To meet the production machinery and process requirements for the design of electrical control circuits
Electrical process design
For the manufacture of electrical control devices, the use of operation, maintenance needs for the production of construction design
Section I. Principles and contents of the design of the electrical control
A, the electrical control design Principles
1) to maximize the production of machinery and production processes to meet the requirements of the electrical control
2) in order to meet the requirements of the premise, so that the control system is simple, economical, reasonable, easy to operate, easy to maintain, safe and reliable
3) the selection of electrical components is reasonable, correct, so that the system can work properly
4) in order to adapt to the improvement of the process, the ability of the equipment should be left with a margin
4) to adapt to the improvement of the process, the equipment should be left with a margin of the capacity of the system. Capacity should be left with a margin
Two, the basic content of the electrical control design
1. Electrical schematic design content
1) the preparation of the electrical design task book
2) selection of electric power dragging program and control mode
3) to determine the type of motor, model, capacity, speed
4) design of the electrical control schematic diagram
5) design of the electrical control schematic diagram
5)Select electrical components and list
6)Preparation of design and calculation instructions
2. Electrical process design content
1)Design of the overall configuration of the electrical equipment, drawing the general assembly diagram and general wiring diagram
2)Drawing the components of the electrical components layout and installation and wiring diagrams, indicating the installation method, wiring
3)Preparation of maintenance instructions
4)Design of the electrical control schematic diagram
5)Selection of electrical components and list
6)Preparation of design and calculation instructions
2. 3) the preparation of the use of maintenance instructions
Section II of the determination of power-driven program and motor selection
One, the determination of power-driven program
1, the choice of the drag mode
2, the choice of speed control program
3, motor speed should be compatible with the characteristics of the load
Second, the selection of the drag motor
(2)
(2)
(2)(2) /p>
(a) the basic principles of motor selection
1) the mechanical characteristics of the motor should meet the requirements of the production machinery, and the characteristics of the load
2) motor capacity to be fully utilized
3) motor structure to meet the installation requirements of mechanical design, suitable for the working environment
4) to meet the requirements of the design, the priority of the use of Under the premise of meeting the design requirements, priority is given to the use of three-phase asynchronous motor
(2) according to the production of machinery speed requirements for the selection of motors
General ---- three-phase cage asynchronous motor, two-speed motor
Speed control, starting torque is large ---- three-phase cage asynchronous motor
High-speed ---- direct current motors, frequency AC motor
(C) the choice of motor structure form
According to the nature of the work, the installation mode, the working environment to choose
(D) the choice of rated motor voltage
(E) the choice of rated speed of the motor
(F) the choice of motor capacity
1, analytical calculations:
Additionally, the motor capacity of similar production machinery can be chosen through the long run In addition, it can also be used for long-term operation of similar production machinery motor capacity survey, and the main parameters of machinery, working conditions for analogies, and then determine the capacity of the motor.
Section III of the electrical control circuit design of a share of the requirements
One, the electrical control should maximize the production of machinery to meet the requirements of the machining process
Prior to the design, should be the production of mechanical performance, structural characteristics, movement, processing technology and machining have a full
Substantial understanding of the control program designed on this basis, consider the control mode, start, start, and the working conditions, then determine the capacity of the motor.
And on this basis, design the control program, consider the control mode, starting, braking, reverse and speed requirements,
Placement of the necessary interlocks and protections to ensure that to meet the requirements of the production of machining processes.
Second, the control circuit current, voltage requirements
Should minimize the control circuit current, voltage type, control voltage should be selected from the standard voltage level. Electrical control power
The common voltage levels shown in Table 10-2.
Three, the control circuit to strive for simple, economical
1. minimize the length of the connecting wires and the number of wires Design of control circuits, should take into account the installation of electrical components
Location, as far as possible to reduce the number of connecting wires, shorten the length of the connecting wires. Such as Figure 10-l.
2. Minimize the variety of electrical components, the number and specifications of the same purpose of the device as far as possible to use the same brand, model of the product, and the number of appliances reduced to a minimum.
3. Minimize the number of electrical components contacts. In the control circuit, minimize the contacts is to improve circuit operation
Reliability. For example, Figure 10-2a shows.
4. Minimize the number of energized electrical appliances, in order to save energy and prolong the life of electrical components, reduce failure. As shown in Figure 10-3a.
Four, to ensure the safety and reliability of the control circuit
1. correctly connected to the coil of the appliance in the AC control circuit, the same time the action of the two coils of the appliance can not be connected in series, the two coils of the electromagnetic coil need to be simultaneously suction when the coils should be connected in parallel, such as shown in Figure 10-4b.
In DC control circuits, two DC voltage coils with very different inductance values cannot be connected in parallel.
2 correct connection of the electrical components of the contact design, should be distributed in different locations in the circuit of the same electrical contacts to the power supply of the same phase, in order to avoid short-circuit faults caused by electrical contacts.
3 to prevent parasitic circuits in the control circuit action process. Accidentally connected circuit called parasitic circuit.
4. In the control circuit control contacts should be reasonably arranged.
5. In the design of control circuits should be considered in the relay contacts on and off capacity.
6, to avoid contact "competition", "risky" phenomenon
Competition: when the control circuit state changes, often accompanied by electrical components in the circuit contact state changes. As the electrical components always have a certain inherent action time, for a timing circuit, often do not occur in accordance with the timing of the action of the situation, the contacts to compete for the first suction, you will get a few different output states, a phenomenon known as the circuit of the "competition".
Adventure: for switching circuits, due to the release of the electrical components of the delay effect, there will be switching components do not require the logic function output, this phenomenon is called "adventure".
7. The use of electrical interlocking and mechanical interlocking double interlocking.
Fifth, with perfect protection
Electrical control circuits should have perfect protection links, commonly used leakage protection, short circuit, overload, overcurrent, over-voltage, undervoltage and zero-voltage, weak magnetism, interlocking and limit protection.
Sixth, to consider the operation, maintenance and commissioning of the convenience
Section IV of the electrical control circuit design methods and steps
One of the electrical control circuit design methods
Design of electrical control circuits, there are two methods, one is to analyze the design method, and the other is the logic design method.
Analytical design method (empirical design method): according to the requirements of the production process to select a number of mature typical basic links to achieve these basic requirements, and then gradually improve its function, and appropriate configuration interlocks and protection and other links, so that it is combined into a whole to become a complete circuit to meet the control requirements.
Logic design method: the use of logic algebra as a mathematical tool to design electrical control circuits.
In relay contactor control circuits, the logic variables that represent the state of the contacts are called input logic variables, and the logic variables that represent the controlled elements of the relay
contactor coils are called output logic variables. The interrelationship between the input and output logic variables is called a logic function relationship, and this interrelationship indicates the structure of the electrical control circuit. Therefore, according to the control requirements, the
these logic variables will be written out of the logic function relationship, and then use the logic function of the basic formulas and arithmetic laws of the logic function
formula for simplification, and then based on the simplified logic relationship to draw the corresponding circuit structure, and then finally further check
and optimization, in order to obtain a more perfect design.
Second, the basic steps of the analytical design method
The basic steps of the analytical design method of designing electrical control circuits are:
l) According to the requirements of the process requirements of the starting, braking, reversing and speed control and other requirements of the design of the main circuit.
2) According to the design of the main circuit, the design of the control circuit of the basic links, that is, to meet the design requirements of the starting, braking,
Reverse and speed control and other basic control links.
3) Determine the control parameters and design the special
links of the control circuit according to the matching and interlocking relationship of the motion requirements of each part.
4)Analyze the possible faults in the circuit and add the necessary protection links.
5) comprehensive review, double-check the electrical control circuit action is correct The key links can do the necessary experiments to further
improve and simplify the circuit a
Three, the analytical design method of design examples
The following beam lifting mechanism of the electrical control design as an example to illustrate the analytical design method of designing electrical control circuits and
Steps. Steps.
The gantry planer is equipped with a crossbeam lifting mechanism, the crossbeam should be clamped on the column when the workpiece is processed, when the height of the workpiece is different, the crossbeam should be loosened from the column first and then move up and down along the column, and then after moving into place, the crossbeam should be clamped on the column.
So, the lifting of the crossbeam is driven by the crossbeam lifting motor, and the relaxing and clamping of the crossbeam is completed by the clamping motor, transmission device and
clamping device.
(A) beam lifting mechanism process requirements:
(1) beam up, automatically in accordance with the first relaxation of the beam a beam up a clamping beam in the order of sequence.
(2) When the beam is descending, it automatically follows the sequence of relaxing the beam, descending the beam, raising the beam and clamping the beam.
(3) After the beam is clamped, the clamping motor stops rotating automatically.
(4) The lifting of the beam should be equipped with up and down travel limit protection, and the clamping motor should be equipped with clamping force protection.
(2) electrical control circuit design process
1. Main circuit design: beam lifting mechanism respectively by the beam lifting motor MI and beam clamping relaxation motor W
driven. The two motors are three-phase cage asynchronous motors, which are required to realize forward and reverse rotation. Therefore, the use of KM1I, KM2.
KM3, KM4 four contactors were used to control the forward and reverse M1 and M2, as shown in Figure 10-9.
2. Control circuit design of the basic link: As the beam lift for the adjustment of movement, so the M1 using point control, a
Point button can only control a movement, so the rise of the point of committing the button with the descending point of committing the button to control the lifting of the beam, but before the move to require the first release the beam, move in place to release the point of the button requires the beam clamped, that is to say, pointing button to control KMI-KM4, KM3, KM4, four contactors, respectively, to control M1 and M2 forward and reverse, as shown in Figure 10-9. Button to control KMI-KM4 four contactors, so the introduction of rising intermediate relay KA1 and falling intermediate relay KA2, and then by the intermediate relay to control the four contactors. So the design of the beam lifting one of the electrical control circuit sketch, as shown in Figure 10-9.
3. Design of the control circuit of the special links
1) beam up, must make the clamping motor MZ first work, the beam will be relaxed, send a signal to stop the MZ
work, at the same time to make the lifting motor MI work, driven by the beam up. Press the rising button, the intermediate relay KAI coil is energized and absorbed, and its normally open contact is closed, so that the contactor KM4 is energized and absorbed, MZ reversed to start the rotation, the beam began to relax; the degree of relaxation of the beam is controlled by the travel switch, when the beam is relaxed to a certain extent, the bumpers press down on your land normally closed contact is disconnected to control the contactor KM4 coil of de-energized, normally open contact is closed to control contactor KMI coil is energized, the contactor KMI coil of energized, the contactor KMI coil of energized, and the contactor KM4 coil of energized, the contactor KMI of energized, and the contactor KMI of energized. KMI coil is energized, the main contact of KMI is closed to make MI positively rotate, and the beam starts to make upward movement.
2)When the lifting motor drags the crossbeam up to the required position, release the lifting push button, the intermediate relay KAI
contactor KMI coil will be de-energized and released, and the contactor KM3 coil will be energized and absorbed, so that the lifting motor will stop working, and at the same time
the clamping motor will start to rotate positively, so that the crossbeam will be clamped. In the process of clamping. Travel switch SQI reset, so KM3 should be added
self-locking contacts, when the clamping to a certain extent, a signal to cut off the power supply of the clamping motor. Here the use of overcurrent relay control
control the degree of clamping, that is, the overcurrent relay KA3 coil in series in the main circuit of the clamping motor in any phase. When the beam clamping
tight, equivalent to motor work in the blocking state, the motor stator current increases, the overcurrent relay action current
set at two times the rated current or so; when the beam clamping current relay action, its normally closed contacts will contactor KM3 coil
circuit cut off.
3)The descent of the beam is still controlled in the way of first relaxing and then descending, but after the descent, there should be a short period of time to return to the movement, and the return movement can be controlled by the time relay with power failure delay type. The coil of time relay KT is controlled by the falling contactor KMZ normally open contact, and its power failure delay open contact is connected in series with the clamping contactor KM3 normally open contact and connected to the two ends of the intermediate relay KAI normally open contact of the rising circuit. In this way, when the beam is descending, the coil of time relay KT will be energized, and the normally open contact of the time-delayed disconnecting relay will be closed immediately, so as to prepare for the work of the ascending circuit. When the beam descends to the desired position, release the descending push button Tian. KMZ coil will be discharged, the time relay KT coil will be discharged, and the contactor will be clamped.
3. Design of the special aspects of the control circuit
1) When the beam rises, you must make the clamping motor MZ first work, the beam will be relaxed, send a signal to stop MZ
IW, at the same time to make the lifting motor MI work, drive the beam up. Pressing the rising button, the intermediate relay
KAI coil is energized, and its normally open contact is closed, so that the contactor KM4 is energized, and MZ reverses to start the rotation, and the crossbeam starts to relax; the degree of relaxation of the crossbeam is controlled by the travel switch, when the crossbeam relaxes to a certain extent, the bumpers are pressed down to the SQI,
using the normally closed contact of KM4 to control the breakage of the contactor KM4 coil. Contactor KM4 coil is de-energized, normally open contact is closed to control the contactor KMI coil
energized, the main contact of KMI is closed to make MI rotate positively, and the crossbeam starts to make upward movement.
2)When the lifting motor drags the crossbeam up to the required position, release the lifting button, the intermediate relay KAI
contactor KMI coil will be discharged and contactor KM3 coil will be energized and absorbed, which stops the lifting motor, and at the same time
makes the clamping motor start to rotate positively, so that the crossbeam is clamped. In the process of clamping, the travel switch ground reset, so KM should be added
self-locking contacts, when the clamping to a certain extent, a signal to cut off the power supply of the clamping motor. Here the use of overcurrent relay control
control the degree of clamping, that is, the overcurrent relay KA3 coil in series in the main circuit of the clamping motor in any phase. When the beam is clamped
tight, equivalent to motor work in the blocking state, the motor stator current increases, the overcurrent relay action current
set at about twice the rated current; when the beam is clamped after the action of the current relay, the normally closed contacts will contactor KM3 coil
circuit cut off. KM3 coil energized to absorb, the beam begins to clamp. At this time, the rising contactor KMI coil through the closed time disconnect KT normally open contacts and KM3 normally open contacts and energized suction, the beam began to rise, after a period of time delay, the delay breaks the normally open contacts KT disconnect, KMI coil power-off release, the end of the rising movement, and the beam continues to be clamped to a certain extent, the overcurrent relay action, the clamping movement stops. At this time, the beam lifting electrical control circuit design sketch shown in Figure 10-10
.
4. Design of interlocking protection links
The beam rising limit protection is realized by the travel switch SQZ; falling limit protection is realized by the travel switch SQ3; up
Lifting and lowering interlock, clamping and relaxing interlock are realized by the intermediate relay KAI and the KAZ normally closed contacts; lifting
Short-circuit protection for the motor is realized by the fuse FUI; clamping and loosening interlock is realized by the intermediate relay KAI and KAZ normally closed contacts; lifting
Short-circuit protection for the motor is realized by the fuser FUI; the clamping motor is protected against short-circuiting by the intermediate relay FUI. The short-circuit protection of the lifting and lowering motor is realized by the fuse FUI; the short-circuit protection of the clamping motor is realized by the fuse FUZ; the short-circuit protection of the control circuit
is realized by the fuse F[J3.
Combined with the above protection, the beam lifting electrical control circuit is relatively complete, thus obtaining the complete
Beam lifting mechanism control circuit shown in Figure 10-11.
Section V. Selection of commonly used control appliances
One, the choice of contactors
Generally the following steps:
1. Selection of the type of contactor: according to the nature of the load controlled by the contactor to the corresponding choice of DC contactor or AC contactor; general occasions to choose the electromagnetic contactor for the frequent operation of AC loads with the occasions, you can use AC contactor with DC magnetic coil.
2. Contactor use category selection: according to the contactor to control the work of the load task to select the corresponding use category contactor. If the load is a general task is selected AC-3 use category; load for heavy duty should be selected AC-4 category, if the load is a general task and heavy duty mixed, according to the actual situation of the choice of AC-3 or AC-4 contactor, such as the choice of AC-3 category, should be downgraded to use.
3. Determination of the rated voltage of the contactor: The rated voltage of the main contacts of the contactor should be determined according to the rated voltage of the load circuit controlled by the main contacts.
4. Selection of contactor rated current Generally, the rated current of the main contact of the contactor should be greater than or equal to the rated current of the load or motor, the formula is
In which I. - the rated current of the main contact of the contactor (A);
H - the empirical coefficient, generally take the main contact of the load circuit. - empirical coefficient, generally take l ~ 1.4;
P.- rated power of the controlled motor (kw);
U.- rated line voltage of the controlled motor (V).
When the contactor is used for frequent starting, braking or reversing of the motor, the rated current can be reduced by one level to choose.
5. Determination of the rated voltage of the contactor coil: The rated voltage of the contactor coil should be equal to the supply voltage of the control circuit. To ensure safety, the general contactor coil selection of 110V, 127V, and by the control transformer power supply. But if the control circuit is relatively simple, the number of contactors used less, in order to save the control transformer, can choose 380V, 220V voltage.
6. The number of contacts: in the three-phase AC system is generally used in three-pole contactor, that is, three pairs of normally open main contacts, when the need to control the winning line at the same time, the use of four-pole AC contactor. In single-phase AC and DC systems, two-pole or three-pole parallel contactors are commonly used. AC contactors usually have three pairs of normally open main contacts and four to six pairs of auxiliary contacts, DC contactors usually have two pairs of normally open main contacts and four pairs of auxiliary contacts.
7. contactor rated frequency of operation 交,直流接触器额定操作频率一般有600次/h,1200次/h等几种，一般来说，额定电流越大，则操作频率越低，可根据实际需要选择。
Two, electromagnetic relay selection
Selected according to the functional characteristics of the relay, applicability, use of the environment, operating system, rated operating voltage and rated operating current.
1. Electromagnetic voltage relay selection
Based on the role in the control circuit, the voltage relay over-voltage relay and under-voltage relay two types.
Table 10-3 lists the types and uses of electromagnetic relays.
AC overvoltage relay selection of the main parameters are the rated voltage and operating voltage, the operating voltage according to the rated voltage of the system 1.l-1.2 times the adjustment.
AC undervoltage relay commonly used general AC electromagnetic voltage relay, its selection as long as the general requirements can be met, the release voltage value of no special requirements. DC undervoltage relay suction voltage according to its rated voltage of 0.3-0.5 times, release voltage according to its rated voltage of 0.07-0.2 times.
2. Electromagnetic current relay selection
Based on the load protection required, divided into two types of overcurrent relay and undercurrent relay.
Over-current relays: AC over-current relays, DC over-current relays.
Undercurrent relay: only DC undercurrent relay, used for DC motors and electromagnetic chuck weak magnetic protection.
The main parameters of the overcurrent relay is the rated current and action current, its rated current should be greater than or equal to the rated current of the motor to be protected; action current should be based on the motor work according to the starting current of 1.back to a 1.3 times. General wire-wound rotor asynchronous motor starting current of 2.5 times the rated current, cage asynchronous motor starting current of 4-7 times the rated current. DC overcurrent relay operating current to DC motor rated current 1.1-3.0 times the setting.
Undercurrent relay selection of the main parameters are rated current and release current, its rated current should be greater than or equal to the rated excitation current of the DC motor and electromagnetic suction cups; release current should be lower than the excitation circuit normal operating range of the smallest possible excitation current, the general release current according to the smallest excitation current of 0.85 times the calibration.
3. Electromagnetic intermediate relay selection
Should make the coil of the current type and voltage level with the control circuit, at the same time, the number of contacts, type and capacity should meet the requirements of the control circuit.
Three, the choice of thermal relay
The thermal relay is mainly used for motor overload protection, so it should be based on the form of motor, the working environment, the starting situation, load conditions, operating system and motor overload capacity and other comprehensive consideration.
1. Selection of the structure of the thermal relay
For star-connected motors, the use of three-phase thermal relay without phase break protection can reflect the overload of a phase after the break, the motor can play a protective role in the operation of the phase break.
For delta connection motor, should use three-phase structure thermal relay with phase break protection.
2. Selection of the rated current of the thermal relay
In principle, according to the rated current of the motor to be protected to select the thermal relay. For long-term normal operation of the motor, thermal relay in the thermal element of the rated current value for the motor rated current 0.95-1.05 times; for the overload capacity of the motor is poor, thermal relay thermal element rated current value for the motor rated current 0.6-0.8 times.
For infrequent starting of the motor, should ensure that the thermal relay in the motor starting process does not produce false operation, if the motor starting current is not more than 6 times the rated current, and the starting time is not more than 6S, can be based on the motor's rated current to select the thermal relay.
For repeated short-time operation of the motor, first of all, to determine the permissible operating frequency of the thermal relay, and then according to the motor starting time, starting current and the duration of energization to select.
Four, the selection of time relays
1) the type of current and voltage level: electromagnetic damping and air-damped time relays, the coil of the type of current and voltage level should be the same as the control circuit; motor or transistorized time relay, the power supply of the type of current and voltage level should be the same as the control circuit.
2) delay mode: according to the requirements of the control circuit to choose the delay mode, that is, power-on delay type and power-off delay type.
3) contact form and number: according to the requirements of the control circuit to select the contact form (delayed closure or delayed disconnection type) and the number of contacts.
4) delay accuracy: electromagnetic damping time relay for delay accuracy requirements of the occasion is not high, motor or transistor time relay for delay accuracy requirements of the occasion is high.
5) delay time: should meet the requirements of the electrical control circuit.
6) operating frequency: the operating frequency of the time relay should not be too high, otherwise it will affect its service life, and even lead to delayed action out of tune.
Five, the choice of fuse
1. General fuse selection: according to the fuse type, rated voltage, rated current and rated current of the fuse to choose.
(1) fuse type: fuse type should be based on the circuit requirements, the use of occasions and installation conditions to choose, its protective characteristics should be protected by the object of the overload capacity to match. For the smaller capacity of lighting and motor, generally consider their overload protection, can choose to melt the coefficient of melting small fuse, for the larger capacity of lighting and motor, in addition to overload protection, should also be considered in short-circuit short-circuit current breaking capacity, if the short-circuit current is small, can choose to use low breaking capacity of the fuse, if the short-circuit current is large, can choose to use a high breaking capacity of the RLI series fuse, if the short-circuit current is quite large, can choose to use the RLI series of fuses, if the short-circuit current is large, can choose to use the RLI series of fuses, if the short-circuit current is large, the short-circuit current is large, can choose to use the RLI series of fuses, if the short-circuit current is large. If the short-circuit current is quite large, you can use the current-limiting role of the Rh and RT12 series of fuses.
(2) fuse rated voltage and rated current: fuse rated voltage should be greater than or equal to the line voltage, rated current should be greater than or equal to the rated current of the installed fuse.
(3) fuse rated current
1) for lighting lines or electric heating equipment and other loads without inrush current, should be selected for the rated current of the fuse is equal to or slightly
greater than the rated current of the load, that is, the IRN ≥ IN
in which the IRN - the fuse IRN - rated current of the melt (A);
IN - rated current of the load (A).
2)For a single motor working for a long period of time, it should be considered that the melt should not be blown when the motor starts, i.e.
IRN≥(1.5~2.5)IN
The coefficient of light load is taken as 1.5, and the coefficient of heavy load is taken as 2.5.
3)For a single motor with frequent starting, the melt should not be blown when the motor starts frequently, i.e.
IRN≥(1.5~2.5)IN
The melt should not be blown if it is blown frequently, i.e.
IRN≥(1.5~2.5)IN
The fuse should not be blown when it is blown frequently. IRN ≥ (3 ~ 3.5)IN
4) for more than one motor for a long time **** with a fuse, the rated current of the fuse is
IRN ≥ (1.5 ~ 2.5)INMmax + ∑ INM
In which INMmax - the largest capacity of the motor's INMmax - the maximum capacity of the motor rated current (A);
∑INM - in addition to the maximum capacity of the motor, the rest of the motor rated current sum (A).
(4) for the distribution system fuse: in the distribution system multi-stage fuse protection, in order to prevent over-stage fuse, so that the upper and lower levels of the fuse has a good match, the choice of fuse should be made on the first level (trunk) fuse rated current than the next level (branch) of the rated current of the fuse is greater than the level of the fuse 1-2 level difference.
2. Fast fuse selection
(l) the rated voltage of the fast fuse: fast fuse rated voltage should be greater than the supply voltage, and less than the reverse peak voltage of the thyristor U., because of the instantaneous breaking current fast fuse, the highest arc voltage up to the supply voltage of 1.5-2 times. Therefore, the rectifier diode or thyristor reverse peak voltage must be greater than this voltage value to work safely. That is
UF ≥ KI URE
UF - a silicon rectifier or thyristor reverse peak voltage (V);
URE - fast fuse rated voltage (V);
KI. -safety factor, generally take 1,5-2.
(2) the rated current of the fast fuse: the rated current of the fast fuse is expressed in rms value, while the rectifier M tube and thyristor rated current is expressed in average value. When the fast fuse connected to the AC side, the rated current of the fuse is
IRN ≥ KI IZmax
where IZmax - the maximum possible rectifier current (A);
KI - with the Rectifier circuit form and conductivity of the coefficient, if the protection of rectifier M tube, KI according to Table 10-4
Take the value, if the protection of thyristors, KI according to Table 10-5 take the value.
When the fast fuse into the rectifier bridge arm, the fuse rated current is
IRN ≥ 1.5IGN
Where IGN - silicon rectifier element or thyristor rated current (A).
Six, the choice of switching appliances
(a) the choice of knife switch
Knife switch is mainly based on the use of the occasion, the type of power supply, the voltage level, the load capacity and the number of poles to choose.
(1) according to the role of the knife switch in the line and the installation location to choose its structure. If used to isolate the power supply, the choice of products without arc extinguishing cover; if used to break the load, should be used with arc extinguishing cover, and use the lever to operate the product.
(2) according to the line voltage and current to choose. The rated voltage of the knife switch should be greater than or equal to the rated voltage of the line; the rated current of the knife switch should be greater than the rated current of the load, when the load is an asynchronous motor, the rated current should be taken for the rated current of the motor 1.5 times more.
(3) The number of poles of the knife switch should be the same as the number of poles of the circuit.
(2)Selection of combination switch
The combination switch is mainly selected according to the type of power supply, voltage level, required number of contacts and motor capacity. The following principles should be mastered when selecting:
(1) The on-off capability of the combination switch is not very high, so it cannot be used to break the fault current. The combination switch used to control the reversible operation of the motor must be allowed to turn on in the opposite direction only after the motor has completely stopped rotating.
(2)There are many kinds of wiring of the combination switch, and the corresponding products should be selected correctly according to the needs.
(3)The operation frequency of the combination switch should not be too high, generally should not be more than 300 times/h, the power factor of the controlled load should not be lower than the specified value, otherwise the combination switch should be used to reduce the capacity.
(4)The combination switch itself does not have overload, short-circuit and under-voltage protection, if you need these protections, you must set up other protection appliances.
(3)Selection of low-voltage circuit breakers
Low-voltage circuit breakers are mainly selected according to the requirements of the protection characteristics, breaking capacity, type and level of grid voltage, load current, operating frequency and other aspects.
(1) rated voltage and rated current: the rated voltage and rated current of the low-voltage circuit breaker should be greater than or equal to the rated voltage and rated current of the line.
(2)Thermal cutoff: the thermal cutoff should be set at the same current as the rated current of the motor or load to be controlled.
(3) overcurrent detector: overcurrent detector instantaneous action setting current is determined by the following formula
IZ ≥ KIS
IZ - instantaneous action setting current (A);
Is - peak current in the line. -The peak current in the line. If the load is a motor, Is is the starting current (A);
K is the safety coefficient to take into account the setting error and the permissible variation of the starting current. When the action time is greater than 20ms, take
K=1.35; when the action time is less than 20ms, take K=1.7.
(4) undervoltage detector: undervoltage detector rated voltage should be equal to the rated voltage of the line.
(4)Power switch interlocking mechanism
Power switch interlocking mechanism and the corresponding circuit breaker and combination switch supporting the use of the power supply, disconnect the power supply and the cabinet
Door switch interlocking to achieve the effect that after cutting off the power supply can not open the door, the door will be closed before the power supply to realize the effect of security
Full protection.
Seven, the choice of control transformer
Control transformer used to reduce the voltage of the control circuit or auxiliary circuit to ensure the safety and reliability of the control circuit. Control transformer is mainly based on the primary and secondary voltage levels and the required transformer capacity to choose.
(1) control transformer primary and secondary voltage should be in line with the AC power supply voltage, control circuit voltage and auxiliary circuit voltage.
(2) control transformer capacity is calculated according to the following two cases, according to the calculated capacity of the larger control transformer capacity.
l)Transformer long-term operation, the maximum working load transformer capacity should be greater than or equal to the maximum working load power required, the formula is
ST ≥ KT ∑ PXC
Style ST - control transformer capacity (VA);
∑ PXC - control circuit maximum capacity (VA);
∑ PXC - control circuit maximum capacity (VA);
∑ PXC - control circuit maximum capacity (VA);
Transformer capacity (VA) PXC - control circuit maximum load when the total power required to work appliances, where PXC for the electromagnetic device suction power
rate (W);
KT a control transformer capacity reserve factor, generally take 1.1-1.25.
2) control transformer capacity should make the Appliances that have been absorbed in the start of other appliances can still maintain the state of absorption, and starting appliances can also be reliably absorbed, the formula is
ST ≥ 0.6 ∑ PXC + 1.5 ∑ Pst
In ∑ Pst _ at the same time as the start of the appliance total absorption power (W).
Section VI of the construction design and construction of electrical control
A, electrical equipment overall configuration design
Components of the division of the principle is:
l) will be similar to the function of the components are composed of components together, constitute the control panel components, electrical control panel components, power supply components.
2)The electrical components with close wiring relationship are placed in the same component to reduce the number of wires between components.
3)Separate strong and weak power control to reduce interference.
4)In order to seek neat and beautiful, will be the same dimensions, the weight of similar electrical components combined together.
5)To facilitate the inspection and debugging, the need for frequent adjustment, maintenance and wear components together.
Electrical equipment, parts and components of the wiring between the usual way:
l) electrical control panel, machine tool electrical wiring in and out of the general use of terminals.
2) between the controlled equipment and electrical box for easy disassembly, handling, as far as possible, the use of porous connectors.
3)Printed circuit boards and weak control components should be used between various types of connectors.
The overall configuration design is to electrical control of the total assembly and the total wiring diagrams expressed in the form of diagrams are used to schematically reflect the location of the main components of each part and each part of the wiring relationship, wiring and the use of piping requirements. Overall design to make the whole system is centralized, compact; to consider the high heat and noise vibration of the electrical components, so that it leaves the operator a certain distance; power emergency control switch should be placed in a convenient and obvious location.
Second, the design of the electrical components layout
Electrical components layout refers to the electrical components in accordance with certain principles of the combination of the installation location map. Electrical components layout is based on the schematic diagram of the components, the same component in the arrangement of electrical components should be implemented in accordance with national standards.
The electrical cabinet of the electrical appliances can be arranged according to the following principles:
l) large or heavy electrical appliances should be placed under the control cabinet.
2)The heating element is installed in the upper part of the cabinet, and the heating element is separated from the temperature sensing element.
3)Strong and weak power should be separated, the weak part should be shielded isolation, to prevent strong power and external interference.
4)The arrangement of electrical appliances should be considered neat, beautiful, symmetrical.
5)Electrical components should be left between a certain distance, in order to facilitate wiring, wiring, maintenance and adjustment operations.
6) the layout of the terminal block: for the connection between adjacent cabinets with the terminal block should be arranged on both sides of the cabinet; for connection with the cabinet outside the electrical
components should be arranged in the lower part of the cabinet, and shall not be less than 200mrn.
Generally through the arrangement of the physical to determine the location of the electrical components, which in turn draws the electrical layout of the control cabinet. Layout
According to the external dimensions of the electrical components drawn to scale, and marked the spacing of the components size, but also marked the number of in and out of the line
quantity and wire specifications, select the appropriate terminal board and connectors and marked on its wiring number.
Three, the electrical control device wiring diagram
According to the electrical control circuit diagrams and electrical components layout to draw the wiring diagram of the electrical control device. Wiring diagrams should be in accordance with the
The following original