Newton-Raphson method is used widely for solving the power flow problems in power system studies. In this method, a set of non-linear algebraic equations describing the electrical power network under steady-state conditions are solved. However, ill-conditioned power systems continue to pose challenge in the analysis as a small change in input parameter produces a large change in the solution. The condition number of the Jacobian of the system matrix indicates the measure of `condition'. In the paper, "Effect of UPFC on Load Flow Studies on Ill-Conditioned Systems", by Sarat Kumar Sahu, S Suresh Reddy and S V Jayaram Kumar, the analysis of ill-conditioned power systems with Flexible AC Transmission System (FACTS) devices like Unified Power Flow Controller (UPFC) is described. It has been observed in a 13-bus ill-conditioned power system that the condition number of a system decreases with the incorporation of the UPFC.

To optimize the operating cost of the power system, while satisfying various system operating constraints, Optimal Power Flow (OPF) programs are used in power system studies. Various methods based on Tabu search algorithm, Simulated Annealing (SA) technique and Particle Swarm Optimization (PSO) method are being used to solve the optimal power flow problem with constraints like ramp rate limits of the generators. In their paper, "Modified Particle Swarm Optimization Based Optimal Power Flow", the authors M Anitha, S Subramanian and R Gnanadass propose Fitness Distance Ratio (FDR) method of PSO to solve the OPF problem considering the line flow, ramp rate and transient stability limits of the generator. The proposed FDR PSO algorithm is tested on 39-bus New England test system. Wheeling transactions and contingency analysis are also carried out on the New England test system and the system stability is checked.

Solitons are `Stable Pulses' that travel without changing their shape. A variety of methods for sending optical solitons over long distances like synchronous modulation, sliding frequency filter, etc., have been developed in optical fiber communications. Manoj Kumar, Ajay K Sharma and T S Kamal in their paper, "Long-Haul Dispersion Managed Soliton Transmission Link Over a Fiber Length of 18,000 km with Loss and Periodic Amplification", study the soliton transmission over a fiber length of 18,000 km with loss and periodic amplification. It has been shown that the dispersion management is achieved through soliton pulse narrowing in anomalous dispersion fiber and broadening at one Dispersion-Compensating Fiber (DCF) span.

Active Power Filter (APF) is used to compensate harmonic distortion caused by power electronic converters. In the paper, "Non-Model Based Control of Active Power Filters", Alka Mahajan and Parmod Kumar developed a fuzzy controller that can replace the Proportional Integral (PI) controller with better dynamic response. The fuzzy controller gives a satisfactory performance in terms of harmonic and reactive compensation.

By installing Series Capacitors (SCs) on long transmission lines several advantages are gained like improved system stability, reduced transmission losses, improved voltage profiles and more flexible power flow control. However, the presence of capacitors causes problems in the operation of protective relays. If the presence of capacitor in the fault loop is detected then appropriate procedure can be followed for protection. In the paper, "A Novel Technique for Distance Protection of Series Compensated Transmission Line", by V J Pandya and S A Kanitkar, a detection method based on the average harmonic distortion present in the third, fifth and seventh harmonics in post-fault one cycle data is presented.

In the condition monitoring of power transformer, dissolved gas analysis is done for fault diagnosis. Jashan Deep Singh ,Yog Raj Sood and Piush Verma, in their paper, "Review of Various Dissolved Gas Analysis (DGA) Techniques for Power Transformers", reviews various conventional and Artificial Intelligence (AI)-based techniques of dissolved gas analysis.

- M S R Murty
Consulting Editor