When I began my career as an electrical technician my first challenge was the problem of checking the continuity of a wire that spans a long distance. My problem was compounded due to the physical layout of the wire under test. Let me use a simple picture to layout the nature of my problem. A bunch of Armoured cables outgoing from the PCC (Power Control Center) in Building 1 feeds a group of distribution panels in Building 2 over 100ft away. Ideally, the cables should be tagged but due to aging and poor maintenance, most of the tags were not visible. The problem was that some Distribution boards in building 2 had power while some others didn't. The DB of interest didn't have power and thorough checks showed that there was no power on the cable feeding that DB. All outgoing cables from Building one PCC had power so I suspected that the cable was no longer continuous. Anyway in the initial design of the facility 3 spare cables was laid underground but without tag
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 other sourc
A Magnetic Overload relay works by detecting the magnetic field strength generated by the current flowing to the motor. In most cases the relay input is a representation of the current (through C.Ts) flowing into the motor. The Magnetic Overload Relay is built in such a way that the magnetic flux set up by current flowing through the coil drags (pulls) the core upward. A typical dashpot type magnetic overload relay is shown in the image below. Construction. The relay consists of two main parts which is the trip mechanism at the top and the dashpot at the bottom. The parts of the relay are further divided into a coil, a plunger (core), an oil-filled dashpot and switching contacts (trip contacts). The plunger is attached to a piston (disc). The piston is suspended in an oil filled chamber. The relay coil is connected in series with the motor supply circuit. During normal operation magnetic flux induced by the coil is not great enough to c
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