高压光纤电流互感器(HIGH VOLTAGE CURRENT OPTIC FIBER SENSOR)

Abstract—Various applications of a fiber optic current sensor are explored. Flexibility and inherent beneficial features of the technology make it appropriate for many applications, including some novel protection applications. These applications include regular high-voltage AC metering and protection, accurate wide dynamic range metering, high voltage DC, high current DC, portable calibration reference, generator monitoring, generator protection, and high-current AC applications. Some novel uses of the technology, including optical summation of currents where conductors are quite large or far from one another, are also discussed.

Index Terms-- current measurement, high-voltage techniques, optics, optical current sensor, transducers, optical fiber devices, power measurement.

I. I NTRODUCTION

PTICAL voltage and current sensors used for high-

voltage (HV) and/or high-current (HC) measurements can offer several attractive features. These benefits include • High accuracy over wide dynamic range,

• Wide bandwidth from dc to > 100th harmonic,

• Light-weight and small size:

• Excellent seismic performance,

• Safe, easy, flexible, and cost-effective installation, • User-adjustable turn-ratio,

• No CT saturation,

• Excellent phase accuracy,

• Voltage and current sensing in one device, and

• Safety & environmental benefits:

• No oil or SF6,

• No open secondaries,

• No ferro-resonance, and

• Galvanic isolation from HV line.

Fiber-optic current sensors offer additional advantages of flexible form factor, “window-CT” design, and ability to measure very high currents. The combination of all these features creates a great deal of flexibility in the use of optical voltage and current sensors. In other words, the same optical products or technology can be used for several applications where traditionally different types of products or even

F. Rahmatian is with NxtPhase T&D Corp., Vancouver, BC V6M 1Z4 Canada (e-mail: frahmatian@).

J. N. Blake is with NxtPhase T&D Inc., Phoenix, AZ 85027 USA (e-mail: jblake@). different technologies were used. In this paper we provide a review of this application flexibility for a fiber optic current sensor (NXCT) technology.

II. A PPLICATIONS

The NXCT uses an in-line fiber optic interferometric design described in detail in [1] and [2]. The sensing head is in the form of an optical fiber encircling the current carrying conductor in a full turn or several turns. It effectively and accurately integrates the magnetic field around the current carrying conductors that it encircles, via the Faraday Effect, measuring the net current through its aperture. The sensing fiber can be packaged in fixed size windows or in a flexible cable.

Figure 1 shows a 362 kV class NXCT with several primary conductor connection options for used in air-insulted substations (AIS). The sensing fiber packaging is the same for all these configurations, and the window aperture is 110 mm in diameter, rated for 4000 A continuous operation. The options shown use different clamps for holding the primary conductor. Figure 1.b shows a flat conductor bar, supplied for connection to standard 4-hole or 6-hole NEMA connections. Figure 1.c shows the dual cable clamp option, allowing the user to run cables through the CT and reduce the number of HV current carrying connections, which are a source of heat and reliability issues for HC CTs. Figure 1.d, shows yet another clamp option, for mounting the NXCT on a 4” solid bus in the substation. In addition to saving on electrical interfaces at high voltage and high current, this option (suspension) can allow elimination of civil work and costs associated with pedestal-mount CTs and can be very attractive in seismically active regions.

Figure 2 shows 145 kV class optical CTs, mounted conventionally, using the 6-hole NEMA conductor bar. In this application, high accuracy (0.15S class) over a wide dynamic range was the main motivation for using the NXCT. The optical current sensor can offer better than 0.15% class accuracy from 0.1% to 200% of rated current [3]. Energy measurements where wide dynamic range is required, e.g., with Independent Power Produces (IPPs) and wind farms, are ideal applications for the NXCT due to its linearity.

Figure 3 shows 72 kV class NXCTs, mounted horizontally from other substation structures. In this case, the light weight (<65 kg), solid insulation (no oil to leak), and high accuracy features combined to provide a very cost-effective solution for

Applications of High-V oltage Fiber Optic

Current Sensors

Farnoosh Rahmatian, Member, IEEE-PES, and James N. Blake

O

© 2006 IEEE. Reprinted with permission from the 2006 IEEE PES General Meeting.

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