Cooler Modification for Air Compressor Motors

1. Basic information

The Air Compressor Motors of two-series synthetic ammonia produced by a company selects a motor factory production of YAKS5600-2 (G) plateau, safety-enhancing double-ended drag motor, dragging the centrifugal compressor unit produced by another company. The centrifugal air compressor has a flow rate of 25,949Nm³/h, a shaft power of 5,600KW, and a rotational speed of 2,989r/min. The air compressor motor has a rated voltage of 10KV, a rated rotational speed of 2,991r/min, a power factor of 0.92, an insulation class of F, a rated power of 5,600kw, a rated current of 360.1A, a connection method of star, and a protection class of IP54.

The Air Compressor Motors in the actual operation process exists in the full load situation, the current can reach 360A ( which has reached the rated current of the motor ), usually, the current of the motor in normal operation is about 80% of its rated current. Motor stator winding in the summer ambient temperature of 30 ℃ can reach 140 ℃, temperature rise of 110 ℃. The insulation level of air compressor motor design is F level, F level insulation material actually assessed according to the B level, and the national standard of B level insulation is 80 ℃, due to the real-time temperature rise of the motor operation has far exceeded the national standard, so there is a serious safety hazard of the motor stator winding insulation.

2. Analysis of causes: Air Compressor Motors

After analysis, the operating current of the air compressor motor in the actual operation up to the rated value and the high temperature of the stator winding is mainly due to the small design power of the motor, and the actual power does not match the nominal power of the nameplate. Secondly, the air circulation speed inside the motor is slow, resulting in poor heat exchange effect of the cooler. Moreover, the cooling tubes of the cooler are copper tubes, and due to the quality of the circulating water, the cooling tubes are fouled and cause the water cooling of the circulating water to become smaller, which can not meet the actual needs of the site.

To address the above issues, the following methods can be considered:

One is to replace the original motor with a high-power motor, the method is not only expensive, but also the installation size of the new motor can not meet the actual installation of the site, which is difficult to realize.

The second is to improve the capacity of heat exchange, change the cooler tube material, the most important is to change the water cooling of the original motor, that is, the original water cooler is transformed into an air – water cooler, so that the heat generated by the motor stator windings through the fan quickly exchange heat with the circulating water, so as to achieve the purpose of controlling the temperature rise of the motor.

3. Feasibility analysis: Air Compressor Motors

Before the modification, the air circuit inside the motor is shown in Figure 1. There was a backpack water cooler above the air compressor motor, the motor rotor’s own air blades fanning the hot air from both ends of the motor rotor to the top of the motor, the negative pressure caused by the rotation of the motor rotor will suck the air from the top of the motor into the motor internal air circulation, the hot air flow via the fins will be transferred to the outer wall of the cooling pipe through convection, and then passed through the wall of the conductive effect of the inner wall of the tube, the heat is taken away by the convection of water inside the tube to complete the heat exchange.

After analyzing and demonstrating with the motor plant, we first need to increase the capacity of the cooler, and secondly, we can add two centrifugal fans on each side of the air compressor motor cooler, and transform the original water cooler into an air-water cooler, and at the same time, make the air outlet of the centrifugal fan is directly in front of the water cooler’s tube bundle, the air circuit accelerates the circulation, and the water cooler effectively absorbs the heat generated in the operation of the motor and improves the reliability of the motor operation. This cooling method is characterized by large heat dissipation area, high heat exchange efficiency and low gas resistance. After the modification, the air circuit inside the motor is shown in Figure 2.

If the water inlet temperature of the cooler is about 30℃, the stator winding temperature of the motor will be reduced by about 30℃ compared with that before remodeling, and if the water inlet temperature of the cooler is below 25℃, the stator winding temperature of the motor will be reduced by more than 40℃ compared with that before remodeling. The feed water temperature of the ammonia circulating water in the second phase is about 25°C at the highest point, the temperature of the motor stator windings does not exceed 100°C even in summer, and the temperature rise is less than 70°C. Since there is no standby unit for the second-phase synthetic air compressor, and the time for renovation during the stopping period is too tight, a new air-water cooler is manufactured by the manufacturer according to the renovation plan, and it is installed and debugged during the stopping period of the plant.

4. Retrofit Program

The modification of ventilation and cooling method of air compressor motor solves the problem of long term high winding temperature during motor operation. The ventilation and cooling modification program is as follows.

(1) The original water cooler above the motor is changed to an air-water cooler, the external dimensions of the modified cooler remain unchanged, and the motor base is not altered in any way. Due to the increase of fan and water cooler capacity on both sides of the cooler, so the water cooler inlet and outlet pipe flange mounting position of the counterparts has changed slightly.

(2) The heat exchange power of the motor cooler is increased from 170KW to 220KW.

(3) The outside of each end of the cooler is equipped with two sets of 15KW, 2P, T4-72 centrifugal fans to enhance the motor into the air volume, the air volume can reach 372,100m³ / h.

(4) The original water cooler tube bundle pipe material is changed to stainless steel pipe, to solve the water quality problems brought about by the corrosion of the pipe, clogging problems.

(5) Equip 4 centrifugal fans with power control box.

(6) Air – water cooler technical parameters: model 5B430, 3233, the number is 1, heat transfer capacity is 220KW, cooling water volume is 51m³ / h, the water temperature is less than 33 ℃, air temperature is less than 40 ℃.

(7) The centrifugal fan motor is an explosion-proof highland motor with explosion-proof grade CT4 and protection grade IP44.

5. Installation and commissioning of motor cooler

(1) Check that the water cooler is in good condition and install it after the air compressor stops.

(2) When installing the water cooler, touch the inlet and outlet pipes.

(3) Tighten the four corner fixing screws after the cooler is installed.

(4) Install the centrifugal fan cable and power distribution control box in the early stage.

(5) Wire centrifugal fan debugging motor steering.

(6) Notify the process personnel to run water through the cooler to ensure that the water pressure is required, and the cooler venting and leakage detection work.

(7) Start the air compressor motor after making sure the cooler is running normally.

6. Conclusion

Two series of ammonia compressor motor operation stator winding temperature is up to 140 ℃, running current is close to the rated value, we initially analyzes, we thought that the small design capacity of the motor and poor cooling effect of the motor cooler restrict the enhancement of the load of the compressor, so it is planned to renovate the compressor motor original water cooler, to enhance the cooling effect of the compressor motor windings. After the completion of the transformation of the air compressor motor water cooler, the maximum temperature of the motor stator winding is 95℃, which is nearly 50℃ lower than that before the transformation, and the transformation effect is remarkable. The transformation program solves the problem of high temperature of air compressor motor winding and constrained load of air compressor motor. Read here.