Coupling Between DC Lines with a Neutral Conductor and Parallel AC Lines

Jenny Z. Zhou, Robert S. Burton, David E. Fletcher, J. Brett Davies

HVDC lines may have use the same right of way as ac lines. This paper discusses the general study methodology that can be used to investigate any coupling between dc and ac transmission lines that share the same right-of-way. The capacitive coupling and the inductive coupling between a dc line with a long neutral conductor and an ac transmission system running parallel to it were investigated. A digital simulation model of the coupling phenomenon was developed to model the induced fundamental frequency voltage on the dc line and the neutral conductor. The induced dc current in the converter transformer secondary winding was also modelled.

HVDC System Performance with a Neutral Conductor

Voislav Jankov and Mark Stobart

The poles of bipolar HVDC transmission systems are often required to be capable of independent operation. In order to maintain the independence of the poles a return path for the current is needed. If a ground return cannot be used a neutral conductor must be installed, either on the same structures as the pole conductors or on separate structures. A fault on one pole of such a system may cause a fault on the neutral and a fault on the other pole; therefore, a fault must be efficiently cleared. This paper examines the effect a neutral conductor has on HVDC system reliability and the effectiveness of fault clearing devices such as arcing horns and neutral grounding breakers.

Design, Implementation and Commissioning of a Hybrid Substation Automation System

Dr. Vajira Pathirana, Mark Mihalchuk, Ralph Kurth

This paper describes the design, implementation and commissioning of a substation automation (SA) system for a 230/63 kV substation located in the interior of British Columbia, Canada. The automation systems uses nearly 60 multifunction Intelligent Electronic Devices, or IEDs, which are integrated together using a combination of technologies including IEC 61850, DNP3 and LON. The IEDs are comprised of bay controllers, a variety of protection relays, transformer monitoring devices, revenue meters, as well as PC based station HMIs and gateways for remote communications to the regional control center. Together, the IEDs perform all of the control, monitoring, protection and metering functions associated with the station including the implementation of two Remedial Action Schemes.

Considerations for the Application of ±800 kV HVDC Transmission From a System Perspective

Dr. S. Rao Atmuri and Bruno Bisewski

The highest voltage dc system in commercial operation today is the Itaipu transmission which has been in service for over 15 years at ±600 kV. Transmission at voltages up to ±800 kV dc is considered to be possible without significant development on major equipment. This voltage level is considered necessary for the transfer of 5000 MW to 6000 MW per bipole over distances of 2000 to 2500 km. To transfer the same amount of power, using the highest commonly applied ac voltage, two 800 kV ac lines with a number of intermediate stations would be required. The choice between the ac or dc transmission is a techno-economic analysis with right-of-way and the availability of reliable equipment as additional factors.

Based on past performance, making the step to the higher voltage and power will undoubtedly result in a new set of challenges and possibly problems. Even without new challenges there are a number of issues that have already been identified as requiring further discussion and analysis prior to application of HVDC at ±800 kV. Many of these issues have been identified in the workshop invitation, and are as follows:

• Impact of transient and permanent outages of very large power blocks on the ac systems
• Large physical size leading to transportation difficulties
• Selection of suitable insulation levels and margins especially for transformers
• Outdoor insulation in substations and lines especially in polluted areas

This paper looks at the implications of these known technical difficulties from a utility perspective and looks at ways in which the risks or impacts can be limited to acceptable levels.

A Power System Protection Scheme Combining Impedance Measurement and Travelling Waves: Software and Hardware Implementation

Dr. Vajira Pathirana

For the stability of the electrical network, it is important to clear faults on high voltage transmission lines quickly with the aid of a high-speed protection system. The conventional method of fault detection is mainly based on impedance measurement techniques. Under fault conditions the measured impedance is proportional to the distance to the fault from the relay location. To calculate the impedance, the fundamental frequency components of the voltage and current signals have to be extracted. The filltering involved in this process has an inherent delay. Any attempt to increase fault detection speed can affect the accuracy of the distance estimation and hence the reliability of the protection scheme.

Fault generated transients or travelling wave signals provide the very first information about a possible isturbance on the line and hence can be used to detect faults very quickly. Ultra-high-speed distance protection schemes based on fault initiated travelling waves measure the distance to the fault using the time taken for a wave to travel from the relaying point to the fault and back. However, travelling wave based protection schemes have reliability issues and have not been well accepted by relay engineers despite their fast fault detection capabilities.

In this paper, a hybrid protection scheme is proposed which uses positive features of both travelling wave algorithm and impedance measurement technique in a single relay. The travelling wave information is used to achieve fast fault detection speeds while the impedance measurement is used to improve the reliability of the overall protection scheme. The thesis also investigates the possibility of accelerating the zone 2 protection of an impedance relay depending on the travelling wave information. The proposed algorithm has been verified through simulations of a practical three phase power system. The relaying functions have been tested using a laboratory prototype implemented on a Texas Instruments digital signal processor. The results indicate that the fault detection speed is improved while maintaining a high reliability level.

Design, Implementation and Commissioning of a Remedial Action Scheme

Ralph Kurth, Robert Henderson, Brent Hancock, Jim Roik and Dr. Robert Burton

In today’s increasingly interconnected electrical world, the protection of the electrical network itself is just as important as the protection of the individual elements that make up the network. Remedial Action Schemes (RAS) are designed to monitor and protect electrical systems by automatically performing switching operations in response to adverse network conditions to ensure the integrity of the electrical system and avoid network collapse.

This paper examines one such system developed to protect a portion of an electrical network in the southern interior of British Columbia, Canada. The system utilizes a number of different Intelligent Electronic Devices (IEDs) interconnected using a variety of networking and communication systems to form an integrated scheme capable of performing automated shedding of load and generation to avoid collapse of the regional electrical network. The paper outlines the design of this system, beginning with comprehensive system studies performed to examine and determine the requirements of the RAS. The implementation of the system is discussed including the architecture of the system as well as the selection of IEDs used and the role each plays in the overall scheme. Finally, the methods employed to commission the scheme are also provided.

Harmonic Domain Analysis of Power System Elements with Non-Linear or Repetitive Switching Components

Dr. Robert S. Burton

Harmonic domain analysis (HDA) is a convenient method of analyzing power systems to determine the impact of harmonics as well as methods for their mitigation. HDA is more than a simple extension of the traditional load flow power frequency analysis tool to include analyses of the system for dc and harmonic components. Some of the most difficult aspects of HDA are the analysis of interactions that can occur between dc, power frequency and harmonic components of the power system.

The major sources of harmonics in a power system are non-linear elements such as saturation and power system electronic switching devices. HDA models of these devices have undergone significant development from fixed magnitude equivalent harmonic current sources used in early HDA models to detailed models where the magnitude and relative phase angle of the harmonics produced by the components are a function of voltage and current wave-forms at dc, power system and harmonic frequencies. Many of these mathematical models rely on information from the ‘time domain’ to establish driving wave-forms, degree of saturation, or ‘turn-on’ and ‘turn-off’ times for electronic switching devices.

This thesis presents a novel approach to modeling these devices entirely in the harmonic domain using a harmonic domain ‘square root’ function as a basic building block. The mathematics and algorithms used in the models are described and the approach is successfully demonstrated for several examples including diode applications, transformer saturation applications, and non-linear elements in power system controls.

Limitations of the mathematics and the model are described along with suggestions for future work to refine and improve the robustness of the model.

Thermal Problems Caused By Harmonic Frequency Leakage Fluxes

J. Alan C. Forrest (Teshmont Consultants LP) and Bill Allard (Vermont)

Harmonic frequency leakage flux can be a limiting factor in 3-phase, 3-winding HVDC converter transformers. Investigation of a 3-phase, 3-winding 240 MVA converter transformer failure indicated the failure was caused by harmonic fluxes. Calculations indicated that the magnitudes of these harmonic fluxes to be approximately 45% of the power frequency leakage flux for the transformer, and are little affected by the transformer impedance or the converter firing angle.

A study of the failed transformer loading during its life was made, and a calculation made of the hot spot temperature considering various insulation half-life factors. Based on published information on insulation half-life factors it was estimated that at full load the hot spot temperature of the transformer was about 159 degrees Celsius. From examination of the insulation in the hot spot area, this estimate of hot spot temperature was considered reasonable.

This paper was published in the IEEE Transactions on Power Delivery, Vol. 19, No. 1, January 2004

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A Case Study in the Design, Testing and Implementation of a Modern Substation Automation System

Ralph Kurth and Robert Henderson

This paper describes the design, testing and implementation of a modern substation automation system for a 63kV transmission substation located in the southern interior of British Columbia, Canada.

Prior to delivery of the substation automation equipment, extensive factory testing was carried out on the complete system, including testing of line protection relays using a real time digital simulator.

This paper examines the architecture and technologies employed in this system, the advantages of extensive factory testing and the experience gained in commissioning such a system.