KEYWORD – Motor Current Load, Micro-Surge Voltage, Temperature, Practical Standard, Countermeasure. In order to move heavy car body in production line, motors are used in automotive plant essentially. But, in case of motor failure, sometimes it can lead to the whole plant down for long time. So, as an effort to prevent the situation, this study was conducted for how to diagnose Motors with two measuring instruments, Oscilloscope and Thermal Imager. Motors have its own current load waveform include ampere and frequency, also it gets heated depend on the state of motor. So diagnosis technique is necessary to check if the state of motor is fine prior to the failure. Study can be started by visualizing electrical state of motor with the instruments first. STEP 1) Measuring current load waveform of motor with oscilloscope : Able to obtain overall information about motor operation status; Allowance rate of rated rurrent and torque, state of break operation, phase loss of motor power and so on. STEP 2) Measuring micro-surge voltage of motor with oscilloscope : If the length of power cable between drive and motor is too long, micro-surge is generated too much to be able to damage motor coil. So it is necessary to figure out how high the surge voltage is. STEP 3) Measuring temperature of motor surface with thermal Imager : If the status of motor is poor, then the result will inform us which part of motor is problem and how serious it is. STEP 4) Classifying the result of measurement and what kind of cause type it was actually and establish the standard so that make the accurate judgement from the inspection. The methodology results in three major items. 1. Over current load caused by lack of motor capacity allowance, break and cabling problems and so on : In these case, current-load is higher than rated-current level compared with normal situation during operation. Therefore, specific standard of current-load is necessary to judge the state of motor. Based on the motor spec., practical standard of motor current-load has been established. 2. High micro-surge voltage caused by over cabling : In case of over-cabling around 100meters, peak micro-surge voltage at the motor terminal was even higher than others which is cabled within 50m, and it can destroy motor coil insulation faster. Based on the voltage withstand capability of motor, standard of micro-surge voltage has been established. 3. Overheat of abnormal motor state : If motors have problem, temperature of motor surface become overheat than others in normal. So, standard of temperature for motors has been established. It is hard to measure accurate temperature of motor, because motor coil is covered with metal frame. So, durability index, airtightness, material type of frame was considered in order to judge with temperature of motor frame. Also, NEMA and IEC standard was referred to establish reliable standard as possible. Beside it, to gather as various case of motor failure as possible taking place in real, it took long period of time to obtain waveforms from the motor failure. Thanks to the application of motor current-load monitoring system these days in new plant, it will be easier to obtain the waveform. Normally, this kind of study is not easy because motor failure is unpredictable and it is hard to obtain various case of motor failure naturally. So it is unavoidable to rely on artificial test result. But in this study, standard of each items contains many types of practical and real failure case. Not only establishment of standard, but countermeasure also studied for each case. Therefore, it can be reliable guide for many engineers who is in charge of Motors in production line. In this study, practical standard and countermeasure was studied to diagnose and predict the failure of motor which is most important equipment in production line these days. The standard is established based not only on the practical case in production line, but also on reasonable criteria for the balance between the management of equipment and the cost. So, through this study, loss of downtime caused by motor failure will be minimized as possible in the production industry.
Mr. TAEJUN PARK, Manager, Hyundai Motors Company