Tuesday, October 11, 2022 · 0 min read
High-voltage Testing of Railway Infrastructure
The High-Voltage Testing Wagon, HPA, is a mobile test unit made especially for railway maintenance. It allows the company ÖBB-Infrastruktur AG to check the functionality and safety of the electrical infrastructure power on the railway at different points across Austria. Yet, the testing wagon needed modernization of its measurement equipment, and Dewesoft delivered a flexible and easy-to-use solution.
With power stations, frequency converters, control centres, traction current lines, and substations, the energy grid of the ÖBB infrastructure is extensive. However, electricity is treacherous: You can't see, hear, or smell it. Your life is in danger if you get too close to 15,000 volts. Safety has the highest priority for railway operators.
ÖBB-Infrastruktur AG is part of the ÖBB-Holding AG, owned by the Republic of Austria. With around 18,700 employees, the company is planning, developing, maintaining, and operating the entire ÖBB rail infrastructure: train stations, routes, buildings, terminals, telecommunication systems, and hydropower plants for environmentally-friendly railways.
The company manages the total property assets and is thus one of the largest property owners in Austria. According to its corporate strategy paper, ÖBB-Infrastruktur AG must maintain the railway as the safest means of transport.
The central control station in Innsbruck performs the control, regulation, and monitoring of the traction current supply, the power plants, and the 55/110 kV traction power grid. From there, the machine deployment of the power plants and frequency converters is centrally controlled according to the load situation in the railway grid and optimized using special software. The 15 kV traction current network is managed in two energy control centers.
Consisting of generators, traction power lines, transformers, and overhead contact lines, the traction power grid of ÖBB-Infrastruktur AG is over 2,000 kilometres long and operates at a frequency of 16.7 Hz. The grid distributes electricity from the power stations and frequency converters to the substations. More than 60 substations transform the voltage from 55 or 110 kV of the traction current lines to 15 kV for the catenary to supply the railway.
Electrical testing is not just essential to prove the safety and reliability of any new and modified electrical system related to the railways. It is also a tool to predict and prevent costly failures. The main applications of the specialized rail vehicle are verification of the electrical safety of the grounding concept and high-current component testing.
The ÖBB testing wagon HPA (“Hochspannungsprüfanlage” - the high-voltage test facility) is a rail vehicle based on a low-loader wagon. Its testing setup consists of a circuit breaker, a power switch, a testing transformer, an explosive-proof test cabin, and an operator cabin. Highly skilled staff, aware of the risks when dealing in the dangerous high voltage environment, is needed for the job.
Since the HPA is already around 20 years old, the hardware and software were no longer up to date. The measurement software used up to now only worked under old operating systems. The old camera did not provide usable videos and was not integrable with the software.
Modernization of the entire measurement technology was necessary. The component testing had been outsourced but should again be carried out directly by ÖBB. In addition, new processes make greater demands on the documentation of measurement and calibration.
Electrical grounding verification
The complex electrical systems of railways require proper grounding and bonding throughout the network. In addition to leaving wayside equipment susceptible to damage, the lack of appropriate grounding systems poses serious safety risks to rail workers and the general public.
Electrical energy needs to dissipate into a grounding system if not current will stray to places where it shouldn’t appear, potentially leading to human touch or step injuries. It could happen anywhere that exposed metal exists in the network if there isn’t proper grounding and bonding. Stray current can cause other hazards placing rail workers and the public at risk, especially in transit networks where the vehicle traction power is high-voltage electrical current.
Specifically, networks powered by a contact rail (third rail) are uniquely susceptible to fires caused by electrical arcing incidents that spark combustion and ignite flammable debris. While there are many causes of arc flash fires, improper grounding and bonding can contribute to these incidents, which can be catastrophic.
Several components within the rail network generally require grounding and bonding:
Overhead catenary and contact rails (third rails)
Wayside equipment (interlockings, switch machines, intermediate signals, etc.)
Electrical/electronic enclosures throughout the network
Communication towers and microwave installations
Building and support facilities
Onboard rolling stock
ÖBB-Infrastruktur must verify the functionality of electrical grounding systems. Such testing is needed on all newly constructed or renovated overhead lines and railway stations, as well as within operating sites, reinforced concrete structures, engineering structures, and noise protection walls.
This verification follows the standard EN 50122-1:2017 - Railway applications - Fixed installations - Electrical safety, earthing, and the return circuit - Part 1: Protective provisions against electric shock.
During this test, the conferring track segment is closed and electrically separated from the mains grid, and the loop is closed at a defined position with grounding rods (Error point 1, Error point 2). The mobile transformer induces a constant test current with 16,7 Hz into the catenary allowing the touch potential, e.g., between rail and earth, can be measured. Other measurement points are: on the station's floor, on metal fences close to the rails, etc.
A 2.2 kOhm resistor simulates the electrical resistance of a human body. The touch potential at different points along the infrastructure is measured as the test current is distributed over the various elements of the grounding structure. Then the sum is checked.
Furthermore, the testing team measure the voltage between the neutral (N) and earthing lines (PE - Protective Earth) on the AC sockets with the test current on and off. This enables analysis of the reverse traction current drag.
There are limit levels (and times) defined. Currents and voltages are measured continuously during the test. The outside weather station logs the actual weather conditions for documentation.
High-current component testing
High-current test systems are applied to ensure the mechanical and thermal stability of equipment and components of the catenary system. This includes cables, generator stators, switching cells, etc. The test system heats the test object by inducing a current. Therefore, the test object is prepared to make a short circuit. In addition to the current, the high current test system then measures the temperature of the test object at various points.
These tests validate the mechanical and thermal strength of the components of the railway line systems. The component tests are necessary so that the ÖBB can be sure that the heating during operation does not exceed impermissibly high values and that the required short-circuit current is tolerated by all components in their systems.
Since the transformer can provide very high currents, the second important application is high-current testing of railway infrastructure components. E.g., “shortcut test” with 30 kA for 1 sec / or “heating test” with 1000 A for a few hours.
Components, such as grounding sockets and connectors, are taken out of the infrastructure and loaded with high-current to check their mechanical and electrical resilience. The components have to pass an initial long-term test - several hours - with a portable constant current source at the operating current. Then the temperature profile is logged.
Then to test the components for short-circuit resistance, the test objects are connected to the test transformer and tested by exposure to a high-test current (30 kA) for about one second. The HPA is then logging the temperature, current, and voltage curves. It also makes video recordings of the test item during the test. Since all is synchronously measured, the high sampling rate is of concern.
Depending on weather conditions and the size of the object under testing, the testing team can perform their tests outside or inside the explosion-proof test cabin.
These tests are essential to ensure the reliable and safe operation of all components in the railway infrastructure - and to reduce downtime. Punctual trains are a prerequisite for satisfied customers.
Dewesoft supplied the solution that met the requirements for the modernization of the ÖBB high-voltage test facility measurement technology:
SIRIUS HS High-Speed DAQ system with various 1 MHz High- and Low-Voltage inputs
MCTS2 unit for current transducer power supply
KRYPTONi-8xDI-8xDO rugged IP67 EtherCAT DAQ module for digital in-/outputs
KRYPTONi-1xTH-HV high isolated temperature modules with the appropriate safety cables
MCTS high precision current transducer (zero-flux principle)
Rogowski coils for up to 30 kA
Temperature/humidity sensor for inside, by RS232 interface
Vaisala Weather station WXT536 (wind speed & direction, rain amount, temperature, air pressure, relative humidity) for outside
DS-CAM-600c synchronized Gigabit-Ethernet camera with onboard compression (optional: thermal camera)
various mounting plates
DewesoftX Profesional base version (lifetime free updates)
Dewesoft SERIALCOM plugin: DewesoftX extension for communication with the RS232 temp/humidity-sensor
Dewesoft NMEA-WS plugin: DewesoftX extension for communication with the Vaisala weather station
At the time of system installation, the HPA team had parked the testing wagon inside a railway substation. Next to it, to the left and right, isolators of a few meters’ height were rising in the air. On the one hand, we from Dewesoft were a bit nervous - we didn’t know how to behave, where to walk, or which safety distances to keep. But on the other, we were fascinated to get an insight into a very familiar type of transportation system, "how it works".
We were impressed by the testing team. The way it handled everything with routine. They mounted the few meters long shorting bars, operated the control system, etc. but always kept an eye on where everyone was at any time.
We enjoyed the pleasant company of the HPA team - these people were both professional and serious but also humorous. They worked somewhat like a team of mountain climbers. It seems working in dangerous environments brings people closer together.
All installed, the test cabin door was closed. For testing purposes, the team loaded some pieces of metal with 30 kA. The aim was to see if signals were plausible and to optimize the view angle of the high-speed camera.
The testing team was even interested in measuring the time delay of the circuit switch since the control system can accurately switch on at, for example, the 90° phase point of the 16.7 Hz sine wave.
After installing the measurement system and placing the sensors in the test wagon, the testing team invited us to do a Dewesoft training.
We enjoyed the great company. The people were both skilled and serious, but also good-humoured, forming a great team like mountain climbers - working in this dangerous environment has brought them closer together.
ÖBB-Infrastruktur AG had required that the DAQ system could be started manually, either by external digital input or, if the secondary current was present, involving a pre-trigger time. The Trigger options in the Storing section in DewesoftX realized this requirement.
The software allows multiple triggers on data, time, or even an FFT reference curve set in parallel. The trigger conditions ensure that high-speed data is only stored when events occur. This functionality saves a lot of disk space.
Also, the synchronous acquisition of high-speed video and analog data like currents, voltages, HV-isolated temperatures, digital in-/outputs, and bus data like RS232 matched requirements. The intuitive user interface combined with the ability to analyze data without an additional software license makes daily work much easier for ÖBB-Infrastruktur AG.
The service company doing the measurements for ÖBB concludes: „The Dewesoft system fulfilled all requirements. And even more is included, functionality which we might use for future tasks. We are glad that the measurement system of this unique infrastructure testing wagon is now again state-of-the-art”.