What are the common protections for refrigeration systems?

2021-07-23

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 send abnormal signals to the high pressure controller. After processing, the refrigeration system will stop working and the fault will be displayed.

Low pressure protection: The low pressure protection detects the return air pressure in the system, which is to prevent the compressor from being damaged because the system pressure is too low or there is no refrigerant running.

Oil pressure protection: to prevent bearings or other compressor internal components from oil damage due to low lubricating oil pressure, compressor oil volume reduction or oil break, will make the high-speed operation of the compressor is seriously damaged, oil pressure protection device is an important part to ensure the safe operation of the compressor.

Anti-freezing protection: if the evaporator is too dirty or frosting is too serious, the cold air can not be fully exchanged with the hot air outside and cause the internal machine to freeze. Indoor anti-freezing protection is to stop the compressor before the compressor freezes and protect the compressor.

Current protection: When the circuit occurs short circuit, one of the important features is that the current in the circuit increases sharply, which requires the corresponding setting when the current flows through a predetermined value, the reaction in the current rise and the action of the protection device is called over-current protection.

Overheat protection: well designed and operating under specified conditions of the motor, the internal temperature will not exceed the allowable value, but when the motor is running at too high or too low voltage, or in the high temperature environment, the internal temperature of the motor exceeds the allowable value, in frequent starting, more due to the starting current over the temperature is too high.

Phase sequence protection: phase sequence protection is a protective relay that can automatically identify the phase sequence, so as to avoid some refrigeration compressors and other power supply because of the reverse phase sequence connection (three live wire sequence connection) back to the motor reversal, resulting in accidents or equipment damage.

For example: scroll compressor and piston compressor structure is different. The inverter of the three-phase power supply will cause the inverter of the compressor, so it cannot be inverter. Therefore, it is necessary to install a phase reversal protector to prevent the chiller from reversing. When the inverting protector is installed, the compressor can work in positive phase. When opposite phases occur, it is necessary to change the two lines of the power supply into a positive phase.

Phase unbalance protection: phase unbalance voltage will lead to three-phase unbalance current, resulting in greater temperature rise - set overload relay. In the maximum phase of the current, the temperature rise increases by about twice the square of the ratio of the voltage imbalance. A voltage imbalance of 3% will produce a temperature rise of about 18%.

Exhaust temperature protection: excessive exhaust temperature will cause refrigerant decomposition, insulation material aging, lubricating oil carbon, air valve damage, but also make capillary and filter dryer clog. The protection method is mainly to use the temperature controller induction exhaust temperature, the temperature controller should be placed near the exhaust port, exhaust temperature is too high, the temperature controller action, cut off the circuit.

Housing temperature protection: housing temperature will affect the service life of the compressor. The high temperature of the shell may be caused by the insufficient heat transfer capacity of the condenser, so the scenery or water amount and water temperature of the condenser should be checked. If air or other non-condensable gases are mixed in the refrigeration system, the condensation pressure will rise and the shell will be overheated. The suction temperature is too high, the housing is easy to overheat, in addition, the motor overheating will also overheat the housing.