Distribution Overhead Line Monitoring with LEM’s ART Rogowski coil
New line current sensors allow utilities to monitor their overhead distribution lines tomaximize their capacity and prevent clearance violations thus improving reliability andefficiency of the MV Distribution Grid.
The High Voltage transmission grid is already highly automated and monitored through SCADA
and Energy Management Systems. In contrast, the Medium-Low Voltage distribution grid hasvery limited monitoring and control. Why? - More often than not, Utilities fail to monitor theirmany medium voltage substations, this is due to the expense of retrofitting with today’s solutions
and of the time it takes to plan and build. The implementation of traditional substation monitoring
requires complicated engineering, this includes the use of remote terminal units with new
conduits, wiring to relays and current transformers. Engineers must schedule outages todisconnect the feeders, which takes time and may only be possible during low power
consumption needs. Once the hardware has been installed, the utility has to program andintegrate all the hardware into a complex SCADA system, which is a significant and difficult
challenge for many utilities. There must be a better way.
Below the feeder level, remote monitoring is absent with the exception of customer billing meter
points where smart meters are becoming prevalent to read, monitor and control. However, thesesmart meters are only collecting and communicating Voltage, Current , Power, Reactive Power,S, Energy data rather than power quality data sets like Cos (Phi), Total Harmonic Distortion,flicker, voltage dips, transients, waveforms, time series etc. The smart meter does not collect alot of data outside of its billing focused function. Substations and distribution power lines are twoof the most valuable assets for utilities that require crucial power flow data to provide the mostreliable service.
The most relevant data in the distribution grid is about the location and cause of faults and nonfault events, high-impedance faults, consumption peaks, handling distributed renewable energy
and EV charging, feeder outages, and many others – all high-value data that is not addressed bytoday’s systems.
Now monitoring overhead power lines has been made possible faster, easier and cheaper with
new Internet of Things telecom networks like NB-IoT and LPWAN.Thanks to a line sensor (1),installed between two MV poles (2), the grid operator can visualize, in real-time, the current flowin order to optimize the power line capacity to distribute more electricity. The wireless line sensor(1) sends data over a telecom relay (3) to a secured database in the cloud (4) or on premise.
The energy management platform (5) can regulate, alert and notify the maintenance team if
needed. New line sensors are now using the LEM Rogowski coil ART (A) to measure the current,
detect line aging depending on the level of current, and prioritize line capacity.
A. LEM ART
1. Line Sensor
2. MV Power Lines
3. Telecom relay
4. Cloud and database
5. Energy Management

1|PageBefore without visibility about the grid, the generated renewable energy distributed through anoverhead line could be overloaded (red). Thanks to the three-phase line sensor system, theextra power in one of the line can be re-distributed to the adjacent lines (black) therefore
reducing the initial line (blue) capacity to an acceptable level. Overall, the capacity output of thepower grid is then maximized (fig. 1).

2|PageFigure 1: Before and after line sensor installation
In addition, the line sensor (1-35kV distribution grid) provides periodic time synchronizedmeasurements to facilitate improved situational awareness and operations: current, both
amplitude and phase, conductor surface temperature and detects fault conditions enabling rapid
identification and notification. This three phase line sensor system in the power distribution areequalized in real-time among the different lines within a meshed network

The AC measurement can now be achieved with the LEM ART split-core rogowski coil, see
below table for the summary of the ART advantages compared to two other current
measurement techniques used in the Line sensor.

3|PageTransformer inside

Resistor inside

Current sensor
technology

Split-core current
transformer

Split-core rogowski coil

LEM ART split-core
Rogowski coil

Current range

Many versions: 80A,
100A, 300A, 400A,
600A, 800A…

One version fits all

One version fits all

Electromagnetic N/Acompatibility

Yes (Resistor)

N/A (Ferrite inside)

Accuracy

0.5%

1%

0.5%

WeightHeavyLight

Lightest (~100g)

Safe output of Precaution (currentcurrent sensoroutput)

SafeSafe (di/dt output)

Protection
ratingIP 65 with protectivehousing

IP 64

IP 57

Operatingtemperature-40 to +80C

-40 to +70C

-40 to +80C

PRICE

$$$

$$

$Ferrite inside

ART is the clear winner of this comparison with a practical one size fits all current loop,
excellent ferrite core, great accuracy, light, safe mV output and water resistant coil

4|PageART Ferrite core
Recent developments have revolutionized the characteristics of ferrite at 50/60Hz, bringing
many advantages. This new type of ferrite has significantly improved permeability and has been
implemented in this ART Rogowski coil (fig. 2). ART takes advantage of the intrinsic ferrite
qualities:•High accuracy and excellent linearity, even at very low current levels•

No phase-shift between input and output currents•

No air gaps and virtually insensitive to ageing and temperature changes•

Low position dependent error close to the clasp of the coil (see ART Sensitivity)•Low cost versus potentiometer based Rogowski coils

Fig. 2. Ferrite core of LEM ART Rogowski coils
ART Sensitivity
The overall sensitivity to the position of the primary conductor can be controlled,
but usually close to the clasp errors are often unavoidable, except for the patented
ferrite based ART Rogowski coil (fig. 3).

Fig. 3. Position sensitivity of ART Rogowski coil

5|PageConclusion
The new ART rogowski coil class 0.5 has made huge progress, allowing small, light, sensitiveand flexible current sensing for MV grids. The major improvements that have been made in thedesign and manufacturing processes have enabled a reduction in both the cost and thesensitivity to the coil positioning around the primary cable.
People consume more electricity than ever before and have an expectation that they will accesstheir electricity without fault or interruption. The line sensor provides situational awareness along
distribution feeders allowing utilities to operate and respond based on prevailing conditions. The
system directs preemptive patrol and maintenance crews to the affected grid locations, enabling
utilities to avoid potential short or long electricity interruptions. It reduces outage frequency,
resulting in the reduction of the momentary average interruption frequency index (MAIFI) andsystem average interruption frequency index (SAIFI). Both indexes serve as valuable tools forevaluating a utility’s performance and reliability because some countries have already put inplace regulations that require a utility to reimburse customers for long electricity interruptions.
When installed with the hot stick or insulated gloves on the overhead power line, LEM ART
rogowski is a safe, easy-to-install, light but robust current measurement alternative to heavy andexpensive current transformers, therefore improving the overall performance, reliability andefficiency of the line sensor.
About the author
Patrick Schuler 苏乐, LEM
Patrick Schuler has been working in the internet, telecommunications, smart grid, powerelectronics and power utility sector for more than 15 years. Since joining LEM in September
2014, Patrick has been responsible for defining the global smart grid offering and managing
smart grid business development. As a smart grid expert, Patrick is a member of the IEC’s world
smart city community in Geneva and was the former smart grid chairman at the China European
Chamber of Commerce in Beijing.
About LEM

LEM is the market leader in providing innovative and high quality solutions
for measuring electrical parameters for a broad range of applications in drives and welding,renewable energies and power supplies, traction, high precision, conventional and green cars
businesses. LEM has production plants in Beijing (China), Geneva (Switzerland), Sofia (Bulgaria)
and Tokyo (Japan). With regional sales offices near its customers’ locations, the company isable to offer a seamless service around the globe. LEM is a mid-size, global company withapproximately 1’450 employees worldwide and reported sales of CHF 264.5 million in financialyear 2016/17. LEM City answers the demand for an accurate, reliable and easy-to-install energy
sensor for future Smart Cities.
6|PageLEM City - at the heart of our planet‘s energy measurements.
www.lemcity.com

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