A
asgkrishnan
Hi All,
I face a strange problem in the converter transformers connected to 11 KV sub station. There is abnormal variation in humming sound of the Transformer 11KV/520 V, 2.25 KVA Dd0 feeding to converter/ inverter drive for rolling mill stand motors. Another transformer 11KV/520V, 4.5 KVA Dd0y11 in the same station behaves similar and the humming sound varies at different times. These transformers are in no-load condition only as the mill is not started yet. There is no variation in either the voltages or currents at 11 KV sub-station (Source to these transformers)
On detailed observation it is found that there is fluctuation in leakage current between 0.25 to 1.0 mA (through ammeter provided with surge monitor ) and when leakage current increase, the sound also increases. Other wise at normal sound, ammeter indicates 0.25 mA continuously. These transformers are of cast resin dry type.
Please suggest the reason for this strange behavior in humming sound of these Converter Transformers. What could be the probable cause for it?
(Kindly note that transformers are not loaded; only outgoing cables are in charged up to converter panel)
Also please tell me why these surge monitor ammeter indicate 0.25 mA at normal sound. I feel that ammeter should read zero .
Regards
I face a strange problem in the converter transformers connected to 11 KV sub station. There is abnormal variation in humming sound of the Transformer 11KV/520 V, 2.25 KVA Dd0 feeding to converter/ inverter drive for rolling mill stand motors. Another transformer 11KV/520V, 4.5 KVA Dd0y11 in the same station behaves similar and the humming sound varies at different times. These transformers are in no-load condition only as the mill is not started yet. There is no variation in either the voltages or currents at 11 KV sub-station (Source to these transformers)
On detailed observation it is found that there is fluctuation in leakage current between 0.25 to 1.0 mA (through ammeter provided with surge monitor ) and when leakage current increase, the sound also increases. Other wise at normal sound, ammeter indicates 0.25 mA continuously. These transformers are of cast resin dry type.
Please suggest the reason for this strange behavior in humming sound of these Converter Transformers. What could be the probable cause for it?
(Kindly note that transformers are not loaded; only outgoing cables are in charged up to converter panel)
Also please tell me why these surge monitor ammeter indicate 0.25 mA at normal sound. I feel that ammeter should read zero .
Regards