Analysis and treatment methods for overcurrent of high and low temperature test chamber compressor
Excessive operating current in the refrigeration system refers to the excessive operating current of the compressor. Simply put, there are three reasons for compressor overcurrent:
The condensation pressure of the refrigeration system is too high; Excessive refrigerant in the refrigeration system; The compressor lacks refrigeration oil;
1、 Poor heat dissipation of the external unit (1) Short circuit in the return and exhaust of the external unit: If the external unit is installed in a closed balcony, narrow aisle, indoor or other poorly ventilated areas, there are obstacles in front of the air outlet. (2) The external unit has low air volume and slow heat dissipation speed: if the external unit condenser is too dirty or blocked by dust and oil stains, the fan motor speed is slow, the fan capacitance decreases, and the temperature around the external unit is high.
2、 External power supply voltage factor:
Low or high power supply voltage can cause high working current of the compressor, and low voltage is the majority in China, especially during peak electricity consumption periods.
If the power supply voltage (i.e. the voltage before startup) is too low, the user should be asked to rewire. If the voltage is around 190V, it is possible to consider installing a voltage regulator. If it is too low, it will be ineffective.
2. Measure the voltage drop after starting up. Under normal circumstances, the voltage drop is only a few tens of volts. If the voltage drop is too large (it is recommended to drop more than 20V and the voltage after starting the compressor is 190V lower), the power cord should be thickened or rewired, and faults such as poor contact of the circuit should be eliminated.
3、 Refrigeration system malfunction:
1. Air is mixed into the refrigeration system: If air is mixed into the system, it often accumulates in the upper part of the condenser because it cannot pass through the condenser's accumulator. Whether there is air in the system can generally be determined by the fluctuation of system pressure. If there is air in the system, it should be vacuumed and treated with fluorine again.
2. Excessive fluorine: The compressor * is in an overloaded state, which can cause the compressor to trip due to overcurrent. In this situation, some fluorine should be released to the standard range (with a suction pressure of around 0.5MPa at an ambient temperature of 35 ℃).
4、 High shell/internal temperature:
1. Poor lubrication of the compressor: If the height difference between indoor and outdoor units is greater than 5 meters, no oil return bend is made, or only one oil return bend is made on one pipe, the system cannot smoothly return oil. The temperature of the compressor slowly rises during operation due to lack of lubrication, which later leads to overheating and tripping. For example, when the outdoor unit is located below and in heating operation, the gaseous working fluid flows upward in the coarse tube and the liquid working fluid flows downward in the fine tube, resulting in poor oil return. The outdoor unit is located above, and the heating process is running. The gaseous working fluid flows downward in the coarse tube, while the liquid working fluid flows upward in the fine tube, resulting in better oil return. When cooling, the situation is opposite to the above. There are two types of oil return bends: U-shaped and S-shaped. The S-shape can be added in the middle of the connecting pipe, while the U-shape is generally installed near the machine, and the radius should be as small as possible.
2. Impurities and excessive moisture in the system: This can cause the lubricating oil to deteriorate, carbonize, and fail to function properly, resulting in a sharp increase in compressor temperature and overheating induced tripping.
This situation usually occurs on machines that have been repaired or have been used for a long time. If the substance in the inspection system appears black, it is certain that this situation exists. At this time, nitrogen should be used to clean the system, replace the compressor and capillary components, and evacuate and fluorinate again.
3. Air conditioning is often used in environments below 0 degrees Celsius: When the compressor starts, the lubricating oil bubbles, causing a large amount of lubricating oil to instantly flow out of the compressor. At this time, no matter how well the system is designed, it is useless. The speed of oil return is much lower than the speed of oil discharge, and the lack of lubrication in the compressor causes temperature rise and overheating protection. In this situation, an oil heater (40W-60W, 220V) should be installed on the compressor. When the compressor stops, the oil heater should continue to be powered on. The connection method is to connect the oil heater in series with the normally closed switch of the contactor, and then connect it to the fire and neutral wires of the power supply.
5、 The cooling effect of the compressor is poor, and the system has too little fluorine. When the compressor is working, the temperature is very high, and the high-temperature coil is cooled by the refrigerant sucked in. If the fluorine is too low, the system flow rate will be small, which cannot meet the load of the evaporator, resulting in an increase in suction superheat. In addition, the low suction flow rate of the compressor greatly reduces the cooling efficiency, which can lead to thermal protection of the compressor after long-term operation.