Choose vertical mill powder motor burn out root cause analysis and solutions

The analysis of the causes of vertical mill choose powder motor burn out and solutions - 2020 11 - 28 Dong Mingliang ( Tangshan Jidong Equipment Engineering Co. , Ltd. ) 1 problems of a company's raw material vertical mill classifier motor is frequency conversion motor, rated power of 200 kw, rated current is 415 a, in the normal production process, vertical abrasive layer becomes unstable, mill also have big change, import and export of pressure difference with the vertical mill vibration, vibration value reach 8 mm/s, triggered downtime equipment protection. 2 stop after cause analysis and solution, through inspection found to be classifier motor burn out, lead to accumulation of material within the mill, material layer instability, grinding of equilibrium is broken, vertical mill vibration, large vertical mill vibration protection chain eventually work downtime. And classifier is burn out because classifier frequency conversion motor cooling fan does not work, frequency conversion motor at low frequency, calorific value is big and can't normal heat dissipation, high temperature and eventually lead to motor burn out. However, cooling fan has been done in the PLC program chain protection, if the cooling fan is no answer, fault alarm and automatically stop, but the reality classifier is not automatic stop. Checker, after having confirmed again check the electric control cabinet, found that the cooling fan response contactor normally open auxiliary signal points in the adhesion and damaged, normally open signals into a normally closed, actual contactor does not suck, but PLC for cooling fan has been reply, so not alarm downtime, and eventually lead to frequency conversion motor overheating burn out. In order to solve the above problem, to avoid a similar situation occurred. The most began to consider side to join in the motor winding temperature measuring device, the motor winding temperature signal transmission is controlled by the implementation, to join in the PLC program temperature, alarm and interlock. This plan is feasible in theory, but as a result of motor structure limited, unable to join the warm resistance measurement, so we can not achieve. Lead to frequency conversion motor burn out the source of the cooling fan is not working, good heat dissipation. After a careful study, the second scheme was proposed, namely to join in the cooling fan control loop current detection, real-time detection of cooling fan running current, when the classifier works, cooling fan will have a normal current value, when the current value is too large or too hours, will trigger chain alarm or stop the program, to ensure that the selected powder motor will not unable to heat dissipation lead to burnout. Specific implementation process: first of all in one phase cooling fan three-phase power circuit current transformer, and then people secondary instrument transformer output signal, secondary instrument 4 ~ 20 ma current connection to the PLC analog input template, make corresponding chain in the PLC program. If the scene without PLC spare channel, can use hard interlock, through the connecting cable, the secondary instrument switch alarm output signal chain to stop control hardware circuit of inverter, when secondary instrument alarm output directly jump stop frequency converter. Due to directly measure the cooling fan current, so the cooling fan is blocked or electrical failure under the condition of PLC system caused by misjudgment, can accurate judgment of cooling fan is working correctly, so can reduce because of equipment downtime, unable to continuous production and equipment maintenance bring economic losses. 3 modification effect after above improvements, has been more than a year of time, vertical mill classifier is in good working order, did not appear again lead to motor damage due to overheating. To plan ahead, the company has all the frequency conversion motor cooling fan is reformed, the investment is not big, but played an important role to the protection of equipment. Source: 'cement project' 01, 2017