Line Protection Roy Moxley Siemens USA

Line Protection Roy Moxley Siemens USA Unrestricted Siemens AG 2017 siemens.com/digitalgrid

What is a Railroad s Biggest Asset? Rolling Stock Share-holders Relationships Shipping Contracts Employees (Engineers) Tracks and Right of Way

Transmission Lines are the Power System s Largest Asset

Exposed to Weather Self-Sustaining Arc Clear Quickly to Avoid Permanent Damage

How Do We Detect and Isolate Faults on Transmission Lines? Overcurrent Distance Differential Travelling Wave (?)

Overcurrent I>PU 1000 A Advantages: Simple Reliable Easy to Set

Overcurrent 900 A Advantages: Simple Reliable Easy to Set Disadvantages: Possible Overtripping Non-Directional Depends on Source Connected

Overcurrent 900 A Advantages: Simple Reliable Easy to Set Disadvantages: Possible Overtripping Non-Directional Depends on Source Solutions: Add Communications Add Directional Polarizing Change to Distance Protection

Distance IZ - V 3 Ω Advantages: Not Dependent on Source Current Fixed Reach Inherently Directional

Distance 3 Ω Disadvantages: Requires Potential Limited Resistance Coverage Impacted by Load Current and Power Swings Reach is Not Perfect

Distance 3 Ω Solutions: Monitor Loss of Potential Use Reactance Element to Increase Resistance Coverage (limited) Apply Power Swing Block / Trip and Load Cutout Add Communications

Differential Iin Iout Iin Iout Advantages: Sensitive Not Influenced by Load or Power Swings Provides Unit Protection, Doesn t Over Reach

Differential Iin Iout Disadvantages: 100% Communication Dependent CT Saturation Must be Accounted For No Inherent Backup

Differential Iin Iout Solutions: Monitor Communications Detect and Account for CT Saturation Provide Backup With No Communications or on Different Channel

Traveling Wave Advantages: Sensitive Minimal Settings Fast Precise Fault Location

Traveling Wave Disadvantages: 100% Dependent on Communications 100% Dependent on Clocks Difficult to Test No Inherent Backup Checkered Past Solutions: Yet to Determine

Every System Has Strengths and Weaknesses

Communications is King Overcomes Weakness Enhances Strengths

Two Basic Communication Schemes I See a Fault I See a Fault too I See a Fault I don t Not see a Fault Permissive: Permits a Trip Under Proper Conditions Blocking: Prevents a Trip on External Fault

Permissive I See a Fault I See a Fault too

Permissive I See a Fault? What If the Remote End Doesn t See the Fault? What if the Signal Doesn t get Through?

Blocking I See a Fault

Blocking I See a Fault What Happens if Block Signal is Late? What Happens if Overreaching Zone sees past Blocking Zone?

Hybrid Scheme I See a Fault Weak Infeed I See No Fault

Power Systems are Almost Never Simple A Line 1 C B Line 2 D Which Breaker Would Trip First? What Happens to the Fault Currents Then?

Power Systems are Almost Never Simple A Line 1 C Changed from forward to reverse Changed from reverse to forward B Line 2 D Timing Becomes Everything!

Three (or More) Terminals Save Money A B C Blocking or Permissive?

Sensitivity 3 Ω 18 Ω On Short Lines Ground Resistance Can Be Higher than Line Impedence But What Can Happen if we Just Increase Resistive Reach?

Load Flow and Sensitivity Load Trajectory

For Sensitivity; Ground Overcurrent or Differential 3 Ω 18 Ω I Diff I Diff N i 0 I i 1 2 3 trip area restraint I Res N i 0 I i area I Res

Differential Relays Have to Accommodate CT saturation relay measures a distorted current signal (red curve) relay calculates the fundamental frequency component (blue curve) deviation between both curves (green area) is a criteria for signal distortion relay determines restrained current depending this signal deviation

Restraining on Errors I I A I B Im I each I is the summation of: I i = I CT-Err. + I Signal-Err. + I Sync-Err. I A I Diff I A I I I B Res I Res_min I Re s _ min I A Trip if differential current exceeds sum of measurement errors I B I B Re I added by safety margin I Res_min

Protection / Communication topology R5 R6 Standard Two Six terminal For application terminal line with line for redundant -two communication terminal communication line: ring topology Three terminal line with communication chain channel line transformer in the protected area topology ring topology I 5 I 6 R1 I 1 I 3 I 4 I 2 R2 R3 R4

Special Conditions - Transformers in Zone Inrush? 2 nd Harmonic Restraint Ratio and Angle Correction for differential Reach for Distance Relay Will the relay see through the transformer for ground faults? Wind Farm

Special Conditions Tapped Loads and Infeed Tapped Loads 10,000 A 10,000 A 2Ω 3Ω Distance Without Infeed = Distance With Infeed =

Special Conditions Tapped Loads and Infeed Tapped Loads 10,000 A 10,000 A 2Ω 3Ω Distance Without Infeed = 5Ω Distance With Infeed = 8Ω

Special Conditions Combined Tapped Loads Differential Multi-terminal Distance Blocking Scheme Distance (no-comms) Sequential Tripping Photo Voltaic Major Industrials Wind Farm

Information sent to all Relays by Transmitting Partial Summation Addressed Data Sent Until All Terminals Have All the Data Relay 1 I1 I1 I2 +I3+I4+I5+I6 Relay 2 I2 I2 +I1 I3+I4 +I5+I6 Relay 3 I3+I2 +I1 I3 I4 I4 +I5+I6 Relay 4 I4+I3+I2 +I1 Hot Standby I6 Relay 6 I5+I4+I3+I2 +I1 I6 I5 Relay 5 I5 +I6

Set Reach to Inside Line With Maximum Infeed But What About Faults Beyond That? Relay 2 Relay 3 Relay 1 Relay 4 Relay 6 Relay 5

Sequential Tripping Clears Strongest Source First Best Stability Response Relay 2 Relay 3 Relay 1 Relay 4 Relay 6 Note: Shape shows reach, not characteristic of the relay Relay 5

Real-World Application Phu My Industrial Area New Plant 720 MW total from Three Units

Things Don t Always End Up How You Expect!! Who Me?

Initial Plans Were Pretty Standard 500 kv Station

Everything Wasn t Ready On Time Changes Connections 220 kv Station 450 MVA 500 / 220 kv 450 MVA 500 / 220 kv GT 1 GT 2 ST 3

Initial Communications Layout

As Installed Communications Layout GT 1 GT 2 ST 3

It s OK

Contact Roy Moxley Siemens Power Systems Protection Consultant Phone: 509-288-0847 E-mail: roy.moxley@siemens.com