to be present. But the capacity here serves as a barrier plus a compensator. An engine of any type detects a pronounced inductive resistance due to windings. As a result, part of the power goes to the jet.

It is important to know that the capacitor compensates for such negative effects. At the same time it becomes part of the filter, the second component of which is the motor winding. In other techniques, a resonant circuit is present in a certain form. If you look at the schematic diagrams, it is easy to notice that proper grounding is required for proper operation: both the phase and the neutral conductor are protected in the imported technology.

If possible, use the NT-S system, which was not used in the USSR.Then the ground loop does not touch the neutral conductor. This ensures true protection of the power supply network from excesses. Misunderstanding, unwillingness to solve the problem correctly leads to negative effects.

The design of network filters

Surge filters of washing machines are the only ones where the element is placed in a separate unit. This is required to prepare voltages for the consumption of electronics, to protect external consumers from the performance of the collector engine. Take a closer look: accessories are not sold for refrigerators. The engine is asynchronous, not sparkling and does not cause trouble. However, it is not forbidden to buy an external filter and connect the equipment through it.

For washing machines, components are produced in an airtight case, where the minimum necessary information is indicated:

  • Product name, by code it is easy to break through the necessary spare part in the store.
  • The electrical circuit diagram helps to find an analogue, which increases the maintainability of equipment, gives the concept of where and what is connected( it is especially important when it is not the original part that is found).

Surge protector available for self assembly. They gave the concept of how difficult it is to assemble an element correctly, and how massive information is taken into account in the design process.

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