Common protection devices for refrigeration systems

Common protection devices for refrigeration systems

Accidents in refrigeration systems may include: liquid shock, excessive exhaust pressure, insufficient lubricating oil supply, freezing of refrigerant in the evaporator, overload of the motor used in the refrigeration compressor, etc. For this reason, the refrigeration system should be equipped with certain protection devices according to specific circumstances.

High-pressure 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 operate and transmit the abnormal signal to the high-pressure controller. After processing, the refrigeration system will stop working and the fault will be displayed.

Low-pressure protection:

Low-pressure protection detects the return air pressure in the system. Its function is to prevent the compressor from being damaged by too low system pressure or no refrigerant. If the system leaks and there is no refrigerant, forced operation will damage the compressor. At this time, low-pressure protection can respond in time, control the system to stop and display faults, and protect the compressor and refrigeration system.

Oil pressure protection:

A device to prevent the bearing or other internal components of the compressor from being damaged due to lack of oil due to too low lubricating oil pressure. If the compressor oil volume is reduced or the oil is cut off, the high-speed compressor will be seriously damaged. The oil pressure protection device is an important component to ensure the safe operation of the compressor.

Antifreeze protection:

If the evaporator is too dirty or frosted too severely, the cold air cannot fully exchange heat with the hot air outside, causing the indoor unit to freeze. The indoor antifreeze protection is to stop the compressor before the indoor unit freezes, which plays a role in protecting the compressor. Antifreeze generally sets a value, such as 3°C. At this time, the outdoor fan or the compressor speed is reduced to increase the condensing pressure and evaporation pressure, thereby increasing the evaporation temperature. If the evaporator temperature is further reduced to below 0°C, the compressor will also stop working. If the indoor evaporator temperature rises to a normal value, such as 6°C, the compressor and outdoor fan will operate normally.

Indoor antifreeze protection is to stop the compressor before the indoor unit freezes, which plays a role in protecting the compressor and the refrigeration system.

Exhaust temperature protection:

Excessive exhaust temperature causes refrigerant decomposition, aging of insulation materials, carbonization of lubricating oil, damage to gas valves, and blockage of capillaries and dry filters. The protection method is mainly to use a thermostat to sense the exhaust temperature. The thermostat should be placed close to the exhaust port. When the exhaust temperature is too high, the thermostat will act and cut off the circuit.

Casing temperature protection:

Casing temperature will affect the life of the compressor. Excessive casing temperature may be caused by insufficient heat exchange capacity of the condenser, so the air volume or water volume of the condenser should be checked, and the water temperature should be appropriate. If air or other non-condensable gases are mixed in the refrigeration system, the condensation pressure will rise and the casing will overheat; if the suction temperature is too high, the casing will easily overheat. In addition, overheating of the motor will also cause the casing to overheat.

Current protection:

When a short circuit occurs in the line, one of the important characteristics is that the current in the line increases sharply, which requires the setting of a corresponding protection device called overcurrent protection that reacts to the increase in current when the current flows through a certain predetermined value.

Overheat protection:

For a well-designed motor operating under specified conditions, the internal temperature will not exceed the allowable value, but when the motor is operated at too high or too low voltage, or when it is operated in a high temperature environment, the internal temperature of the motor will exceed the allowable value. When it is started frequently, the temperature will be too high due to excessive starting current.

Delayed start protection:

During the operation of the air conditioner, the compressor will stop running for 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 pressure problems, burning the air conditioner. Therefore, the current air conditioners are equipped with delayed start protection, that is, each time the compressor stops running, it will be delayed for 3-5 minutes before it can be started again.

Phase sequence protection:

Phase sequence protection is a protection relay that can automatically identify the phase sequence to prevent some refrigeration compressors from reversing the motor due to the reverse phase sequence of the power supply (the three live wires are connected in reverse order), which may cause accidents or equipment damage.

For example: The structure of the scroll compressor and the piston compressor is different. Since the inversion of the three-phase power supply will cause the inversion of the compressor, it cannot be inverted. Therefore, a reverse phase protector needs to be installed to prevent the reversal of the chiller. When the reverse phase protector is installed, the compressor can work in the positive phase. When the opposite phase occurs, it is necessary to change the two lines of the power supply to the positive phase.

Phase unbalance protection:

Phase unbalanced voltage will cause three-phase unbalanced current, resulting in greater temperature rise - set overload relay. In the phase with the largest current, the temperature rise increases by about twice the square of the voltage unbalance ratio. For example, a 3% voltage unbalance will produce about 18% temperature rise.