Several Common Protection Measures for Refrigeration System
Errors in the refrigeration system may include: liquid slamming, high exhaust pressure, insufficient supply of lubricating oil, freezing of the refrigerant in the evaporator, overload of the motor equipped with the refrigeration compressor, etc. Adaptive protection measures.
High Voltage Protection:
High-pressure protection is to detect whether the refrigerant pressure in the system is normal. When the pressure exceeds the allowable range, the pressure switch will act, and the abnormal signal will be transmitted to the high-pressure controller. After processing, the refrigeration system will be stopped and the fault will be displayed.
Low Voltage Protection:
The low pressure protection detects the return air pressure in the system to prevent damage to the compressor due to low system pressure or no refrigerant running. If the system leaks and there is no refrigerant, forced operation will damage the compressor. At this time, the low pressure protection can respond in time, the control system will stop and display faults, and the compressor and refrigeration system will be protected.
Oil pressure protection:
A device to prevent oil shortage of bearings or other internal components of the compressor due to low lubricating oil pressure. If the oil volume of the compressor is reduced or the oil is cut off, the compressor running at high speed will be seriously damaged. The oil pressure protection device is exactly An important component to ensure the safe operation of the compressor.
Freeze Protection:
If the evaporator is too dirty or the frost is too serious, at this time, the air-conditioning cannot fully exchange heat with the hot air outside, which will cause the indoor unit to freeze. to protect the compressor. Anti-freeze is generally set to a value, such as 3 ℃, at this time, the outdoor fan or compressor speed is reduced, the condensation pressure and evaporation pressure are increased, and the evaporation temperature is increased. If the evaporator temperature falls further below 0°C, the compressor also stops working. If the indoor evaporator temperature rises to a normal value, such as 6°C, the compressor and outdoor fan operate normally. Indoor anti-freeze protection is to stop the compressor before the compressor freezes in the internal unit, which protects the compressor and the refrigeration system.
Exhaust temperature protection:
Excessive exhaust temperature will cause refrigerant decomposition, aging of insulating materials, carbonization of lubricating oil, damage to air valves, and blockage of capillaries and drying filters. The protection method is mainly to use the thermostat to sense the exhaust temperature. The thermostat should be placed near the exhaust port. When the exhaust temperature is too high, the thermostat will act to cut off the circuit.
Case temperature protection:
The case temperature will affect the life of the compressor. If the temperature of the casing is too high, it may be caused by the insufficient heat exchange capacity of the condenser. Therefore, you should check the air volume or water volume of the condenser and whether the water temperature is appropriate. If air or other non-condensable gases are mixed into the refrigeration system, the condensing pressure will rise and the casing will rise. Overheating; if the suction temperature is too high, the casing is prone to overheating. In addition, if the motor is overheated, the casing will also be overheated.
Current protection:
When a short circuit occurs in the line, one of the important features is that the current in the line increases sharply, which requires setting a corresponding protection device that responds to the increase of the current when the current flows through a certain predetermined value. The protection device is called overcurrent protection.
Overheating protection:
For a motor that is well designed and operates under specified conditions, the internal temperature will not exceed the allowable value, but when the motor runs at too high or too low voltage, or when the motor operates in a high temperature environment, the internal temperature of the motor exceeds the allowable value, and the motor is frequently started. When the temperature is too high, the temperature will be too high due to excessive starting current.
Delay start protection:
During the operation of the air conditioner, the compressor will stop running due to various reasons. At this time, the high and low pressures in the system will not be balanced immediately. If the compressor is started at this time, the starting current may be too large due to the pressure problem and the air conditioner will be burned. Therefore, the current air conditioners are equipped with delayed start protection, that is, each time the compressor stops running, it can be restarted after a delay of 3-5 minutes.
Phase sequence protection:
Phase sequence protection is a protection relay that can automatically identify the phase sequence, to avoid accidents or equipment damage caused by the reversed phase sequence of the power supply (three live wires connected in reverse order) to the motor reversed for some refrigeration compressors. For example: scroll compressors and piston compressors have different structures. Since the inversion of the three-phase power supply will cause the inversion of the compressor, it cannot be inverted. Therefore, it is necessary to install a reverse phase protector to prevent the reverse rotation of the chiller. When the reverse phase protector is installed, the compressor can work in normal phase. When the opposite phase occurs, it is necessary to change the two lines of the power supply to be in positive phase.
Phase unbalance protection:
Unbalanced voltages between phases will cause unbalanced currents in three phases, resulting in greater temperature rise - set overload relays. In the largest phase of the current, the proportion of the increase in temperature rise is about twice the square of the proportion of the voltage imbalance. Such as 3% voltage unbalance will produce about 18% temperature rise.
