Research Article |
Corresponding author: Stefan Kornhuber ( s.kornhuber@hszg.de ) Academic editor: Sara Santos
© 2022 Stefan Kornhuber, Hans-Peter Pampel, Jana Görlich, Marion Leiblein-Wild, Christoph Jöckle.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Kornhuber S, Pampel H-P, Görlich J, Leiblein-Wild M, Jöckle C (2022) Preliminary results on the bird protection effectiveness of animal deflectors on railway overhead lines based on electrical current evaluation. In: Santos S, Grilo C, Shilling F, Bhardwaj M, Papp CR (Eds) Linear Infrastructure Networks with Ecological Solutions. Nature Conservation 47: 317-333. https://doi.org/10.3897/natureconservation.47.70704
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In contrast to other transportation systems, railway systems feature special characteristics, which may cause specific hazards to birds. Among other things, there is the risk of electrocutions resulting from short circuits. To protect the birds and minimize these short circuit events, the DB Netz AG has installed so-called animal deflectors on the insulators of the overhead lines. Since this effort, the number of short-circuit events in the respective sections has decreased, according to DB Netz AG. The principal mechanism of action of the animal deflectors is based on mechanical defense, combined with electrostatic discharge on contact. Although the number of short circuit events has been reduced by using animal deflectors, the detailed function of the animal deflector in different environmental conditions has not been investigated up to now. This research project aims to determine whether, and to what extent, the use of animal deflectors in retrofitting overhead lines may contribute to bird protection and which currents can be measured at retrofitted insulators under different environmental conditions. Hence the current should be measured when using animal deflectors on railway overhead lines for different isolator states and body resistances (5 kΩ, 3 kΩ, 1kΩ, 0.5 kΩ). The results show an influence of measured current depending on the insulator state. Our preliminary results indicate that the use of an animal deflector (KTA) to the tested polymeric insulator and pollution severity can be recommended, since, based on the investigations, no danger to small birds and small animals can be identified. However, the use of the animal deflector (KTA) for the tested porcelain insulator and pollution severity should not be recommended as they showed high animal hazards during pollution and fog conditions. However, these results cannot be transferred to other different insulator types and pollution severities. Investigating the electrical current to the type of insulator used and the expected pollution severity is recommended.
Animal deflector, overhead railway line, polymeric insulator, porcelain insulator, stationary current, transient impulse current
Compared to other transport infrastructures, electric railways have unique features that can cause specific hazards for birds. Overhead line systems of electric railways provide birds with a variety of resting places. In particular, simultaneous contact with system components of different electrical potentials can risk damaging currents flowing, or even trigger a short circuit.. In order to reduce the number of circuits caused by birds and small mammals, the company DB Netz AG is increasingly using a so-called animal deflector (German: Kleintierabweiser – KTA, shown in Fig.
The animal deflector (KTA) does not protect larger birds and does not meet the requirements of the Federal Nature Conservation Act (§ 41 BNatSchG, according to which only constructive measures are to be provided for new installations). Thus, it only can be used for retrofitting existing overhead lines. The animal deflector provides a mechanical defense in combination with a repelling effect caused by discharging static electricity. DB Netz AG estimates KTA as a suitable tool to protect birds and small animals efficiently, as the number of short-circuit events of retrofitted sections seems to decrease. Some nature conservation organizations, however, criticize the functionality of animal detectors and suspect an additional hazard to birds and small mammals, instead.
However, up to now, the detailed function of the animal deflector under different environmental conditions has not been investigated. To close this gap of knowledge and to enable data-based evidence on the question of the suitability of animal detectors for bird protection, a research project of the German Centre for Rail Traffic Research (DZSF) was conducted. In this research project, the following questions were addressed:
However, no reproducible and repeatable measurement results gauging electrical current through the small animal or small bird during contact with the animal deflector (KTA) at different polluted and wetted insulators are available. So, the aim of the presented experiments and results is to determine practice-relevant electrical parameters that can affect birds when they touch an animal deflector (KTA) mounted on an insulator. Furthermore, a measurement setup and process, and an electric model schematic, which allows a calculation-based investigation, have been developed.
To control the scope of the experiment and the variety of parameters, conditions close to “real conditions” are defined for the respective influences and simulated as far as possible by means of introduced reproducible experimental methods. For this reason, international common-sense standards and documents (e.g. IEC and CIGRE) and the investigation procedure based on a consensus of an interdisciplinary project advisory group (e.g. ornithology experts, railway experts, bird-life conservation NGOs) were used.
The following parameters are defined as relevant to practice, i.e., influencing the magnitude of the electrical effects in practice (reality):
The electrical resistance of birds can vary due to their physical characteristics (size, density, and type of feathers, total proportion of water contained in the body). The small birds and animals are simulated by technical resistors. The measurements are carried out with four different equivalent resistors (5, 3, 1, and 0.5 kΩ).
The electrical quantities recorded during the experiments are the alternating voltage across the insulator and the transient behavior of the current flowing through the equivalent resistor from the moment of contact with the KTA. The current at the time of contact is pulse-shaped (Fig.
Measured electrical current at the moment of contact (left) and during the steady-state condition (right), S: Switch; RK: Animal Resistor.
The dimensions, the material, and the design of the insulator can have a strong influence on the amount of charge available on the electrodes of the KTA and thus on the pulsed current flowing at the time of contact with the KTA. Furthermore, the electrical current flowing through the bird when the KTA is then permanently touched also depends on the material and the dimensions of the insulator. A special dependency exists regarding the behavior with pollution and/or moistened insulating material surfaces. For example, the surfaces of polymeric insulators might be water-repellent (hydrophobic). This property can be transferred to the layers of dirt adhering to the insulating material. Due to this hydrophobic transfer, there is no or not such a strong reduction of the insulating capacity compared to the porcelain insulator. When a polluted porcelain insulator is moistened, on the other hand, a closed conductive layer can be formed, which can lead to a lower insulating capacity with increased flow through the bird and to an increased risk of a flashover. For the investigations done within this research, one typical polymeric insulator type (Fig.
In Fig.
The animal deflector is mounted in accordance with the procedure, and two independent metal spikes are connected to each other for reflection in the worst case in a real application, which is leading to an increased electrical charge. By using a switch, the spikes of the animal deflector are conducted with a combination of resistors which provide the body resistance of the birds and also include the measurement shunt for measuring the current, which is recorded by using a transient analyzer.
In Fig.
In Fig.
During the investigations the following conditions were applied to the polymeric insulator:
During the investigations following conditions were applied to the porcelain insulator:
The polluted conditions were applied by using the recommendations of the CIGRE
Overview of the used artificial pollution suspension for light and heavy pollution.
Light pollution | Heavy pollution |
---|---|
1000 g Water | 1000 g Water |
20 g Highly dispersible silica | 25 g Highly dispersible silica |
0,2 g NaCl | 2,5 g NaCl |
Conductivity of suspension: 450 µS/cm (at 20 °C) | Conductivity of suspension: 4,1 mS/cm (at 20 °C) |
A corresponding number of test specimens is taken from the quantity of cleaned, prepared insulators. The contamination suspension is applied to these using the immersion method in accordance with
The impurity layer is then dried and stored for 24 h under the atmospheric conditions prevailing in the test room (air temperature 23 °C to 24 °C, humidity 45% to 50% r.h.).
At the test specimen standard rain according to
In addition to the specifications in
The pollution layer is moistened with a modified clean fog specified in CIGRE
The generated fog leads to slow moisture penetration of the pollution layer without washing off. This simulates the dewing or fogging of pollution layers in reality.
The approach described by the Institute of Electrical and Electronics Engineers (IEEE) Task Force on Insulator Icing Test Methods in
The current measurement is done as described using a resistor as a shunt and recorded by a transient recorder.
In Fig.
In contradiction to the very fast transient behavior at the moment of the contact, the steady-state current follows in line with the theory of the source frequency of 50 Hz and is shown in Fig.
For the evaluation of the measurement results the following values were derived from the measurement data:
Based on the theoretical considerations and the measured values, three basic scenarios have to be distinguished with regard to the exposure of birds and small animals to electric currents flowing through the KTA:
The third scenario with the current or direct thermal effects of the arc on a bird or small animal leads to direct damage to the living creature in addition to the electrical effects, especially due to the thermal effects. The occurrence of this scenario shall be prevented. Consideration of limit and guide values for this scenario is not expedient.
transient current when the switch is closed (bird or small animal is indicated with a bow).
Flow with stationary current during continuous contact (bird or small animal is indicated with an arc).
For the assessment of the measured values, the following values are defined for the respective scenarios presented in this project:
The “reference value stimulus threshold” describes a current value above which the animal can feel a biological effect. Current values that fall below this value are not noticeable due to biological effect mechanisms.
If the “threshold value danger” is exceeded, it can be assumed that the bird will be directly or indirectly harmed by the electrocutions.
In the following, the determination of limit and reference values for current will therefore concentrate on scenarios 1 (transient current) and 2 (stationary current).
The values are gained by using a detailed literature study and intensive discussions in the interdisciplinary project advisory group and summarized in Table
Transient current pulse stress | Stationary current stress | |
---|---|---|
Time interval of the stress | few 10 ns | ms to s |
Hazard threshold | 1 Joule | 2 mA |
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|
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Reference stimulus threshold | Not available | 500 µA |
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Based on the measurement results and its derived values, the evaluation was done by comparing with the reference values according to Table
Insulator Typ | Insulator Condition | Ambient | Reference Stimulus Threshold | Hazard Threshold | |
---|---|---|---|---|---|
Stationary current stress Time interval of the stress ms to s | Stationary current stress Time interval of the stress ms to s | Transient current puls stress Time interval of the stress few 10 ns | |||
Polymeric insulator | Cleaned | Dry | Not exceeded | Not exceeded | Not exceeded |
Rain | Not exceeded | Not exceeded | Not exceeded | ||
Ice | Not exceeded | Not exceeded | Not exceeded | ||
Polymeric insulator | light polluted | Dry | Not exceeded | Not exceeded | Not exceeded |
Rain | Not exceeded | Not exceeded | Not exceeded | ||
Fog | Not exceeded | Not exceeded | Not exceeded | ||
Polymeric insulator | heavy polluted | Dry | Not exceeded | Not exceeded | Not exceeded |
Rain | Not exceeded | Not exceeded | Not exceeded | ||
Fog | Not exceeded | Not exceeded | Not exceeded | ||
Porcelain insulator | Cleaned | Dry | Not exceeded | Not exceeded | Not exceeded |
light polluted | Fog | Exceeded | exceeded | Not exceeded | |
heavy polluted | Fog | Exceeded | exceeded | Not available Due to flashover no measurement was possible |
In detailed for each insulator following summarized results can be found:
For the polymeric insulator investigated for the risk at the moment of contact it can be concluded that for all environmental conditions the energies measured at the body resistance are below the hazard limit value of 1 J. The current pulse of the investigated polymeric insulators (or comparable types) is below the hazard limit value.
For the polymeric insulator examined for the risk at stationary contact it can be concluded that for all insulator situations that the currents measured at the body resistance are below the hazard limit of 2 mA. This can be attributed to the hydrophobic properties of polymeric insulators. When the polymeric surface is wetted, no closed pollution layer is formed, but instead, individual droplets are formed, which greatly reduces the current. This effect also occurs with polluted polymeric insulator surfaces since the layer of dirt also takes on a water-repellent effect due to the hydrophobic transfer.
For the evaluation of the stimulus results in the moment of contact, it was not possible to determine a reference value for the stimulus threshold for pulsed flow. For this reason, no statement can be made about the triggering of the receptors on the basis of the measured values. Thus, it cannot be conclusively clarified whether small birds react when touching the animal deflector.
For the polymeric insulator investigated for the stimulus result at stationary contact it can be concluded for all insulator states that the currents measured at the body resistance are below the defined reference value of the stimulus threshold of 500 μA.
For the examined porcelain insulator for the risk at the moment of contact it can be concluded that for the insulator states cleaned and light-polluted (in case of moisture penetration with mist) that the energies measured at the body resistance are below the limit value of hazard of 1 J. An evaluation of the heavily polluted, wetted fog porcelain insulator is not possible due to the spontaneous flashover.
For the examined porcelain insulator for the risk at stationary contact it can be concluded that for the insulator states cleaned and dry that the currents measured at the body resistance are below the limit value of the risk of 2 mA. For the examined porcelain insulator, it can be determined for the insulator states light-polluted wetted with fog that the currents determined at the body resistance are above the limit value hazard of 2 mA. In the case of a heavy-polluted porcelain insulator, spontaneous flashover occurs with a current-starved arc, whereby a bird would be exposed to thermal damage in addition to electrical damage.
For the evaluation of the stimulus results at the moment of contact, no reference values for the irritation threshold could be determined. For this reason, no statement can be made about the triggering of the receptors based on the measured values.
For the evaluation of the stimulus results for stationary contact for the examined porcelain insulator, it can be determined for the insulator states cleaned dry that the currents determined by measurement on the body resistance are below the defined reference value of the stimulus threshold of 500 μA. It can be assumed that no stimulus is triggered due to the electrical flow. In the case of the examined light pollution wetted by fog, the reference value of the stimulus threshold but also the danger threshold is exceeded. In the case of a heavily polluted porcelain insulator, spontaneous flashover with a high-current arc occurs, whereby a bird would be exposed to thermal damage in addition to electrical damage.
Compared to other transport infrastructures, electric railways have unique features that can cause specific hazards for birds. Overhead line systems of electric railways provide birds with a variety of resting places. In particular, the simultaneous contact with system components of different electrical potentials possesses a risk of damaging currents flowing or even triggering a short circuit for birds. The company DB Netz AG is increasingly using an animal deflector (German: Kleintierabweiser – KTA) mounted on the insulating part of the high-voltage insulators. The animal deflector does not provide protection for larger birds and does not meet the requirements of the Federal Nature Conservation Act (§ 41 BNatSchG, according to which only constructive measures are to be provided for new installations). They may, therefore, only be used for retrofitting existing plants. This investigation was done because no measurement results of the electrical current at animal deflectors in different conditions are available. With these results a measurement-based evaluation of the effectiveness of the animal deflector is supported.
Basically, a distinction must be made between three scenarios:
To assess the electrical flow through birds and small animals, hazard thresholds (damage) and reference values for the stimulus threshold for stationary electrical flow were determined based on literature research, physiological principles, and analogy relationships. A reference value for the stimulus threshold for transient impulse current could not be determined.
Regarding the examined polymeric insulator, the following conclusions can be made:
For the examined porcelain insulator following conclusions can be done:
However, besides the extensive investigations undertaken, the following areas can be listed as possible investigation areas:
Our preliminary results indicate that the use of an animal deflector (KTA) to the tested polymeric insulator and pollution severity can be recommended because, based on the investigations, no danger to small birds and small animals can be identified. However, the use of the animal deflector (KTA) for the tested porcelain insulator and pollution severity should not be recommended as they showed high animal hazards during pollution and fog conditions. However, these results cannot be transferred to other different insulator types and pollution severities. Investigate the electrical current to the used type of insulator and the expected severity of pollution is recommended..
We thank the “BMVI Network of Experts” of the Federal Ministry of Transport and Digital Infrastructure of Germany (BMVI) for funding through the Federal Railway Authority, Germany (project number 2018-U-10-1217). The authors also thank the interdisciplinary project advisory group for their discussions and valuable contributions in the project meetings.