The root cause of compressor coil burning

The motor of semi enclosed refrigeration compressor (fluorine resistant motor) directly contacts refrigerant and refrigeration oil, and works under certain pressure and temperature for a long time The working environment of fluorine resistant motor (hereinafter referred to as motor) is relatively poor And in the process of operation and maintenance of the unit, if the use and maintenance are improper, the motor will often burn out, making the system unable to work normally However, the motor of the unit repaired in the past is still easy to burn down This paper analyzes the main reasons for the burnout of this kind of refrigeration compressor motor Motor fault analysis of semi enclosed compressor unit 1 Power supply voltage is too low: when the power supply voltage is too low, it starts to run At this time, the current through the motor is very large, which causes the thermal relay to open and close frequently Zui eventually causes the contact melting and adhesion, which leads to the failure of the thermal relay Under the action of high current, the binding wire of the winding is burnt out, and the outer insulation layer of the electromagnetic wire is burnt out, which makes part of the winding short circuited and causes the abnormal resistance value of the winding If the power supply voltage is too low, the power supply capacity is not enough, there are other high-power electrical appliances on the power supply line, and the line diameter of the power supply line is too small or there is a fault, it may cause the failure of the refrigeration compressor 2 Motor power control circuit fault: power switch and contactor are important parts of compressor motor control circuit Unreasonable selection and lack of maintenance can destroy Zui good refrigeration compressor It is very important to select switch and contactor correctly according to load It should be specially emphasized that if the contactor contacts are welded, all the controls (such as high and low pressure control, oil pressure control, defrost control, etc.) that depend on the contactor to disconnect the power circuit of the compressor will all fail, and the refrigeration compressor will be in unprotected state Therefore, when the motor is burnt out, it is necessary to check the contactor, because the contactor is an important cause that often forgotten 3 Motor fault caused by three-phase current imbalance: abnormal voltage and phase loss can easily destroy the motor The three-phase voltage imbalance shall not exceed 5% The three-phase voltage imbalance may cause the three-phase current imbalance of the motor, in which the current of one phase (or two phases) is too large, so that the winding first heats up and breaks down or burns down, and the current of other windings also rises sharply and burns down When the motor is running, the average value of current value of any phase and three-phase current shall not exceed 10% As a result of voltage imbalance, unbalanced voltage percentage can cause 4-10 times of current imbalance 4 Abnormal load and locked rotor: the load of compressor motor includes the load required for compressed gas and the load required for overcoming mechanical friction Too much pressure ratio and too much pressure difference will make the compression process more difficult, and the increase of friction caused by lubrication failure, as well as the motor locked rotor in extreme cases, will greatly increase the load of the motor The motor torque of high-power semi enclosed compressor is very large, and the local wear will not cause locked rotor generally, but the output power of motor will increase with the increase of load in a certain range, resulting in more serious wear, even causing cylinder biting, connecting rod fracture and other serious damage The current (locked rotor current) during locked rotor is about 4-7 times of the normal working current Thermal protection can protect the motor during locked rotor, but generally it will not respond quickly (PTC is slightly faster) to prevent the winding temperature change caused by locked rotor, thus reducing the insulation performance of enameled wire 5 Problems of motor itself: The national standard has corresponding regulations and requirements for the production and manufacturing of fluorine-resistant motors However, due to the different levels of technical strength, testing instruments, production equipment, especially quality awareness of various production enterprises, especially those products from small workshops without professional ability are difficult to avoid the inherent hidden dangers of the motor itself, so it is not difficult to avoid this problem, because often such products Some problems can be found by visual inspection of appearance and general inspection means (megger measurement) For example, the binding at the end of motor winding is loose and uneven, the insulation paint is uneven and even sticky, the selection of outgoing line is not standardized, there is no import mark (such as AMP) on the plug, the arrangement of enameled wire is disordered, the selection of insulation material is not standardized, the insulation resistance to ground and between phases is less than 20m Ω, and the three-phase resistance is unbalanced 6 Poor oil return of the refrigeration system: due to the poor oil return of the refrigeration system, it will cause the compressor to be short of oil and unable to deliver enough refrigeration oil to all lubrication parts, which will aggravate the friction of all lubrication parts (shaft sleeve, piston), cause the piston and crankshaft to jam in a short time, lead to the sharp rise of the compressor motor current, and then burn the motor coil There are various reasons for poor return oil, such as: return liquid, block of shut-off valve, blocked return oil hole, improper size of hole, or overload operation of system, and oil shortage caused by leakage 7 Large water content in the refrigeration system: because the coil of the motor of the refrigeration compressor is subject to the immersion of refrigerant and refrigeration oil for a long time, when the water content in the refrigeration system increases, the water reacts with the refrigeration oil and refrigerant to produce acid substances, which can corrode the insulation layer of the coil of the motor winding under a certain temperature and pressure In addition, the moisture content of the refrigeration system will cause the insulation resistance of the winding to drop Under the influence of electromagnetic force, mechanical force and temperature, the chemical reaction will cause the insulation layer of the winding to crack, crisp and other aging phenomena, so that the motor winding coil inter phase or inter turn breakdown short circuit Zui will eventually cause the motor to burn The sources of water in the refrigeration system include: the water content of refrigerant and refrigeration oil is too high, which is brought in during filling; when the refrigeration system is opened for maintenance, it is exposed to the air for a long time and absorbs water from the air; after maintenance, the refrigerant and refrigeration oil are injected without sufficient drying and timely replacement of the desiccant of the filter 8 Lack of refrigerant operation: due to the lack of refrigerant for a long time, the temperature of the compressor cylinder is getting higher and higher, the expansion deformation is getting larger and larger, resulting in hard friction between the cylinder and the piston, and the temperature is also getting higher and higher, causing the carbonization of the refrigeration oil, causing the inner cavity and the piston to be burnt black, and in serious cases, it will cause the piston to pull out, knock the cylinder or get stuck, causing the motor to generate a large current, The continuous high current will cause the motor winding to burn out 9 Vacuum operation: due to the vacuum operation, the temperature of the compressor cylinder rises rapidly, the winding coil of the refrigeration compressor motor heats up, causing tiny bubbles in the coil insulation body At this time, the outside of the winding is a high vacuum, which is easy to cause bubbles to expand and the insulation layer to fall off, Cause motor failure, vacuum operation about two minutes motor winding coil will be damaged, so that the compressor can not work properly The causes of compressor vacuum operation generally include: power on operation without opening the valve, use the compressor to directly vacuumize the pipeline system or operate without opening the low-pressure valve 10 Foreign matters entering the compressor: As foreign matters enter into the compressor compression cavity, the piston and cylinder will crack during reciprocating motion, which will aggravate the friction Foreign matters move at high speed in the cylinder, damaging the suction and exhaust valve plates The rising temperature of the cylinder will make the piston elongate, knock or block, which will cause motor failure The metal chips in the winding are the main culprit of short circuit and low ground insulation resistance It is only a matter of time before a short circuit occurs after the metal chips are gathered on the motor winding coil As for the source of the foreign matter: molding sand and metal chips produced in the processing and manufacturing of the compressor, including the copper pipe chips and welding slag left during the construction; the refrigerant and refrigeration oil are added inadvertently during the maintenance; It may also be broken valve plate or burnt copper slag of winding, worn shaft sleeve and motor stator and rotor scavenging, etc The failure of the motor of the semi enclosed refrigeration compressor is related to the manufacturing, installation, use and maintenance of the motor Its burnout is generally the result of the comprehensive effect of various factors If attention is paid to methods in the installation, maintenance and maintenance, the possibility of burnout will be greatly reduced In order to avoid the burnout of the repaired compressor motor soon again, it is necessary to The cause of the fault is solved, and new fault factors cannot be brought into the maintenance Therefore, the correct installation and use of refrigeration compressor, as well as reasonable daily maintenance, can prevent the occurrence of adverse factors, which is the fundamental method to avoid the damage of refrigeration compressor motor