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Analysis of air-conditioning compressor overload protection device effect

In Electronic Infomation Category: A | on February 22,2011

General will have a dedicated air conditioning system components such as pressure switches, exhaust temperature, etc. for the protection of the compressor package, but with the increasingly fierce market competition, increasing pressure on the cost of air conditioners, especially in small home air conditioners, the basic components are not specifically protect the compressor, the compressor overload protection device has become the most important and AD9220AR datasheet and the last barrier.

1 overload the working principle and AD9220AR price and features

1.1 overload the working principle and AD9220AR suppliers and classification

Air conditioning compressor overload protection are generally sudden jump by double metal protection, the heating wire, dual-metal contact and the two components of static circuit, series circuit in the compressor. When the current in the circuit is too large, heating wire heating, double-metal baking dish, when the double-metal will heat the opposite direction when the arch, so that the contacts to open; When the compressor housing or the motor temperature is too high even when the normal operating current, heat the heating wire is very small, deformed bimetal will bend upward, away from the two static contact, the circuit is cut off. This protection can be automatically reset, with over-current, over temperature dual protection.

Different ways depending on the installation can be divided into external and built-in two:

(1) External protection: the seal installed in the terminal on the compressor housing, close to the roof, to sense the temperature of the compressor housing. As heat from the motor heat to the outer shell has a process of conduction and convection, heat from the shell and then there is a process of protection action, therefore, this protection is the accuracy and reliability are relatively poor, but because of its simple manufacturing , with a double metal, by adjusting the height of the screw, can create different protection and easy installation and maintenance, low cost, low power, generally used in home air conditioning compressor.

(2) built-in protection: is divided into type and plug-lashing, lashing is protector-type coil banding together with the motor, direct induction coil temperature changes, rapid response and accurate; Plug-in is will protect the device plugged into a sealed terminal, through the refrigerant heat transfer to sense the temperature of the motor abnormalities did not occur in the refrigerant leak in the circumstances to protect the more accurate, but if there is leakage of refrigerant, the protection performance is poor.

In short, the motor built-in protection than the external temperature sensor is more sensitive and more accurate, more reliable, wider scope of application (air conditioner compressor can be applied in general.) However, as installed in the compressor house, requiring small size, able to adapt to the internal compressor temperature, high pressure changes and other harsh environment, so its design and manufacture of high demands put forward, cost several times more expensive than external.

1.2 work overload protection features

Overload protection device has three main features: temperature characteristics, the minimum operating current characteristics and properties of the initial movement time.

Temperature characteristics: There is action temperature and reset temperature, the operating temperature is not carrying current overload protection device, or only signal current through the case to the separation of static and dynamic contact temperature, when the protection value reaches the temperature sensor action temperature, the protection is broken; when the temperature sensing protection down to reset the temperature, the protection will be re-closed.

Minimum operating current characteristics: at a certain temperature, the overload protection will be at a certain current value of the jump, cut off the compressor motor current, the current - temperature curve shown in Figure 1.

Time characteristics of the initial action: room temperature, current overload protection device at different times under different actions, its time - current curves shown in Figure 2.

2. Overload protection device for air conditioning compressor results

Air conditioning compressor high temperature, high pressure refrigerant and lubricant mixed environment, so the material itself can withstand a certain degree of high temperature and high pressure compressors for air temperature usually is 120 or 130 . If more than temperature limit the damage to the compressor, including damage to the pump, the motor burned or both, therefore, need to protect the case, including the compressor stall, overheat and high-pressure, air-conditioning system in some abnormal conditions may cause the compressor to the above three situations occur. No special components in the air-conditioning system to protect against the above exception, the overload protection has become a protective barrier last compressor, accurate and timely action can play a vital role on the compressor. Abnormal type of integrated air-conditioning system and overload the working principle of exceptional circumstances, the role overload protection of the statistics in Table 1.

For small home air conditioners, the air conditioning system is running in overload protection can not play the situation mainly occurs in the case of no current linkage, including the lack of refrigerant, high compression ratio, inadequate cooling and excessive refrigerant , insufficient cooling performance with low refrigerant similar, so the back will be focused on lack of refrigerant, refrigerant and a high compression ratio over the three situations experiments.

2.1 insufficient refrigerant overload protection device authentication

Select two air-conditioning system, the compressor overload internal and external, respectively, in the indoor 32 / 23 , the outdoor 48 / - conditions to hold refrigerant, refrigerant and put put 50% 62% refrigerant experiment to observe whether the lack of refrigerant after the overload protection device for the effective protection of the air conditioning system, the experimental results shown in Table 2.

Seen from Table 2, in the absence of sufficient refrigerant, overload protection actions have been achieved when the exhaust temperature above 140 , 10 temperature difference calculated in accordance with the motor winding temperature should be above 150 , and the general compression Machine-level heat-resistant grade of E or B, temperature is 120 or 130 , heat-resistant enameled wire for the H-class level, the temperature is 150 , that is, despite the overload protection operation, but not from role to protect the compressor, this time has caused damage to the compressor. Let go of 50% of the refrigerant when the external overload protection action within the exhaust temperature is relatively close to the action only external overload the built-in longer time than 5min, but the protective effect is the same. But let go of 62% of the refrigerant, the built-in overload of the exhaust temperature is still above 140 , has not significantly increased, and no longer operating time, indicating lack of increase in the refrigerant can play after the built-in overload with the same protective effect before, and external overload the movement time was lengthened, the exhaust temperature increased significantly, can not play with the same protection before the effect on the extent of damage to the compressor with less than the amount of refrigerant added to increase the large.

2.2 refrigerant excessive overload protection device authentication

Too much refrigerant is the most direct impact brought back to the compressor fluid, excess fluid will bring oil back to dilute, to increase oil and liquid discharge risk of attack, the compressor wear and tear caused by poor lubrication, or even stuck damage due to wet compression, especially in long-term damage to the compressor during operation is very large, so too much refrigerant in the system when it is necessary to protect the compressor.

Were selected both high and low temperature refrigerant working conditions of excessive experiment to test the exhaust refrigerant after too many changes of temperature and current, at rated voltage and rated frequency, change the system only the amount of refrigerant charge, the results Table 3.

Experimental data from Table 3 can be seen that when the refrigerant compressor motor due to excessive cooling effect, and suction temperature and exhaust temperature has decreased, due to temperature and overload protection does not protect; current due to refrigerant increase increase, but increased marginally, up less than the current value of the protection action. Therefore, the refrigerant can not be too many cases, protect the compressor overload protection role.

2.3 high compression ratio when the overload protection device authentication

Air compressor compression ratio in the range between 3 to 5, generally no more than 6, the compression ratio over the General Assembly led to the internal compressor valves, bearings and other components of the damage. Air-conditioning systems high compression ratio generally occur in low-temperature conditions, when the system pressure is not high, but low pressure is very low, resulting in a high compression ratio, respectively, three outdoor conditions for testing, observation system compression ratio and overload protection can properly protected.

We can see from Table 4, in the non-low-temperature conditions, the compression ratio did not exceed 5, and in the outdoor temperature dropped to -15 , although low-temperature high-pressure conditions than non-even lower, but the sharp decline in low-voltage, resulting in significant increase in compression ratio, compressor, etc. The temperature inside the compression chamber will be increased, while inspiratory time decreased because the compressor caused the current smaller, exhaust temperature and the motor winding temperature due to low temperature and the refrigerant suction less reason not high, the overload protection does not move, indicating that mechanical components within the compressor at this time despite the harsh high temperature but not to be reflected through the protection, it can not be effectively protected, can be protected only by low-pressure effective control.

3 Conclusion

(1) configured in different ways compressor overload protective effect of the compressor is different, built-in protection than the external protection of high sensitivity, the protective effect of the relatively large compressor; (2) refrigerant insufficient, either external or built-in protection protection protection of the compressor are very limited, so air-conditioning system to the increased lack of protection for refrigerant; (3) excessive refrigerant can not play a protective role overload , the system need to use high-pressure switch high-voltage protection measures to avoid excessive refrigerant compressor damage; (4) Overload protection under high compression ratio can not play the role of protection must be a separate low-voltage protection measures to protect the compressed machine.

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