Three-phase asynchronous motor current sampling resistance

 General sampling resistor value will be selected in the following one ohm, belongs to the milliohm resistance, but part of the single phase motor price resistance, a sampling voltage requirements, such as have to choose large ac motor resistance values, but such a large resistance, the error is large. In this case, the need to select the high precision than letter resistance, shenzhen jie than letter technology co., LTD is specialized in the production and sales of power supply for high precision SMD resistor (to 0.01% accuracy, namely one over ten thousand precision), so that sampling data is wholesalemotor.blogspot.com credible. Patch ultra-low resistance values (0.0005 ohms, 2 milliohm, lamination 3 milliohm, 10 milliohm, etc.), patch alloy resistance, high power resistance (35 w, 30 w, 20 w, 50 w and 100 w) and other products, can achieve the positive and negative temperature coefficient of 5 PPM.

Three-phase asynchronous motor speed control method

Three-phase asynchronous motor's very logarithmic p and s slip can be too much to change speed. From the perspective of the nature of speed regulation, different ways of governing is nothing but change synchronous ac motor synchronous speed or not turn two. Widely used in the production of machinery is not the change in speed control method of synchronous speed of wound rotor motor rotor series resistance speed governing, chopping speed regulation, cascade speed regulation and application of the electromagnetic slip clutch, hydraulic coupling, such as oil film clutch speed regulation. Changes of the synchronous speed logarithmic multi-speed motor, stator can change of the stator voltage, frequency, frequency control of motor speed has no commutator motor speed regulation and so on. From energy point of view, when there is high speed control method and low speed control method of two kinds: an induction refers to the effective speed control is constant, so there is no slip loss, such as multi-speed motor, frequency control of motor speed and slip loss can be recovered speed control methods (such as cascade speed regulation, etc.). Have slip loss speed regulation method belongs to the low speed, such as rotor series resistance speed control method, the energy loss in the rotor circuit; Electromagnetic clutch speed regulation method of energy loss in the clutch coil; Hydraulic coupler speed regulation and energy loss in the oil of hydraulic coupling. In general slip loss increases with expanding range of speed regulation, if the speed range is not big, energy loss is small. This control method is used to change the stator winding of red way to change the cage ac motor stator polar logarithmic to achieve speed, features below: With a hard mechanical properties, good stability; No slip loss, high efficiency; Wiring is simple, convenient control, low price; Have used differential is bigger, cannot obtain smooth speed regulation; Can be used with regulating speed control, electromagnetic slip clutch, smooth speed characteristics of high efficiency. 

This method is suitable for don't need a stepless speed regulation small electric motors of production machinery, such as metal cutting machine tools, elevators, lifting equipment, fan, water pump, etc. Cascade speed regulation refers to the motor rotor winding circuit in series with adjustable additional potential to change the slip of the motor, to Motor vehicle achieve the purpose of speed control. Most of the slip power is absorbed by series of additional potential to recycle produce additional device, the absorption of returning the slip power grid or conversion of energy use. According to the slip power utilization way, cascade speed regulation can be divided into Y series three-phase asynchronous motor cascade speed regulation, mechanical cascade speed regulation and thyristor cascade speed regulation form, adopts thyristor cascade speed regulation, its characteristic is: Slip loss in the process of speed regulation can be back to the grid or production machinery, high efficiency; Installed capacity is proportional to the speed range, the investment province, apply to speed range in production machinery from 70% to 90% of the rated speed; Speed regulating device failure can switch to run at full speed, avoid production; Thyristor cascade speed regulating power factor is low, the influence on harmonic. This method is suitable for the fan, water pump and the rolling mill, mine hoist, the extrusion machine use. Frequency control method Frequency control of motor speed is to change the frequency of the motor stator power, to change its synchronous speed control method. Variable frequency speed regulation system is the main equipment to provide frequency conversion power of inverter, the inverter can be divided into ac - dc - ac frequency converter and ac - ac frequency converter two kinds big, cross - straight - to pay inverter are mostly used in China at present. Its features: There is no additional loss of high efficiency and speed the process; Application range is wide, can be used in the cage type asynchronous motor; Large range of speed regulation, and the characteristics of hard and high precision; Technology is complex, high cost, maintenance difficulties. This method is suitable for the requirement of high precision, better speed control performance.

Star delta start

1 the principle Learn the electrician will not star triangle how line. 1. When the load on the motor has no strict requirements and to limit the start torque motor starting electric fan motor parts current and motor can use 380 v/Δ connection condition star triangle boot method; 2. The method is: in the motor when the motor first starts, connect into the star connection, when the motor start again after successful will convert into triangular connection (via double-throw switch switch); 3. Because of the motor starting current is proportional to the power supply voltage, the power grid provided by the starting current is only 1/3 of the full voltage start current, but also start torque only 1/3 of the full voltage start torque. 4. Star triangle start, step-down starting at the expense of his power in exchange for a lower cost of starting current. So it defies and with the size of the motor power to determine whether to need to use the star triangle start, also depends on what kind of load, the general load when need to start the runtime negative light load can be used star triangle start, usually a squirrel-cage motor starting current is 5 to 7 times that of the running current, and voltage requirements for power grid is usually plus or minus 10%, in order not to form the impact to power grid voltage is too large to adopt star triangle start, general requirements in squirrel-cage motor power by more than 10% of the rated power transformer will be will use the star triangle. 

5. In the process of actual use, found to be the star triangle step-down starting motor starting electricalmotor1.blogspot.com 11 kw are needed, such as fan, 11 kw electric current when it starts at about 7-9 times (100) A, according to the normal configuration of the thermal relay can't start, it's no use (the draft) thermal relay with big and does protect the motor, so suggest using step-down start. Two conditions 1, the capacity of 7.5 KW three-phase asynchronous motor. 2, motor in starting the instant power grid voltage fluctuation is less than 10%, for not often start the motor can be up to 15%; If there are special transformer S transformer or 5 p motor, motor asynchronous motor allows direct frequently. 3, meet the experience formula: Ist/IN < 0.75 + ST \ 4 pn ST - public transformer capacity, KVA; PN - motor rated power, KW; Ist / - IN the ratio of the motor starting current and the rated current. 4, star triangle step-down starting motor three-phase winding six external terminal: A - X, Y and C - B - Z (hereinafter with rated voltage 380 v motor as an example) A. start star: X - Y - Z, A, B, C three termination three-phase ac voltage 380 v, the voltage of each phase winding, 220, A 380 v directly start current is greatly reduced, to avoid the excessive starting current impact on grid form. At this time of the torque are relatively small, but the motor can reach a certain speed. B. angular run: star start the motor for a period of time (about) a few seconds after reaching a certain speed, electric switch connect six terminals into a triangle, and again from 380 v power supply when each phase winding voltage of 380 v, torque and rotational speed is greatly increased, the operation process of motor in the rated conditions.

Permanent magnetic synchronous permanent magnet synchronous motor motor application prospect

Visible, dc thoughts have excellent authorized functions, its mechanical characteristics and speed characteristics are parallel lines, this is the characteristics of all kinds of switch electric thoughts have not. In addition, in fact, permanent magnetic iron remover. Dc current idea and starting torque, high efficiency, speed control, good static characteristic features such as easily. Good duty characteristics make dc thought for a long time before the 70 s, in the situation of speed regulation, duty supplications, nearly became a unique selection. However, direct current (dc) thought the authority of the fluff, the field winding on the stator attacks the main magnetic field, the large dc power idea often also equipped with commutating ac electric motor parts pole, in order to improve of the reversing of the motor function. Dc motor armature winding and been planted on the rotor commutator, dc power supply through the brush and commutator will direct current to the armature winding translates into alternating current in the armature winding, namely mechanical current commutation. Tumultuous authority limit the dc thought to further reduce the volume and weight, is double brush and commutator of the sliding contact caused by mechanical wear and spark, the direct current idea obstacle, the more trustworthy authenticity is low, life is short, cherish the maintenance of large amount of doing things. Commutation spark both the commutator of electric corrosion caused by nuisance source, or a radio will be harmless influence on the surrounding electrical equipment. Motor capacity, rotational speed is higher, the greater the subject becomes more important. 

So, in fact, permanent magnetic chuck. Ordinary direct current thoughts of brush and commutator limits the thoughts to burning with high speed, large capacity, depression and goods. On the switch power grid, people still usually manipulated exchange asynchronous electrical idea to drag xing machinery. Simple exchange asynchronous electrical thought has no authority, trustworthy real and long service life, low capital, cherish the simple maintenance. Compared with direct current (dc) idea, however, its speed control function is poor, small starting torque, overload talent and low efficiency. Carnegie-give must be the onset of a rotating magnetic field from the grid reactive power, so the power status is low, especially when the light load, which adds lines and large power consumption. Permanent, since you know that a strong permanent magnet. Without beg speed control of the situation, such as fan, water pump, the common machine tool drive, asynchronous electric thought according to a leading fame, of course, this type of drag, visible in a large number of energy wastage. Domain before the electric drive, rarely color synchronous electric thoughts, learn to permanent magnetic iron remover. Its main cause motor fan is synchronous electrical thought cannot under grid voltage starting, movement of the rotor pole under the effect of rotating magnetic field, uniform torque is zero. They are also great frequency conversion power can solve the starting and speed control of synchronous motor was thought subject, but in the 70 s, variable frequency power supply of equipment are to think about. So, before the domain of electric drive, using synchronous motor was thought as the original thoughts is seldom seen. In high power within the boundaries, has no intention of occasional synchronous electric thoughts running example, but it is often used to improve power factor of power grid enterprises.

The operation of the three-phase asynchronous motor monitoring

Three-phase asynchronous motor running monitoring: 1, monitoring, motor overheating 2, monitoring the working current of the motor is more than the rated current 3, monitor power supply voltage with or without changes 4, monitor whether the three-phase power supply voltage and current balance Note: in the operation of the three-phase asynchronous motor 1, pay attention to the ventilation of the motor and the environment 2, pay attention to the motor vibration 3, pay attention to the noise of the rotor cutting machine motor with or without abnormal situation 4, pay attention to whether motor abnormal smells 5, pay attention to the working condition and fever motor bearing Daily monitoring master electrician motor five often: 1, often listen to. Motor issue during normal working uniform "buzzing" sound. Particularly heavy motor part when I heard the "buzzing" sound, or "utter the word" sound, motor open phase running. If heard a continuous "guru" or "giggle" sound, that there is something wrong with the motor bearings 2, often have a look. See the ammeter or a voltmeter indicates whether or not the normal; See if three phase current balance; See whether the power supply voltage of three-phase; See if motor on the basis of solid, etc. 3, often monitoring environment temperature. The output power of the motor temperature has a great relationship with the surrounding environment, the environment temperature is higher, the smaller the motor output power. When the environment temperature below 35 ℃, motor power output will be greater than the rated power output, the increase of amplitude of (35) % (t for the actual environment temperature), but not more than 8% - 10%; When the environment temperature above 35 ℃, the output power of the motor than rated output power reduction (t - 35) %. 4, often feel. Back with your fingers touch the motor shell, temperature rise is too high. As the hot hand, motor has overheating. 5, often smell. Whether with his nose close to the motor, smell the smell of insulating varnish or anxious burnt flavour. If have, could be the result of a coil www.facebook.com/dongfeng.motor of motor overheating and short circuit, etc.