NxtPhase Optical I, V Transducers for High Voltage
NxtPhase Corp., Vancouver BC, has developed a family of optical sensors to measure current, voltage, and power in high voltage power systems. These devices appear to be on the verge of becoming a commercial reality, and offer high accuracy, bandwidth and dynamic range. Integrated into the all-digital electronic substation measurement and control system of the future, they will help revolutionize metering, protection, and power quality management.
These optical voltage and current sensing technologies came out of two parallel independent development programs – one in the US and the other in Canada.
Honeywell applied fiber-optic gyro technology developed for demanding civil and military navigation applications to the measurement of current, and teamed with Texas A&M to produce a sensor. The first deployment was with Arizona Public Service at the Cholla Generating Station in 1997 where accuracy of 0.03 per cent has been demonstrated. Honeywell entered into a partnership NxtPhase, who has a complementary voltage technology and a similar market vision.
The other half of the NxtPhase story begins with Carmanah Engineering Ltd. – a successful hi-tech spin-off from the University of British Columbia (UBC). Carmanah, UBC and BC Hydro partnered to develop an integrated optic voltage sensing technology based on a unique electric field sensor called the Integrated Optic Pockels Cell (IOPC). Significant technological breakthroughs led to an extremely accurate optical voltage transducer that avoids the environmental concerns of alternative optical or conventional technologies. The first IOPC sensor was successfully deployed in 1997 at the Ingledow substation of BC Hydro.
Optical Voltage and Current Transducer–
The NXVCT combines both the optical voltage and current transducers in one instrument, over the range of transmission voltages from 69 kV to 765 kV.
– Accurate metering of independent power plants (The dynamic range means accuracy at 1 amp and at 100,000 amps. This can have substantial revenue implications, with the ability to measure power inflow when a plant is not producing power);
– High bandwidth monitoring of power plants, i.e. transients and harmonics; and
– High voltage power quality measurements, to diagnose equipment failures.
Very shortly a technology alliance with BC Hydro will be announced. BC Hydro will conduct field trials to test and demonstrate the devices at one of its high voltage substations to verify performance over time, and at various operating temperatures. The company is looking for customers, partners and investors. They are already in discussions with several UFTO companies and others.
For more information about the company and its products, the website is:
Richard MacKellar, CEO, NxtPhase Corp., Vancouver BC
604-215-9822 x 222, firstname.lastname@example.org
Steve Dolling, Director, Marketing
604-215-9822 x233, email@example.com
Further details on the technology are available:
“Design Options Using Optical Current and Voltage Transducers
in a High Voltage Substation”
IEEE PES Substation Committee Annual Meeting May 1, 2000
Powerpoint presentation gives a good overview.
Here is the first page of each of two articles, and links for the pdf downloads.
“Optical Voltage Transducers for High-Voltage Applications”
Optical methods for the measurement of current and voltage in high-voltage (HV) environments have been attracting more and more attention in the recent years. This is mostly due to the advantages that they offer over conventional instrument transformers. They provide immunity to electromagnetic interference, are typically non-intrusive, provide excellent galvanic isolation, are much lighter and, therefore, easier to transport and install. Early work on optical current and voltage sensing in the HV environment started in the 1970’s [1-5] leading to more practical and accurate systems developed in the 1980’s and 1990’s [6-13]. Also, at the commercial level, current sensing technology (both for technical and economical reasons) led voltage sensing technology. In this paper, we present results obtained using NxtPhase’s optical voltage transducer, NXVT.
Most practical optical voltage sensors use electric field sensors that operate using the linear electro-optic (or Pockels) effect. It should be noted that the sensors themselves are, strictly speaking, electric field sensors and not voltage sensors. However, various means of getting a one-to-one relationship between the voltage applied and the electric field sensed are used to derive voltage. For example the entire voltage can be applied across the electro-optic crystal, or a capacitive divider can be used to apply a well-known fraction of the voltage to be measured across an optical electric field sensors. There are advantages and disadvantages to each of these methods. Nevertheless, most successful devices in the past have used optical fibers for the transmission of light, bulk electric field sensors as sensing elements, and SF6 gas for insulation.
The NXVT introduced here combines the typical benefits of optical sensing technology with some additional features that provide further benefits to the user. For example, it does not use SF6 or oil-paper insulation, making it more environmentally friendly and much safer to use. The NXVT uses multiple miniature electric field sensors inside a high-quality post insulator, in a proprietary manner, to measure voltage with high accuracy.
“Optical Current Transducers for High Voltage Applications”
Over the past 15 years, optical current sensors have received significant attention by a number of research groups around the world as next generation high voltage measurement devices, with a view to replacing iron-core current transformers in the electric power industry. Optical current sensors bring the significant advantages that they are non-conductive and lightweight, which can allow for much simpler insulation and mounting designs. In addition, optical sensors do not exhibit hysteresis and provide a much larger dynamic range and frequency response than iron-core CTs.
A common theme of many of the optical current sensors is that they work on the principle of the Faraday effect. Current flowing in a conductor induces a magnetic field, which, through the Faraday effect, rotates the plane of polarization of the light traveling in a sensing path encircling the conductor. Ampere’s law guarantees that if the light is uniformly sensitive to magnetic field all along the sensing path, and the sensing path defines a closed loop, then the accumulated rotation of the plane of polarization of the light is directly proportional to the current flowing in the enclosed wire. The sensor is insensitive to all externally generated magnetic fields such as those created by currents flowing in nearby wires. A measurement of the polarization state rotation thus yields a measurement of the desired current.
The optical current transducer being developed by NxtPhase (the NXCT) is an offshoot from the Honeywell fiber optic gyro program. Honeywell has been producing fiber optic gyros for a variety of commercial aviation applications since 1992. Extensive life and reliability testing has been carried out on the product to meet the stringent flight qualification criteria. Early on, Honeywell realized that this technology, with only minor modifications, could be applied to the field of current sensing, and a program to diversify into this area was maintained by Honeywell for several years. In late 1999, Honeywell joined with Carmanah Engineering to launch NxtPhase with the charter of commercializing the technology.
Principle of Operation
The NXCT uses the Faraday effect, but in a different architecture than the more well known polarimetric technique. The NXCT is a fiber optic current sensor and it works on the principle that the magnetic field, rather than rotating a linearly polarized light wave, changes the velocities of circularly polarized light waves within a sensing fiber wound around the current carrying conductor . The effect is the same Faraday effect but differently formulated. We have found in our experience and heritage from the Honeywell fiber-optic gyroscope program that, for a variety of reasons, it is easier to accurately measure changes in light velocity than changes in polarization state. Chief among these reasons is that by using a velocity measurement scheme, we do not need to construct the sensing region from annealed fiber which is brittle and difficult to work with in a production environment.