Retrofit solution for capturing lightning strikes
Nils Lesmann on Phoenix Contact Electronics GmbH claims his company's lightning evaluating solutions have improved uptime and lower maintenance costs
If damage to wind turbines caused by lightning remains undetected, this can have dire consequences – in particular for offshore wind farms.
In order to prevent costly downtimes of existing systems, Phoenix Contact developed a retrofit solution for the continuous capture and evaluation of corresponding events.
With a view to accelerating the ROI of wind farms, operating companies are setting up ever larger and more powerful wind turbines.
The latest generation of wind farms soon to be erected will comprise individual turbines delivering eight megawatts each.
When installed at an offshore site, reliable availability of such high-end farms is of particular importance. After all, any fault that goes undetected due to difficult accessibility of the power array can lead to days of downtime because, for example, offshore farms cannot be reached by ship or helicopter in stormy weather.
As a result, the operator suffers financial losses and the turbine manufacturer’s reputation becomes tarnished.
With this in mind, condition monitoring, i.e., permanent monitoring of the individual components of each wind turbine, is of critical importance to both parties.
The earlier a fault is detected, the faster the required maintenance task can be scheduled; and quite often, even a small repair can ward off large damage.
On top of this, the turbine manufacturer can cut down on servicing hours since the technicians no longer have to regularly check the system for faulty components – because detecting and indicating such faults is the condition monitoring system’s job.
Measuring system based on the Faraday effect
The rotor blades are among the most critical and most expensive components of a wind turbine. They require particularly intensive monitoring as it is possible to patch up small cracks.
However, if the damage goes unnoticed for too long, the crack can widen, dangerously weakening the glass fiber reinforced special plastic. In this case, the rotor blade must be repaired on the ground or replaced completely. Lightning strikes are a common cause of blade damage.
The resulting damage depends on the strength and energy of the lightning flash, which also takes a toll on the external lightning protection system. The lightning monitoring system (LM-S) from Phoenix Contact provides a solution that helps to evaluate such defects and coordinate the necessary maintenance tasks.
The measuring system of the LM-S is based on the Faraday effect. It leads polarized light through a special medium, where it is bent by a magnetic field over a predefined distance.
The lightning current measurement system captures the delta of the light signal and calculates the measurement reading from this. As opposed to copper, light-based measurement delivers electrical isolation between the lightning arrester and the analysis electronics because communication between the sensor and analysis unit takes place via fiber optics.
Lightning currents in close proximity or any other EMC effects thus do not impact the measurement.
Automatic polling by the higher-level system
The evaluation unit stores hundreds of measurement readings, which are made available to the manufacturer and/or operator in a variety of ways.
First, the solution implements a Web server, allowing users to access the LM-S and read measurements with a Web browser.
Second, data can be downloaded as a CSV file for further processing in a spreadsheet program such as Excel. Moreover, the LM-S comprises a TCP server, which facilitates automated polling.
This means the higher-level control or SCADA system can pull the latest measurement readings from the LM-S at predefined intervals.
For example, users download data after a specific event and forward it to the operating company to generate automatic alerts to the on-site service team.
Phoenix Contact has just developed a corresponding easy-to-integrate system for existing wind turbines. It is implemented via an encapsulated retrofit solution. Setting it up in the existing control cabinet would take up much more time and would involve a much bigger effort.
This is due to the fact that previously installed control cabinets for pitch control do not provide enough space for mounting the analysis unit.
Also, in order to feed through the fiber optic cables, holes must be drilled into the control cabinet wall. The resulting metal shavings have proven to be a hazard in the cabinet, especially if it rotates on an ongoing basis. This situation can lead to short circuits, which can bring the entire system to a standstill in the worst case.
Another problem is that the power supplies of the existing solution generally do not have the capacity to support additional devices.
Comprehensive protection against surge voltages
Better yet, an end-to-end system can be offered as an option for implementation into new wind turbines. If so desired by the operator, the turbine manufacturer orders the solution from Phoenix Contact and installs it into the system.
What makes this attractive is that no new version of the existing control cabinet for pitch control needs to be set up. The retrofit system comprises a space-saving control cabinet that houses the analysis unit of the LM-S. It comes with its own Quint power supply.
As an option, an uninterruptible version of the Quint product family can be installed. The Quint series has been successfully used in wind turbines for many years, including in the hub. Thanks to reliable starting at -40°C and a maximum operating temperature of 70°C, the power supply units are highly suitable for cold- and hot-climate wind turbines.
Their high MTTF (Mean Time To Failure) further makes them a top choice for utilisation in remote offshore farms.
And to ensure that the retrofit system runs smoothly even when lightning strikes, all incoming and outbound wires are sheltered by surge voltage protection from Phoenix Contact.
The power supply is protected by a new VAL-SEC surge voltage protector with active energy control. Given a compact unit width of 12.5 mm per channel, it perfectly fits into the slender control cabinet. A DT LAN CAT 6+ device protects the Ethernet line against surge voltages, guaranteeing that the analysis unit does not take damage in the event of a lightning strike.
Various data transmission options
There are multiple channels for exchanging data between the LM-S and higher-level systems. For instance, the free contacts on the slip ring can be used to set up SHDSL communication.
This transmission route proves much more robust than standard Ethernet communication, but it is not as fast. Also, the slip ring contacts do not have to support CAT-5 signals.
If there are no more free slip ring contacts, a radio solution from Phoenix Contact is a good alternative. GSM modems can be programmed to send a text message via radio after lightning has struck, or the user accesses measuring data via GSM.
Another option would be to use Bluetooth and WLAN components. Ethernet port adapters of the FL BT EPA product family make it possible to connect two modules via a mode button without the need for complex coding by on-site service technicians.
If greater distances or obstacles need to be bridged, the FL WLAN 510x WLAN access point is an excellent choice. Cutting-edge WLAN technologies and three antennas deliver all that is needed for reliable data transfer in rugged industrial environments.
What characterises the lightning current measuring system of the retrofit solution is a simple yet robust design. This quality has already convinced several offshore wind farm operators to purchase the system and upgrade their existing wind turbines. Introduction of the system offers reliable early recognition of rotor blade damage, significantly increasing the uptime and thus profitability of wind turbine installations.