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Power System Dynamic State Estimation Based Protection and Fault Location

Rui Fan

Pacific Northwest National LaboratoryGeorgia Institute of Technology

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System Events

Fault Conditions

Normal Transients

Relay ActionsTrip Dependable

Secure

Mis-operation

No-Trip

No-Trip

Trip

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Source: NERC, Misoperation, https://www.eiseverywhere.com/file_uploads/fa776bec5502184fa6cb828ea07ff129_BauerHORSpresentation.pdf

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Root causes:– Incorrect setting– Incorrect coordination– Incapability

0 0.02 0.04 0.06 0.08 0.1

Seconds

-400

-200

0

200

400

Amp

Trip

Undependable

Unsecure

Load change

High impedance fault

Solution: Dynamic State Estimation (DSE) Based Protection Scheme (a.k.a. Settingless Protection)

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DSE-Based Protection Scheme--inspired from Differential protection

Analytics: Dynamic State Estimation (systematic way to determine observance of physical laws)

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DSE-Based Protection: Logic• Dynamic State Estimation

• Chi-square Test– Compute degree of freedom and chi-square critical value

• Confidence Level (Goodness of Fit)– Probability that the measurement errors are distributed within their expected range

𝑥𝑥𝑘𝑘 = 𝑓𝑓(𝑥𝑥𝑘𝑘−1) + 𝜔𝜔𝑘𝑘𝑧𝑧𝑘𝑘 = ℎ(𝑥𝑥𝑘𝑘) + 𝜈𝜈𝑘𝑘

estimated state 𝑥𝑥

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1

ˆ( ),m

i i

i i

h x zm nν ζσ=

−= − =

∑

A low confidence level (large ζ ) means something bad happens.

DSE-basedProtection

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DSE-Based Protection: HIL Test

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DSE-Based Protection: ExampleEvent: Transformer Fault

• 14.4/2.2kV, 1000 kVA single-phase saturable-core transformer

• A 5% turn-ground fault near neutral terminal of the transformer at 3.5 s

List of Measurements:

• 𝑉𝑉1,𝑉𝑉2: voltages at two sides

• 𝐼𝐼1, 𝐼𝐼2: currents at two sides

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Traditional Differential ProtectionSettings:• Operating Current:

• Restraining Current:

• Differential Ratio:

𝐼𝐼𝑜𝑜𝑜𝑜 = 𝑰𝑰𝑠𝑠1 + 𝑘𝑘𝑰𝑰𝑠𝑠2

𝐼𝐼𝑟𝑟𝑟𝑟𝑠𝑠 = 𝑰𝑰𝑠𝑠1

𝑅𝑅 = 𝐼𝐼𝑜𝑜𝑜𝑜/𝐼𝐼𝑟𝑟𝑟𝑟𝑠𝑠

Differential Relay Will Trip If:• Operating Current > 5 A, AND

• Differential Ratio > 15%

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Results: Differential Protection

<5 A

<15%

Traditional Differential Protection Relay MISSES the Fault

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Results: DSE-Based Protection

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DSE-Based Protection: a Generic Protection Scheme

“One of the most promising techniques to solve the protective challenges in next 10 years”― 2018 report “Future State of Protective Relaying” to

DOE

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Conventional Fault Location• Minimize labor and outage time.• Conventional methods:

– Single-ended algorithms

– Dual-ended algorithms

• Shortages:– Accuracy is affected by 𝑅𝑅𝐹𝐹 and line coupling– Require 3~4 cycles of measurements after the fault

Im( / )Im( )

S S

L

V ImZ

=

( )S R L R

L S R

V V Z ImZ I I− +

=+

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DSE-Based Fault LocationModify original DSE model to include the fault location as a variable 𝒎𝒎

Left Side Right Side

𝑦𝑦𝑘𝑘 = 𝑓𝑓(𝑦𝑦𝑘𝑘−1,𝑢𝑢𝑘𝑘−1) + 𝜔𝜔𝑘𝑘𝑧𝑧𝑘𝑘 = ℎ(𝑦𝑦𝑘𝑘 ,𝑢𝑢𝑘𝑘) + 𝜈𝜈𝑘𝑘

where 𝑦𝑦 = [𝑥𝑥,𝑚𝑚]𝑇𝑇

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DSE-Based Fault Location: Example

System Configuration

500 kV, 4330 MVA, 135 miles transmission line;

3 phase current and voltage instantaneous measurements at both terminals;

10 Ω A-N fault, every 10 milesfrom bus A1

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DSE-Based Fault Location: ResultsComparison Over the Line Sensitivity Studies

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Conclusions

• DSE-based protection can enhance relays dependability, security, and action speed; DSE-based fault location can accurately pinpoint the fault with less than one-cycle data

• The technology exists. We need to continue developments to bring these approaches to a practical level.

I would like to thank my colleagues at,PNNL: Renke Huang, Shaobu Wang, Tom McDermott, Zhenyu HuangGaTech: Sakis Meliopoulos, Yu Liu, Liangyi Sun, George Cokkinides , Zhenyu Tan