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Measures and characteristics of protection control for screw compressors. 1. What are the protection control measures for screw compressors? The protection and control measures for screw air compressors fall into two categories: individual unit protection and control, and interlinked protection and control systems. Single-unit protection control refers to a control system for each air compressor, with its control objectives being the various protection settings of that individual air compressor. The interlocked protection control system involves multiple air compressors sharing one control cabinet. Its control targets are the multiple air compressors connected to the interlock cabinet, and it can also be linked to the DCS operating system in the control room ； The main contents of the coordinated control protection include the setting and switching of the air compressor units, as well as the sequencing and timing for starting and stopping the compressors individually, in order to ensure balanced operating times for all air compressors. 2. Explain the features of the single-unit controller for screw air compressors. The control unit for single screw air compressors typically uses an IC board control panel or a microcontroller-based control panel. The controller for screw air compressors is an electronic device that ensures the proper operation of the compressor as a whole, and it provides functions such as automated control, real-time monitoring, and fault handling. The appearances of screw air compressor controllers vary among brands, but their functions are largely similar. Automatically control the shutdown, standby, startup, loaded, unloaded, prolonged idling, emergency stop, and other states of the unit ； Real-time monitoring of multiple sets of data such as exhaust pressure and exhaust temperature to enable automatic maintenance and protection functions for the unit ； The service life of the three filters in the air compressor can be set; when the operating time exceeds the corresponding set time, an indicator light turns on to alert that the components need to be replaced ； Functions can be expanded through software upgrades, allowing flexible use in various industrial and mining applications ； It is simple to operate and easy to master. 3. Introduction to the interlocking function of the air compressor interlocking control cabinet. (1) In the interlocked mode, pressing the start button of any air compressor unit will cause that unit to start running after 2 seconds. Twenty seconds later, the next unit starts, and this continues until all units are in operation. If the pipeline network pressure has reached the preset lower limit, the unstarted units will no longer be started. (2) Once the pressure reaches the upper limit specified on the official website, the interlocking control cabinet issues a command to unload; after a 5-minute delay, the standby unit stops automatically ； If it is still in the unloading state, the auxiliary unit will automatically stop after a 10-minute delay ； If the uninstallation signal persists, there will be a further 20-minute delay before the last host automatically shuts down. (3) The data that can be entered and modified include the set limits for the pressure in the compressed air main pipeline, the switching time of the main unit, the interval between shutdowns and restarts of the air compressor, the startup delays for the main unit, auxiliary units, and backup units, as well as the shutdown delays for these same units. When the pipeline network pressure falls below the lower set value, a load signal is issued; the auxiliary unit then automatically starts up after a 20-second delay. If the pipeline network pressure remains below the set value, the standby unit automatically starts up after a 20-second delay. (4) When any unit fails, it will be automatically removed from the interlocked control mode; the remaining units will continue to start and stop automatically according to the pre-set programmed requirements in order to meet the pressure demands of the pipeline network, while simultaneously generating fault sounds and light signals. (5) It automatically times the operating duration of each unit and performs automatic master unit switching, so as to balance the operating times of all units. (6) Depending on the system’s requirements, each air compressor can be taken out of the interlocked control mode as needed. (7) It has the function of transmitting signals to the central control room, such as operation signals, signal of prolonged idling, severe fault signals, minor fault signals, audible alarm signals, signal for obtaining permission to start from the central control room, main unit status signals, and air compressor power supply status signals; all operations and displays are available on the control panel. 4. What precautions should be taken when switching between single control and coordinated control for the air compressor coordinated control cabinet? (1) On the electrical control panel of each air compressor, turn the selection switch to the off state for inter-control; this way, that unit is removed from the inter-control mode, allowing individual operation of its processes via the air compressor’s control panel. (2) On the electrical control panel of each air compressor, by turning the single-control/combined-control selection switch to the single-control mode, it is possible to operate each unit individually on the panel of the combined-control cabinet. (3) On the electrical control panel of each air compressor, turn the selection switch to the interlocked control mode; on the operation panel of the interlocked control cabinet, turn the single-control/interlocked control selection switch to the interlocked control mode, and then interlocked control operations can be performed on the panel of the interlocked control cabinet. (4) When switching from single-control mode to joint-control mode, the status of each unit remains unchanged. Then, the start button on the operation panel of the intercontrol cabinet must be pressed to enter the intercontrol mode. (5) Under the coordinated control mode, after a serious fault occurs in the air compressor, the program automatically removes it from this coordinated control state, causing the air compressor to stop operating automatically. Next, turn the interlock knob on the air compressor’s electrical control panel to the cut-off position. Cut off the power supply separately for maintenance. After the maintenance is complete, turn on the power supply and adjust the intercontrol knob to the on position; the unit will then be able to enter intercontrol mode automatically. 5. What are the considerations for selecting an inverter? (1) Selection of load type and frequency converter. Inverters cannot be used properly in all situations; therefore, it is necessary to have a better understanding of the load, environmental conditions, and the inverters themselves. Different loads connected to motors require different specifications from inverters. a. Fans and pumps. This is the most common type of load, and the requirements for the frequency converter are the simplest – it is sufficient that the capacity of the frequency converter matches that of the motor (for air compressors, deep well pumps, sludge pumps, and fountains with rapidly changing patterns, a higher capacity is required). b. Crane-type loads. The characteristic of such loads is a large impact during startup; therefore, the frequency converter needs to have a certain degree of headroom. At the same time, energy is recovered when the heavy load is lowered; therefore, a braking unit or a common bus system must be used. c. High-inertia loads. Loads such as centrifuges, punching machines, and the rotary kilns in cement plants have high inertia; as a result, they may oscillate during startup, and energy is regenerated when the motor slows down. A frequency converter with a slightly larger capacity should be used to speed up startup and avoid oscillations. Works in conjunction with the braking unit to eliminate regenerated electrical energy. d. Uneven load distribution. Such loads can be light at times or heavy at other times; in such cases, the capacity of the frequency converter should be selected based on the heavy-load condition, as in the case of rolling mills, crushing machinery, mixers, etc. (2) During long-term operation at low speeds, the motor generates a high amount of heat, which reduces the fan’s cooling capacity; therefore, it is necessary to increase the reduction ratio or switch to a 6-stage motor in order to allow the motor to operate at a higher frequency. (3) The installation location of the frequency converter must meet the requirements of a standard environment; otherwise, it is likely to cause failures or reduce its service life ； The distance between the inverter and the drive motor should generally not exceed 50 m; if a longer distance is required, the carrier frequency must be reduced or an output reactor option added to ensure proper operation. 6. What are the energy-saving monitoring methods and requirements for air compressors? (1) Monitoring must be carried out under normal operating conditions of the air compression unit and air supply system, and such conditions should be representative of the statistical data. (2) For air compression units with a stable load, the inspection cycle is 2 hours; for those with an unstable load, the inspection cycle is one or several load variation cycles. (3) During the testing period, the various parameters under consideration under the same operating conditions should be sampled simultaneously, and these parameters should be sampled more than three times each ； The sampling interval is 10~20 minutes ； The average value of the readings from each group is used as the calculated value. (4) Flowmeter method for detecting the volumetric flow rate of air compressors. For air compressor units with water-cooled intercoolers, the measurement can also be carried out according to the heat balance method specified in relevant regulations. (5) Requirements for measuring instruments. Voltage, temperature, pressure, and flow measurements should be taken within the operating range specified by the instrument. The accuracy of the measuring instruments shall meet the specified requirements. The instrument should be within its calibration validity period.