The components of a circuit diagram are controlled by the secondary control diagram. For the secondary schematic diagram, the steps are step-by-step from left to right and from top to bottom.
Secondary wiring diagram content
The secondary wiring diagram is a low-voltage circuit composed of secondary equipment. It includes AC current loops, AC voltage loops, circuit breaker control and signal loops, relay protection loops, and automatic device loops. The secondary wiring diagram is a graphic symbol and a text symbol of the secondary device, indicating the electrical wiring diagram of the secondary devices connected to each other. In actual work, the secondary wiring diagram is not only often encountered, but also has a large number, and it must be fully understood.
Classification of secondary wiring diagram
The secondary wiring diagram can be divided into two categories: schematic diagram and installation diagram. The schematic diagram is divided into general schematic diagram and unfolded schematic diagram. The installation diagram is divided into screen layout diagram and screen connection diagram.
(1) Schematic
The secondary wiring diagrams that represent the principle of operation are collectively referred to as schematics. Due to the different representation of the components, the schematic includes:
a, return to the total principle diagram, that is, the components in the figure is represented by the overall form, such as the current relay in the graphics, the following is the coil, the above is closed or disconnected DC link contacts.
b. Expanding principle diagram is to decompose each component into several parts. For example, the above current relay is divided into two parts: coil and contact. They are not located together in the diagram but are scattered in the relevant circuit.
(2) Installation diagram
According to the requirements of installation and construction, the figure showing the specific location and wiring of the secondary equipment is called the installation diagram.
The installation diagram includes a screen layout and a screen connection diagram. In the layout of the screen, the dimensions and mutual distances of the components must be specified in detail to facilitate the installation on the screen. The wiring diagram on the screen adds numbers to each element and circuit. During construction, it is connected according to the number, which is very convenient to use.
Commonly used graphic symbols in secondary wiring diagrams
In the secondary wiring diagram, in order to illustrate the connection status of each component, each component must be represented by a graphic and text symbol with certain characteristics to avoid confusion. For example, the current relay text symbol is LJ; the time relay text symbol is SJ; the test button text symbol is YA; the start button text symbol is QA; and the stop button text symbol is TA and so on.
General Schematic
It is customary to refer to the master schematic as the schematic. The overall schematic diagram, due to the overall form of the components, looks intuitive, and is drawn together with the primary device, it is easy to understand the relationship between them and the role, easy to form a clear concept, this wiring diagram for the principle of narrative operation It is advantageous. Its disadvantage is that if there are many components, the wirings will appear to be messy, and the terminals and wirings of the components will be unmarked.
Expanded schematic
The expanded schematic is also referred to as the unfolded diagram. It is completely drawn from another form. The AC circuit and the DC circuit are separate from each other. In the AC circuit, it is divided into AC current loop and AC voltage loop.
In the unfolded diagram, the coils and contacts of the relay are separated, and they are specified by the specified figures and text symbols, and their functions are easily displayed. Any circuit is the direction through which the buttons, contacts, coils, etc. pass through the current, from left to right, arranged from top to bottom, to constitute a complete development. On the right side of the figure, there are texts explaining the effect of the loop, which can further help to understand the action of the loop. Since the development plan is clear and can be analyzed and checked one by one, it is used most in practical work.
Screen layout
The screen layout should meet the following requirements:
1. All meters and relays that need to be constantly monitored should not be placed too high;
2. The height of the operating elements, such as control elements, adjustment switches, and buttons, should be moderate, so that the operation is easy to adjust and there should be a certain distance between them. When operating, it will not affect the adjacent equipment;
3, for the inspection and testing more equipment, should be located in the middle of the screen, and the same type of equipment should be arranged together, so that inspection and testing are more convenient. In addition, the compact and beautiful appearance should be sought.
Screen after wiring diagram
The wiring diagram behind the screen is an indispensable drawing for field installation. Each device in the figure is programmed with a certain sequence number and code number. Terminals are also marked on the equipment terminals. This label completely corresponds to the position on the product. In addition, each terminal is also marked with a definite destination. This wiring diagram is used for inspection and installation and is far more convenient than the schematic.
How to understand the electrical schematic
(1) DC loop from positive to negative
For example, control loops, signal loops, etc. From the DC positive pole of one loop, the cathode is seen in the direction of current flow.
(2) AC loop from FireWire to Neutral
For example, current, voltage loops, transformer air-cooled loops. From the live line of one circuit (phases A, B, and C, the neutral line (N pole) is seen in the direction of current flow).
(3) See contacts for coils, see coil contacts
See the contact to find the coil position of the relay or contactor that controls the contact. The loop where the coil is located is the control loop of the contact to analyze the conditions of the contact action. See the coil to find all its contacts in order to find all contacts (objects) controlled by the relay.
(4) Using Ohm's law to analyze relays to determine if they are operating
The basis for the discrimination is that a sufficient voltage is applied to both ends of the voltage coil, and a sufficient current is applied to both ends of the current coil. For coil circuits of voltage type relays, relays (contactors) are considered to act (excite) when the ends of the coil pass through the contacts or current coils of several relays and the positive and negative poles of the respective power supplies are connected. The relay (contactor) is considered to be inactive (not energized) when the contact or winding circuit is connected in series with a relatively large resistance, or when the coil is shorted with the connected contact. Such as: switch open circuit, when the switch is in the closed position, the positive polarity of the opening coil is connected in series with the position relay (high resistance), it is considered that it does not move. When the protection trip contact is closed and the coil is directly connected to the positive pole of the power supply, the opening coil is considered to act. For the current type (such as the tripping circuit anti-skipping relay), when the two ends of the coil through a number of relay contacts or resistance of the coil and the power supply respectively, positive and negative poles through, then that the relay (contact) action (excitation) . When the circuit has a short open contact, or the coil circuit is connected in series with a relatively large resistance, or the coil is shorted by the connected contact, it is considered that the relay (contactor) does not act (do not energize).
(5) After reading all the branches
When a loop looks at the loop from the positive pole to the negative pole, if there are multiple branches connected to the negative pole in the middle, each branch must be read. Otherwise, the analysis loop will miss some important conditions.
(6) Use the relative numbering method and circuit label to clarify the corresponding relationship between the equipment in the schematic diagram of the installation diagram and the development diagram.
The main purpose of verifying the correspondence between the installation diagram and the deployment diagram:
The first is to check whether the installation map corresponds to the deployment diagram.
Second, find out where each device on the map is located on site. From the installation diagram (such as the terminal strip line diagram of the protection screen), find out the position of the terminal of a certain terminal block in the unfolded drawing, first find out the circuit label on the terminal, and then check the circuit label in the unfolding diagram. The loop label is the same loop, and the loop can be quickly found in the unfolded diagram, and its role in the entire loop can be ascertained in the unfolded diagram. If there is only an installation diagram in the hand or the schematic wiring diagram of the installation diagram and the development diagram cannot be mapped, the number marked on the terminal of each device in the installation diagram is used to find out the other equipment connected according to the relative numbering method. Terminals, and then find the other devices connected to the terminal until you find the positive and negative pole of the DC power supply or the live and neutral lines of the AC circuit.
Finally, the entire relevant circuit is detected, and after the drawing, it can be analyzed whether the connection accords with the principle of operation. When you want to find out the position of the device on the unfolded map, use the position provided by the device table on the unfolded map, and then go to the corresponding installation drawing to check it. The second is to clarify the terminal symbols in the diagram, which are the terminals of the panel terminal block, which are the terminals of the (protected or automatic) device, and then go directly to the possible screen cabinets and terminal boxes.
(7) Solution to the problem of identifying special issues.
a. How to use the actual state of the equipment (the equipment state can be seen on the site) to describe the operating conditions of the circuit or relay: First, the conditions of the circuit are described in terms of the points of the circuit's contacts, and then the state of the circuit is divided according to the state of the contacts. Correspondences between the states of the equipment and the replacement description (for example, the "far/proximity switch" of the switch mechanism box is used at the "distant" position to replace the contact status of the "far/close switch" in the remote control loop. Form this ability, otherwise look at the drawings will stay in the original state, only to see whether the contacts of the points, together and whether the relay is excited, can not be combined with the monitoring and operation of the equipment state.
b. How do you clarify the connection between the box drawing device and the rest of the external part in the expanded drawing? First check the terminal number of the box drawing equipment, and then use the device manual or the manufacturer's drawing that can show the internal wiring diagram of the equipment. Find the external connection terminal number in these drawings, connect it with the internal circuit, and then go through The connected terminals are then associated with the external circuit.
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