RESEÑA AUTORESDaniel Ricardo Poveda Pineda es ingeniero electricista de la Universidad Nacional de Colom-bia 2008, Magister en ingeniería eléctrica en 2016, trabajo durante 5 años en el Laboratorio de Ensayos Eléctricos Industriales como ingeniero de pruebas. Actualmente se desempeña como Director Técnico de CERTECNICA.

Francisco Javier Amórtegui Gil es ingeniero electricista de la Universidad Nacional de Colom-bia en 1983, Especialista en planeación educati-va, Docente de las áreas de sistemas eléctricos y alta tensión de la Facultad de Ingeniería de la Universidad Nacional desde 1988, Jefe técnico de ensayos del Laboratorio de Ensayos Eléctricos Industriales –LABE-

The importance of control the power transformer energization

distribution systems.

Using CS when energizing power transfor-mers has a positive effect on circuit breakers (CB), power transformers, potential transfor-mers (PTs) and current transformers (CTs), as a CSD:

• Decreases its risks of failures caused by stresses induced by electrical tran-sients.• Lowers its maintenance costs.• Extends its lifespan.

Benefits for the power system can also be expected, as a CSD:

• Improves the system’s power quality by mitigating voltage transients and inrush current.• Decreases probabilities of power outa-ges caused by equipment failures or undesired protection trips.

This paper describes the issues that may arise from uncontrolled energization of power transformers and how they can be mitigated by using an enhanced CSD. It illustrates bene-fits of this evolving technology and includes a description of Hydro-Québec’s experience using controlled switching for over twenty years. Outcomes of tests using Gang Opera-ted (GO) CBs and Controlled Switching Device are also presented.

Abstract—Uncontrolled energization of power transformers can produce excessive inrush currents as a result of the asymmetrical magnetic flux and core saturation. One of the most critical effects is voltage dips maintained over time, which in some cases harms the electrical system stability. In addition, high inrush current produces thermal problem, increased vibration and mecha-nical stress, can result in protection relays malfunctioning and decreased power equipment life expectancy. By energizing the transformer with an enhanced controlled switching device (CSD) these issues can be mitigated. Controlled closing taking into account the residual magnetic flux is one of the most efficient and reliable solu-tions to limit inrush current and voltage distur-bances.

Key Words—Controlled switching (CS), power transformers, circuit breakers, inrush currents, voltage transients

I. INTRODUCTION

Energizing transformers causes disturbances triggered by inrush current. This inrush current reduces the transformer remaining life and it may generate temporary overvoltage on the network. It may also lead to unwanted protective relay operation and reduction of the power quality delivery [4]. In addition, other phenomena can appear like mechanical stress and heat in the coils of the transformer, sympathetic inrush in neighbor transformers, etc.

Several utilities have been using CS for the attenuation of switching transients in high-volta-ge (HV) power systems. New technological advances have led to the development of affor-dable CSD for medium voltage applications, opening the door for innovative applications for

AUTORES

Marc Lacroix Eng, M. Eng, Senior Member IEEE

Andrea Gutierrez Eng, M. Eng.

VIZIMAX Inc. – Canada

II.IMPACT OF RANDOMPOWER TRANSFORMERENERGIZATION

Techniques with different performance results, including no mitigation at all, could be used to energize an unloaded transformer.

A practical comparison was performed during the commissioning of a CS system at BC Hydro (138 kV, 16 MVA power transformer). Tests were carried out under various mitigation techniques. Figure 1 shows the inrush currents associated with uncontrolled operations (blue), controlled closing at peak voltage (red), and controlled closing taking into account the residual magnetic flux (green).

Inrush current and voltage transients are direct results of energizing power transformers at the wrong moment. One in six random energisations generates considerably high inrush current and

electrical stress on the transformer winding [4]. These phenomena are a threat to the relia-bility, availability and quality [2][3] of electrical energy supplies. In addition, it reduces equip-ment life expectancy and increases its mainte-nance cost.

This inrush current is mainly related to the CB’s closing time and to the remaining residual flux in the transformer’s core after its previous de-energization.

Figure 2 shows field results of a 138kV, 16 MVA power transformer uncontrolled energization.

Figure1:Field results of three mitigation techniques Figure2:

Disturbances caused by random closing of atransformer’s circuit breaker

www.cidet.org.co 51

II.IMPACT OF RANDOMPOWER TRANSFORMERENERGIZATION

Techniques with different performance results, including no mitigation at all, could be used to energize an unloaded transformer.

A practical comparison was performed during the commissioning of a CS system at BC Hydro (138 kV, 16 MVA power transformer). Tests were carried out under various mitigation techniques. Figure 1 shows the inrush currents associated with uncontrolled operations (blue), controlled closing at peak voltage (red), and controlled closing taking into account the residual magnetic flux (green).

Inrush current and voltage transients are direct results of energizing power transformers at the wrong moment. One in six random energisations generates considerably high inrush current and

electrical stress on the transformer winding [4]. These phenomena are a threat to the relia-bility, availability and quality [2][3] of electrical energy supplies. In addition, it reduces equip-ment life expectancy and increases its mainte-nance cost.

This inrush current is mainly related to the CB’s closing time and to the remaining residual flux in the transformer’s core after its previous de-energization.

Figure 2 shows field results of a 138kV, 16 MVA power transformer uncontrolled energization.

Figure1:Field results of three mitigation techniques Figure2:

Disturbances caused by random closing of atransformer’s circuit breaker

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2016Revista

III. CONTROLLED SWITCHING SOLUTIONThe primary purpose of the CSD is to reduce the inrush current and associated network overvolta-ge. For transformer energization, the optimal closing target is not the same for each operation and depends on the prevailing conditions at that particular moment. Figure 3 illustrates results of tests done on a 138kV, 16 MVA power transformer when the CB is closed taking into consideration the residual magnetic flux in its core. It can be noted that the disturbance is almost eliminated.

In 2004, CIGRÉ WG A3.07 produced three techni-cal brochures [4][5][6] on this subject. One of their conclusions was that CS is a powerful solution to mitigate inrush currents and voltage transients.

Figure 4 displays the average inrush current between three tested inrush current mitigation techniques. The figure’s 4th column shows that the most effective inrush current mitigation tech-nique uses a CSD that takes residual flux into account.

In addition, CS reduces capital investment. The initial cost of a solution with CSD is lower than one with pre-insertion resistors (PIR) by 5% to 25%. The maintenance costs of circuit breakers using PIR are about twice as expensive as those for standard circuit breakers and maintenance is required more often. Finally, since only a limited range of circuit breakers are designed for use with PIR, the adoption of a controlled switching solution may create the possibility of purchasing a more cost effective standard circuit breaker [4].

Another important aspect of the CSD installa-tion is its integration into the communication network for remote access support, including CSD, CB, load events reporting and CSD configu-ration. The access to the CSD is granted using a secured internal web interface available only for authorized users or it could be done by the Scada. Figure 5 shows a CSD operation environ-ment.

Figure3:Inrush current when controlled closing of a transformer’scircuit breaker

Figure4:Comparison of inrush currents (PU)

Figure5:CSD operation environment

According with Cigré 262 [4], technical and economic benefits can be expected by transmis-sion, distribution and generation utilities, as an advanced CSD:

Figure 6 illustrates schematically that reducing the number and amplitude of the impulse surges reduces the breakdown probability and increa-ses the remaining life of the transformer provi-ding lightning impulses do not occur late in the transformers life. [4]

Figure6:Schematic transformer failure curve

This technology has evolved considerably in the last years. Initially used only for indepen-dent pole operated (IPO) CB this proven technology is now successfully applied to reduce inrush current when using simulta-neous pole operated CB (GO). Moreover, now it is possible to energize 2 or 3 power trans-

formers in parallel from a single CB without electrical disturbances.

IV. HYDRO-QUÉBECEXPERIENCEFor over twenty years, Hydro-Québec has been using CS as a cost effective alternative to PIR for the attenuation and elimination of switching tran-sients.

During all these years, CSD has proved their positive impact on maintenance strategies, extension of

the useful life of the existing CB and prevention of its costly replacement.

Initially used for shunt reactors, then for shunt capacitor banks, this proven technolo-

gy is now often applied to the energization of unloaded power transformers, as well.

These systems have been commissioned in Hydro-Québec’s transmission network on more than 245 CBs from a variety of manu-facturers and technologies at various voltage levels from 120 kV to 735 kV, and under extreme environmental conditions on the CBs, ranging from 40 °C to +40 °C.

Hydro-Québec’s experience has demonstra-ted that CSD is reliable and stable over the long term. It also confirms that precise control of CBs is not only feasible, but can also extend the life of existing equipment. In fact, CS has proven to be the optimal solu-tion, provided that diligent CSD commissio-ning, ongoing system monitoring and CB maintenance are performed.

Increases power transformers life expectancy as illustrated on figure 6.

Increases CBs lifespan. Cigré found a 96% electrical wear reduction.

Increases PTs and CTs lifespan.

Reduces stress on equipment.

Decreases the probability of failures.

Lowers maintenance costs. Cigré found a CB electrical life extension of 92%.

Increases the overall system availability.

Improves the system’s power quality and reliability.

Decreases probabilities of power outages caused by equipment failures or undesired protection trips.

Allows system monitoring and sends alarms.

www.cidet.org.co 53

2016Revista

III. CONTROLLED SWITCHING SOLUTIONThe primary purpose of the CSD is to reduce the inrush current and associated network overvolta-ge. For transformer energization, the optimal closing target is not the same for each operation and depends on the prevailing conditions at that particular moment. Figure 3 illustrates results of tests done on a 138kV, 16 MVA power transformer when the CB is closed taking into consideration the residual magnetic flux in its core. It can be noted that the disturbance is almost eliminated.

In 2004, CIGRÉ WG A3.07 produced three techni-cal brochures [4][5][6] on this subject. One of their conclusions was that CS is a powerful solution to mitigate inrush currents and voltage transients.

Figure 4 displays the average inrush current between three tested inrush current mitigation techniques. The figure’s 4th column shows that the most effective inrush current mitigation tech-nique uses a CSD that takes residual flux into account.

In addition, CS reduces capital investment. The initial cost of a solution with CSD is lower than one with pre-insertion resistors (PIR) by 5% to 25%. The maintenance costs of circuit breakers using PIR are about twice as expensive as those for standard circuit breakers and maintenance is required more often. Finally, since only a limited range of circuit breakers are designed for use with PIR, the adoption of a controlled switching solution may create the possibility of purchasing a more cost effective standard circuit breaker [4].

Another important aspect of the CSD installa-tion is its integration into the communication network for remote access support, including CSD, CB, load events reporting and CSD configu-ration. The access to the CSD is granted using a secured internal web interface available only for authorized users or it could be done by the Scada. Figure 5 shows a CSD operation environ-ment.

Figure3:Inrush current when controlled closing of a transformer’scircuit breaker

Figure4:Comparison of inrush currents (PU)

Figure5:CSD operation environment

According with Cigré 262 [4], technical and economic benefits can be expected by transmis-sion, distribution and generation utilities, as an advanced CSD:

Figure 6 illustrates schematically that reducing the number and amplitude of the impulse surges reduces the breakdown probability and increa-ses the remaining life of the transformer provi-ding lightning impulses do not occur late in the transformers life. [4]

Figure6:Schematic transformer failure curve

This technology has evolved considerably in the last years. Initially used only for indepen-dent pole operated (IPO) CB this proven technology is now successfully applied to reduce inrush current when using simulta-neous pole operated CB (GO). Moreover, now it is possible to energize 2 or 3 power trans-

formers in parallel from a single CB without electrical disturbances.

IV. HYDRO-QUÉBECEXPERIENCEFor over twenty years, Hydro-Québec has been using CS as a cost effective alternative to PIR for the attenuation and elimination of switching tran-sients.

During all these years, CSD has proved their positive impact on maintenance strategies, extension of

the useful life of the existing CB and prevention of its costly replacement.

Initially used for shunt reactors, then for shunt capacitor banks, this proven technolo-

gy is now often applied to the energization of unloaded power transformers, as well.

These systems have been commissioned in Hydro-Québec’s transmission network on more than 245 CBs from a variety of manu-facturers and technologies at various voltage levels from 120 kV to 735 kV, and under extreme environmental conditions on the CBs, ranging from 40 °C to +40 °C.

Hydro-Québec’s experience has demonstra-ted that CSD is reliable and stable over the long term. It also confirms that precise control of CBs is not only feasible, but can also extend the life of existing equipment. In fact, CS has proven to be the optimal solu-tion, provided that diligent CSD commissio-ning, ongoing system monitoring and CB maintenance are performed.

Increases power transformers life expectancy as illustrated on figure 6.

Increases CBs lifespan. Cigré found a 96% electrical wear reduction.

Increases PTs and CTs lifespan.

Reduces stress on equipment.

Decreases the probability of failures.

Lowers maintenance costs. Cigré found a CB electrical life extension of 92%.

Increases the overall system availability.

Improves the system’s power quality and reliability.

Decreases probabilities of power outages caused by equipment failures or undesired protection trips.

Allows system monitoring and sends alarms.

www.cidet.org.co54

V. CONCLUSIONUncontrolled energization of power transformers can produce high inrush currents that have a negative impact on the power system. This inrush current reduces the equipment remaining life, it may generate temporary overvoltage and it could lead to unwanted protective relay operation and reduction of the power quality delivery.

CSD technology has demonstrated to be mature and ready to solve the problems associated with inrush currents. It is a cost effective solution to mitigate disturbances during power transformer energization. Moreover, it provides extensive monitoring of the system that help to better manage CBs maintenance.

During several years, utilities have experienced real benefits on HV systems by using CS. This technique has a positive effect not only on their power stability and reliability but on the manage-ment of their critical assets like power transfor-mers.

Previously, CS advantages were reserved for HV systems but thanks to recent technological advances, MV systems can now also benefit from them.

VI. BIBLIOGRAPHY [1] R. Smeets, et al. Switching in Electrical Trans-mission and Distribution Systems. Wiley, 2015.

[2] M. Stanek, A.C. Carvalho, et al. Experience with improving power quality by controlled switching. CIGRÉ session #13/14/36-01, 2000.

[3] CIGRÉ WG 36.05/CIRED 2 CC02. Capacitor swit-ching and its impact on power quality. ELECTRA No. 195, April 2001, pages 27-37.

[4] CIGRÉ Working Group A3.07. Controlled swit-ching of HVAC circuit breakers: Benefits & econo-mic aspects. CIGRÉ TB 262, 2004.

[5] CIGRÉ Working Group A3.07. Controlled swit-ching of HVAC circuit breakers: Guidance for

further applications including unloaded trans-former switching, load and fault interruption and circuit-breaker uprating. CIGRÉ TB 263, 2004.

[6] CIGRÉ Working Group A3.07. Controlled swit-ching of HVAC circuit breakers: Planning, speci-fication and testing of controlled switching systems. CIGRÉ TB 264, 2004.

[7] R.J. Rajotte, et al. Controlled switching of 735-kV reactor circuit breakers at Hydro-Qué-bec. CIGRÉ session #13-201, 1996.

[8] A. Mercier, Y. Filion, E. Portales, A. Salibi. Transformer controlled switching taking into account the core residual flux: A real case study. CIGRÉ session #13-201, 2002.

VII. CURRICULUMMarc Lacroix has received a Master degree in Electrical Engineering (1995) from École Polyte-chnique de Montréal. He is an IEEE Senior Member and active in IECS TC58 working groups 10, 15 and 17. Marc is Vice-President of Innovation and Business Development at VIZIMAX, a manufacturer of power system auto-mation solutions. Before joining VIZIMAX, Marc Lacroix worked for 33 years at Hydro-Québec where he has developed a unique expertise related to automation technologies applied to transmission and distribution systems and has led the deployment of technologies used in Hydro-Québec Distribution’s smart grid.

mlacroix@vizimax.com

Andrea Gutierrez is an electronic engineer and she has received a Master degree in Quality Systems Engineering from Concordia University of Montreal, Canada. Andrea is Latin America Manager at VIZIMAX, a manufacturer of power system automation solutions.

agutierrez@vizimax.com

2016Revista

EL MÁS GRANDE CERTAMENDE CENTROS DE I+D+I DEL MUNDOBajo el tema: “Alianzas Público Privadas para Innovar la Innovación”, el 23 Congreso de Centros de I+D+i & Asamblea General WAITRO, planea tomarse la ciudad de Medellín y contagiar a propios y visitantes de todas las ideas que traerán los centros de I+D+i que a nivel mundial se reunirán en el Congreso.

WAITRO es la red global líder para las organizaciones de investigación y tecnología, enfocada en la solución de los grandes desafíos sociales, construir mejores oportunidades y alcanzar nuevos mercados. Los objetivos de la organización son tratar de perfeccionar las capacidades de gestión en esos centros, con programas que intentan mejorar las habilidades de los encargados de gestión de los centros de investigación, así como promover el desarrollo de capacidades de investigación entre organizaciones miembro. A lo largo de los 46 años con los que cuenta esta red; el Congreso se ha realizado alrededor de tres pilares o ejes temáticos: compartir, conectar y colaborar y de ahí se derivan las actividades del evento.

COMPARTIREn el eje temático de compartir se encuentran los conferencistas, gurús y expertos internacionales en temas de innovación. Serán charlas inspirado-ras donde también estarán presentes centros de I+D con personas del gobierno para hacer una transferencia de conocimiento

CONECTAREn conectar se encuentran las visitas de relacio-namiento en energía, salud y biotecnología que son tres temas fundamentales del congreso. Además también va a haber una exhibición de los centros de I+D+i que tendrán participación con un stand dentro del congreso.

COLABORAREn colaborar están las diferentes convocatorias que se realizarán durante el Congreso. El Congre-so será dinámico, durante todo este tiempo y hasta su fecha de inicio se darán a conocer diferentes convocatorias que apuntarán a temas de interés en materia de innovación.

ALIANZAS PÚBLICO PRIVADAS PARA INNOVAR LA El buen desempeño innovador es una condición necesaria para el desarrollo en el futuro, pero los

resultados de innovación de los países en desa-rrollo todavía no son satisfactorios y la mayoría de los sistemas nacionales de innovación no están ganando impulso suficiente. La respuesta a desarrollar sistemas de innovación con la cooperación entre los actores públicos y priva-dos de la innovación, incluso en las economías desarrolladas, puede ser crucial para impulsar la innovación y hacer una mejora en el rendi-miento económico.

Hay presiones y a la vez restricciones para que en el sector público, los gobiernos inviertan más en innovación, y por ende también el sector privado. Lo que se quiere es buscar espacios, buenas prácticas, para que se afiancen las alianzas entre el sector público y el sector priva-do para poder materializar el desarrollo econó-mico a través de actividades de innovación.

WAITRO tendrá conocimiento de vanguardia del estado del arte y de cómo se está operando en materia de I+D+i en países desarrollados, cómo tener mejores prácticas para gerenciar un centro de I+D+i, se verán casos de éxito y lecciones aprendidas en proyectos que han promovido la innovación desde este tipo de alianzas. La idea es desde la perspectiva del congreso, poder conocer de primera mano qué desafíos tienen los CDT en estos momentos a nivel de países en desarrollo y países desarro-llados y cómo hacer que esas mejoras hagan parte de un potenciamiento no solo desde lo económico sino desde el quehacer tecnológico de los centros.

INNOVACIÓN