A Website on Maintenance of Electrical Systems

  Contact resisting test is a kind or commissioning, or maintenance test done to measure the resistance of an electrical connection. The connection could be pressed together,  bolted, soldered, clamped or welded. Contact theory assumes that at some scale the metal surfaces are never completely flat. The main purpose is to confirm the integrity of an electrical connection and catch problems very early if one exists. The Contact Resistance measurement  can detect the following problems loose connections, bolted joints that are not adequately tensioned, corroded contacts surfaces and eroded/pitted contact surfaces.  This test is usually carried out on, circuit breakers, contactors, relays and switches in closed condition to verify that the contacts make properly and there would be no heating on load. It is also carried out on cable terminations, joints, and busbar sections for the same reason listed above. In the case of circuit breakers and fused c...

  A DOL starter  is the  simplest and most common method for starting and stopping electric motors under 5 hp/4Kw.  It typically comprises of some form of a circuit breaker, contactor and an overload protection. It offers no way to limit the starting / inrush current consequently its components most me properly sized to accommodate he magnitude of voltage and current the system is expected to carry. Components of a DOL Starter: Fuse or circuit breaker : This device provides protection to the motor from overcurrent conditions caused by short circuits. Contactor : This is the main switching device that that is energized to connect the motor to the power supply. It is it is energized and de-energized by a start/stop pushbutton or other control signal. Overload relay : This device protects the motor from overcurrent conditions caused by motor overload. It trips and disconnects the motor from the power supply if the current exceeds a safe limit. Typica...

  Synchronizing Generators: Using Synchroscope and Synchronizing Lights Synchronizing two generators or synchronizing a generator to the grid is done with the help of a synchroscope and synchronizing lights.  Synchroscope and Synchronizing Lights Conditions for Synchronization: Certain conditions must be met for successful synchronization of two alternators. They are listed below. Ø   Phase Sequence  - It is important that both generators are rotating in the same direction with ABC sequence. Ø   Voltage Magnitude  - It is important that the voltage produced by both generators should be of the same magnitude. This ensures that the incoming generator doesn't  absorb reactive power and be motored by the running generator. Ø   Frequency  -  The frequencies of the generators must match to avoid in high acceleration and deceleration of the prime mover.   This can lead to increased transient torque. Ø ...

  There are many reasons why gravel is used to cover the topsoil in a transformer yard but before we delve into the reasons behind this practice, we will explore the important concepts of step and touch voltage: 1. Insulation : Gravel primarily acts as an insulator, reducing both step and touch voltage. This is vital to ensure safety in the transformer yard. To understand this better, let's explain the concepts of step and touch voltage:    - Step Voltage : Step voltage refers to the voltage that develops between the two feet of a person standing on the ground when fault current flows through it. For instance, if an energized 11KV cable falls to the ground (topsoil), the fault current dissipates into the ground. As you walk towards the cable, there's a voltage differential between the points where your feet meet the topsoil. If this step voltage is sufficiently high, it can potentially push current sufficient enough to cause injury or death through your body....

A distribution transformer is the type of transformer that performs the final voltage transformation in a distribution grid. They are normally rated less than 200 MVA and the output is usually 3~ 415V/1~ 240V or whatever the service voltage is in the customer's premises. Basic Operating Principle  A transformer operates according to Faradays Law of Induction.  Faraday’s law states that a current will be induced in a conductor which is exposed to a changing magnetic field.  An electric current produces a magnetic field around it. In an AC circuit, the magnetic field produced is constantly changing as a result of current that oscillates back and forth. The primary and the secondary coils are wrapped together around a common “iron core”. This soft iron core is made up of individual laminations stacked together to help reduce the core’s magnetic losses. When alternating current is introduced on the primary coil, the coil develops a changing magnetic field. That magnet...

  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....