ENGINEERING ARTICLES

Let us consider the case of two platinum electrodes dipped in dilute sulphuric acid solution. When a small potential difference is applied across the electrodes, no current is found to flow. When, however, the applied voltage is increased, a time comes when a temporary flow of current takes place. The H +  ions move towards the cathodes and O -  ions move towards the anode and are absorbed there. These adsorbed ions have a tendency to go back into the electrolytic solution, thereby leaving them as oppositely-charged electrodes. This tendency produces an emf that is in opposition to the applied voltage which is consequently reduced. "This opposing emf which is produced in an electrolyte due to the absorption of gaseous ions by the electrolyte from the two electrodes is known as the back emf of electrolysis or polarization." The value of this back emf is different from different electrolytes. The minimum voltage required to decompose an electrolyte is called ...

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...

A power system can be referred to as an islanding system when it is disconnected from other systems and does not exchange power through tie-lines. Due to the fact that frequency is the same within the entire system, frequency control in an islanding system can be achieved in a relatively simple way. The turbine speed governors should be provided with supplementary elements that change the settings according to frequency variations. After a load change, the frequency reaches a new steady-state level, different from the initial value. The frequency (or rotational speed) error causes an additional integral term to generate a signal which modifies the value of the power setting of a generating unit. With a sufficiently large number of generating units supplied with control systems of this type, the power system yields such a change in the generated power that frequency returns to its initial value. This concept of frequency control can be referred to as decentralized since it...

Comparison Between STATCOM and SVC — Which One Fits Your System? Author: Engr. Aneel Kumar Figure 1: Infographic comparing STATCOM and SVC — technology, operation, and applications. Introduction In modern AC power systems, dynamic reactive power control is essential for voltage stability, power quality, and efficient transmission. Two prominent technologies deliver shunt reactive power compensation: STATCOM (Static Synchronous Compensator) and SVC (Static Var Compensator) . Both belong to the FACTS (Flexible AC Transmission Systems) family, but they differ in topology, dynamic performance, cost profile, harmonic behavior, and typical applications. This article provides a practical, technical comparison to help engineers, planners, and grid operators choose the right solution. Related posts: Comprehensive Guide to Static VAR Compensators Operatin...

It depends on what is limiting the power flow and how much of an increase is needed to solve the problem. In most circumstances, power flow limits are the result of concerns over electrical phase shift, voltage drop or thermal effects in lines, cables or substation equipment. SURGE IMPEDANCE LOADING LIMITS As power flows along a transmission line, there is an electrical phase shift, which increases with distance and with power flow. As this phase shift increases, the system in which the line is embedded can become increasingly unstable during electrical disturbances. Typically, for very long lines, the power flow must be limited to what is commonly called the Surge Impedance Loading (SIL) of the line. Surge Impedance Loading is equal to the product of the end bus voltages divided by the characteristic impedance of the line. Since the characteristic impedance of various HV and EHV lines is not dissimilar, the SIL depends approximately on the square of system voltage. T...

In order to prevent over voltages at light loads, it is necessary to have devices for absorbing reactive power (like shunt reactors) not only at either end of a long line but even at intermediate points. Generators connected at the ends of the line have limited reactive power absorption capability as defined by their capability curves. If transmission redundancy exists (i.e., parallel transmission paths exist), then a very lightly loaded long line may be tripped to avoid overvoltage. However this may be detrimental to system security if some additional line trippings take place due to faults. If shunt reactors are permanently connected, they result in large sags in the voltage under heavy loading conditions. Moreover, reactive power demanded by long transmission lines under these situations may be excessive and may lead to system-wide low voltage conditions. Compensation of a line involves changing the effective line parameters by connecting (lumped) capacitors in series and shun...

As the network becomes complex, application of Ohm’s law for solving the networks becomes tedious and hence time consuming. For solving such complex networks, we make use of Kirchhoff’s laws. Gustav Kirchhoff (1824-1887), an eminent German physicist, did a considerable amount of work on the principles governing the behaviour of electric circuits. He gave his findings in a set of two laws: (i) current law and (ii) voltage law, which together are known as Kirchhoff’s laws. KIRCHHOFF'S CURRENT LAW The first law is Kirchhoff’s current law (KCL), which states that the algebraic sum of currents entering any node is zero. Let us consider the node shown in Figure 1. The sum of the currents entering the node is -i a +i b -i c +i d =0 Or i a -i b +i c -i d =0 Which simply states that the algebraic sum of currents leaving a node is zero. Alternately, we can write the equation as i b +i d =i a +i c Which states that the sum of currents entering a node is equal to the s...