brief overview of optical current and voltage sensors - … · brief overview of optical current...

Brief Overview of

Optical Current and Voltage Sensors

in the Electric Power Industry

Farnoosh RahmatianNuGrid Power Corp

NASPI Distribution Task Team – June 1, 2017

©2017 NuGrid Power Corp 1

Modern Grid Measurement Needs• Voltage and current sensors are the eyes and ears of the electric power system

• A smarter grid can benefit from seeing and hearing better• Measurement needs

• Safer• More accurate• More reliable• Wider dynamic range• Wider bandwidth• High speed communication• Ease of use• Accurate timing


Optical Voltage and Current Sensor Systems

Sensor Electronics and

Merging Unit

Optional Cable Management Box

Cabling System

Optical Transformers Secondary Devices

(e.g., meters and relays)

Optical and/or Electrical Cables

Optical and/or Electrical Cables

Schematic of a typical optical sensor system


Potential Benefits of Advanced Optical Sensors

• Performance Features• Accuracy over a very wide dynamic range

• Exceptional phase accuracy (e.g., synchrophasor applications)

• Bandwidth, DC and harmonic• Seismic performance• User‐adjustable sensitivity

• Safety & Environmental Concerns• Avoiding insulating oil or SF6 (depending on design)

• No open secondaries• No ferro‐resonance• Galvanic isolation from HV line

35kV Optical

VT


Potential Benefits of Advanced Optical Sensors

• Installation features• Small size and weight• Multi‐function, e.g.,

• metering & protection in one device • Voltage & current in one device

• Self monitoring

• Simple, linear, and scalable• Simplifies substation/feeder design by allowing a simple template design for multiple applications

• Digital communicationsx kV Optical CT


Optical Instrument Transformers –Technology Overview

• Faraday and Pockels effects• Product R&D in 1960s and 1970s• Field prototypes/products in 1980’s and early 1990’s• Cost‐effective and high‐MTBF optical/electronic components availability in the 1990’s

− Thanks to the telecom boom/evolution.• Commercial products available since late 1990’s


Current Sensors Technology Overview

Electrical Measuring Devices

Iron Core

Air Core

Optical Sensors

Resistive Shunt

“Hybrid” Optical SensorsSignal sensing with electrical technologySignal transmitted digitally over fiber opticsOptical isolation from HV

Bulk Optic Fiber Optic

Limited number of turnsPhysical size limitations

Any number of turnsNo size limitsInterferometricdesign

Hall Effect

Current Measurement


Industrial Optical Current Sensors


Voltage Sensors Technology Overview

Electrical Measuring Devices

Iron‐core wound

voltage Txfr(PT)

Capacitive Divider

Optical Sensors

ResistiveDivider

“Hybrid” Optical SensorsSignal sensing with electrical technologySignal transmitted digitally over fiber opticsOptical isolation within substation yard

Bulk OpticSingle sensing element with voltage applied across full crystalUses SF6 gas for insulation

Voltage Measurement

Distributed Sensor

Multiple sensing elementsNitrogen gas filled

Capacitive Voltage Txfr(CCVT)


Industrial Optical Voltage Sensors

138 kV classCombined OVT/OCT

(Mobile)



500 kV classmobile OVT

35kV OVT


Challenges• Newer technology / products• User familiarity / comfort• Standards and Guides• Regulatory approval and certification• Maintenance and deployment practices• …


Standards and Guides• IEEE/ANSI C57.13• IEEE C37.92 (low energy analog interface)• IEEE 1601‐2010 (Optical CT VT)

• Accuracy terminology, e.g., 0.3DR0.5‐150 (RF=1.5)

• IEC 60044 series (‐7/8 for non‐conventional VT/CT)• And associated CSA series C60044‐7/8

• IEC 61869 series (new standards – not all published yet)• IEC 61869‐6:2016• IEC 61869‐9:2016

• IEC 61850‐9‐2 (digital interface)• UCA Guide – 61850‐9‐2 light• IEC 61869‐9 with IEEE 1588 profile for Merging Units (MU)

• IEEE Std. PC 37.241 (IEEE PES PSRC WG I‐11)• Application of optical sensor systems in Protection – in balloting.


Applications• General metering & protection• Synchrophasors• Grid intertie metering• Wind farms and Independent Power Producers • HCDC ‐ high current DC (e.g., aluminum smelters)• Power cable protection (differential)• UHV measurements• HVDC (high voltage DC) and High voltage platforms (series Capacitors)

• FACTS, SVC, …• Power quality applications and transient monitoring• Synchronized switching (lines, capacitors, reactors, transformers, …)• Cable Monitoring• Portable Calibration• Testing (for laboratory and field testing)

• E.g., field calibration of synchrophasor systems


Synchrophasors using Optical Digital Sensors• Similarities of PMUs (Phasor Measurement Units) and MUs (Merging Units)Digital Time‐Tagged measurementsPrecision timing

• Excellent phase accuracy regardless of current/voltage level

• Linearity over wide dynamic range of current/voltage• Integrated PMU in optical sensor electronicsSynchrophasors can be just another digital output format


Questions?


Supplementary Information

See the following slides for various examples of optical sensor applications / installations


Arizona –230 kV

Combined Voltage &

Current Sensor

British Columbia –

500 kV Combined Voltage &

Current Sensor

United Kingdom

420 kV -OCT

DC CT 25 kA Quebec


SVC Substation Harmonics Measurement

550 kV class testing for harmonics

(Bandwidth 20 kHz)0

0.2

0.4

0.6

0.8

1

1.2

1.4

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Harmonic #

% o

f Fun

dam

enta

l Fre

quen

cy Phase C

Phase B

Phase A


High‐Frequency Measurements

Impulse and fast transient voltage and current measurements, e.g., for reactive switching test (in laboratory and on site)

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

-4.E-06 -2.E-06 0.E+00 2.E-06 4.E-06 6.E-06 8.E-06

Opt

ical

CT

Out

put V

olta

ge (V

)

Time (s)

-0.05

0

0.05

0.1

0.15

0.2

0.25

0.3

-4.E-07 -2.E-07 0.E+00 2.E-07 4.E-07 6.E-07 8.E-07 1.E-06

Dete

ctor

Out

put V

olta

ge (V

)

Time (s)

Sample Current Measurement Waveform: 26 kA peak at

0.7 MHz

Sample Voltage Measurement Waveform: 283 kV peak with <100 ns rise-time


Series Capacitor Staged Fault Testing

Fiber Optic CT and VT were used because of– Wide bandwidth (harmonics-rich signals)– Wide dynamic range (10 to 12000 A were expected)– Safety: passive optical isolation from high-voltage

• varying ground voltage during the fault

– Immunity to electromagnetic interference

• May be strong in the presence of fault arc

– Ease of set up


• OVT-138kV, Bandwidth ~ 40 kHz, Ratio = 201,250:10

• OCT for MOV current, Bandwidth ~ 6 kHz, Ratio = 12,000 A : 10 V

• Window OCT for fault current, Bandwidth ~ 6 kHz– Ratio 1 = 12,000 A : 10 V– Ratio 2 = 750 A : 10 V

• Time delay ~ 43 s

OVT‐138kV for MOV Voltage OCT for MOV Current


OCT for Fault Current


Results – 5 Shots

-15

-12

-9

-6

-3

0

3

6

9

12

15

-0.01 0.00 0.01 0.02 0.03 0.04 0.05 0.06Time (s)

Cur

rent

and

Ene

rgy

-250

-200

-150

-100

-50

0

50

100

150

200

250

MO

V Vo

ltage

(kV)

NXVCT MOV Energy (MJ) NXCT MOV Current (kA)NXCT Fault Current (kA) NXVT MOV Voltage (kV)

-15

-12

-9

-6

-3

0

3

6

9

12

15

0.14 0.15 0.16 0.17 0.18 0.19 0.20 0.21Time (s)

MO

V C

urre

nt a

nd E

nerg

y

-250

-200

-150

-100

-50

0

50

100

150

200

250

MO

V Vo

ltage

(kV)

NXVCT-2 MOV Energy (MJ)NXCT-2 MOV Current (kA)NXVT MOV Voltage (kV)

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35Time (s)

Cur

rent

(kA

)

Secondary Arc CurrentUnits

Fault number 1 2 3 4 5Primary arcing time ms 36 36 36 36 42Secondary arcing time ms 425 863 606 290 276Number of voltage peaks clipped by MOV 1 3 3 2 5MOV energy absorbed MJ 2.39 10.7 10.2 3.42 13.6MOV Voltage Peak (absolute value) kV 196 204 204 202 205MOV Current Peak (absolute value) kA 6.4 12 12 12.8 13Approx. MOV Voltage ringing frequency Hz 610 610 620 620 620Primary Fault Current Peak (absolute value) kA 11 11 11 11 11Approximate secondary fault current (peak-to-peak) A 120 160 120 160 160

Summary Results


Shunt Capacitor BanksExample: Capacitor Unbalance Protection

– Two outputs per optical CT• Output 1 Ratio, 1A:1A (Max 2 A), connected to an over current relay

– Alarm level set at 0.8A (2+ can’s failing)– Trip level set at 1.4A (4+ cans failing).

• Ratio 25A:0.2V (Max 1000 A), for fault monitoring (connected to a recorder).

– Bandwidth 6 kHz


Shunt Capacitor Banks

-0.01 0 0.01 0.02Time (s)

Mea

sure

d Si

gnal

s (A

rb. u

nit)

UnfilteredFiltered

Showing Primary

Current of 0.5 A


OCT‐DC for HVDC/SVC/De‐Icer

69 kV classBandwidth: DC to 10 kHzDistance between CT columns and

electronics = 1 kmMultiple output per CTElectronics for 3 CTs in one

chassis

Quebec, Canada©2017 NuGrid Power Corp 26

PS1/Q5 F. RAHMATIAN(Canada) & P. MAZZA (Italy) SC A3 Discussion Group Meeting – 2016‐08‐25 Slide 1



Question: Is there a need for voltage transformers that are better suited to measure harmonics?

Response: • At the distribution levels, we strongly believe

there is an increasing need for harmonics measurements due to the addition of more distributed generation, microgrids, etc. and the associated inverters.

• At the transmission levels, with more HVDCand FACTS deployment, as well as increasing interest in higher frequency measurements (e.g., TRV, switching phenomena, and lightning strikes), there seem to be growing need too.



Question: What technology is proposed?

IEC 61869‐103:2012, Figure 9 – Voltage Transformer technologies’ frequency range according to present experience

Inductive VT

CVT

50 Hz

10 MH

z

1 MH

z

100 kHz

10 kHZ

1 kHz

100 Hz

15 Hz

DC

Electronic VT

Optical VT/RCVT

R divider

C divider

HV MV LV



Question: What technology is proposed?

Response: • Have successfully used:

o Capacitive dividerso RC dividerso Optical VTso CVTs with a special tap/equipment to bypass the inductive

transformer (very similar to a capacitive divider)o Voltage transformers, mostly at distribution voltages for lower harmonics

• Do not recommend to use CVTs and VTs without special provisions.• With analog outputs, particularly from resistive and capacitive dividers,

attention has to be paid to cabling as it may have impact on bandwidth if it is not properly accounted for.

• Digital output at 14.4 kHz sampling rate (for power quality) per IEC 61869‐9 and the frequency mask as given in IEC 61869‐6 also impose limitations for higher harmonics measurements.


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