1. Where are the individual components installed?
The blade detection units (BDUs) are installed above the down conductor in each blade root using a two-component adhesive.
The data logger (DL) and Rogowski coil are inside the nacelle:
The data logger is installed in one of the switch cabinets and the Rogowski coil is mounted at the entrance from hub to nacelle or around the yaw system.
2. Is a cable required between the hub and nacelle to connect BDUs with the data logger?
No, BDUs communicate with the data logger wirelessly via ZigBee.
3. How are the BDUs supplied with power?
The BDUs have an inbuilt battery that will last for about 5 years, so no external power supply is needed.
4. Can the battery inside the BDUs be replaced?
Yes, it is easily replaced.
A new battery is readily available on the market.
5. How is the Rogowski coil connected to the data logger?
It is connected using a coaxial shielded cable with a max length of 15m.
6. Which parameters are measured and provided in case of a lightning event?
Peak amplitude, charge value, specific energy, maximum rise time, complete waveform with 4Mhz, time stamp and duration.
7. Can DDT measure the polarity of events?
Yes, the polarity is measured.
This is visible with the minus or plus sign for the peak amplitude and it is also visible in the waveform.
8. How can the data logger communicate with other monitoring systems?
There are 3 possibilities:
- Modbus TCP communication which can be used to send all data to the WT local SCADA system
- Ethernet connection (MQTT protocol) and then into the internet via a router
- Via an LTE inbuilt modem (MQTT protocol) if the wind park is covered by a mobile network.
9. Can DDT be used purely for lightning detection (no detailed measurement)?
Yes, this is possible with the basic version.
This comprises the BDUs and the data logger.
The full version with an additional Rogowski coil allows accurate measurement of the whole event.
The system can be upgraded from the basic to the full version at any time.
10. Must blade detection units be installed for a DDT system to work?
No.
A DDT system can work also without BDUs and in such case you still get measured values.
On the other hand, DDT can be used only with BDUs without a Rogowski coil and in this case you get info about which blade was hit, the time stamp and 2 threshold values of peak current (event was above 100A and below 5kA or event was above 5kA).
11. How can you check that the DDT is still working properly?
We have 2 options:
- A self-test which shows whether the integrator of the Rogowski coil is working properly.
- Manually triggered measurement whereby the values obtained show whether the system is online and able to measure events.
12. Is DEHNdetect (DDT) only suitable for new wind turbines (WTs) or can the system be retrofitted in older ones?
DDT was designed for installation in both new and older wind turbines.
DDT is a system that can also be easily installed in older WTs without compromising other systems (electrically or mechanically).
13. Can DDT provide evidence of a lightning strike for insurance claims or disputes about who shall cover the costs of the damage caused by a lightning event?
Yes, because DDT measures lightning events in very wide range and with an accuracy of +/-5% of the measured value.
14. Does IEC 61400-24 insist on lightning measuring systems (LMS)?
No, but it does recommend them so that operators can obtain reliable information as to whether and how urgently inspection is needed.
15. What does IEC 61400-24 recommend in terms of LMS?
LMS should be capable of measuring initial continuous currents (ICC) which are not characterized by the peak amplitude but by the charge value – this means that charge values should also be provided.
16. Can lightning events with small current, e.g. upward flashes, damage the blade?
Yes, they can cause damage. Even if the lightning event only has a low current of a few 100 A, the charge value can still be correspondingly high due to the long duration.
The charge causes melting, e.g. at receptors.
In addition, small current of only a few 10s of kA can have negative effects on the carbon fibre parts inside the blade if the slope (rise time) of such an event is very high.
