压缩机英文论文百度文献

Refrigeration CompressorCompiled from material originally presented in Volume 1 (1992) of the Bell Jar with various updates and additions.--------------------------------------------------------------------------------The Scientific American Amateur Scientist column, when under the leadership of C.L. Stong, devoted a considerable amount of attention (relatively speaking) to projects involving vacuum. Much of the information on the pumping systems was provided by Franklin B. Lee, one of Stong’s contributors. Lee correctly recognized that one of the major barriers to amateur involvement in vacuum was the availability of low cost mechanical pumps. To address this, he developed a number of practical conversions of then-available sealed and belt-driven rotary refrigeration compressors. These conversions were detailed in a booklet authored in 1959 by Lee. (This booklet will be reproduced on this site in the near future.) Supplemental information was provided in a number of Stong’s columns. From our perspective, Lee’s conversions are now of limited interest as the compressors which he modified and characterized were all of pre-1960s vintage. Furthermore, at least to my knowledge, no refrigerator of current manufacture uses a rotary pump. They are all sealed piston units (see picture below) and their vacuum capabilities are limited to several 10s of Torr. However, modern room air-conditioners frequently use compressors of the rotary-piston type. The ones I have come across are manufactured by Matsushita and they are easy to differentiate from their piston brethren (see the photo to the left). The sealed piston units tend to be as wide as they are tall. Also, as the internal reciprocating mechanism is spring-mounted, a gentle shaking of the compressor will yield a tell-tale thunking from within the compressor shell. The innards of the rotary units are welded to the cases and the cases are considerably taller than their diameter. A typical unit would be 5 or 6 inches in diameter and 9 to 10 inches tall. The figure below shows the general layout of one of these compressors. Unlike the older compressors that Lee dealt with, the Matsushita units have no internal check valves or other features that impede their use as vacuum pumps. Thus, their use is pretty straightforward. As appliances are frequently retired for reasons other than a malfunctioning compressor (they more often have other functional defects or may have just gotten “ratty” looking), working compressors may often be obtained for next to zero cost from your local dump (recycling center) or from an appliance repair shop. Air-conditioner brands that use this type of compressor, based on my informal surveys at the dump and in an appliance store, include GE, Whirlpool, Sharp, Amana and Westinghouse. Some of the manufacturers (e.g. GE) don’t show the Matsushita name on the compressor. Matsushita makes compressors for air-conditioners with capacities ranging from 5670 BtuH to 24880 BtuH. A compressor from an average size air-conditioner (8000 BtuH) will have a free-air throughput of about 1.5 cfm. Since refrigeration systems contain freon (at least the older systems you are likely to encounter at the dump) and since releasing freon into the atmosphere is a no-no, it is best to have a refrigeration service shop purge the system of freon before removing the compressor. Once that is done, the inlet and outlet tubes may be cut with a tubing cutter. Never use a saw - the filings will invariably find their way into the compressor. The starting capacitor will also have to be removed from the system. Frequently this will be a dual section capacitor with one section for the compressor, the other for the fan motor. Make a note of which section goes with the compressor. The three motor terminals are inside a plastic cap at the top of the unit along with a thermal cut-out switch. Leaving this switch in place is important. When used in a refrigeration system, a cold freon/oil mixture is constantly being drawn into the compressor. This doesn't happen when pumping a vacuum chamber. As a result, overheating is more likely to occur and this will cause the compressor to fail. Mount the compressor on a wood base along with the starting capacitor and a switch. The compressor requires enough oil to cover the exhaust valve. Since it is not possible to see the oil level, make an estimate (the refrigeration shop should be able to help here) and, with a tube connected to the inlet, start the compressor and suck some oil into the unit. If you get too much oil, it will spit out of the exhaust. (Some spitting will always occur and it is best to have the unit exhaust through a tube into a small container stuffed with lint-free rags. This will contain the expelled oil and will also limit the amount of mist introduced into the air.) A compressor such as this will evacuate a small chamber to about the 1 Torr range. While it is theoretically possible to obtain a better vacuum with two compressors connected in series, I have only had limited success with this. Lee was able to achieve pressures to 10 mTorr with two series-connected 1950s vintage Frigidaire Meter-Miser compressors and you should feel free to experiment. Refrigeration BasicsBrought to you by... This material explains in basic terms the principals that are used to create the refrigeration effect. First of all, did you know that there is no such thing as cold? You can describe something as cold and everyone will know what you mean, but cold really only means that something contains less heat than something else. All there really is, is greater and lesser amounts of heat. The definition of refrigeration is The Removal and Relocation of Heat. So if something is to be refrigerated, it is to have heat removed from it. If you have a warm can of pop at say 80 degrees Fahrenheit and you would prefer to drink it at 40 degrees, you could place it in your fridge for a while, heat would somehow be removed from it, and you could eventually enjoy a less warm pop. (oh, all right, a cold pop.) But lets say you placed that 40 degree pop in the freezer for a while and when you removed it, it was at 35 degrees. See what I mean, even "cold" objects have heat content that can be reduced to a state of "less heat content". The limit to this process would be to remove all heat from an object. This would occur if an object was cooled to Absolute Zero which is -273� C or -460� F. They come close to creating this temperature under laboratory conditions and strange things like electrical superconductivity occur. How do things get colder?The latter two are used extensively in the design of refrigeration equipment. If you place two objects together so that they remain touching, and one is hot and one is cold, heat will flow from the hot object into the cold object. This is called conduction. This is an easy concept to grasp and is rather like gravitational potential, where a ball will try to roll down an inclined plane. If you were to fan a hot plate of food it would cool somewhat. Some of the heat from the food would be carried away by the air molecules. When heat is transferred by a substance in the gaseous state the process is called convection. And if you kicked a glowing hot ember away from a bonfire, and you watched it glowing dimmer and dimmer, it is cooling itself by radiating heat away. Note that an object doesn't�t have to be glowing in order to radiate heat, all things use combinations of these methods to come to equilibrium with their surroundings. So you can see that in order to refrigerate something, we must find a way to expose our object to something that is colder than itself and nature will take over from there. We are getting closer to talking about the actual mechanics of a refrigerating system, but there are some other important concepts to discuss first. The States of MatterThey are of course; solid, liquid and gas. It is important to note that heat must be added to a substance to make it change state from solid to liquid and from liquid to a gas. It is just as important to note that heat must be removed from a substance to make it change state from a gas to a liquid and from a liquid to a solid. The Magic of Latent HeatLong ago it was found that we needed a way to quantify heat. Something more precise than "less heat" or "more heat" or "a great deal of heat" was required. This was a fairly easy task to accomplish. They took 1 Lb. of water and heated it 1 degree Fahrenheit. The amount of heat that was required to do this was called 1 BTU (British Thermal Unit). The refrigeration industry has long since utilized this definition. You can for example purchase a 6000 BTUH window air conditioner. This would be a unit that is capable of relocating 6000 BTU's of heat per hour. A larger unit capable of 12,000 BTUH could also be called a one Ton unit. There are 12,000 BTU's in 1 Ton. To raise the temperature of 1 LB of water from 40 degrees to 41 degrees would take 1 BTU. To raise the temperature of 1 LB of water from 177 degrees to 178 degrees would also take 1 BTU. However, if you tried raising the temperature of water from 212 degrees to 213 degrees you would not be able to do it. Water boils at 212 degrees and would prefer to change into a gas rather than let you get it any hotter. Something of utmost importance occurs at the boiling point of a substance. If you did a little experiment and added 1 BTU of heat at a time to 1 LB of water, you would notice that the water temperature would increase by 1 degree each time. That is until you reached 212 degrees. Then something changes. You would keep adding BTU's, but the water would not get any hotter! It would change state into a gas and it would take 970 BTU's to vaporize that pound of water. This is called the Latent Heat of Vaporization and in the case of water it is 970 BTU's per pound. So what! you say. When are you going to tell me how the refrigeration effect works? Well hang in there, you have just learned about 3/4 of what you need to know to understand the process. What keeps that beaker of water from boiling when it is at room temperature? If you say it's because it is not hot enough, sorry but you are wrong. The only thing that keeps it from boiling is the pressure of the air molecules pressing down on the surface of the water. When you heat that water to 212 degrees and then continue to add heat, what you are doing is supplying sufficient energy to the water molecules to overcome the pressure of the air and allow them to escape from the liquid state. If you took that beaker of water to outer space where there is no air pressure the water would flash into a va pour. If you took that beaker of water to the top of Mt. Everest where there is much less air pressure, you would find that much less heat would be needed to boil the water. (it would boil at a lower temperature than 212 degrees). So water boils at 212 degrees at normal atmospheric pressure. Lower the pressure and you lower the boiling point. Therefore we should be able to place that beaker of water under a bell jar and have a vacuum pump extract the air from within the bell jar and watch the water come to a boil even at room temperature. This is indeed the case! A liquid requires heat to be added to it in order for it to overcome the air pressure pressing down on its' surface if it is to evaporate into a gas. We just learned that if the pressure above the liquids surface is reduced it will evaporate easier. We could look at it from a slightly different angle and say that when a liquid evaporates it absorbs heat from the surrounding area. So, finding some fluid that evaporates at a handier boiling point than water (IE: lower) was one of the first steps required for the development of mechanical refrigeration. Chemical Engineers spent years experimenting before they came up with the perfect chemicals for the job. They developed a family of hydroflourocarbon refrigerants which had extremely low boiling points. These chemicals would boil at temperatures below 0 degrees Fahrenheit at atmospheric pressure. So finally, we can begin to describe the mechanical refrigeration process. Main ComponentsThere are 4 main components in a mechanical refrigeration system. Any components beyond these basic 4 are called accessories. The compressor is a va pour compression pump which uses pistons or some other method to compress the refrigerant gas and send it on it's way to the condenser. The condenser is a heat exchanger which removes heat from the hot compressed gas and allows it to condense into a liquid. The liquid refrigerant is then routed to the metering device. This device restricts the flow by forcing the refrigerant to go through a small hole which causes a pressure drop. And what did we say happens to a liquid when the pressure drops? If you said it lowers the boiling point and makes it easier to evaporate, then you are correct. And what happens when a liquid evaporates? Didn't we agree that the liquid will absorb heat from the surrounding area? This is indeed the case and you now know how refrigeration works. This component where the evaporation takes place is called the evaporator. The refrigerant is then routed back to the compressor to complete the cycle. The refrigerant is used over and over again absorbing heat from one area and relocating it to another. Remember the definition of refrigeration? (the removal and relocation of heat). Heat Transfer RatesOne thing that we would like to optimize in the refrigeration loop is the rate of heat transfer. Materials like copper and aluminum are used because they have very good thermal conductivity. In other words heat can travel through them easily. Increasing surface area is another way to improve heat transfer. Have you noticed that small engines have cooling fins formed into the casting around the piston area? This is an example of increasing the surface area in order to increase the heat transfer rate. The hot engine can more easily reject the unwanted heat through the large surface area of the fins exposed to the passing air. Refrigeration heat transfer devices such as air cooled condensers and evaporators are often made out of copper pipes with aluminum fins and further enhanced with fans to force air through the fins. Metering DeviceWe will now take a closer look at the individual components of the system. We will start with the metering device. There are several types but all perform the same general function which is to cause a pressure drop. There should be a full column of high pressure liquid refrigerant (in the liquid line) supplying the inlet of the metering device. When it is forced to go through a small orifice it loses a lot of the pressure it had on the upstream side of the device. The liquid refrigerant is sort of misted into the evaporator. So not only is the pressure reduced, the surface area of the liquid is vastly increased. It is hard to try and light a log with a match but chop the log into toothpick sized slivers and the pile will go up in smoke easily. The surface area of zillions of liquid droplets is much greater than the surface area of the column of liquid in the pipe feeding the metering device. The device has this name because it meters the flow of refrigerant into the evaporator. The next graphic shows a capillary line metering device. This is a long small tube which has an inside diameter much smaller than a pencil lead. You can imagine the large pressure drop when the liquid from a 1/4" or 3/8" or larger pipe is forced to go through such a small opening. The capillary line has no moving parts and can not respond to changing conditions like a changing thermal load on the evaporator. I have also added a few labels showing the names of some of the pipes. The EvaporatorThe metering device has sprayed low pressure droplets of refrigerant into the evaporator. The evaporator could be the forced air type and could be constructed of many copper tubes which conduct heat well. To further enhance heat transfer the pipes could have aluminum fins pressed onto them. This vastly increases the surface area that is exposed to the air. And this type of evaporator could have a fan motor sucking air through the fins. The evaporator would be capable of reducing the temperature of air passing through the fins and this is a prime example of the refrigeration effect. If that evaporator was located in a walk in cooler, the air would be blown out into the box and would pick up heat from the product; let's say it is a room full of eggs. The flow of heat would be egg core/egg shell/circulating air/aluminum fins/copper evaporator pipe/liquid droplet of refrigerant. The droplet of refrigerant has the capability of absorbing a large quantity of heat because it is under conditions where it is just about ready to change state into a gas. We have lowered it's pressure, we have increased surface areas and now we are adding heat to it. Just like water, refrigerants also have ratings for Latent Heats of vaporization in BTU's per LB. When heat is picked up from the air stream, the air is by definition cooled and is blown back out into the box to take another pass over the eggs and pick up more heat. This process continues until the eggs are cooled to the desired temperature and then the refrigeration system shuts off and rests. But what about our droplet of refrigerant. By now it might have picked up so much heat that it just couldn't stand it anymore and it has evaporated into a gas. It has served it's purpose and is subjected to a suction coming from the outlet pipe of the evaporator. This pipe is conveniently called the suction line. Our little quantity of gas joins lots of other former droplets and they all continue on their merry way to their next destination. The CompressorThe compressor performs 2 functions. It compresses the gas (which now contains heat from the eggs) and it moves the refrigerant around the loop so it can perform it's function over and over again. We want to compress it because that is the first step in forcing the gas to go back into a liquid form. This compression process unfortunately adds some more heat to the gas but at least this process is also conveniently named; The Heat of Compression. The graphic shows a reciprocating compressor which means that it has piston(s) that go up and down. On the down stroke refrigerant va pour is drawn into the cylinder. On the upstroke those va pours are compressed. There are thin valves that act like check valves and keep the va pours from going back where they came from. They open and close in response to the refrigerant pressures being exerted on them by the action of the piston. The hot compressed gas is discharged out the...you guessed it; discharge line. It continues towards the last main component. The CondenserThe condenser is similar in appearance to the evaporator. It utilizes the same features to effect heat transfer as the evaporator does. However, this time the purpose is to reject heat so that the refrigerant gas can condense back into a liquid in preparation for a return trip to the evaporator. If the hot compressed gas was at 135 degrees and the air being sucked through the condenser fins was at 90 degrees, heat will flow downhill like a ball wants to roll down an inclined plane and be rejected into the air stream. Heat will have been removed from one place and relocated to another as the definition of refrigeration describes. As long as the compressor is running it will impose a force on the refrigerant to continue circulating around the loop and continue removing heat from one location and rejecting it into another area. Superheat and SluggingThere is another very common type of metering device called a TX Valve. It's full name is Thermostatic Expansion Valve,

文献名称《空气压缩机操作工》基本信息作者：李总根 编丛 书 名：矿山特种作业人员安全技术培训考核统编教材出 版 社：中国劳动社会保障出版社，出版时间：2007-10-01版次：1页数：176装帧：平装开本：大32开内容简介空气压缩机操作工》主要内容包括法律法规常识、矿井安全生产技术知识、空气压缩机基础知识、压缩机的结构原理、压缩机的电气控制、压缩机的安全操作、矿山救护与职业病预防及压缩机典型事故案例分析等。《矿山特种作业人员安全技术培训考核统编教材：空气压缩机操作工》主要介绍矿山大量使用的L型往复活塞空气压缩机的同时，还分别对螺杆式空气压缩机及隔爆移动式空气压缩机进行了介绍。《矿山特种作业人员安全技术培训考核统编教材：空气压缩机操作工》主要作为《空气压缩机操作工》全国通用安全培训教材，也可供矿山企业有关专业技术人员、安全管理人员参考。《矿山特种作业人员安全技术培训考核统编教材：空气压缩机操作工》由湖南安全技术职业学院（长沙安全技术培训中心）李总根主编，彭伯平、李西京副主编，王捍湘、肖丹、曾敏、谢琳伟参与编写。安全生产专家、高级工程师彭新其主审。《节能产品惠民工程高效节能容积式空气压缩机推广实施细则》关于印发《节能产品惠民工程高效节能容积式空气压缩机推广实施细则》的通知财建〔2012〕851号各省、自治区、直辖市、计划单列市财政厅（局）、发展改革委、工业和信息化主管部门，新疆生产建设兵团财务局、发展改革委、工业和信息化主管部门：为促进节能家电等产品消费，经国务院同意，根据《财政部 国家发展改革委关于开展节能产品惠民工程的通知》（财建〔2009〕213号）规定，我们制定了《节能产品惠民工程高效节能容积式空气压缩机推广实施细则》，现印发给你们，请遵照执行。附件：节能产品惠民工程高效节能容积式空气压缩机推广实施细则财政部 国家发展改革委 工业和信息化部附件：节能产品惠民工程高效节能容积式空气压缩机推广实施细则一、推广产品范围及条件（一）推广产品为微型往复活塞空气压缩机、全无油润滑往复活塞空气压缩机、一般用固定的往复活塞空气压缩机、一般用喷油螺杆空气压缩机、一般用喷油单螺杆空气压缩机。（二）申请高效节能容积式空气压缩机（以下简称高效节能空压机）推广的产品必须满足以下要求：1.依据GB 19153《容积式空气压缩机能效限定值及能效等级》现行有效版本，空压机能效为2级及以上；2.通过能效标识备案；3.通过国家认可的第三方机构能效检测和节能产品认证（进入第一批推广目录的产品应在目录公布后三个月内通过节能认证）；4.在中国大陆境内生产和使用；5.近三年内国家产品质量监督抽查中，该品牌产品无不合格。（三）高效节能空压机的配套电机应优先选择能效等级2级及以上的高效节能电机。二、推广企业条件申请高效节能空压机推广的生产企业必须满足以下条件：1.为中国大陆境内注册的独立法人；2.年推广高效节能活塞式空压机的配套电机功率不少于1万kW，或螺杆式空压机的配套电机功率不少于2万kW；3.拥有所申请推广产品的自主品牌或品牌合法使用权，同一品牌只能由一家生产企业申请推广；4.具有完善的销售网络和产品销售、安装、售后服务及用户信息管理系统；5.具备完善的质量管理体系和环境管理体系。三、推广期限推广期限暂定为2012年11月1日至2013年10月31日。四、推广补贴标准高效节能空压机推广财政补贴标准具体为： 产品类型 能效水平 补贴标准（元/kW） 微型往复活塞空气压缩机 1级 80 2级 45 全无油润滑往复活塞空气压缩机 1级 160 2级 90 一般用固定的往复活塞空气压缩机 1级 80 2级 45 一般用喷油螺杆空气压缩机 1级 200 2级 100 一般用喷油单螺杆空气压缩机 1级 220 2级 120 五、推广企业资格申请申请高效节能空压机推广的企业，将申请报告（具体格式见附件1）及下述材料（复印件加盖公章）逐级上报，经省级节能主管部门、财政部门、工业和信息化部门审核后，报国家发展改革委、财政部、工业和信息化部。（一）营业执照、税务登记证和生产许可证；（二）推广产品能效检测报告和节能认证证书；（三）推广产品能效标识备案证明；（四）质量管理体系和环境管理体系认证证书；（五）商标注册证明及授权书；（六）其他相关材料。国家发展改革委会同财政部、工业和信息化部组织专家对上报材料进行审核，公示推广企业、产品规格型号，并根据推广企业产品规格型号调整等情况对目录实行动态管理。六、补贴资金申请和拨付（一）省级节能主管部门、工业和信息化部门对本地区年度推广使用情况进行调查摸底，组织用户推广高效节能空压机，将有关情况告知同级财政部门，并上报国家发展改革委、工业和信息化部。（二）财政部根据调查摸底和各省需求情况测算补贴资金规模，并将补贴资金预拨到省级财政部门。（三）有关单位、企业购买并安装国家公布的目录内高效节能空压机后，填报购买安装情况、补贴资金申报表（具体要求见附件2），并提供购买发票复印件等证明材料，到企业所在地财政部门申请补贴资金。具体资金拨付办法由省级财政部门制订。（四）各地财政部门根据购买安装单位、企业提供的相关材料及时拨付补贴资金，并会同节能主管部门、工业和信息化部门及时将相关信息录入“节能产品惠民工程”信息管理系统。（五）月度终了后10日内，省级财政部门、节能主管部门、工业和信息化部门将本地区上月推广使用和资金拨付情况进行汇总审核，并上报财政部、国家发展改革委、工业和信息化部（具体要求见附件3）。（六）工业和信息化部会同财政部、国家发展改革委组织有关机构对推广使用情况进行监督检查。（七）年度终了后30日内，省级财政部门提出年度补贴资金清算报告，上报财政部、工业和信息化部、国家发展改革委。（八）财政部将根据地方上报的补贴资金清算报告及工信部出具的监督检查意见，对补贴资金进行清算。七、罚则（一）对企业弄虚作假，采取通报批评、取消高效节能空压机推广资格、列入诚信“黑名单”并在媒体上曝光、追缴补贴资金并加倍处罚等方式予以处罚。（二）对未按规定进行检测或出具虚假检测报告的第三方能效检测机构，将采取通报批评、取消其节能产品惠民工程能效检测资格等方式予以处罚，并追究相关责任。（三）地方相关部门对申请材料的真实性负责。一经查出有弄虚作假行为，将依照相关规定予以处罚。附件：1.高效节能空压机推广生产企业申请报告2.高效节能空压机购买单位财政补贴申请报告3.高效节能空压机月度推广情况报告

电动机压缩机（以下简称压缩机）的故障可分为电机故障和机械故障(包括曲轴，连杆，活塞，阀片，缸盖垫等)。机械故障往往使电机超负荷运转甚至堵转，是电机损坏的主要原因之一。 电机的损坏主要表现为定子绕组绝缘层破坏（短路）和断路等。定子绕组损坏后很难及时被发现，最终可能导致绕组烧毁。绕组烧毁后，掩盖了一些导致烧毁的现象或直接原因，使得事后分析和原因调查比较困难。 然而，电机的运转离不开正常的电源输入，合理的电机负荷，良好的散热和绕组漆包线绝缘层的保护。从这几方面入手，不难发现绕组烧毁的原因不外乎如下六种：(1)异常负荷和堵转；(2)金属屑引起的绕组短路； (3)接触器问题；(4)电源缺相和电压异常；(5)冷却不足；(6)用压缩机抽真空。实际上，多种因素共同促成的电机损坏更为常见。 1. 异常负荷和堵转 电机负荷包括压缩气体所需负荷以及克服机械摩擦所需负荷。压比过大，或压差过大，会使压缩过程更为困难；而润滑失效引起的摩擦阻力增加，以及极端情况下的电机堵转，将大大增加电机负荷。 润滑失效，摩擦阻力增大，是负荷异常的首要原因。回液稀释润滑油，润滑油过热，润滑油焦化变质，以及缺油等都会破坏正常润滑，导致润滑失效。回液稀释润滑油，影响摩擦面正常油膜的形成，甚至冲刷掉原有油膜，增加摩擦和磨损。压缩机过热会引起使润滑油高温变稀甚至焦化，影响正常油膜的形成。系统回油不好，压缩机缺油，自然无法维持正常润滑。曲轴高速旋转，连杆活塞等高速运动，没有油膜保护的摩擦面会迅速升温，局部高温使润滑油迅速蒸发或焦化，使该部位润滑更加困难，数秒钟内可引起局部严重磨损。润滑失效，局部磨损，使曲轴转动需要更大力矩。小功率压缩机（如冰箱，家用空调压缩机）由于电机扭矩小，润滑失效后常出现堵转（电机无法转动）现象，并进入“堵转－热保护－堵转”死循环，电机烧毁只是时间问题。而大功率半封闭压缩机电机扭矩很大，局部磨损不会引起堵转，电机功率会在一定范围内随负荷而增大，从而引起更为严重的磨损，甚至引起咬缸（活塞卡在气缸内），连杆断裂等严重损坏。 堵转时的电流（堵转电流）大约是正常运行电流的4－8倍。电机启动瞬间，电流的峰值可接近或达到堵转电流。由于电阻放热量与电流的平方成正比，启动和堵转时的电流会使绕组迅速升温。热保护可以在堵转时保护电极，但一般不会有很快的响应，不能阻止频繁启动等引起的绕组温度变化。频繁启动和异常负荷，使绕组经受高温考验，会降低漆包线的绝缘性能。 此外，压缩气体所需负荷也会随压缩比增大和压差增大而增大。因此将高温压缩机用于低温，或将低温压缩机用于高温，都会影响电机负荷和散热，是不合适的，会缩短电极使用寿命。 绕组绝缘性能变差后，如果有其它因素（如金属屑构成导电回路，酸性润滑油等）配合，很容易引起短路而损坏。 2.金属屑引起的短路 绕组中夹杂的金属屑是短路和接地绝缘值低的罪魁祸首。压缩机运转时的正常振动，以及每次启动时绕组受电磁力作用而扭动，都会促使夹杂于绕组间的金属屑与绕组漆包线之间的相对运动和摩擦。棱角锐利的金属屑会划伤漆包线绝缘层，引起短路。 金属屑的来源包括施工时留下的铜管屑，焊渣，压缩机内部磨损和零部件损坏（比如阀片破碎）时掉下的金属屑等。对于全封闭压缩机（包括全封闭涡旋压缩机），这些金属屑或碎粒会落在绕组上。对于半封闭压缩机，有些颗粒会随气体和润滑油在系统中流动，最后由于磁性聚集在绕组中；而有些金属屑（比如轴承磨损以及电机转子与定子磨损（扫膛）时产生的）会直接落在绕组上。绕组中聚集了金属屑后，发生短路只是一个时间问题。 需要特别提请注意的是双级压缩机。在双级压缩机中，回气以及正常的回油直接进入第一级（低压级）气缸，压缩后经中压管进入电机腔冷却绕组，然后和普通单级压缩机一样，进入第二级（高压级气缸）。回气中带有润滑油，已经使压缩过程如履薄冰，如果再有回液，第一级气缸的阀片很容易被打碎。碎阀片经中压管后可进入绕组。因此，双级压缩机比单级压缩机更容易出现金属屑引起的电机短路。 不幸的事情往往凑到一块，出问题的压缩机在开机分析时闻道的常常是润滑油的焦糊味。金属面严重磨损时温度是很高的，而润滑油在175oC以上时开始焦化。系统中如果有较多水分（真空抽得不理想，润滑油和制冷剂含水量大，负压回气管破裂后空气进入等），润滑油就可能出现酸性。酸性润滑油会腐蚀铜管和绕组绝缘层，一方面，它会引起镀铜现象；另一方面，这种含有铜原子的酸性润滑油的绝缘性能很差，为绕组短路提供了条件。 3．接触器问题 接触器是电机控制回路中重要部件之一，选型不合理可以毁坏最好的压缩机。按负载正确选择接触器是极其重要的。 接触器必须能满足苛刻的条件，如快速循环，持续超载和低电压。它们必须有足够大的面积以散发负载电流所产生的热量，触点材料的选择必须在启动或堵转等大电流情况下能防止焊合。 为了安全可靠，压缩机接触器要同时断开三相电路。谷轮公司不推荐断开二相电路的方法。 在美国，谷轮公司认可的接触器必须满足如下四项： ? 接触器必须满足ARI标准780-78“专用接触器标准”规定的工作和测试准则。 ? 制造商必须保证接触器在室温下，在最低铭牌电压的80％时能闭合。 ? 当使用单个接触器时，接触器额定电流必须大于电机铭牌电流额定值(RLA). 同时，接触器必须能承受电机堵转电流。如果接触器下游还有其它负载，比如电机风扇等，也必须考虑。 ? 当使用两个接触器时，每个接触器的分绕组堵转额定值必须等于或大于压缩机半绕组堵转额定值。 接触器的额定电流不能低于压缩机铭牌上的额定电流。规格小或质量低劣的接触器无法经受压缩机启动，堵转和低电压时的大电流冲击，容易出现单相或多相触点抖动, 焊接甚至脱落的现象，引起电机损坏。 触点抖动的接触器频繁地启停电机。电机频繁启动，巨大的启动电流和发热,会加剧绕组绝缘层的老化。每次启动时，磁性力矩使电机绕组有微小的移动和相互摩擦。如果有其它因素配合（如金属屑，绝缘性差的润滑油等），很容易引起绕组间短路。热保护系统并未设计成能防止这种毁坏。此外，抖动的接触器线圈容易失效。如果有接触线圈损坏，容易出现单相状态。 如果接触器选型偏小，触头不能承受电弧和由于频繁开停循环或不稳定控制回路电压产生的高温，可能焊合或从触头架中脱落。焊合的触头将产生永久性单相状态，使过载保护器持续地循环接通和断开。 需要特别强调的是，接触器触点焊合后，依赖接触器断开压缩机电源回路的所有控制（比如高低压控制，油压控制，融霜控制等）将全部失效，压缩机处于无保护状态。 因此，当电机烧毁后，检查接触器是必不可少的工序。接触器是导致电机损坏的一个常常被人遗忘的重要原因。 4．电源缺相和电压异常 电压不正常和缺相可以轻而易举地毁掉任何电机。电源电压变化范围不能超过额定电压的±10%。三相间的电压不平衡不能超过5％。大功率电机必须独立供电，以防同线其他大功率设备启动和运转时造成低电压。电机电源线必须能够承载电机的额定电流。 如果发生缺相时压缩机正在运转，它将继续运行但会有大的负载电流。电机绕组会很快过热，正常情况下压缩机会被热保护。当电机绕组冷却至设定温度，接触器会闭合，但压缩机启动不起来，出现堵转，并进入“堵转－热保护－堵转”死循环。 现代电机绕组的差别非常小，电源三相平衡时相电流的差别可以忽略。理想状态下，相电压始终相等，只要在任一相上接一个保护器就可以防止过电流造成的损坏。实际上很难保证相电压的平衡。 电压不平衡百分数计算方法为,相电压与三相电压平均值的最大偏差值与三相电压平均值比值. 例如，标称380V三相电源，在压缩机接线端测量的电压分别为380V,366V,400V. 可以计算出三相电压平均值382V, 最大偏差为20V,所以电压不平衡百分数为5.2％。 作为电压不平衡的结果，在正常运行使负载电流的不平衡是电压不平衡百分点数的4－10倍。前例中, 5.2％不平衡电压可能引起50％的电流不平衡。 美国国家电器制造商协会(NEMA)电动机和发电机标准出版物指出，由不平衡电压造成的相绕组温升百分比大约是电压不平衡百分点数平方的两倍。前例中电压不平衡点数为5.2，绕组温度增加的百分数为54％. 结果是一相绕组过热而其他两个绕组温度正常。 一份由U.L.(保险商实验室，美国)完成的调查显示，43％的电力公司允许3％的电压不平衡，另有30％的电力公司允许5％的电压不平衡。 5．冷却不足 功率较大的压缩机一般都是回气冷却型的。蒸发温度越低，系统质量流往往越小。当蒸发温度很低时（超过制造商的规定），流量就不足以冷却电机，电机就会在较高温度下运转。空气冷却型压缩机（一般不超过10HP）对回气的依赖性小，但对压缩机环境温度和冷却风量有明确要求。 制冷剂大量泄漏也会造成系统质量流减小，电机的冷却也会受到影响。一些无人看管的冷库等，往往要等到制冷效果很差时才会发现制冷剂大量泄漏了。 电机过热后会出现频繁保护，有些用户不深入检查原因，甚至将热保护器短路，那是非常糟糕的事情。过不了多久，电机就会烧掉。 压缩机都有安全运行工况范围。安全工况主要的考虑因素就是压缩机和电机的负荷与冷却。由于不同温区的压缩机的价格不同，过去国内冷冻行业超范围使用压缩机是比较常见的。随着专业知识的增长和经济条件的改善，情况已明显改善。 6.用压缩机抽真空 开启式制冷压缩机已经被人们淡忘了，但制冷行业中还有一些现场施工人员保留了过去的习惯――用压缩机抽真空。这是非常危险的。 空气扮演着绝缘介质的角色。密闭容器内抽真空后，里面的电极之间的放电现象就很容易发生。因此，随着压缩机壳体内的真空度的加深，壳内裸露的接线柱之间或绝缘层有微小破损的绕组之间失去了绝缘介质，一旦通电，电机可能在瞬间内短路烧毁。如果壳体漏电，还可能造成人员触电。 因此，禁止用压缩机抽真空，并且在系统和压缩机处于真空状态时（抽完真空还没有加制冷剂），严禁给压缩机通电。 总结 电机烧毁后，掩盖了绕组损坏的现象，给故障分析造成了一定的困难。然而引起压缩机电机损坏的根本原因并不会消失。润滑不良或失效时引起的异常负荷甚至堵转，散热不足，都会缩短绕组的寿命；绕组中夹杂了金属屑更是为短路提供了变利；接触器焊合将使压缩机的保护无法执行；电机赖以运转的电源出现异常，将从根本上毁掉任何电机；用压缩机抽真空，可能引起内接线柱放电。 不幸的是，上述不利因素还会相互引发：异常负荷和堵转时的大电流可能导致接触器焊合；单个触点拉弧甚至焊合会引起相不平衡或单相；相不平衡会引起散热问题；散热不足会引起磨损；磨损会产生金属屑… 因此，正确安装使用压缩机，以及合理的日常维护，可以防止不利因素的出现，是避免压缩机电机损坏的根本方法。