At present there is no industry standard or recommended guidelines for the application of DC surge arresters. It appears that such devices are applied based upon the rule of thumb without the benefit of analyzing characteristics, wave shape, and energy content of the expected overvoltage surges against the capabilities of the surge arrester. AC surge arresters are re-rated for de application. A difficulty arises due to lack of clear published application literature on the DC surge arresters, as well as lack of measured data on the DC power system transient surges. This leads to the application of surge protective devices, which may be inappropriate. This paper describes the application of DC surge arresters to a typical light rail transit (LRT) traction power system, and makes a recommendation of a need of a standard on DC surge arresters test requirements and application guidelines.

Light rail transit DC traction power system surge overvoltage protection

Computer modeling with the EMTP code has been applied to several configurations and earthing practices in use in various countries to show the effect of any differences in the dispersion (sharing) of a lightning stroke current among the available paths for the earth-seeking lightning current. Simplifying assumptions have been made to some details of the configurations to focus on the main difference-earthing practices. Identifying such differences provides the necessary perspective on their significance and the strong need to take them into consideration when developing international standards on surge-protective device applications.

The effect of neutral earthing practices on lightning current dispersion in a low-voltage installation

The growth in power electronics has impacted many loads that traditionally were considered linear in nature. As a result, the number of nonlinear loads has increased and is expected to increase dramatically in the years ahead. Which in turn polluting the power quality and creating problems. This paper discusses about harmonics, power quality problems, their analysis and terms defining their limits. The presentation is done with giving a detailed mathematical analysis of harmonics, power quality indices, parameters effecting electric power etc.

Power quality: an important aspect

Reality checks can and should be applied to proposals for characterizing the surge environment and application of surge protective devices (SPDs) to end-user, low-voltage power systems. One such check is the fact that driving a large current with steep front toward an SPD installed at the far end of a branch circuit cable could require such a high voltage that the connections at the near end of the cable will flashover, limiting the stress applied to the far-end SPD. Tests and numerical modeling were performed to support this thesis. The results of real-world measurements and modeling, presented in this paper, are in good agreement and validate each other. From that point on, the model allows parametric variations of power cable length and surge current amplitude and waveform, of which several examples are presented.

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Driving high surge currents into long cables: more begets less

The coordination of two surge arresters in the low voltage power system protection field has been thoroughly discussed to date. This subject is especially dealt with in IEC standards. The problem is that nowadays, due to a lot of papers being published and study results apparently conflicting with field experience, it is very difficult for someone who intends to install a surge arrester to know how to coordinate them. This paper explains that one of the major reasons for this situation is that the real characteristics of the arresters needed for performing the coordination study are difficult to obtain except from the manufacturers themselves. It is also shown that between theoretical studies and practical cases, many differences exist which need to be addressed. After listing the relevant parameters based on an analytical study, the paper describes the many tests and computer models which have been developed in order to clarify the situation and give practical guidance. Finally, a new criterion is proposed for arrester coordination which seems more practical than present IEC recommendations.

Coordination of surge arresters in the low voltage field

Cascading surge protection devices located at the service entrance of a building and near the sensitive equipment are intended to ensure that each device shares the surge stress in an optimum manner to achieve reliable protection of equipment against surges impinging from the utility supply. However, depending on the relative clamping voltages of the two devices, their separation distances, and the waveform of the impinging surges, the coordination may or may not be effective. Computations with experimental verification of the energy deposited in the devices for a matrix of combinations of these three parameters is provided. Results show coordination to be effective for some combinations and ineffective for some others, which is a finding that should reconcile contradictory conclusions reported by different authors making different assumptions. From these results, improved coordination can be developed by application standards writers and system designers. >

F.D. Martzloff

Papers

Coordinating cascaded surge protection devices: high-low versus low-high