There are many high-voltage motors used in thermal power plants, and the running time is long. The long-term operation of the motor leads in a high temperature environment, which accelerates the insulation aging. Conventional test methods can only measure the insulation to the ground, and the leads are fixed on the insulation board, so the conventional test can not find the problem of poor insulation between the phases (the motor is usually a star internal dead connection). In this way, when the lead insulation is aged to a certain extent, if the routine test is qualified, the phase-to-phase short circuit in the operation causes the high-voltage motor to stop, and in severe cases, the shutdown will be stopped, which greatly threatens the safety of the unit and even the system. Stable operation. Here are a few examples of such events and their treatment methods in our company and the application of heat shrink tubing.

Example of the phenomenon of motor phase short circuit in operation

In August 2015, a company's No. 5 furnace B suction motor was fired at high speed and low speed. It was found that the low-speed winding three-phase lead-out line was tied and fixed at the fixed part, and the local damage was serious, resulting in two types of assessment obstacles. Decomposition inspection of the motor found that the rubber insulation of the lead wire was severely aged and cracked and cracked, and the core of the wire was exposed, and the rubber insulation was broken.

When a company's No. 2 furnace air supply motor was in operation, the No. 2 machine was forced to stop, causing a class of assessment obstacles. The motor decomposition inspection found that the three-phase lead wire was tied to the fixed part and the phase was short-circuited, and the local damage was serious. The insulation aging condition of the lead wire was the same as above.

Cause Analysis

The motor lead wires are rubber insulated cords, which are fixed in the hot air zone, the operating environment is bad, the temperature in the hot air zone is high (the highest operating temperature in summer is 60-70 ° C), and the lead wires are under the action of hot air for a long time, the rubber insulation pole Easy to age and crack. After investigation, it was found that after three years of motor operation, the insulation of the lead wires showed different degrees of embrittlement and cracking.

The three-phase lead-out wire of the motor is tied and fixed together, so that the tying and fixing is extremely unreasonable. Once the lead wire insulation is aged and cracked, the bare metal part is close, and the phase-to-line voltage acts to release the gun, and the motor stops.

improvement measures

The three-phase lead-out wires of the high-voltage motor are fixed at a certain interval to solve the problem of phase-to-phase short-circuit shooting;

The three-phase lead-out wires are respectively heat-shrinked by a high-voltage insulated heat-shrinkable tube to solve the insulation problem after aging cracking. For the lead insulation, there is no aging crack, and the high-voltage insulated heat-shrinkable tube is heat-shrinked to increase the anti-aging cracking ability of the rubber insulated cord and prolong the aging period.

in conclusion

It is recommended that the manufacturer separate the three-phase lead-out wires at a certain distance during production, and increase the heat-shrinkable tube protection to avoid phase-to-phase short-circuit and solve the phase-to-phase insulation problem from the production source.

It is recommended that the manufacturer improve the operating environment of the lead wire part to solve the problem of lead aging cracking.

It is recommended that the brother units should strengthen the inspection of the high-voltage motor lead-out line for three years on-site operation and learn from our company's experience and lessons.

热缩管对高压电机的保护

火力发电厂的厂用高压电动机比较多，运行时间长，电机引线长期运行在较高的温度环境下，使其绝缘老化加快。常规的试验方法只能测量对地绝缘，而引线又固定在绝缘板上，所以常规试验根本无法发现相间绝缘不良问题（电机通常为星形内部死连接）。这样，当引线绝缘老化到一定程度时，常规试验合格的情况下，运行中相间短路，造成高压电动机停转，严重时将导致停炉停机，这极大危胁了机组、甚至于系统的安全稳定运行。下面就我公司几起此类事件及其处理方法作以叙述以及热缩管的应用。

运行中出现电机相间短路事故事例

2015年8月，某公司5号炉乙吸风电机运行中由高速倒低速时放炮，检查发现低速绕组三相引出线绑扎固定部位相间短路所致，局部破坏严重，造成二类考核障碍。对电机分解检查发现引出线橡胶绝缘严重老化脆裂和龟裂，并露线芯，橡胶绝缘一捏就碎。

某公司2号炉送风电机运行中放炮，2号机被迫停机，造成一类考核障碍。对电机分解检查发现三相引出线绑扎固定部位相间短路所致，局部破坏严重，引出线的绝缘老化状况同上所述。

原因分析

电机引出线都为橡胶绝缘软线，且固定在热风区，运行环境恶劣，热风区的温度较高(夏季最高运行温度达60-70℃)，引出线在热风长时间作用下，橡胶绝缘极易老化和龟裂。经调查：发现电机运行三年以后，引出线绝缘均出现不同程度脆化和龟裂现象。

电机三相引出线是绑扎在一起固定的，这样绑扎固定极为不合理，一旦引出线绝缘老化出现龟裂，因金属裸露部分距离近，就会造成相间在线电压作用下放炮，电动机停转。

改进措施

将高压电动机的三相引出线分开一定间距固定，解决相间短路放炮问题；

将三相引出线分别用高压绝缘热缩管热缩，解决老化龟裂后的绝缘问题。对引线绝缘未出现老化龟裂的也进行套高压绝缘热缩管热缩处理，以增加橡胶绝缘软线抗老化龟裂能力，延长老化期。

结论

建议厂家在生产时，将三相引出线分开一定间距固定，并增加热缩管保护，避免相间短路，从生产源头解决相间绝缘问题。

建议厂家改进引出线部位的运行环境，解决引线老化龟裂问题。

建议兄弟单位，应加强对现场运行达三年的高压电机引出线部位加强检查，吸取我公司的经验教训。