Fahrudin Mekic

Power Transformer Characteristics and Their Effects on Protective Relays

There are a variety of protective relays using different measuring techniques to provide reliable and secure transformer protection. This includes electro-mechanical, solid state and numerical relays. Within each group, various algorithms exist. Advancements made to transformer technology and design over the past 3 decades, have changed the characteristics of the transformer inrush current, and have often introduced incorrect operations in the existing harmonic restraint relays during energization

Advanced Multi-terminal Line Current Differential Relaying and Applications

Current differential relaying has long been an alternative to directional comparison relaying, especially for short line applications. Current transformer performance has always been one of the limiting factors is using a current differential scheme. Summing the current transformer currents before entering the relay deepens the problem. With the advent of multi-terminal current differential relays, individual currents can be kept isolated throughout the differential process, mitigating the problem. This paper describes differential relaying techniques and shows examples of how keeping currents separate helps solve real application problems

Distributed automation for back-feed network power restoration

Smart Grid refers to electric power systems that enhance grid reliability and efficiency by automatically anticipating and responding to system disturbances. To achieve smart grid at the power distribution system level, various automatic technologies have been attempted in the areas of system metering, protection, and control. Within these technologies, automated power restoration is an important part of the Smart Grid puzzle. This paper presents an on-line method for the automated power restoration application previously described. The developed method conducts an analysis to achieve back-feed power restoration, i.e., healthy load zones that have lost power will be restored through their boundary tie switching devices from neighboring sources, and no reconfiguration beyond the tie devices will be considered. The back-feed restoration should not overload any part of the back-feeding network.

Protecting a high horsepower motor

Protecting the motor is obviously the most important task of protection relays regardless of the technology that they are based on. Microprocessor-based relays are capable of processing the measured data (i.e., current, voltage, and status indication) in many different ways. Registered data in the relay can be sent through a communication network to the operation/engineering headquarters for continuous monitoring or fault analysis. In addition to being used for motor protection, relays provide useful information to other departments (maintenance, planning, etc.).

Field experience using a microprocessor relay to protect a 14,000 hp motor

The protective relays discussed in this paper along with individual solid-state relaying protect a 14,000 hp 4-pole compressor induction motor. All protection is located in an outdoor breaker cubicle located at a Gulf coast petrochemical plant without the benefit of HVAC. The protection scheme was designed so that all fault types and abnormal operating conditions are properly detected and cleared. The installation includes unique protection functions for locked rotor protection, blown fuse detection, customized logic for the upstream breaker tripping, customized relay display, and condition monitoring of the primary equipment (breaker, current transformer (CT), voltage transformer (VT) etc). A novel approach using non-saturating current and voltage sensors is also discussed in this paper.