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Any complex thing is composed of simple things, and this is also true for electrical engineering diagrams; it serves as the basic starting point for analyzing complex circuit diagrams. In electrical engineering and automation, the field mainly encompasses six areas: power generation, power transmission, power conversion, control technology, power storage, and power utilization. Among these, control technology (including relay protection) is the core technology, as well as the most challenging aspect; it can often be quite complex. In this article, Changhui Instruments provides a detailed explanation of the methods, steps, techniques for analyzing complex circuit diagrams, control circuits, automation instrument control circuits, and microcomputer-controlled detection and protection circuits, as well as guidelines for reading such diagrams. http://yunrun.com.cn/upload/201810/25/201810251332284355.png Changhui Instruments, yunrun.com.cn/ Methods and approaches for analyzing complex circuit diagrams: 1. Break it down into individual circuit units or components. Under normal circumstances, functions and roles that produce the same effect are often depicted together (but the actual objects are not necessarily placed together; this is something to keep in mind! ). 2. Determine the functions and roles of each component within each unit or assembly. 3. Determine the power supply settings for each component, such as AC, DC, voltage, etc. 4. Determine what type of signals are the inputs and outputs of each component, as well as their signal values or ranges. This includes contact signals (normally open, normally closed, and their distribution within the circuit), analog signals (0-10mA, 4-20mA, 1-5V) with determination of their signal nature (AC, DC, pulsating), digital signals (number of input points, number of output points, and contact capacity, such as DC30V, DC0.1A), and input or output impedance (such as 250Ω, 75Ω, etc.). Do not overthink or analyze the internal structure and principles of each component; the key is to understand its functions as well as its input and output signals. 5. Determine the interface components or circuits between various elements within a unit or component, as well as their functions, such as transmitters, converters, safety barriers, power distributors, and their input and output signals. 6. Determine the interface elements or circuits between units or components and their functions. 7. Determine the feedback loops between various components and units, as well as the corresponding components or circuits, and identify the nature of their feedback signals. 8. Draw the above analysis in a block diagram, indicating the signals between components or circuits. 9. Analyze the functions and roles of this circuit based on the block diagram. 10. Based on the above analysis, the dissection must be thorough, with no step overlooked. Methods and techniques for analyzing contactor-relay control circuits. Contactors and relays, together with signal contacts provided by limit switches, control devices, buttons, and sensing devices or instruments, can be used to create complex control circuits for applications such as elevators, electric cranes, large boiler fans, feedwater pump motors, large motors driving important loads, as well as relay protection systems in power supply and distribution systems. Analysis and interpretation can be carried out using the above method. 1. Determine the functional roles of contactors and relays (including relays for current, voltage, phase error, grounding, differential protection, short circuit, temperature, pressure, flow rate, time, power, gas, circulating current, intermediate signals, status signals, flashing signals, reclosing functions, impedance, zero-sequence currents, frequency, etc.) as well as the distribution of their contacts (normally open, normally closed, timed, etc.). This distribution is very important; it is key to analyzing complex circuits, and none of the contacts should be overlooked ； 2. Determine the effect of the contact actions of contactors and relays after they are powered or de-energized within the respective circuits, namely whether the circuits are disconnected, connected, or what happens to the components in those circuits ； 3. The operation of the circuit contacts in 2 and its effect on the operation of other circuits ； 4. The operation of other circuits in turn triggers the operation of various other circuits ； 5. Analyze the operation of each circuit one by one according to 1-4, and finally the operation result of the entire circuit can be determined. During the analysis process, the setting value or operating value of the relay should be determined. Methods and techniques for analyzing automated instrument control circuits. An automated instrument control circuit consists of sensors (such as thermocouples, thermal resistors, pressure sensors, orifice plates, etc.), transmitters or converters or distributors, safety barriers, calculators, setpoints, regulators, displays, auxiliary units, and actuators. In addition to performing control functions, such circuits also display the values being measured or record the cumulative values of those measurements. 1. Determine the output signal values of the quantity being measured and the sensor (mV or mA or Ω), as well as the category and number of quantities being measured ； 2. Determine how each transmitter converts the output signals from the instruments or sensors to a unified standard DC signal value, and determine the location at which these standard signals are fed into the display instruments or regulators, as well as the functions of those display instruments or regulators ； 3. Determine the connection method between the 0-10mA, 0-10mV, or 20-1000kPa signals converted by each converter and other instruments in the series ； 4. Determine the way in which the signals generated by each calculator within the calculation unit—after performing operations such as addition, subtraction, multiplication, division, square root extraction, and integration on standard DC signals—are connected to its regulator ； 5. Determine the set value of the regulator; compare the signal obtained from the above calculations with this set value to find the deviation ； 6. Determine the location where the deviation is introduced and the nature of the regulator (proportional, integral, derivative); the control signal generated as a result of these calculations is sent to the actuator to achieve closed-loop control ； 7. The actuator operates in response to the control signal to drive the adjustment mechanism and change the control variable, thereby enabling automatic control ； 8. Determine the functions of other devices, such as operators, selectors, dampers, limiters, and safety gates, as well as their power supply, input, and output signals ； 9. Determine the functions and wiring of auxiliary devices such as indicators, recorders, accumulators, and alarms ； 10. Analyze each testing system one by one from 1 to 9, as well as its connection or relationship with other systems ； 11. Thoroughly understand the functions and roles of all components in the instrument self-check system, as well as their input and output signals; among these, the distributor serves as the link that connects the transmitter to the microcomputer control unit. Essentially, it is a modulator-converter, a device that converts analog signals into digital signals. The microcomputer control unit only recognizes digital signals, and then outputs the corresponding signals according to the preset program, using electric actuators and servo amplifiers to drive the actuators. Methods and approaches for analyzing microcomputer-controlled, protection, and detection circuits. Microcomputer-controlled, protection, and detection circuits are developed based on the aforementioned circuits, with the difference being that they simplify the structure of those circuits. If we ignore the structural principles and operating programs of the microcomputer itself, the microcomputer-controlled, protective, and monitoring circuits are the simplest types of circuits. 1. Determine the nature of the control quantity (whether it is a digital value, such as open or closed) ； Still digital quantities, such as voltage, current, frequency, power, temperature, pressure, flow rate, level, mechanical quantities, composition analysis values, etc ； 2. Determine the transmitter or sensor, which will convert the control value into a standardized electrical signal (mA or mV or Ω) ； 3. Determine the analog-to-digital converter, which will convert electrical signals into digital signals that can be recognized by microcomputers ； 4. Microcomputer control devices are generally designed and manufactured specifically for particular control or detection systems. Their program control systems are configured randomly and are developed in accordance with the requirements of control or detection ； 5. Determine the output signal of the microcomputer and the interface with the actuator, which are generally composed of an operator and an amplifier ； 6. Determine the settings for the server room and bus, such as printing, monitors, and common operation procedures ； 7. The monitoring network for microcomputer-based relay protection circuit systems is a new technology that has emerged in recent years. Substation equipment of all types now comes equipped with microcomputer-based relay protection circuits, and their actual circuit structure is much simpler than that of relay-based protection circuits. ①The main components of a transformer protection cabinet are measurement and control devices, such as transformer differential protection devices, transformer backup protection devices, and non-electrical quantity protection devices. The signals of the non-electrical protection devices come from sensors such as those for temperature, gas, and oil analysis, with the signals being transmitted via converters ； The signals for differential protection and backup protection devices come from current transformers, which is the same as in relay protection. ②The main components of the line protection cabinet are the line protection device and the line measurement, control, and protection device; their signals come from current transformers, just as in relay protection. ③The signal of the electric energy metering device comes from current transformers. ④The outputs of the above three devices are connected to the network switch via Ethernet gateway devices, and then routed to the Ethernet through the intermediate layer. In other words, all signals are routed to Ethernet; in simpler terms, Ethernet is the bus for computer communication networks. ⑤Connected to the Ethernet are mainly the devices in the control room, such as GPS (Global Positioning System), remote communication units, and the computers used by operators; these systems are equipped with printers and telephones to receive instructions from remote dispatchers, with all operations being carried out via computers.