Easy to understand electrical secondary wiring diagram and schematic

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 an electrical wiring diagram showing the interconnection of secondary equipment by graphical symbols and text symbols of the secondary equipment. In actual work, the secondary wiring diagram is not only often encountered, but also a large number, it must be fully understood.

The secondary wiring diagram can be divided into two major categories: schematic diagram and installation diagram. The schematic diagram is divided into the general schematic diagram and the extended schematic diagram. The installation diagram is divided into the screen layout diagram and the screen rear wiring diagram.

(1) Schematic

The secondary wiring diagrams that represent the principle of operation are collectively referred to as schematic diagrams. Due to the different representation of the components, the schematic includes:

a. The schematic diagram of the total, that is, the components are represented in the overall form in the figure, such as the representation of the current relay, the lower part is the coil, and the upper part is the contact for closing or disconnecting the relevant DC circuit.

b. Expanded schematic diagram, which is to break down the components into several parts. For example, the above current relay is divided into two parts: the coil and the contact. They are not located together in the figure, but are scattered in the relevant loop.

(2) Installation diagram

According to the requirements of installation and construction, the figure indicating the specific position and wiring mode of the secondary equipment is called the installation drawing.

The installation diagram includes the screen layout and the rear panel wiring diagram. In the layout of the screen, the dimensions and mutual distance of each component must be specified in detail to facilitate installation on the screen. The rear panel wiring diagram adds numbers to each component and circuit. When it is used, it is wired according to the number, which is very convenient to use.

In the secondary wiring diagram, in order to explain 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.

It is customary to refer to the general schematic diagram as a schematic diagram. The general schematic diagram, because the components are in the overall form, looks more intuitive, and is drawn together with the primary equipment, easy to understand the relationship and role between them, to facilitate the formation of a clear concept, this wiring diagram for the narrative action principle It is advantageous. Its disadvantage is that if there are many components, the wiring crosses each other and becomes messy, and the component terminals and wires are not labeled, which is often inconvenient to use.

The expanded schematic, also referred to as the expanded graph, is completely drawn from another form. The AC loop and the DC loop are separated from each other. In the AC circuit, it is divided into an AC current loop and an AC voltage loop.

In the unfolded view, the coils and contacts of the relay are separated and marked with the specified figures and text symbols, which are easy to display their functions. Any loop is a direction in which the current is passed by buttons, contacts, coils, etc., from left to right, from top to bottom, forming a complete unfolded view. On the right side of the figure, there is a text explaining the role of the loop, which can further help understand the action process of the loop. Since the unfolding diagram is clear, it can be analyzed and checked one by one, so it is used most in practical work.

The layout of the screen should meet the following requirements: 1. Do not place the instruments and relays that need to be monitored frequently; 2. The operating components, such as control components, adjustment switches, buttons, etc. should be moderate in height, so that the operation adjustment Conveniently, there should be a certain distance between them, and the adjacent equipment should not be affected during operation; 3. For equipments with more inspection and testing, it should be located in the middle of the screen, and the same type of equipment should be arranged together. This is convenient for inspection and testing. In addition, the arrangement is compact and aesthetically pleasing.

The post-screen wiring diagram is an indispensable drawing for on-site installation. Each device in the figure has a certain sequence number and code. Labels are also added to the equipment terminals. This label corresponds exactly to the location on the product. In addition, each terminal is also marked with a clear direction. This wiring diagram is used for inspection and installation, much more convenient than the schematic.

(1) DC circuit from positive to negative: listed as control loop, signal loop, etc. Starting from the DC positive pole of a loop, the negative pole is seen in the direction of current flow.

(2) AC circuit from the live line to the neutral line: such as current, voltage loop, air-cooled circuit of the transformer. From the fire line of one circuit (A, B, and C phases, the neutral line (N pole) is seen according to the flow direction of the current.

(3) See the contact to find the coil, see the coil to find the contact: When you see the contact, you need 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 joint to analyze the conditions of the joint action. See the coil to find all its contacts in order to find all the contacts (objects) controlled by the relay.

(4) Analyze the relay to determine whether it is operated by Ohm's law: The basis for the discrimination is that a sufficiently large voltage is applied to both ends of the voltage coil, and a sufficient current is applied to both ends of the current coil. For the coil circuit of a voltage type relay, when the two 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, the relay (contactor) is considered to be active (excitation), and when there is a short opening in the circuit. When the contact or the coil loop is connected in series with a relatively large resistance, or when the coil is short-circuited by the parallel connection, the relay (contactor) is considered to be inoperative (not excited). For example, the switch opening circuit, when the switch is in the position, the positive end of the opening coil is connected in series with a relay (large resistance), it is considered to be inoperative. When the protection trip contact is closed and the coil is directly connected to the positive pole of the power supply, the trip coil is considered to be active. For the current type (such as the anti-skip relay of the trip circuit), when the two ends of the coil pass through the contacts of several relays or the coils with small resistance and the positive and negative poles of the respective power supplies, the relay (contactor) acts (excitation). . When there is a short open contact in the loop, or if the coil loop is connected in series with a relatively large resistor, or if the coil is shorted by the parallel joint, the relay (contactor) is considered to be inactive (not excited).

(5) After reading all the branches: When a loop is seen 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 situations.

(6) Use the relative numbering method and the circuit label to clarify the correspondence between the equipment in the wiring diagram of the installation diagram and the expansion diagram: the main purpose of verifying the correspondence between the installation diagram and the expansion diagram: The first is to check whether the installation diagram and the expansion diagram Corresponding. Second, find out the location of each device on the site in the expanded view. From the installation diagram (such as the protection screen terminal block wiring diagram) to find out the position of the terminal of a terminal block in the unfolded picture, first find the circuit label on the terminal, and then check the circuit label in the expansion diagram, the same The loop label is the same loop, and the loop can be quickly found in the unfolded graph, and the expanded graph is used to find out its role in the entire loop. If there is only the installation drawing on the hand or if the wiring diagram of the installation drawing and the unfolding drawing cannot be corresponding, then the number marked on the terminal of each device in the installation drawing, according to the relative numbering method, the other device connected to the device is found. Terminal, and then find the other equipment connected to the terminal until the positive and negative poles of the DC power supply or the live and neutral lines of the AC circuit are found. Finally, the entire relevant loop is detected. After drawing the graph, it can be analyzed whether the connection conforms to the action principle. When you want to find out the location of the device on the unfolded map, use the location provided by the device table on the expanded graph, and then check the corresponding installation map. The second is to first find out the terminal symbols in the unfolding diagram, which are the terminals of the panel terminal block, which are the terminals of the (protective or automatic) device, and then go directly to the possible panel and terminal box to find.

(7) A solution to the problem of identifying special problems.

a. How to describe the operating conditions of the loop or relay by the actual state of the equipment (the state of the equipment that can be seen in the field): first describe the condition of the loop by the joint state of the joint of the loop, and then according to the state of the joint and the joint The corresponding relationship of the state of the device, replace the description (such as the "far/near control switch" of the switch mechanism box in the "remote" position instead of the contact state of the "far/near control switch" in the remote control loop. This ability is formed, otherwise the drawing will remain in the original state, and only the separation and closing of the contacts and the excitation of the relay can be seen, and cannot be combined with the monitoring and operation of the state of the equipment in operation.

b. How to find out the part of the expanded picture using the box drawing device to connect with other parts of the outside? First check the terminal number of the box drawing device, and then use the device manual or manufacturer's drawing that can display the internal wiring diagram of the device, find the terminal number to the external connection in these drawings, connect it to the internal circuit, and then go out. The connected terminals are then connected to the external circuit.