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 ...
Draw-Out Circuit Breaker A trip unit is the part of a circuit breaker that automatically opens the contacts of the circuit breaker in the event of a short circuit, ground fault, or thermal overload. There are two types of trip units; the thermal-magnetic trip unit, and the electronic trip unit. A thermal-magnetic trip unit has moving parts. It consists of a bimetallic thermal device that opens the circuit breaker with a delay depending on the magnitude of overcurrent. It also consists of a system where magnetic forces proportional to the current flowing through the circuit breaker are used to actuate the breaker. Simply put, in the event of a short circuit, high current flows and a strong magnetic field is created. This magnetic field is used to actuate the trip mechanism. An electronic trip unit is a programmable device that measures and times the current flowing through a circuit breaker and initiates a trip signal when appropriate. There are 6 common curre...
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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