SES Contributions

The complete articles are available in the 2007 Users Group Meeting Conference Proceedings.

When communication circuits parallel high voltage transmission lines over long distances, special protective devices are required to protect communication equipment against faults on the high voltage transmission line or substation [ANSI/IEEE Std 487-2000, 2000]. Damages to the communication equipment generally occur as a result of inductive and capacitive couplings between the faulted phases carrying large fault currents and the communication circuits, as well as conductive coupling through soil between power system grounds such as substation and line structures and communication equipment grounds. For grounded and shielded communication cables, the voltages on the communication cables are primarily caused by the inductive and conductive coupling mechanisms.

This article describes an incident where a fault on a 110 kV system at a substation of a power company resulted in significant damages to its communications equipment about 3.5 km away. The communication line is a hybrid fiber optic and coaxial cable communication system. The damage raised concerns about the company’s present grounding and isolation practices. The dramatic failure of equipment also presents a hazard to workers.

The primary objective of the study that was carried out following this incident was to investigate the cause of the equipment damages, and to provide possible mitigation measures.

A parametric analysis was performed in order to determine the degree to which neutral-to-earth voltages (NEV) are sensitive to transmission line configuration, feeder placement, and neutral-to-shield bonding in a simple joint-use corridor. More specifically, the impact of the following factors on NEV was examined:

à Burial of the distribution feeder (versus overhead circuit),

à Placement of the feeder on either side of the road,

à Bonding of the neutral to the transmission line shield wire (for both underbuilt and buried feeders),

à Vertical separation distance between the neutral and the bottom transmission line phase for underbuilt feeders,

à Geometrical arrangement of transmission line phase conductors,

à Presence of a second, underbuilt, transmission line shield wire (with the distribution feeder not on the transmission line pole),

à Shield wire type.

Electromagnetic interference caused by electric power lines sharing a common corridor with railways can compromise the safe operation of the signal and protection systems of the railways under both load and fault conditions. Excessive induced voltage along rails can result in electrical shock hazards for people touching or standing nearby the rail track. Therefore, this proximity effect is a major concern that requires a thorough analysis to evaluate the electromagnetic interference levels and determine if mitigation is required. Studies involving electromagnetic interference from electric power lines on railroad tracks require that the equivalent circuit parameters of the rail ballast leakage resistance be computed accurately in the circuit model and electromagnetic field simulation model, respectively.

This article is specifically concerned with the accurate modeling of the rail ballast leakage resistance.

Many CDEGS users are already familiar with the use of CDEGS in the analysis of electromagnetic interference problems involving pipelines and railways. The focus of these interference problems is usually on human safety and equipment integrity. Using CDEGS in the analysis of harmonic interference problems involving telecommunication cables may not be as well-known as the above mentioned interference problems. The main concern here is the excessive noise in the telecommunication cables generated by the harmonics in the power line which affects the quality of the telecommunication signal. This article shows the general procedures in the analysis of such a problem. It should be pointed out that such an interference problem usually exists under the following conditions: (1) The power lines have large harmonic current components (such as collector transmission lines originating from wind turbine generators); (2) The telecommunication cables which run parallel to the power lines are in rural areas where there is little shielding effect due to other infrastructures.

Equipment Protection Against Ground Potential Rise Due to Faults At Substations: A Case Study

Modeling the Equivalent Shunt Impedance of a Rail and the Connection Impedance between Two Rails

Reducing Neutral to Earth Voltages Induced by Transmission Lines

Using CDEGS for the Analysis of Harmonics Interference

Short Articals by ses employees

Damaged broadband Line Extender

CDEGS Program

Plan view of 2-mile exposure of distribution feeder to long transmission line

Rail model and rail shunt and connection impedances

In a right-of-way interference study, pipelines, railways or other victim lines may continue for significant lengths without being coupled directly to the electric lines along the right-of-way under study. As you probably already know, ignoring the effects of this additional length may lead to unnecessary conservative designs and may prevent you from assessing the effects of transferred stress voltages to remote locations. This extra length of victim lines may provide a good grounding system at the ends of the exposed zone that can reduce the interference levels as well as the distribution of EMF along the exposed zones.

Two methods can be used to model the non exposed portion of victim lines in the ROW software.

Modeling Pipelines, Railway or Other Victim Lines that Extend Outside the Parallel Zone in ROW

Right-Of-Way Program

This article presents a typical study of electromagnetic interference on railways caused by electrical transmission lines under steady state and fault conditions with a particular emphasis on the modeling of rail track arresters. The computerized analysis has been conducted based on a real case study.

The railroad signal equipment is protected against high-current events such as lightning or transmission line phase-to-ground faults, by rail track arresters that are installed at signal-equipment locations. These arresters will fire if the induced rail-to-ground potential exceeds the spark-over potential of the arresters. The fired arresters will protect the railroad signaling equipment from damage during the short duration of the fault, if the arrester rating is not exceeded by the fault-induced current that flows through the arrester.

The electromagnetic interference level on the rail track will be different whether or not the arresters fire under fault conditions. The firing of the rail-to-ground arresters in one track circuit will increase the voltage across the unfired arresters in adjacent track circuits. Thus, these arresters will also fire. In general, a single phase-to-ground fault on the transmission line near the railways will cause the arresters to fire in a cascade throughout the common-corridor. All simulations have been carried out using the MultiGroundZ^®frequency domain grounding analysis module of the CDEGS^® software package, and the circuit-based Right-of-Way^® Pro software.

Modeling the Rail Track Arresters in Electromagnetic Interference Studies

Rail track arrester located at one end of an insulating joint

When substations are located in urban areas, sometimes for aesthetic reasons, metallic chain fences surrounding substations are replaced by walls which are made of concrete or unistone. These walls contain steel rebars which may or may not be connected to the grounding system of the substation. It is therefore important to study safety around these walls during faults at the substations, especially during wet conditions. This article describes how to use CDEGS to model concrete wall. Please note that the objective of this article is to discuss methods to model a concrete wall, therefore we will focus only on computing touch voltages against the concrete wall.

Model Concrete Wall Using CDEGS

Electric circuit of person touching concrete wall

Consider the following question: In a power plant, is it possible to have a fault current contribution from the generation side when the generation is turned off? The obvious answer is NO. The reasoning is that how can a non-operating generation provide power when it is off? This interesting case arises from a support question in which current fault split calculation was considered for a fault at a power plant.