The electricity cost of air compressors is relatively high. For some factories that use a large amount of equipment, as long as the energy consumption is reduced by 5%, a lot of money can be saved, but the total replacement cost of the whole machine will be very high. Many manufacturers Businesses may not be able to afford it. In this case, how can enterprises spend a small cost to save energy? At this time, we have to mention the inverter transformation. Everyone knows that inverter air conditioners are much more energy-saving than traditional air conditioners. The principle of inverter transformation of air compressors is the same.
From the aspect of energy saving: after the use of frequency conversion speed regulation, once the gas consumption of the equipment is reduced, the speed of the motor can be reduced, and the power of the motor can be reduced, thereby realizing the function of energy saving. We found that the speed of the air compressor motor has a quadratic relationship with the actual power consumption of the compressor. Therefore, in order to reduce the actual consumption of the air compressor, it is necessary to reduce the motor speed to achieve. The energy saving principle and effect are as follows:
① After using the inverter, the pressure setting of the air compressor can be a little bit, that is, the minimum pressure that meets the requirements of the production equipment can be used as the set pressure. Even the unloading operation of the air compressor is eliminated, saving electric energy.
② Due to the frequency converter in the system, the pressure on the pipe network can be stabilized, which can reduce or even eliminate pressure fluctuations, so that all the compressors running in the system operate at a lower pressure that meets the production requirements, reducing the pressure caused by upward fluctuations. power loss.
③ Since the air compressor cannot rule out the possibility of running for a long time under full load, the capacity of the motor can only be determined according to the maximum demand, so the design capacity is generally too large. In actual operation, the proportion of light-load operation time is very high. If frequency conversion speed regulation is adopted, the work efficiency during operation can be greatly improved.
④ Some adjustment methods cannot reduce the operating power of the motor even when the demand is small. After the frequency conversion speed regulation is adopted, when the demand is small, the speed of the motor can be reduced, and the operating power of the motor can be reduced, thereby further realizing energy saving.
⑤ Most of the single-motor drag systems cannot be continuously adjusted according to the weight of the load. After adopting the frequency conversion speed regulation, it can be very convenient to carry out continuous adjustment, and can keep the pressure, flow, temperature and other parameters stable, thereby greatly improving the working performance of the air compressor.
From the perspective of operating cost: the operating cost of the variable frequency air compressor is much higher than the procurement cost. main.
After using the frequency conversion function, the impact in the equipment is effectively reduced, the damage rate of each component is greatly reduced, and the maintenance and repair costs are reduced. In addition, it also has the effect of saving energy consumption, which greatly reduces the operating cost.
From the perspective of the use time limit of the screw air compressor: after the screw air compressor uses the frequency conversion function, it can effectively reduce the impact of electrical components and mechanical parts when the machine is running. In addition, it also effectively reduces current fluctuations, etc., effectively extending the use time.
From the point of view of noise: after the variable frequency air compressor uses variable frequency speed regulation, the speed of the motor is significantly slowed down, thereby reducing noise.
The failure of frequency conversion transformation is closely related to the level of the transformation engineer, and there are also many problems:
1. The selection of the inverter and the matching load characteristics are different. The selection of the inverter is different. The compressor is a constant torque load. Whether the appropriate inverter is selected.
2. The inverter cable will produce coupling capacitance to the ground, resulting in insufficient output of the inverter.
3. Affect the protection level.
4. The inverter output contains high-order harmonics, which will cause the power factor and efficiency of the motor to deteriorate.
5. When the inverter is powered, the motor current increases by 10% and the temperature rise increases by 20%.
6. The calorific value of the ordinary motor increases at low speed, and the air volume of the self-cooling fan decreases drastically.
7. Bearing current, the high-frequency current in the bearing is generated by the high-speed opening/closing of the switch, which will cause fluctuations in the rotating parts, which in turn affects the lubrication of the bearing. At the same time, there will be craters caused by electric sparks, and if not protected, the bearings can be easily damaged.
8. There are electromagnetic compatibility problems, which interfere with surrounding electrical equipment and are also susceptible to surrounding interference.
9. Insulation failure, the switching frequency in the inverter will cause the peak voltage to reach 3.5 times the nominal voltage.
10. At low speed, condensed water is easily generated in the main engine of the oil-injected screw compressor, resulting in oil emulsification, resulting in lubricating failure and rotor seizure.
11. The compressor with a fixed speed still has a loading and unloading valve, and the oil/gas separator needs to be emptied when starting, and there is waste during unloading.
In addition, improper use of the inverter will not only fail to play its excellent function, but also may damage the inverter and its equipment, or cause interference, etc. Therefore, the following matters should be paid attention to during use:
The inverter must be selected correctly;
● Read the product manual carefully, and connect, install and use according to the requirements of the manual;
● The inverter device should be grounded reliably to suppress radio frequency interference and prevent the inverter from electric shock due to leakage;
● When the motor speed is controlled by the inverter, the temperature rise and noise of the motor will be higher than when the grid power (power frequency) is used; when running at low speed, due to the low speed of the motor fan blades, attention should be paid to ventilation and cooling and appropriately reduce the load to avoid the motor The temperature rise exceeds the allowable value;
● The impedance of the power supply line should not be too small. When the inverter is connected to the voltage grid, when the capacity of the distribution transformer is greater than 500kVA or the capacity of the distribution transformer is greater than 10 times the capacity of the inverter, or when the inverter is connected very close to the distribution transformer, due to the small loop impedance , the input moment will cause a large surge to the inverter, which will damage the rectifier components of the inverter. When the line impedance is too small, an AC reactor should be installed between the power grid and the inverter;
● When the three-phase voltage unbalance rate of the power grid is greater than 3%, the peak value of the input current of the inverter will be very large, which will cause the inverter and its connections to overheat or damage the electronic components. At this time, an AC reactor should also be installed. Especially when the transformer is V-shaped, it is more serious. In addition to installing a reactor on the AC side, it is also necessary to install a DC reactor on the DC side;
● Do not install too large capacitors on the incoming side to increase the power factor, nor install capacitors between the motor and the inverter, otherwise the line impedance will drop, resulting in overcurrent and damage to the inverter;
● Compensation capacitors cannot be connected in parallel on the output side of the inverter, nor can capacitors be connected in parallel to reduce the high-order harmonics of the output voltage of the inverter, otherwise the inverter may be damaged. In order to reduce harmonics, reactors can be connected in series;
The start and stop of the motor whose speed is regulated by the frequency converter cannot be directly operated by the circuit breaker and the contactor, but should be operated by the control terminal of the frequency converter, otherwise the frequency converter will be out of control and may cause serious consequences;
● Generally, it is not advisable to install an AC contactor between the inverter and the motor, so as to avoid overvoltage between the interruptions and damage the inverter. If additional installation is required, the output contactor should be closed first before the inverter runs;
● For the occasions where the frequency converter drives the ordinary motor for constant torque operation, long-term low-speed operation should be avoided as much as possible, otherwise the heat dissipation effect of the motor will become poor and the heat generation will be serious. If you need to run at low speed and constant torque for a long time, you must choose a variable frequency motor;
● For the occasion of lifting the load and frequent starting and stopping, there will be a large torque, and it is necessary to select an appropriate braking resistor, otherwise the inverter will often trip due to overcurrent or overvoltage faults;
● When the motor has a brake, the inverter should work in the free stop mode, and the brake action signal will not be issued until the inverter sends a stop command;
● The resistance of the external braking resistor of the inverter cannot be less than the requirement of the braking resistor allowed by the inverter. On the premise of meeting the braking requirements, the braking resistor should be larger. Do not directly short-circuit the terminals that should be connected to the braking resistor, otherwise, a short-circuit accident will occur through the switch tube during braking;
● When the inverter is connected to the motor, it is not allowed to use a megohmmeter to measure the insulation resistance of the motor, otherwise, the high voltage output by the megohmmeter will damage the inverter;
● Correctly handle the acceleration and deceleration problems. If the acceleration and deceleration time set by the inverter is too short, it is easy to suffer from "electric shock" and may damage the inverter. Therefore, when using the inverter, the acceleration and deceleration time should be extended as far as possible under the premise of the load equipment.
● If the load is heavy, increase the acceleration and deceleration time; otherwise, reduce the acceleration and deceleration time appropriately. If the load equipment needs to accelerate and decelerate in a short time, it must be considered to increase the capacity of the inverter, so as to avoid too much current that exceeds the rated current of the inverter. If the load equipment needs a very short acceleration and deceleration time (for example, within 1s), the braking system should be considered on the inverter. Generally, the inverter with larger capacity is equipped with a braking system;
● Avoid the mechanical resonance point of the load equipment. Because the motor is within a certain frequency range, it may encounter the mechanical resonance point of the equipment, resulting in mechanical resonance and affecting the operation of the system. To this end, it is necessary to set the jump frequency (or avoidance frequency) for the inverter, and jump over (avoid) the frequency to avoid the resonance point;
● Before the motor is used for the first time or connected to the inverter after being placed for a long time, the insulation resistance of the motor must be measured (with a 500V or 1000V megger, the measured value should not be less than 5MΩ). If the insulation resistance is too low, the inverter will be damaged;
● The inverter should be installed vertically with ventilation space, and the ambient temperature should not exceed 40℃;
● Anti-interference measures must be taken to prevent the inverter from being disturbed and affecting its normal operation, or the high-order harmonics generated by the inverter from interfering with the normal operation of other electronic equipment;
● Pay attention to the thermal protection of the motor. If the motor and the inverter capacity are adapted, the thermal protection inside the inverter can effectively protect the motor. If the two capacities do not match, the protection value must be adjusted or other protection measures must be taken to ensure the safe operation of the motor.
● The electronic thermal protection value of the inverter (motor overload detection) can be set within the range of 25%-105% of the rated current of the inverter. The air compressor frequency conversion speed regulation energy saving transformation has reliable technology, simple installation, convenient operation, low failure rate, and considerable economic benefits. , to avoid unnecessary economic losses.