Electric fan fires are mainly caused by layer short circuit of motor windings. Insulation deterioration and temperature rise of windings are the main causes of layer short circuit. The insulation deterioration can be accelerated by the use environment such as the ambient temperature and self-heating...
Electric fan fires are mainly caused by layer short circuit of motor windings. Insulation deterioration and temperature rise of windings are the main causes of layer short circuit. The insulation deterioration can be accelerated by the use environment such as the ambient temperature and self-heating, and as a result of these factors, the degree of deterioration of the winding can be increased as the years of use increase.
The temperature rise is a characteristic of the motor, but if the abnormal load is applied or the mechanical load is increased due to the failure of the bearing, the over temperature rise due to overheating will occur. Over temperature rise causes pyrolysis of flammable materials in the motor and short-circuit between layers induces a fire.
In order to reduce the fire risk of the fan, it is necessary to find out the main parameters affecting the insulation deterioration and temperature rise of the motor. The years of use and the temperature of the windings are the main parameters of insulation deterioration. High temperature environment, abnormal voltage, load increase, blade blocked due to clothes hanging, and cooling failure are the main parameters of over temperature rise.
Therefore, this study suggests a method to improve fire safety by deriving insulation characteristics and temperature rise data which are the main cause of fan fires. For this purpose, insulation resistance, polarization index, and dielectric breakdown voltage were measured and analyzed for unused fans and used fans(5 and 10 years of use) at winding temperatures of 20, 40, 60, 80, and 100℃. In the case of temperature rise, data were measured and analyzed for normal state, temperature change due to ambient temperature change, voltage change, load change, blade blocked operation and cooling failure.
In this study, the insulation resistance decrease of the motor winding was considered to be the most important factor to increase the fire risk of the fan motor. This study proposed regression equations which can predict the insulation resistance by the winding temperature and years of use by using the change data of the insulation resistance value according to the winding temperature and the years of use. Using the proposed equation, it was found that the insulation is broken during operation when the fan is used for 13 to 16 years. As a result of complying with the fire statistics of the fan, it will be necessary to check the insulation resistance of the fan for 10 years or more.
The polarization index of the motor was not influenced by the ambient temperature change. However, as the years of use increased, the polarization index tended to decrease, which could be interpreted as aged deterioration due to external moisture or contaminants. As a result, it was suggested to use the regression equation to predict the polarization index according to the years of use, and the years of use required to reduce it to less than the reference value of ‘2.0' were calculated as 38 to 45 years.
In case of dielectric breakdown voltage, insulation breakdown voltage also decreased with increasing winding temperature. The regression equations for predicting the breakdown voltage according to the temperature of the windings and the years of use were presented. As a result of calculation, it decreased to less than 1.44 ㎸ at an ambient temperature of 40℃ or less which is the withstand voltage performance standard, and it was calculated as 5∼6 years.
Over temperature rise occurred in voltage change, load change and blade blocked operating environment. In all environments, the temperature and the current value were the highest in case of blade blocked operation. In case of blade blocked operation, the temperature rise limit reached 120℃ within 9 minutes. Therefore, if a safety device such as an overload relay that operates within 9 minutes is installed in order to extend the insulation life and a thermal fuse is installed for backup protection purpose, it is possible to reduce the occurrence of fire due to overvoltage, overload and blade blocked operation of the fan motor.
As an environmental factor, the fan was operated in high temperature environment and cooling failure. In environmental problems, anomalous signals were not detected except for the temperature rise of the windings. Since the high temperature environment and the cooling failure environment correspond to user carelessness, it is necessary to develop checklists or user manuals for prevention of carelessness fire. The analysis data presented in this study can be used to develop fire safety checklist and user manual.
Analysis results for the insulation characteristics and temperature rise of fan motors in this study are expected to contribute to the maintenance of the fan users and the safety engineers to reduce the fire risk of the fans.
Electric fan fires are mainly caused by layer short circuit of motor windings. Insulation deterioration and temperature rise of windings are the main causes of layer short circuit. The insulation deterioration can be accelerated by the use environment such as the ambient temperature and self-heating, and as a result of these factors, the degree of deterioration of the winding can be increased as the years of use increase.
The temperature rise is a characteristic of the motor, but if the abnormal load is applied or the mechanical load is increased due to the failure of the bearing, the over temperature rise due to overheating will occur. Over temperature rise causes pyrolysis of flammable materials in the motor and short-circuit between layers induces a fire.
In order to reduce the fire risk of the fan, it is necessary to find out the main parameters affecting the insulation deterioration and temperature rise of the motor. The years of use and the temperature of the windings are the main parameters of insulation deterioration. High temperature environment, abnormal voltage, load increase, blade blocked due to clothes hanging, and cooling failure are the main parameters of over temperature rise.
Therefore, this study suggests a method to improve fire safety by deriving insulation characteristics and temperature rise data which are the main cause of fan fires. For this purpose, insulation resistance, polarization index, and dielectric breakdown voltage were measured and analyzed for unused fans and used fans(5 and 10 years of use) at winding temperatures of 20, 40, 60, 80, and 100℃. In the case of temperature rise, data were measured and analyzed for normal state, temperature change due to ambient temperature change, voltage change, load change, blade blocked operation and cooling failure.
In this study, the insulation resistance decrease of the motor winding was considered to be the most important factor to increase the fire risk of the fan motor. This study proposed regression equations which can predict the insulation resistance by the winding temperature and years of use by using the change data of the insulation resistance value according to the winding temperature and the years of use. Using the proposed equation, it was found that the insulation is broken during operation when the fan is used for 13 to 16 years. As a result of complying with the fire statistics of the fan, it will be necessary to check the insulation resistance of the fan for 10 years or more.
The polarization index of the motor was not influenced by the ambient temperature change. However, as the years of use increased, the polarization index tended to decrease, which could be interpreted as aged deterioration due to external moisture or contaminants. As a result, it was suggested to use the regression equation to predict the polarization index according to the years of use, and the years of use required to reduce it to less than the reference value of ‘2.0' were calculated as 38 to 45 years.
In case of dielectric breakdown voltage, insulation breakdown voltage also decreased with increasing winding temperature. The regression equations for predicting the breakdown voltage according to the temperature of the windings and the years of use were presented. As a result of calculation, it decreased to less than 1.44 ㎸ at an ambient temperature of 40℃ or less which is the withstand voltage performance standard, and it was calculated as 5∼6 years.
Over temperature rise occurred in voltage change, load change and blade blocked operating environment. In all environments, the temperature and the current value were the highest in case of blade blocked operation. In case of blade blocked operation, the temperature rise limit reached 120℃ within 9 minutes. Therefore, if a safety device such as an overload relay that operates within 9 minutes is installed in order to extend the insulation life and a thermal fuse is installed for backup protection purpose, it is possible to reduce the occurrence of fire due to overvoltage, overload and blade blocked operation of the fan motor.
As an environmental factor, the fan was operated in high temperature environment and cooling failure. In environmental problems, anomalous signals were not detected except for the temperature rise of the windings. Since the high temperature environment and the cooling failure environment correspond to user carelessness, it is necessary to develop checklists or user manuals for prevention of carelessness fire. The analysis data presented in this study can be used to develop fire safety checklist and user manual.
Analysis results for the insulation characteristics and temperature rise of fan motors in this study are expected to contribute to the maintenance of the fan users and the safety engineers to reduce the fire risk of the fans.
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