A Website on Maintenance of Electrical Systems

Single phasing fault is the worst case of voltage imbalance in a three-phase supply where there is a break on one of the phases in a 3- phase supply hence the remaining phases draw excess current w hich quickly overheats the motor windings and reduces the power output of the motor drastically. Causes Of voltage imbalance and single phasing on an induction motor. 1) Faulty Circuit breaker – This is a situation where there is an open pole in the circuit breaker and that phase becomes absent. 2) Blown fuse – One of the three fuses use for protection if the circuit melts and supply is current is lost on that phase. 3) Faulty contactor- One of the phases of a contactor could be damaged or coated due to rust and not conducting. 4)  Partial Contact – also known as high resistance connection. A  l oose connection  anywhere on the power circuit could create a very high resistance joint which will cause  a severe  voltage  drop at that point. This could ...

The nameplate of a power transformer contains the following details as per standard, then additional information could be provided varying from manufacturer to manufacturer. Name Of Manufacturer Serial Number Year Of Manufacture Connection Symbol – This tells you the HV winding and LV winding configuration of a transformer and difference in phase angle between them. Example DYN11 where the first letter represents the HV winding and indicates that it is connected in delta, the second letter represents the LV winding and indicates that it is connected in Star(wye)  and the third letter N indicates that the LV winding has a Neutral while 11 denotes a 30 degree lead in phase angle. This article explains more on the Vector group of a transformer and why it is important.  (Transformers connected in parallel must have the same vector group i.e. same phase angle shift to avoid circulating currents. This is a situation where one source will become load to the ot...

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