Application of Soft Starter in Cooling Tower Fan Motor Starting
There are 8 cool water towers in my unit circulating water installation, each with a 160kW fan motor. The 8 fan motors are all powered by low circulating water, using direct start mode. The working characteristics of the cooling tower fan load make the motor start current large and long starting time, which has caused great impact damage to the motor and its control equipment. According to statistics, 4 of the 8 motors have been burned due to insulation damage, and the circuit breakers and contactors in the main circuit of the motor control are also damaged. In the new transformation of low circulating water, we also improved the starting control of the fan motor, using the soft starter to replace the original direct starting mode, and the effect is very good after the application. Since the power of the 8 fans is the same, in the low circulation of the circulating water, there are two sections of power supply, 4 in each section. To save cost, one soft starter per section is responsible for the starting of 4 fans. At the same time, only one motor can be started for each soft starter, and one soft starter is not allowed to start two or more motors at the same time. The control system has improved reliability and strong fault tolerance, and even if it is mishandled, it will not cause serious harm. Taking into account the complexity of the control system and simplifying the external wiring, the programmable controller (PC) is used to implement the control function. In addition to the soft starter, the motor start must have a function to switch to the direct start mode to ensure that the fan can start up in an emergency when the soft starter or PC is not working. The design of the power distribution and control equipment should be considered convenient. (1) Selection of soft starter and parameter setting In this example, we consider the cooling tower fan motor to have a high starting torque requirement, and it is a starting mode in which one soft starter drives multiple motors to start. Large-scale soft starter: ABB's maximum starting power is 200kW; the starting mode is soft-start mode, the initial torque is set to 30%, the starting time is set to 30s, the main circuit is designed to be 4 motors share one soft. A schematic diagram of the main circuit of the starter. The K4 that protects the soft starter from FU is the soft starter start contactor, and K11 is the normal operation contactor. In order to facilitate maintenance and mutual backup, the FU and soft start are assembled in a same cabinet when the components are arranged; QF1 and KU, and K33, QF4 and K44 are respectively assembled in 4 drawers, 4 drawers are wired. The same, they can be used as spares, and can be taken out for maintenance in case of failure. The cable is connected between the starting contactor and the running contactor. When the soft starter or pc can't be used, the fan can still be started directly through the four drawers. It should be pointed out here that in the normal operation loop, the thermal element should be a secondary thermal element, which is slightly omitted. The control loop design control loop is divided into two parts, one is the PC control part, as shown, and the other part is the conventional control part, see . (2), (3), the input of the PC must include the start signal of the fan, the status signal of the start contactor and the running contactor, the status signal of the soft starter, and the low voltage of the start switching signal flow output by the system fault reset signal PC. A large current is used to weld the workpiece. At the same time, the power supply passed the RP to C3 Liu Qingli in the development of the sealed relay. It is necessary to braze the lead pin, the moving reed, the static reed and the core of the electromagnetic mechanism, and a brazing machine is urgently needed. Considering that the warehouse has a scrap welder (no nameplate, model is similar to Zhuzhou Welding Equipment Factory No.205), its r-stage, mechanical system and 2kVA welding transformer can also be used, so it is transformed into a brazing machine. The control can no longer meet the brazing requirements, and now it is changed to the time base circuit control, which can be arbitrarily adjusted within 2s. In order to meet the requirements of different workpieces, a 2kVA autotransformer is added in the front stage, and its output voltage is displayed by a voltmeter. The circuit principle is shown in the figure, the power supply is closed Q, and the red power signal light HL1 is on. According to the requirements of the workpiece to be welded, adjust the autotransformer T1 to the set value, adjust the delay potentiometer RP to the set value, put the butyl parts in position, step on the foot switch S, the electrode ftr parts and the solder, and then When stepping on, the contact I - 2 of s is closed, the electromagnet Y is energized, pre-stressing is applied to the 7: part, then the contact 3-4 is closed, the delay circuit is energized T, and the output of the foot 3 of U2 is high. Level, triode VT saturation conduction, relay KM is charged, contactor K is closed, green work signal HL2 is on, welding transformer generates charging, to fV, delay time to set value, U2 foot 3 Output low level, VT cutoff, KM loses power, K loses power, and the welding stops. Release the pedal and complete a weld (C3 discharge at this time). Two points worth noting: First, the capacity of C1 and C2 should be chosen to be smaller, so that when the pedal is released at the end of welding, the voltage can drop rapidly: C3 voltage also drops rapidly. When the C3 voltage is less than or equal to +Q, it is the next welding. Prepare, this shortens the time interval between two welds, and when one weld is not ideal, it can be quickly repeated. Second, capacitor C4 is used to eliminate the foot 3 of U2 caused by interference. At the end of the welding, a few pulses are output after the low level is output, which eliminates the chattering phenomenon of the contactor. In the actual welding, in order to facilitate the operation and improve the welding quality, we used some fixtures and graphite-made diced. Proof of use, the equipment after the transformation is stable in performance, easy to operate, good in welding quality, not only capable of brazing but also spot welding, and the use department is satisfied. (Edit Ye Fan) Machinery and equipment automatic control technology transformation number, etc., total 15 points; output signal should include 4 soft start contactor closure signals, 4 start switching signals, 1 soft starter running signal, 1 system Alarm output signal, etc., a total of 1 point. We chose a FX2-32MR programmable controller from Japan's Ziling Company, which has 16 points of input and point output, which meets the requirements. The system control function is realized by software programming, which greatly improves the reliability of the system. The external wiring is also greatly simplified, and the fault point is reduced. In the conventional control circuit diagram, K represents Kl, which represents the soft start/direct start switching signal output from the PC. SST, SSTP for the site start and stop control button signal does not directly enter the PC, but the signal is sent to the PC through the intermediate relay KM; and a soft start and direct start switch button SW is added to ensure the PC and soft start When the device is not working, the fan motor can still be started and stopped as usual. In addition, it should be noted that in the direct start, due to the large starting current and long starting time, in order to ensure normal starting, the intermediate relay and time relay should be added, and the hot components should be short-circuited in a short time after starting, and then the hot components should be used after the start is completed. : In order to simplify the narrative, it is not mentioned in detail. It is no longer detailed. There are two parts in the internal program of c PC. First, after receiving a motor fan start signal, first check if there are other fans using the soft starter. If not, first disable the other fans from using the soft starter, and then check if the running contactor of the fan motor is closed (direct start). If it is not closed, the soft start program can be started to start the fan motor. This avoids the simultaneous start of multiple fan motors and avoids the use between soft start and direct start. Second, when switching to the normal running circuit after the soft start is finished, the contactor should be operated first, and then the soft start contactor can be used to avoid the secondary current impact of the motor during the switching process. For the motor and the normal running circuit components, Can play a very good role in protection. (Edit Wei Ming) Technical Reform of Blower Starter
1. The pump body
is made of PP material, which has the characteristics of corrosion resistance
and aging resistance.
2. Use a dry
liquid seal (1~10HP):To ensure that motors and bearings are protected from
chemical gas corrosion and that the service life of the motor and pump is
prolonged.
3. It is
suitable for use in jet washing equipment, exhaust scrubber, cooling cycle and
matching filter. The pump can be used without water and will not
be damaged.
4. Innovative use of PP material for the motor
is connected with the base, compared with the traditional motor bracket can
greatly reduce the acid gas corrosion, and body weight.
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