POWER QUALITY MEASURABLE QUANTITIES

VOLTAGE DIP

is a reduction in the RMS voltage in the range of 0.1 to 0.9 pu (retained) for duration greater than hall a mains cycle and less than 1 minute, Often referred to as a ‘sag’, Caused by faults, increased load demand and transitional events such as large motor starting.

VOLTAGE SWELL

is an increase in the RMS voltage in the range of 1.1 to 1.8 pu for a duration greater than half a mains cycle and less than 1 minute, Caused by system faults, load switching and capacitor switching.

TRANSIENT

is an undesirable momentary deviation of the supply voltage or load current. Transients are generally classified into two categories: impulsive and oscillatory.

HARMONICS

are periodic sinusoidal distortions of the supply voltage or load current caused by non-linear loads. Harmonics are measured in integer multiples of the fundamental supply frequency. Using Fourier series analysis the individual frequency components of the distorted waveform can be described in terms of the harmonic order, magnitude and phase of each component.

INTER HARMONICS

Distorted voltage or current wave-forms containing periodic distortions of a sinusoidal nature that are not integer multiples of the fundamental supply frequencies are termed inter harmonics.

FLICKER

is a term used to describe the visual effect of small voltage variations on electrical lighting equipment (particularly tungsten filament lamps). The frequency range of disturbances affecting lighting appliances, which are detectable by the human eye, is 1-30 Hz.

VOLTAGE IMBALANCE

is defined as a deviation in the magnitude and/or phase of one or more of the phases, of a three-phase supply, with respect to the magnitude of the other phases and the normal phase angle (l20⁰).

FREQUENCY DEVIATION

is a variation in frequency from the nominal supply frequency above/below a predetermined level, normally plus minus 0.1 percent.

TRANSIENT INTERRUPTION

is defined as a reduction in the supply voltage, or load current, to a level less than 0.1 pu for a time of not more than 1 minute. Interruptions can be caused by system faults, system equipment failures or control and protection malfunctions. Interruptions are considered to be measurable events coining under the field of ‘quality of supply’.

OUTAGE

is defined as an interruption that has duration lasting in excess of one minute.

PRIMARY SECONDARY AND TERTIARY FREQUENCY CONTROL IN POWER SYSTEMS

Primary, Secondary and Tertiary Frequency Control in Power Systems Author: Engr. Aneel Kumar Keywords: frequency control, primary frequency control, automatic generation control (AGC), tertiary control, load-frequency control, grid stability. Frequency control keeps the power grid stable by balancing generation and load. When generation and demand drift apart, system frequency moves away from its nominal value (50 or 60 Hz). Grids rely on three hierarchical control layers — Primary , Secondary (AGC), and Tertiary — to arrest frequency deviation, restore the set-point and optimize generation dispatch. Related: Power System Stability — causes & mitigation Overview of primary, secondary and tertiary frequency control in power systems. ⚡ Primary Frequency Control (Droop Control) Primary control is a fast, local response implemented by generator governors (dro...

Advantages of Per Unit System in Power System Analysis | Electrical Engineering

Advantages of Per Unit System in Power System Analysis In electrical power engineering, the per unit (p.u.) system is one of the most widely used techniques for analyzing and modeling power systems. It is a method of expressing electrical quantities — such as voltage, current, power, and impedance — as fractions of chosen base values rather than their actual numerical magnitudes. This normalization technique provides a universal language for system calculations, minimizing errors, simplifying transformer modeling, and enabling consistency across multiple voltage levels. Because of these benefits, the per unit system is essential in fault analysis, load flow studies, transformer testing, and short-circuit calculations . ⚡ What is the Per Unit System? The per unit system is defined as: Q u a n t i t y ( p u ) = A c t u a l V a l u e B a s e V a l u e Quantity_{(pu)} = \dfrac{Actual \ Value}{Base \ Value} Q u an t i t y ( p u ) = B a se ...

PHASOR DIAGRAM OF A TWO AXIS SALIENT POLE GENERATOR

Following phasor is phsor diagram of a two-axis salient pole generator . The following points apply to the drawing of phasor diagrams of generators and motors:- • The terminal voltage V is the reference phasor and is drawn horizontally. • The emf E lies along the pole axis of the rotor. • The current in the stator can be resolved into two components, its direct component along the ‘direct or d-axis’ and its quadrature component along the ‘quadrature or q-axis’. The emf E leads the voltage V in an anti-clockwise direction when the machine is a generator. Each reactance and resistance in the machine has a volt drop associated with it due to the stator current flowing through it. Consider a generator. The following currents and voltages can be shown in a phasor diagram for both the steady and the dynamic states. E the emf produced by the field current If . V ...

DISTRIBUTION STATCOM D-STATCOM

The D-STATCOM is basically one of the custom power devices. It is nothing but a STATCOM but used at the Distribution level. The D-STATCOM is a voltage or current source inverter based custom power device connected in shunt with the power system. It is connected near the load at the distribution systems. The key component of the D-STATCOM is a power VSC that is based on high power electronics technologies. Basically, the D-STATCOM system is comprised of three main parts: a VSC, a set of coupling reactors and a controller. The basic principle of a D-STATCOM installed in a power system is the generation of a controllable ac voltage source by a voltage source converter (VSC) connected to a dc capacitor (energy storage device). The ac voltage source, in general, appears behind a transformer leakage reactance. The active and reactive power transfer between the power system and the D-STATCOM is caused by the voltage difference across this reactance. The D-STATCOM is connected in shunt w...

ADVANTAGES AND DISADVANTAGES OF CORONA EFFECT IN TRANSMISSION LINES | ELECTRICAL ENGINEERING GUIDE

Advantages and Disadvantages of Corona Effect in Power Systems In high-voltage overhead transmission lines , the corona effect plays a critical role in system performance. Corona occurs when the air around a conductor becomes ionized due to high electric stress. While often seen as a drawback because of power losses and interference , it also provides certain engineering benefits . This article explains the advantages and disadvantages of corona effect in detail, with examples relevant to modern electrical power systems. ✅ Advantages of Corona Effect Increase in Virtual Conductor Diameter Due to corona formation, the surrounding air becomes partially conductive, increasing the virtual diameter of the conductor. This reduces electrostatic stress between conductors and minimizes insulation breakdown risks. Related Reading: Electrostatic Fields in High Voltage Engineering Reduction of Transient Surges Corona acts like a natural cushion for sudden ...

DC GENERATORS

Principle: An electrical generator is a machine which converts mechanical energy into electrical energy. The energy conversion is based on the principle of the production of dynamically induced emf, where a conductor cuts magnetic flux, dynamically induced emf is produced in it according to Faraday’s Laws of electromagnetic Induction. This emf causes a current to flow if the conductor circuit is closed. Hence, two basic essential parts of an electrical generator are (i) a magnetic field and (ii) a conductor or conductors which can so move as to cut the flux. The following figure shows a single-turn rectangular copper coil rotating about its own axis in a magnetic field provided by either permanent magnets or electromagnets. The two ends of the coil are joined to two slip-rings ‘a’ and ‘b’ which are insulated from each other and from the central shaft. Two collecting brushes (of carbon or copper) press against the slip-rings. Their function is to collect the current induced in the coi...

Operation of Thyristor Controlled Series Capacitor (TCSC): Mechanism and Working Principles

Introduction In modern power systems, maintaining voltage stability and optimizing power transmission is crucial. One of the most effective FACTS (Flexible AC Transmission System) controllers for this purpose is the Thyristor Controlled Series Capacitor (TCSC) . TCSC dynamically adjusts line impedance , allowing for enhanced power flow, transient stability improvement, and subsynchronous resonance (SSR) mitigation . Unlike conventional fixed series capacitors, TCSC uses thyristor-controlled switching to regulate the compensation level in real-time, ensuring grid reliability and efficiency . In this article, we will explore: ✅ The working principle and internal structure of TCSC ✅ Modes of operation and impedance control mechanisms ✅ How TCSC enhances power system efficiency and stability Understanding the Thyristor Controlled Series Capacitor (TCSC) What is a TCSC? A Thyristor Controlled Series Capacitor (TCSC) is a power electronic-based controller used in transmission systems to ...

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