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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
©2017 NuGrid Power Corp 2
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
©2017 NuGrid Power Corp 3
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
©2017 NuGrid Power Corp 4
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
©2017 NuGrid Power Corp 5
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
©2017 NuGrid Power Corp 6
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
©2017 NuGrid Power Corp 7
Industrial Optical Current Sensors
©2017 NuGrid Power Corp 8
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)
©2017 NuGrid Power Corp 9
Industrial Optical Voltage Sensors
138 kV classCombined OVT/OCT
(Mobile)
500 kV classCombined OVT/OCT
230 kV classCombined OVT/OCT
500 kV classmobile OVT
35kV OVT
©2017 NuGrid Power Corp 10
Challenges• Newer technology / products• User familiarity / comfort• Standards and Guides• Regulatory approval and certification• Maintenance and deployment practices• …
©2017 NuGrid Power Corp 11
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.
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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
©2017 NuGrid Power Corp 13
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
©2017 NuGrid Power Corp 14
Questions?
©2017 NuGrid Power Corp 15
Supplementary Information
See the following slides for various examples of optical sensor applications / installations
©2017 NuGrid Power Corp 16
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
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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
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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
©2017 NuGrid Power Corp 19
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
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• 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
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OCT for Fault Current
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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
©2017 NuGrid Power Corp 23
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
©2017 NuGrid Power Corp 24
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
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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
©2017 NuGrid Power Corp 27
PS1/Q5 F. RAHMATIAN(Canada) & P. MAZZA (Italy) SC A3 Discussion Group Meeting – 2016‐08‐25 Slide 2
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.
©2017 NuGrid Power Corp 28
PS1/Q5 F. RAHMATIAN(Canada) & P. MAZZA (Italy) SC A3 Discussion Group Meeting – 2016‐08‐25 Slide 3
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
©2017 NuGrid Power Corp 29
PS1/Q5 F. RAHMATIAN(Canada) & P. MAZZA (Italy) SC A3 Discussion Group Meeting – 2016‐08‐25 Slide 4
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.
©2017 NuGrid Power Corp 30