Electromechanical Protective Relays Research Articles

Migration Between Two Inverse Time-Overcurrent Curves of Different Standard: Experience at Siguragura Power Station

The inevitable replacement of electro-mechanical protection relays with more recently-developed microprocessor-based protection relays poses challenges to engineer, one of which is migration from existing manufacturer’s non-standard inverse time-overcurrent curve to, usually, IEC 60255-151 or IEEE Std C37.112-1996 curve. To satisfy the required protection coordination, one may perform new study of protection coordination for the system in total, prior to replacement program. However, this exhaustive approach can be avoided by emulating existing non-standard inverse time overcurrent curve on the new microprocessor-based protection relay, provided that such curve is still adequate to be re-implemented. This paper aims to develop general procedure using nonlinear curve fitting to determine the most appropriate setting of microprocessor-based protection relay. The general procedure has been tested during renewal of feeder protection relay at Siguragura Power Station.

Microcontroller Based Under/Over Frequency Relay for Power System Protection

This paper investigates the frequency fluctuation in power system and protect the power system from its harmful effects. Therefore we design a Microcontroller Based Under/Over Frequency Relay. In this paper we use microcontroller AT89S52 for protecting the power system from the problem of frequency fluctuation. When frequency goes below or above from desired value then electromagnetic relay trip and isolate our power system from its harmful effect. Electromechanical protective relays operate by either magnetic attraction, or magnetic induction. Frequency Variation also decrease the life of the equipment and directly affect the overall production of the plant.

Field tests for assessing electrical protection performance regarding electromechanical protection relays

This article describes designing and using a series of field tests (such as pick-up test and operating characteristics) aimed at ascertaining the correct operation of relays' electromechanical protection. The characteristic elements involved in adjusting electromechanical protection relays are presented.

“Survival of the fittest” — EMC in electric power substations

When a short circuit occurs in a transmission substation (usual definition - voltages above 100,000 volts), the resulting fault current is spectacular. In some substations, it may be as high as 80,000 amperes. Let's assume the fault was caused by the flashover of a porcelain insulator supporting a section of the high voltage power line a few towers away from the substation, due to a buildup of sea salt. The protective relays monitoring this transmission line detect this abnormally high current, and close their “trip” contacts - which then cause both the high voltage circuit breakers connected to this transmission line to open - and thus “clear the fault”. But while the fault exists, this high current is flowing from the tower to ground, then through the earth back to the substation. And since there is a finite (non-zero) resistance to “true earth ground”, this causes the entire substation ground matt voltage to rise. However, this is a 60 Hertz voltage, and adequate insulation - in control circuits and electromechanical protective relays - for this well recognized “ground potential rise” has been defined for years in protective relay standards (e.g. ANSI C37.90).

Hybrid reed: Solid-state devices are a new generation of protective relays

Research and development in the field of electromechanical protective relays has not been conducted for tens of years. Author?s approach allows viewing the problem of re-equipment of relay protection in a new way. In the author?s opinion combination of reed switches with magnetic circuits and semiconductor elements opens new avenues in development of the promising protective relays featuring reliability, simplicity and low cost. Examples of protective relays made with these elements are given below.

Automatic test system advances transformer protection

In the last 10 years, computers have become part of every aspect of power system protection engineering. Multifunctional microprocessor-based relays with increasing complexity require the development and application of sophisticated computer software for the analysis, setting coordination, data acquisition and testing of such intelligent electronic devices (IEDs). Their functionality is modular and, at the same time, very specialized, as required by the protected substation or power system equipment. Conventional methods and test devices used for the testing of electromechanical protective relays are no longer adequate for the testing of advanced microprocessor relays.

Operating characteristics of protective relays in positions other than vertical

While electromechanical protective relays are designed to operate in the upright position, which is the manner in which they are normally used, some applications, such as on ships, may require these relays to operate normally while exposed to tilting and oscillatory motion. A variety of electromechanical and solid-state protective relays were tested for pickup and time-delay characteristics while tilted in several directions from vertical and while undergoing oscillatory motion. These test showed that induction disk and induction cup relays were seriously affected by tilting and motion, but that hinged-armature and solid-state relays were not affected.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>