Some high-voltage ring main units (HV RMUs) may produce abnormal noises during operation. How do these noises occur? Let’s analyze them with the editor:
1、Significantly increased but relatively uniform noise inside the HV RMU
This type of abnormal noise is generally caused by excessive load. It can be determined by measuring the load or touching the temperature of the distribution transformer casing. Identify the cause of the overload and reduce the load to within the allowable range. In case of severe overload, the possibility of insulation degradation or damage to the distribution transformer should also be considered, and further necessary tests shall be conducted.
2、Intermittent and irregularly changing noise with sudden increases and decreases
This is caused by the distribution transformer carrying impact loads, such as frequent starting of large motors or intermittent operation of the HV RMU.
3、Strong and uniform noise
It occurs when there is a remote short circuit or grounding in the system, but the fuse link fails to blow in time. Under the action of the short-circuit current, severe imbalance in the magnetic circuit of the magnetic flux leads to this noise.
4、Increased noise with intermittent interference
This is due to loose iron cores or clamps inside the distribution transformer. If tests show that the load current is small, the temperature is low, and the secondary no-load voltage is basically balanced, the operation can continue without monitoring; if the noise continues to increase, the distribution transformer should be replaced for maintenance.
5、Characteristic abnormal noises
● In case of inter-turn short circuit: Severe local overheating occurs in the short-circuited turns, causing local boiling of the transformer oil and a "gurgling" sound like boiling water.
● In case of poor tap contact or insulation breakdown: A "crackling" sound of discharge is produced.
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、Handling measures for abnormal noises during patrol inspections
If no instruments are available for testing when abnormal noises are detected in the distribution transformer:
● First, ensure the distribution transformer casing is reliably grounded, then touch the casing to check the temperature and observe if the oil level in the oil conservator has risen.
● Then disconnect the secondary load of the distribution transformer to put it in a no-load state. If the noise of the HV RMU returns to normal at this time, it indicates the noise is caused by an external fault.
This article is edited and organized by DAYA Electric Group Co., Ltd. (https://www.hygraphics.com/). Please indicate the source when reprinting.