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.

Auto Transformer Tap Changing

Auto Transformer Tap Changing: Working Principle, Switching Sequence and Applications Auto transformer tap changing is a practical method of adjusting transformer output voltage without unnecessarily interrupting the electrical supply. In power transmission and distribution networks, the load does not remain constant throughout the day. As load current changes, voltage drops across transformers, cables, feeders, and transmission lines also change. A tap-changing arrangement compensates for these variations by modifying the effective number of turns in the transformer winding. A reactor-type on-load tap changer uses a center-tapped reactor, selector switches, and a bypass or short-circuiting switch to transfer the load from one tap to the next. The reactor limits the circulating current during the transition, allowing the tap position to change while the transformer continues supplying the connected load. This article explains the auto transformer tap-changing working principle , switch...

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 ...

Top 10 Transformer Manufacturers in the World

Top 10 Transformer Manufacturers in the World Transformers are among the most important and expensive assets in electrical generation, transmission, distribution, renewable-energy, industrial, infrastructure, and data-center projects. A power transformer changes voltage and current levels through electromagnetic induction while maintaining the system frequency. Generator step-up transformers increase generating-station voltage for efficient transmission, while grid and distribution transformers reduce voltage progressively before electricity reaches industrial, commercial, and residential consumers. The global transformer market continues to expand because of grid modernization, renewable-energy integration, industrial electrification, data-center development, replacement of aging equipment, and construction of new transmission infrastructure. One 2026 market assessment estimates that the global transformer market could grow from approximately USD 72.5 billion in 2026 to about USD 137....

Reversing the Direction of a Universal Motor: Methods and Circuit Diagram

How to Reverse the Direction of Rotation of a Universal Motor Introduction A universal motor is a high-speed electric motor that can operate on either an alternating-current or direct-current supply when designed for the applicable voltage and frequency. It is widely used in portable electric drills, grinders, vacuum cleaners, mixers, sewing machines, small machine tools, and other equipment requiring high starting torque and compact construction. The direction of rotation of a universal motor can be changed by reversing the direction of current through either the armature winding or the field winding relative to the other. The current must be reversed in only one of these windings. If the connections of both windings are reversed simultaneously, the relative direction of the field flux and armature current remains unchanged, and the motor continues rotating in the same direction. Before studying the reversing methods, readers may review the Universal Series Motors Electric Motors and...

Top 10 Power-System Protection Relays and Their Applications

A power system must continuously transport electrical energy while remaining within the thermal, mechanical, and insulation limits of generators, transformers, busbars, transmission lines, cables, motors, and switchgear. When a short circuit, insulation failure, overload, abnormal voltage, frequency disturbance, or equipment malfunction occurs, the affected section must be disconnected quickly. A delay of even a fraction of a second during a severe fault can increase equipment damage, expose personnel to danger, and threaten the stability of the wider electrical network. A protection relay monitors electrical quantities such as current, voltage, frequency, phase angle, impedance, power, and temperature. When measured values meet predefined operating criteria, the relay initiates an alarm, trips a circuit breaker, starts an automatic control action, or blocks an unsafe operation. The three basic duties of a protection relay are: Measure electrical quantities Detect abnormal or fault co...

MAIN AND PILOT EXCITER

Main Exciter The exciter (sometimes called the main exciter) is a synchronous generator that has its stator and rotor windings inverted. Its field winding is fixed in the stator, and the rotor carries the armature or AC . In addition the rotor carries the semiconductor bridge rectifier that converts the armature voltages to a two-wire DC voltage system. The AC voltages and currents in the armature are often alternating at a higher frequency than those in the main generator, e.g. 400 Hz. The higher frequency improves the speed of response of the exciter. The DC power circuit is coupled to the field of the main generator by the use of insulated conductors that pass coaxially inside the rotor of the exciter and the rotor of the main generator. This eliminates the use of slip rings, which were traditionally used before shaft mounted rectifiers were developed. A slight disadvantage of this technique is that the derivative feedback cannot be taken from the output of the exciter. Howeve...

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