Wireless technologies such as the short range Bluetooth specification are starting to be used to improve the safety of high voltage power systems.

The technology is reaching the point where it can be used reliably, safely and securely in the field, bringing the safety advantages and improving productivity, as well as being used in the laboratory for measuring data in high voltage systems.
The safety issue is even more pressing from a regulatory point of view, as the Health and Safety Executive in the United Kingdom now requires that power engineers have no direct contact with RTUs following a recent fatal accident in Ireland which resulted from an engineer touching a corrodedRS232 port.

Remote terminal units

One power equipment maker - Lucy Switchgear, headquartered in Oxford - now uses Bluetooth to give access to its remote terminal units (RTUs). These are often installed at the top of poles or in remote locations, and using a Bluetooth link means engineers can sit in a van and configure the RTUs without having to climb up a pole to plug in a laptop.
This is part of a trend for power equipment makers, says Peter Flittner, project manager for industrial applications at leading Bluetooth chip maker, Cambridge Silicon Radio (CSR).
"I don't think there's any problem in putting Bluetooth into high voltage or high power areas and the electronics should survive and it can be used to transmit voice and with isolation, which is a key advantage," he said.
CSR is one of the leading suppliers of Bluetooth silicon, supplying its BlueCore2 chip to mobile phone and headset makers. This is a single chip that includes the Bluetooth modem with the RF and the required flash memory, as well a version with a built-in analogue to digital converter.
This integration also makes the part relevant for industrial applications for data monitoring, and the isolation aspects of the short range wireless link of Bluetooth has been attractive to several high voltage projects.
The high voltage switchgear developed by Lucy uses several different communication approaches. A wide area radio networks such as a mobile phone network is used for controlling RTUs from a central controller, but Bluetooth is being used for localised configuring and diagnostics of the units in the field, specifically replacing the need to climb up the pole or trek across a muddy filed.
"Bluetooth gives us a longer range and the data rate is very good compared to other radio technologies," said Ernie Wollard, managing director of the Power Isolation division of Lucy Switchgear.
The RTUs use Bluetooth modules developed by Brainboxes of Liverpool to be a 'software-less' cable replacement. Unlike Bluetooth in the PC, the modules for the Lucy RTUs use no software drivers and are simple to install, plugging directly into the RS-232 port that is standard on the RTU and provide a simple cable replacement over a range of 100m.
Brainboxes started out in 1984 making RS-232 interfaces and now specialises in the design and the manufacture of PC add-on cards suitable for mission critical applications. The company's product range, which now exceeds 100 products, incorporates PCI, PCMCIA, USB and Bluetooth technology geared towards Serial Communications, EPOS and Mobile Data Communications.
It is supplying its BL-521 RS-232 Bluetooth converter and the BL-565 Bluetooth CompactFlash card with PCMCIA adapters to Lucy for the project.
The BL-521 converter can turn any RS-232 serial device, such as PC, printer, oscilloscope or any device which can be connected via a simple serial port.
Future generations of RTUs may be designed with embedded Bluetooth technology, such as Brainboxes BL-730 Class 1 Bluetooth module - fundamentally the same device fitted in the BL-521, also capable of 100m range.
To access the RTU, the engineer uses a password to access the RTU, configure the system and access the diagnostics.
Bluetooth offers more protection than that, says Eamonn Walsh, managing director of Brainboxes. There is additional encryption, and the nodes can be made 'undiscoverable' so that only laptop that has been previously partnered with the RTU can access it.
"There have been over 100 million Bluetooth units shipped and as far as I know the encryption has still yet to be broken, unlike many other wireless standards," he said.

Connection reliability

The reliability of the connection is a key issue, as Bluetooth sends the data in packets in the unlicensed radio band at 2.4GHz where there is a lot of electrical noise.
To counter that, a Bluetooth link, once set up, hops around the spectrum 1600 times a second to avoid problems with noise.
There are also provisions in the latest version of the standard - version 1.2 - to increase its resistance to noise.
However, the Bluetooth links are not being used to switch off the high voltage lines at the RTUs, says Woollard. Instead this is handled by a separate wide area radio network such as GPRS linked to the central control centre.

Security is a key concern, as previously the remote locations helped to restrict access to the units. Now, potentially anyone with a Bluetooth enabled personal digital assistant could try to access the system and re-configure the RTUs.
Lucy also uses the Bluetooth access in the factory, says Woollard, and the units are now being shipped to customers to be used in Northern Ireland and the Middle East.
There are other areas in power engineering where Bluetooth is making an impact, says Flittner at CSR.
"We have been working with a research group at Cambridge University who have developed a brushless double induction motor. With two motors you can control the phase of the motors and so control the speed, rather than having a constant speed motor," he said.
But with two power supplies there is no way to monitor the induction currents which are flowing in the core of the machine. So they wrap a coil around one of the bus bars in the motor to measure the current up to 3000A. Previously they were using slip rings, which could be unreliable, but now they have taped a Bluetooth module to the coil. Measurements can now be taken by equipment on the other side of the lab via the Bluetooth link.
Such a system could also be used for tasks such as monitoring the resistance of insulation in high voltage systems such as turbines, and could even be self powering, says Flittner. "The Bluetooth device only needs sub milliamp currents and it's very easy to scavenge power from the environment to power the module with a coil and a capacitor," he said.

Critical measurement applications

CSR is working with the Bluetooth Special Interest Group, a collection of Bluetooth companies that set the standards for the technology, on profiles that can be used for more critical measurement applications.
"When we start getting into instrumentation, people want to know about latency so we are working on adapting the technology so we can get low latency I/O," he said. CSR is part of a working group looking at how to improve the link protocols to reduce the latency but still maintain the reliability of the connection.
"That's one of the main pushes for additions to the Bluetooth specification for industrial applications," he said.
Version 1.2 of the specification goes some way to tackling the problems found in industrial environments by including Adaptive Frequency Hopping (AFH) technology.
This minimises the interference between Bluetooth andWi-Fi radios when operating in the same environment. This improves the performance of a link performance in a busy RF environment - such as in offices with wireless LANs and laboratories with high voltages creating large amounts of electrical noise.
Increasing the resistance to electrical noise will also help reduce the latency as less packets are therefore lost and have to be re-sent.
AFH is implemented in CSR's BlueCore3 chip, which also uses a new 'Fast Connect' protocol, which significantly improves the usability of Bluetooth devices by reducing device discovery times by up to a factor of ten. This can help reduce the latency in capturing signals from multiple sources.
Another addition to version 1.2 is the eSCO facility (Extended Synchronous and Connection Oriented link) that provides high quality voice links for cordless phones, but it can also be used to improve the quality of data running over the link.

Error checking voice channels

eSCO channels are error checking voice channels which allow polled retransmissions so that raw data can be sent and data rates may also be negotiated. This allows the detection andre-transmission of lost or destroyed packets with a minimum impact on real-time performance.
It could also be used to help improve the performance in data gathering applications
BlueCore3 has now been designed into a notebook PC to make gathering and managing data even easier, and such a PC could be used as the central point in a wireless data acquisition system.
So Bluetooth is making its way into several applications in power control and monitoring, overcoming the problems of noise and, to a certain extent, latency.
But it also offers increasing levels of isolation and control in power applications while providing higher levels of security where needed.