Introduction

Motor lead wire cables are important components that connect motor windings and distribution cables. In order to ensure the quality stability of motor products and prevent damage to the entire motor winding due to local damage and improper selection of performance parameters, the parameter selection of the lead wires is , installation, fixation and later maintenance must be strictly controlled.

1   Selection requirements for motor lead wires

Lead wire cables for motors require the same electrical conductivity and insulation properties as ordinary cables, but also have some special requirements. 1 ) Voltage level requirements. For motor products with different rated voltages, the rated voltage of the lead wire should match the rated voltage of the motor, and should not be lower than the maximum working voltage of the motor, and meet the requirements for ground insulation and phase insulation during use of the motor. . Normally, a motor with a rated voltage of 380 V uses a cable with a voltage of 500 V. A cable with a rated voltage of 500 V can also meet the needs of motors with rated voltages of 400 V , 420 V , 440 V , 480 V , etc. The insulation of the lead wires The strength can meet the power frequency withstand voltage test requirements of the circuit. 2 ) Heat resistance level requirements. According to the requirements of different insulation levels of the motor, the temperature rise of the motor is specified in the technical conditions of the corresponding product. As an important component of the motor electrical circuit, the motor lead wire and cable must meet the insulation performance at the corresponding temperature. , select lead wires with temperature tolerance and insulation level according to the temperature limit corresponding to the motor insulation level. Specific parameters can be selected by referring to the data in Table 1 . 3 ) Corrosion resistance requirements. Most of the motor windings are dipped in paint after installing the lead wires. The lead wires must be dipped in paint and dried together with the motor windings. The impregnating paint itself will have a certain corrosive effect on the cable insulation layer. The winding drying process It has a significant impact on lead wires; for operating environments with corrosive gases, there are also anti-corrosion requirements for cables. 4) Flexibility requirements. The movable space of motor cables is generally relatively small. For increased capacity motors, the space available for lead wires is limited, and they need to be bent when exiting. Therefore, the cable must be flexible enough to facilitate the exit of lead wires. , ensuring that its insulation layer is not damaged. 5 ) Mechanical strength requirements. During the operation of the motor, different degrees of vibration, especially operation in a hot state, will cause the lead wire to be stretched or squeezed, especially if the free length is long, the space for movement is large, and If related parts have sharp burrs, the insulation layer of wires and cables must have sufficient mechanical strength to prevent ground faults.

Table 1 Typical selection of motor insulation grade corresponding to lead wire temperature

2   The importance of reliable connection of motor lead wires

Reliable connection is the basis for the reliability of lead wire connection quality. If the connection is unreliable, it will be a fatal quality defect for the motor winding. Due to the special role of lead wires in motor products, there are some unfavorable factors in the length and fixation of lead wires, as well as the lead path from the winding to the wiring position. If not handled properly, serious quality failures will occur. Considering the motor assembly and the customer's maintenance and use requirements during later use, the length of the motor's lead wire must be left with a certain margin. The vibration during motor operation will have adverse effects on the lead wire itself and the connecting parts, so the motor manufacturing Links must be secured by necessary restraints to free running of lead wires. The motor lead wire is led out from the winding part and passes through the motor frame outlet hole. Its path involves the non-machined surface and the machined surface of the component, especially for castings, the flash produced by the casting process, and the sharp edges on the machined surface. Any side will cause fatal damage to the lead wire. During the disassembly and inspection of the faulty motor, it was found that the bumps and squeezes during the lead-out process caused the motor to be grounded, and inter-turn faults accounted for a large part, especially for the lead wires that were dipped in paint along with the windings. If not handled properly, more It is easy to cause damage to the lead wire. Figure 1 shows the lead wire that was damaged during the motor installation process. The fault directly caused the motor to be grounded. This severe damage requires replacement of the damaged motor leads.

Figure 1 Motor lead squeeze diagram

Measures for fixing and reliably connecting the motor lead wires focus on the following aspects: 1 ) During the welding and wrapping process of the lead wires and winding electromagnetic wires, the insulation protection of this part must be solved. On the other hand, the insulation during the lead dipping process must be solved. The problem of paint penetration can be solved by using a fusion insulating tape sealing process to ensure the insulation performance of the welding joint. The shaping effect and smoothness of the lead wire welding position should be more conducive to the binding of windings. While the physical space is sufficient, sharp points that are not conducive to insulation should be avoided as much as possible. 2 ) The connection reliability of the lead wire connection terminal. In most motor production processes, the connection terminals adopt a cold pressing process. While ensuring a reliable connection between the terminal and the lead wire, it can better ensure that the insulation part of the lead end is not damaged. When using the cold pressing process, attention should be paid to the cold pressing process. Involving pressure control and mold suitability, if they are not suitable, the cooperation between the two will loosen, resulting in poor contact. Sometimes the lead wire conductor will be broken due to excessive pressure. 3 ) Fixing of lead wires. For most motor lead wires, they are relatively short and do not require special fixing. However, for some low-voltage, high-power and high-voltage motors, the motor lead wires have a relatively long path and need to pass through some relatively sharp parts of the machined parts, which may The insulation layer may be damaged due to vibration during the operation of the motor. For this reason, the fixation and insulation protection of key links must be focused. 4 ) The electrical connection of the lead wire is fixed. For most motor products, special wiring boards will be used. In order to ensure the fixation effect of the lead wires and the wiring board, anti-loosening measures must be in place, including for running motor products, the connection effect at the wiring board should be checked regularly, and the cable The electrical clearances and creepage distances between joints and between cable joints and other metal parts must meet the requirements of electrical specifications to prevent wiring board ablation or other serious electrical short circuit faults caused by unreliable connections.

3   Common heating faults of motor lead wires and cables

As an important part of the electrical connection of motor products, motor lead wires involve the electrical insulation and conductivity of the motor itself. They must be selected and used according to the specified current density to ensure that there is no heating failure in the lead wire part. However, in actual use, the motor lead wires often become heated, and their manifestations are mainly divided into the following categories: 1 ) All lead wires are heated. In this regard, the focus is on the compliance of the conductor diameter of the lead wire and the conductor material of the lead wire. This situation is generally caused by improper selection of the lead wire. The standard stipulates that the current carrying capacity of the lead wire is at least equal to the load current of the selected service factor or 125% of the full load rated current, whichever is larger. According to the rated current when the motor is running, the selection of the motor lead can be made by referring to the values in Table 2 .

Table 2 Motor lead wire cross-sectional area selection table

2 ) Some lead wires are heated. This is a relatively common fault characteristic during motor operation. Generally, faults are often accompanied by wiring board ablation. This is caused by poor local connection of the lead wire, which may occur at the connection position between the motor winding main line and the lead wire. It usually occurs when the motor lead wire is fixed to the connection terminal or the connection terminal is fixed to the terminal board. The connection between the lead wire and the main winding wire, as well as the connection between the lead wire and the connecting terminal, are motor manufacturing quality issues; the connection between the lead wire and the terminal board is directly related to the incoming connection of the power cord. During the motor production and manufacturing process, necessary anti-loosening measures have been taken to fix the wiring board leads, such as using anti-loosening elastic washers. However, during the installation of the motor, if necessary anti-loosening measures are not taken, or the motor may generate heat during operation. Poor contact at the fixed position caused by vibration and vibration will lead to heating. 3 ) Heating problems caused by low-pressure operation. When the motor is in low-voltage operation for a long time, the current will increase significantly, and the lead wires will also bear a larger current. Especially if the cross-sectional area of the lead wires is selected, a lead with a small margin will be selected. The larger current density will cause the lead wires to fever. 4 ) Connection terminal material and cleanliness. The connection terminal of the motor lead wire not only plays a role in fixing the lead wire and the terminal board, but also must have good electrical conductivity. If the material of the connection terminal is poor, in addition to the breakage problem that occurs during the installation process, it will more seriously increase the number of connection parts. The contact resistance will cause the lead wire to heat up; in addition, when the lead wire is dipped in paint together with the winding, if the insulating sheath of the enameled wire at the connection end is not completely cleaned, it will cause excessive local resistance, causing the lead wire to heat up . 5 ) The rationality of the wiring board structure. If the structure of the wiring board is unreasonable, the connection parts may become loose during the operation of the motor, and the lead wires and windings may become heated.

4   Conclusion

As an important part of the electrical connection of the motor, the motor lead wire is similar to the electromagnetic wire. There are phase-to-phase and ground voltage breakdown faults. For this reason, the insulation layer of the lead wire must meet the needs of the matching motor. In order to ensure the insulation performance of the lead wire Compliance, to avoid factors such as vibration during motor operation, tugging during installation, and damage to the insulation layer of the lead wires by related components during the wiring process. To avoid failure of the motor lead wires, the wires and cables used need to be inspected. More protective measures should be taken, and some specific measures to avoid problems with the lead wire should be considered in the design of the motor, such as necessary fixing and other protection. In actual operations, pay attention to the refinement of the process and the implementation of standardized protection requirements to avoid ground breakdown damage to the lead wires, and to minimize the adverse effects of processing and assembly manufacturing factors on the lead wires.