Intermediate Relay is a circuit breaker operating in discrete circuits, acting as an auxiliary device. A more precise definition will be given below because it contains complex terms, unfamiliar to the unprepared reader.
Why does a person need an intermediate relay
; Intermediate relays are used when there is a need to amplify a signal; galvanic isolation of circuits is required. The thermostat outputs the unit voltage of a volt, the heating is powered by a standard industrial network of 230( 400) volts. The ideal solution is for the installed equipment to amplify the signal using a relay. Actual for large areas, the power of a standard thermostat is very limited, productive costs money.
A similar situation with the abundance of devices. Dozens, hundreds of convectors hung along the walls. Expensive thermostat is physically unable to control a lot of technology. Put an intermediate relay. Vosled include other types of power relays, a bunch controls the heaters on a single thermostat signal throughout the area of the object.
A trivial example explaining the purpose of intermediate relays. They are used where aiming is possible, coarsening the requirements for the input signal. A pulse relay with a trigger threshold of 1 mV is easily deceived by the 230-volt pickup that occurs in the network. Actual for lines of considerable length.
Intermediate relays will unload the main contactors. Otherwise, the requirements for extinguishing the arc will become strict, causing the disadvantage of production. Powerful sources of electricity, thermal power plants are being built near natural resources, they have blocks with a capacity of hundreds or thousands of MW.Operation of such facilities is inconceivable without relay protection circuits. The composition of the latter is the object of review review.
A relay in electrical engineering is a device that abruptly changes conductivity from infinity to zero and back under the influence of a certain factor. It is accepted to call the factor the affecting value, as a rule, current, voltage, power( including reactive), phase shift, circuit resistance, frequency, sequences of harmonics. The parameter is composed of several others, called input. The classification of the relay is taken as follows:
- At the point of connection:
- Primary - they make up the protected circuit directly.
- Secondary - connected via inductive, capacitive coupling.
- By the method of action:
- Straight lines - directly open the protected circuit.
- Indirect - act indirectly.
- To destination:
- Measuring - with adjustment in some limits of the level of operation.
- Logic - triggered on the same level, in discrete circuits.
- Combined - several measuring, united by logical connection.
- By the nature of the switch:
- Maximum - work on raising the parameter to a certain limit.
- Minimum - work on dropping a parameter to a certain limit.
According to this classification, we give the following definition:
Important. Intermediate relays are logical relays designed for discrete circuits, extending the functions of other relays located on the electrical grid section.
In addition to the intermediates, the family of logic also includes: indicating( indicating the operation of other relays present on the circuit section), a time relay( for counting intervals specified by the service personnel), slowed down( triggered with a delay).It is accepted to classify the protection relay on the principle of action:
- Electromagnetic work according to the law of action of a conductor with a current on the compass needle, opened by Oersted in the first half of the XIX century. The ferromagnetic core moves.
- Polarization differs from electromagnetic depending on the state of the contacts on the direction of current flow.
- Magnetoelectric exploit a similar principle, a magnet made from a special alloy is stationary, the frame with the winding rotates, driving the contact.
- Induction principle of operation resembles asynchronous motors, in a closed winding current is induced by a winding that feeds current.
- Semiconductor relays are the most common, built on the element base with pn-junctions, metal-semiconductor junctions.
Intermediate relays can be of any principle of operation. Previously, they were mostly electromagnetic. Often used for reproduction, signal amplification of other relays. For example, there are many executive devices, respectively, beyond the measure of control lines. Obviously, one relay with the task of switching will not cope. Then an intermediate is put, each exit controls one executive. The number of end relays increases significantly, together coping with the task.
Similarly, with a large current through the line can be divided into several branches, each is wound up on the executive relay. Manages armful intermediate. It serves for simultaneous operation, saving individual contactors from an excessively large arc, which always occurs if a load is placed on one stage. Uncontrolled ionization process can easily burn switching, protective equipment. Repair is required. An intermediate relay, ensuring the coordinated operation of others, protects the system from an accident.
Electromagnetic Intermediate Relays
RP series relays are manufactured according to the modifications for alternating, direct current. Structural differences are very specific, not everyone understands, they are not of great interest. Relay AC RP-25 is similar to the structure of RP-23.The anchor is located on the side, not on top. Alternating current creates a field that gives the magnet greater acceleration. Consequently, there is no need for the actuation of the relay to be helped by the own weight of the armature.
According to the design features, the product customization process is different. For each type of relay goes according to its scheme, described by the instruction. Find information in reference books. One relay is capable of operating at different voltages. It is provided by winding the corresponding number of turns on the working coil and by varying the diameter of the core. The voltage is higher - the more turns are taken, the thinner they are. It is necessary to reduce the flowing current, reduce the magnetic field strength. Will not affect the modernization of the anchor.
For masters in reference books, information about the type of winding wire will be interesting. For RP-25 single-core PEV-2 with double-layer vinifleksovoy insulation.
In one electromagnetic relay, the contact part is closed, the part is disconnected. It is permissible to use indirectly to control the start of asynchronous motors. Collaboration of a large amount of technological equipment is impossible without intermediate relays. Simple, effective tools will ensure system synchronization.
Characteristics of electromagnetic relays
The main characteristics are the type of current( constant / alternating), durability, and the conditions of operation. For RP-25 alternating voltage with a frequency of 50 Hz, an average effective value of 100, 127, 220 V. The relay is used to turn off the circuit when the voltage drops to 85% of the nominal. The thickness of the hysteresis loop is 3%.Durability is characterized by the number of cycles of response and return to its original state. The relay RP-25 weak point is called the metal contacts. The mechanism will last an order of magnitude longer.
An important parameter is the transition time from one contact position to another. Guided by the criterion, we estimate the security of the equipment from the effects of undesirable factors. For RP-25, the parameter does not exceed 0.06 s. As for modern discrete circuits, electronic keys are able to act much faster. Less is the recovery time to its former state.
Sometimes even there are special requirements for maximum performance. It is impractical to use the relay RP-23, it is more appropriate to put the RP-220.The design for reducing inertia, due to the action of induction eddy currents, contains laminated core. Steel is cut into thin plates glued together with insulating varnish. The cuts go across the magnetic field, resulting in the formation of eddy currents. The weight of the armature is reduced to the maximum to eliminate the inertia of movement; a non-magnetic plate is located between the poles, accelerating the separation of the contacts at the moment of switching. Response time reduced to 0.011 s.
Relay is able to function within certain limits. Temperature boundaries within which the mechanical part of the product is capable of performing functions. The factors involved include: resistance of the alloys to the vagaries of the weather, the prudence of the designers, protection of the hull by IP.In each case it is stipulated: when the significant factor changes in certain limits. For example, changing the frequency of the network by 3% leads to the departure of the operating point by about 10%.Such nuances should be taken into account, avoiding going beyond the permissible limits for the protected equipment.
Acceleration cost is reduced durability. The number of switching to failure is reduced, is about 1000 at RP-220( for the mechanism - 5000).To keep the anchor is spent energy field. In the characteristics of the relay you can read about the power involved. At RP-25 - 8 watts. It is clear, modern power transistors will spend less effort on work. Semiconductor technology systematically replaces other element bases.
Dimensions are important for electromagnetic relays. In fairness, I must say, for high voltages, mechanical structures are still relevant. Until the discovery of superconductivity at room temperature, high-voltage circuits cannot do without powerful contactors. The p-n junction is strongly heated by the passing current. And it will not always be possible to choose a radiator of such large dimensions in order to ensure the temperature regimes. Overheating of semiconductors is unacceptable, leading to irreversible changes.
In military affairs, on aircraft, spacecraft, railways, and motor vehicles, the factor of mechanical loads is important. Many relays are developed for linear accelerations, vibrations, shocks, and other destructive attributes of long and hard operation. At the same time, the admissible position of the product in space is specified. Clearly, it affects the speed, the value of the control parameter at which the trigger will occur.
Each contactor is characterized by a breaking capacity. The maximum current value at which the system is able to cycle. The limit is a destructive factor, it exceeds by two times the working values of the system. Sometimes the breaking capacity can be expressed in watts, which at a given voltage again leads to the current value in amperes.