Gear Motor is used several ways
In the process of industrial automation, Gear Motors with various power sizes are widely used in various equipment. The common starting mode of ac Gear Motor is divided into: direct start, star - triangular step-down, auto - voltage starting, soft start, frequency conversion.
1. Direct startup
Direct start, also known as full-voltage start, is the most commonly used starting mode. This kind of starting mode is to direct the rated voltage of the Gear Motor to the stator winding, so that the Gear Motor starts directly under the rated voltage. When the equipment is started with a big torque, Gear Motor in order to overcome the resistance moment, need to have enough starting torque, so the Gear Motor at startup, will produce a large starting current, no-load starting current can be up to 4 to 7 times the rated current, load can reach 8-10 times or more).
1.1 advantages of direct startup
It is the simplest, most economical and most reliable way to start the start-up with a large torque and short starting time.
1.2 drawbacks of direct startup
Due to the high torque and short starting time, the equipment of the Gear Motor will be caused by excessive electrical and mechanical impact, accelerated Gear Motor aging or mechanical damage.
Due to the large starting current, will have impact on power grid, the pressure drop caused by power grid, make the other electrical equipment produces false under-voltage protection action, cause harmful tripping of electrical equipment, affect the normal, even cause electrical accident.
According to article 10.2.1.1 of the JGJ/t16-92 civil construction electrical design specification, the voltage drop of the power grid at starting point of the Gear Motor cannot exceed 15%. According to this rule, the direct start-up only applies to a small power Gear Motor under 11Kw, while a large power Gear Motor does not apply. The general solution has two kinds: one, increase transformer capacity, consider from economic Angle is not advisable. 2. By reducing the starting voltage, the starting current of the Gear Motor is reduced, and the influence of the high power Gear Motor on the power grid is reduced. This results in the star-delta reduction and the auto-transformer reduction.
2 star - triangular depressurization
Star delta step-down starting is to Gear Motor stator winding of six terminals to the contactor, change Gear Motor stator winding connection mode, make the Gear Motor stator winding with y connection starts, the y connection of the stator winding of each phase winding under phase voltage of the voltage of 220 v, after the Gear Motor speed close to the rated speed, and then switch Gear Motor stator winding of the delta connection, so that each phase winding withstand voltage of 380 v line voltage. At startup, due to the Gear Motor stator winding voltage is only 0.578 times the rated voltage and starting current is only 2 to 3 times the rated current, at this time of the Gear Motor starting torque is only 1/3 of the delta connection.
2.1 advantages of star - triangular step-down
The star - triangular depressurization has greatly reduced the influence of the large current on the power network at startup, and is also the lowest cost and simplest structure of the two kinds of step-down methods.
2.2 shortcomings of star - triangular step-down
During the start-up process, two large shocks will occur, so the failure rate of the equipment is high, which needs to be maintained frequently, and it is generally not suitable to be used on the equipment that starts more frequently. The torque loss is only a third of that of the triangular joint method, which is only applicable for no-load and light load situations and does not apply to the start-up of the high voltage Gear Motor.
3 autotransformer voltage drop start
Autotransformer step-down start refers to the use of autotransformer motor startup, choose suitable for the buck than k (k for autotransformer than < 1), the start of the gear on the motor stator winding voltage is reduced to kUe, Gear Motor starting current is reduced to K2Iq, starting torque k2 Mq. After the Gear Motor is started, the motor is separated from the autotransformer, and the normal motion is under full pressure.