Elsevier

Engineering Failure Analysis

Volume 90, August 2018, Pages 64-81
Engineering Failure Analysis

Circuit breakers 500 kV degradation in substation reactors caused by inductive current

https://doi.org/10.1016/j.engfailanal.2018.03.002Get rights and content

Highlights

  • The circuit breakers have heavy degradation in substation reactors caused by inductive currents.

  • Degradation parameters and electrical tests have been considered with a new proposal for diagnosis.

  • Needs of update the international standard IEC, for inductive current for power shunt reactors and breakers.

Abstract

During the interruption of inductive currents, once the switch contacts start to move, and as the current approaches zero, there is an unstable interaction between the resulting arc inside the switch chambers and the equivalent capacitance between the terminals of the switch. This interaction results in a negative damped oscillation in the current that eventually produces the current chopping. A chopping current phenomenon is caused energy stored in the line reactors, in the form of an electric field, causing high transient overvoltage in the line reactors and high requirements of the Transient Recovery Voltage (TRV) on the associated switches. The analysis describes the failure engineering analysis and the maintenance experience in a real case study, which develops the methodology to obtain improvements inside the switch chambers, in an electrical substation for 500 kV overhead lines; besides a proposal for diagnosis and remaining life for this assets in the power industry.

Introduction

In long transmission lines, with line reactors installed, the control of small inductive currents is one of the most common problems, they are called chopping currents. Once, the displacement starts the contacts, the current approaches zero and the density is infinite. This interaction results in a damped negative oscillation in the current that eventually produces the abrupt cut in the current [1]. This phenomenon of current cut leaves stored energy in the line reactors (in the form of electric field) causing high transient overvoltage in the line reactors and high demands of the transient recovery voltage (TRV), the degradation analysis is the objective of this research, and the knowledge contribution is a correct way to understand this phenomenon with a mathematical and statistics approach with international standard recommendation for an asset management [2].

The severity degree of the mentioned phenomenon is directly related to the situation of the earth system used for the line reactors caused for overvoltage in their terminals, being the most critical condition of the operation with line reagents, totally isolated from the earth and the least expensive condition, the operation with line reactors solidly grounded [3].

In several energy transmission companies, the design and configuration of the substations and overhead lines are important factors for chopping current contribution, it operates with line reactors connected to ground through a neutral reactor for minimizing the overvoltage in the terminals of the circuit breakers. The objective of the neutral reactor is neutralizing the capacity of the line to achieve secondary arc currents, which allows its extinction during the monopolar closure cycle [4], however, the case study demonstrates the circuit breakers degradation at the moment of carrying out the electrical maneuvers of its degradation, and useful life. The present research proposed a methodology for degradation assessment, and proposed a new recommendation based on the international standards IEC 62271-306 [5]; in this research, the primary arc in the switch chambers to analyze the interaction are analyzed, the resulting arcs are expected in the installation point; which allows to determine the conditions of transitory demand, which must be considered in the design of switches associated with reactors derived from the transmission line to mitigate the resulting phenomenon [6]; the needed to implement new methods for the diagnosis is one of the biggest challenges in this new era, for example fuzzy logic [25] and expert systems should be considered in the new methodologies [26].

The comparison and complement to the IEC 62271-306 standard of December 2012 was made (based on the selection of the lowest number λ of the switch offered by the manufacturer, the minimum capacitance Cp of the switch offered by the manufacturer and the minimum time of arc “arc time” offered by the manufacturer [5], in addition, the efficiency of the synchronized control and its effect on the complementary reagents of the research carried out in [7] are analyzed, because of that, the new research should consider the new knowledge contribution for update the new standards based on technical data [27], test, and maintenance experience for a significant failure. The Section 2 develops the failure assessment method for circuit breakers, it is composed by the power lines reactors description, the influence of the grounding system in the design and the life assessment with the asset degradation in circuit breakers, in the Section 3, the case study has been presented with the electrical simulation and circuit breaker degradation has been indicated and the case study results have been developed in the Section 4, a discussion with the mitigation methods, it is written with advantages and disadvantages in the Section 5, finally in the Section 6 the conclusion has been included with the international standards recommendations and the needed to change some paragraphs in order to obtain a better behavior of the circuit breaker.

Section snippets

Power lines reactors

During the opening maneuver of line reactors, the primary arc can be extinguished, before the 60 Hz current. This can occur when the resistance equals R *, the vector in the switch terminals becomes negative, which generates a circuit with unstable, with an arc that tends to extinguish before the natural crossing of the current by zero [8]. Mathematically, it is represented in Eq. (1) and Fig. 1.R=RaRiRa+Ri+w2RaLa2Ra+Ri2+w2La2.

It should complete the following consideration:RaRiRa+Ri+w2

Circuit breakers for shunt reactors

It is located on Perú, it has been realized on 40 circuit breakers (120 poles) in 500 kV powers lines Fig. 10. The main characteristics are developed in the Table 3, the shunt reactors are in both substations of each power lines, they're banks of single-phase units.

The model represented in ATP includes an equivalent of the central zone of Peru, for the year 2018 in minimum demand for low water and the new line and substations associated. For this model, the electrical parameters for all the

A case study results

With the Section 3 result, a visual inspection process has been required, the information is relevant for maintenance diagnosis, there are small footprints left on the surface left by sizzling generated from the arc extinction according to Fig. 16.

In Fig. 16, has been demonstrated decomposition residues of SF6 gas and components detached from the worn parts.

The degradation index is 1.33, or 98.67%. it has indicated the degradation of 51.6 years, to −2.98, it means that the circuit breaker is in

Discussion

In the case study, the main contacts and the loss of the surface layer of the coating of the material has been detected for TRV effects [30], although the electrical studies and transient simulations have been made, the real effect of the overvoltage is real, and it has a process degradation in the circuit breaker with each operation; the advantages and disadvantages for analyzing and detecting the degradation of the contacts in the power circuit breakers.

Several are the methods usually applied

Conclusions

The interruption maneuver of small inductive currents carries a very special electromagnetic transient requirement for line shunt reactor, for circuit breakers, it requires a specification for the advantages and disadvantages of the mitigation alternatives.

In the case of shunt reactors applied to overhead lines, it is recommended that they be fixed with their reactors neutral tuned (if required) and available at both ends of the overhead line (to ensure symmetry) in such a way that the

Acknowledgment

Recognition of the company Freeport-McMoran Inc. Sociedad Minera Cerro Verde, Red de Energía del Peru, Consorcio Transmantaro S.A., ENEL GREEN POWER and Pontificia Universidad Católica del Perú (PUCP), Doctoral engineering program for the support and development of this research.

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