A Website on Maintenance of Electrical Systems

A Relay is an electrically operated switch, it basically consists of an electromagnetic coil which builds up a magnetic field when current is passed through it. This magnetic field is used to operate the relay contacts to an OFF or ON state. A Contactor is an electrically operated switch, it basically consists of an electromagnetic coil which builds up a magnetic field when current is passed through it. This magnetic field is used to move the contactor contacts into an OFF or ON state. So what is the difference between a relay and a contactor. In the most simplistic terms, a contactor is a  relay  is used to switch a large amount of electrical power through its contacts . Other notable differences are stated below. 1)     Relays tend to be for logic switching while contactors are for Power switching 2)     Relays don’t come with auxiliary contacts while many contactors have provision for auxiliary contacts 3)   ...

Mercury Vapor lamp is one of many kinds of electric lamps designed to produce light from electricity. Other types of electric lamps available in the marled include the Incandescent bulb, LED bulb, Florescent, sodium Vapor, and Metal Halide. Electric lamps could be broadly divided into two categories. 1)     Incandescent 2)    Gaseous Discharge Lamp. Gaseous discharge lamps could be further divided into High pressure and low-pressure gaseous discharge lamps. Mercury Vapor lamps fall under the Gaseous discharge lamp category. Other lamps in this category are Metal halide and high and low-pressure sodium lamp and fluorescent lamp. All gaseous discharge lamps generate light using the same principle i.e. passing an electrical arc through a gas. Mercury Vapor lamps fall under the High-Pressure Gaseous Discharge lamp category. They are also commonly referred to as High Intensity Discharge (HID) lamps. Metal Halide and High-pressure Sodium (HPS) lamps are a...

NEMA frame size refers to the physical dimensions and mounting of the electric motor.  They are a key part of motor interchangeability; in essence, a motor from one manufacturer can be replaced with a similar motor from another company provided they are both of the same frame size. The shaft length, shaft diameter, mounting foot dimensions, distance from the center of the shaft to the bottom center of the mounting foot are all part of the frame size standard. The physical dimensions of an electric motor have also been standardized by NEMA where “D” dimensions refers to the distance from center of shaft to bottom center of mounting foot, “U” dimensions refers to the diameter of the shaft, “N-W” dimensions refers to the length of the shaft, “F” dimensions refers to the distance from the center of the mounting foot to the center of base mounting hole in the side view and so on and so forth. A standard Frame size designation for electric motors is either made up of either 2 ...

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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As an electrical engineer / electrical technician you will come across this scenario a from time to time. In my case, the transformer has already been installed, and this transformer fed a block of offices and a small fabrication shop. As the company expanded they decided to add a machine shop with a new machinery like  Lathe machine, Milling machine, drill presses, machines for electroplating and the installed transformer could no longer feed the added load. The a new transformer had already been procured before management asked the question of what size of Circuit breaker would be used to protect this new Power Transformer from overload and short circuit. There a lot of factors to be considered when sizing a circuit breaker but the four major ones that should be on your mind are         The ambient temperature of the environment where the breaker is to be installed.       Continuous running current when all connected loads are switched...