Key Points in Quality Control of High Voltage Motor Manufacturing Process

The electric motor is a relatively simple machine. A stator and a rotor combined together with a cover at both ends is a complete electric motor. However, such a simple machine integrates the electromechanical energy conversion and the essence of many disciplines. It is not easy to design such a flawless high voltage motor. Any small defect or negligence may bring disastrous consequences.

Generally,  Electric motors include the electrical and the mechanical parts. The key to electrical technology is insulation, and the mechanical part involves the transmission theory and the fluid mechanics. In addition, in the process of achieving the energy conversion and the transmission functions, various forms of loss are represented by heat, and naturally, the problems of heat transfer and heat exchange cannot be ignored. Therefore, it is not easy to make a good electric motor, and it is even more than difficult for a high voltage motor. Shandong Langrui electric motor manufacturer will not talk about topics that involve too much theoretical analysis today, but specifically talk about some common problems and measures to be taken.

In addition to encountering welding problems, some occasional failures such as slot wedges, various abnormal vibrations and noises caused by bearing system problems, insulation treatment defects, high temperature rises, etc., often occur, and are similar but not duplicate and extremely difficult to prevent. When such problems occur on high voltage motors, they are often more sensitive and have more serious consequences.

一、Welding Problems And Avoidance Measures

The connection between the high voltage induction motor winding pole-to-pole connection, the winding main line and the lead, and the lead and the joint are the frequent parts of welding problems. Problems such as false welding and impervious welding during processing often lead to de-soldering of the electric motor operation, resulting in increased resistance at the welding site and localized heat severely disconnects the welding position. Most of this problem occurs in the rotor and headgear of the wound rotor induction motor (also known as slip ring induction motor), the welding position of the stator rotor lead and the main line. There are often many star points and wire ends of the wound rotor induction motor. Welding imperfections occur frequently. To solve such problems, we should work hard to improve the process:

1. Use highly reliable equipment and processes. For example, many electric motor manufacturers use relatively reliable methods such as intermediate frequency welding, argon arc welding, and cold-pressed splice tubes to assist silver-copper solder filling.

2. Improvement of stator binding. After the connection, the binding and curing of the welding position should be ensured. It is strictly forbidden that the welding position is suspended, so as to prevent the welding point from being forced to open due to the vibration of the high-voltage motor during operation.

3. The rotor bracket is used to ensure that the ends of the wound rotor winding are supported to prevent radial force from welding.

4. Special attention should be paid to the welding point of the lead wire and the wire, and try not to select the thin-sheet electromagnetic wire, that is, to avoid the situation where the cross-section of the flat wire has a large difference in length and width.

二、Slot Wedge Falling Problem And Preventive Measures

During the manufacturing process of high voltage motors, some electric motor manufacturers use immersion technology. If the stator core coil slot full rate is low, the curing effect of the winding cannot be guaranteed when the paint is immersed, the coil vibrates under the influence of electromagnetic force in the core slot when the motor is running. The action and vibration cause the slot wedge to fall off due to the vibration, which causes the problem of burnout and winding heating.

At present, many China electric motor manufacturers use magnetic slot wedges. Although the improvement of motor efficiency and performance is obvious, the problem of slot wedge falling is more prominent. To address this, control should be in the following areas:

1. Control the matching relationship between the stator slot and the slot wedge, and the cooperation between the two should not be too loose;

2. The slot full rate should not be too low when embedding wires. If this problem persists, the filling effect should be ensured by means of necessarily plugging insulation materials and improving the effect of dipping paint, such as the use of vacuum dipping process, controlling the paint viscosity, secondary dipping and other specific measures.

三、Bearing System Problems And Countermeasures

Due to the relatively troublesome maintenance of sliding bearing motors, most high voltage electric motors use rolling bearing structures. In the design of high voltage motors, C3 clearance bearings are generally used, and C4 clearances are also used in extra large high voltage motors. This design change brings new problems: many customers can find that the ball bearing inner ring surface has a bit of abrasion when the motor is overhauled during use, and the cylindrical bearing has stripe abrasion. The reason is caused by the rotor shaft current. When the shaft current passes through the bearing, the roller path is turned on and off irregularly, which causes electric sparks to ablate the rollers and raceways, forming point-like pits, resulting in increased bearing vibration and wear. In severe cases, the bearings are loosened and the stator and rotor are rubbed and burned.

Experienced customers install a carbon brush on the high-voltage motor rotor coupling, and the brush holder is fixed on the motor end cover, and the shaft current is directly grounded across the bearing to reduce or avoid this failure. Some electric motor manufacturers use insulated bearings or insulated bearing sleeves to block the path of shaft current through the bearing.

The bearing is also directly related to the problem of grease. The choice of grease must be matched with the high-voltage motor and the operating conditions. The use of inferior grease is strictly prohibited to prevent bearing problems caused by it.

四、Temperature Rise Problem And Motor Cooling

Large high voltage motors are all designed with cooling devices. At present, air-to-air coolers and water coolers are commonly used. In addition to the temperature rise control in the product design process, the following issues should be noted during use:

1. The cooler must be working when the motor is running.

2. The rotation direction of the air cooler motor must meet the requirements.

3. The water quality of the water cooler must meet the requirements.

五、Rotor insulation treatment

High voltage slip ring induction motor ( also called wound rotor induction motor ) have many insulation faults on the rotor, slip ring, and lead. Common fault cases are: the rotor lead is not fixed firmly, causing the insulation bandage to loosen, and the insulation material wears out during the rotation of the rotor, which shorts to ground; the insulation ring between the three phases of the slip ring is loosened and worn to cause a short-to-phase; Rotating the rotor lead due to centrifugal action causes the lead to be disconnected from the star point.

Regarding the insulation treatment of the stator, Shandong Langrui electric motor manufacturer will explain it in detail later.