Technical articles on Electronics and Electrical Engineering topics focused on Basics of EE, Electronic components, power systems and equipment used for generation, transmission, operation, and controls of electricity.
A form of protection against faults on long-distance power lines is called distance relaying, so named because it is actually able to estimate the physical distance between the relay’s sensing transformers (PTs and CTs) and the location of the fault. In this way, it is a more sophisticated form of fault detection than simple overcurrent … Read more
One of the fundamental laws of electric circuits is Kirchhoff ’s Current Law, which states the algebraic sum of all currents at a circuit node (junction) must be zero. A simpler way of stating this is to say “what goes in must come out.” We may exploit this principle to provide another form of protection … Read more
Perhaps the most basic and necessary protective relay function is overcurrent : commanding a circuit breaker to trip when the line current becomes excessive. The purpose of overcurrent protection is to guard against power distribution equipment damage, due to the fact that excessive current in a power system dissipates excessive heat in the metal conductors … Read more
In the United States, the ANSI and IEEE organizations have standardized a set of numerical codes referring to different types of power system devices and functions (IEEE C 37.2). Some of these codes refer to specific pieces of equipment (e.g. circuit breakers) while other codes refer to abstract functions (e.g. overcurrent protection). Two partial listings … Read more
Potential transformers (PTs or VTs) tend to behave as voltage sources to the voltage-sensing instruments they drive: the signal output by a PT is supposed to be a proportional representation of the power system’s voltage. Conversely, current transformers (CTs) tend to behave as current sources to the current-sensing instruments they drive: the signal output by … Read more
An important characteristic to identify for transformers in power systems – both power transformers and instrument transformers – is polarity. At first it may seem inappropriate to speak of “polarity” when we know we are dealing with alternating voltages and currents, but what is really meant by this word is phasing. When multiple power transformers … Read more
Electrical power systems typically operate at dangerously high voltage. It would be both impractical and unsafe to connect panel-mounted instruments directly to the conductors of a power system if the voltage of that power system exceeds several hundred volts. For this reason, we must use a special type of step-down transformer referred to as a … Read more
At voltages 46 kV and above (classified as “high voltage” in the electrical power industry), the challenge of extinguishing the electric arc formed by separating breaker contacts becomes severe. Two popular strategies for mitigating contact arc in modern high voltage circuit breakers are oil immersion and gas quenching. A set of three oil-bath circuit breakers … Read more
In Electrical Power Distribution industry the term medium voltage refers to voltage range extending from 2.4 kV to 35 kV. Circuit breaker design and construction becomes more complicated at higher voltages, such as the voltage range extending from 2.4 kV to 35 kV commonly classified as “medium-voltage” in the electrical power distribution industry. Aside from … Read more
In the United States, the term “low voltage” with reference to power circuits usually refers to circuits of 600 volt or less potential. This photograph shows a typical low-voltage (480 volt) circuit breakers in a “Motor Control Center” (MCC) panel, for 480 volt 3-phase industrial power circuits: Note how each circuit breaker has its own on/off … Read more