Distance Protection: Why Have We Started With a Circle, Does It Matter, and What Else Is Out There? What Is a Distance Protection Element?

Transcription

1 Distance Protection: Why Have We Started With a Circle, Does It Matter, and What Else Is Out There? Edmund O. Schweitzer, III and Bogdan Kasztenny Schweitzer Engineering Laboratories Copyright SEL 2017 What Is a Distance Protection Element? I Reach Setting V Z Reach Point Uses local voltage and current only Responds to faults within a predetermined reach Operates independently of fault current level, pre-fault load, fault type, or fault resistance 1

2 Distance Element Applications Line protection without a pilot channel Underreaching element (Zone 1) Stepped distance (time coordinated) Directional comparison schemes Applications that require impedance elements Out-of-step, power swing, loss of excitation Why Did We Start With a Circle? Trip Contact I N 1 Spring N 2 Pivot R V Z R N 1 I > V R N 2 V I < Z R Z R = R N 1 N 2 Directional Supervision 2

3 Z R Z EXT Innovation and Progress Directional Mho Characteristic Z R Z EXT Z R Z INT Z R Z INT Z R Z APP vs Z R Z R V I vs Z R I Z R V vs V Implementation With a Cylinder-Unit Relay S OP, S POL < ±90 I POL Trip Contact S POL = V I OP S OP = I Z R V Replica Current I POL I OP 3

4 Shaping Distance Characteristics Using Phase Comparators Directional Mho Z R Reverse Offset Mho Z R1 Forward Offset Mho Z R1 Z R2 Z R2 SOP = I ZR V SPOL = V SOP = I ZR1 V SPOL = (I ZR2 + V) SOP = I ZR1 V SPOL = I ZR2 V Shaping Distance Characteristics Using Phase Comparators Nondirectional Mho Reactance Resistive Blinder Z R Z R R B SOP = I ZR V SPOL = (I ZR + V) SOP = I ZR V SPOL = I ZR SOP = I RB V SPOL = I RB 4

5 Shaping Complex Characteristics Z R Enhanced Resistive Coverage Immunity to Load Encroachment Need for Speed, 1969 A.R. van C. Warrington Protective Relays Their Theory and Practice: Vol. 2: Faults on E.H.V. links must be cleared as fast as possible to prevent instability on the H.V. system. Modern relays can trip in less than 1 cycle but half-cycle tripping time is the desirable goal, making an overall clearing time of 2½ cycles. There is very little possibility of improvement in electromagnetic relays in these respects and this may be a reason for accelerating the acceptance of transistorized relays. Page 363 5

6 Static Implementations Analog machines with electronics Speed vs security is a design choice (filtering) Coincidence timing as a phase comparator S OP POS NEG Both Positive 0.25 cyc 0 MHO S POL POS NEG Both Negative 0.25 cyc 0 Microprocessor-Based Implementations First mp-based relays sampled at low rates Phasors were the only practical solution Cosine filter, or Fourier with mimic prefiltering Full-cycle band-pass filtering set the speed vs security balance Operating characteristics through calculations on complex numbers, such as I Z R V, V < ±90 6

7 Incremental Quantity Distance Element v PRE Dv F Dv, Di Line Parameters (Z1,Z0) TD Distance Intended Z1 Reach Voltage v PRE Dv F Internal Fault Actual Voltage Change at the Fault Local Bus Dv Di Pre-Fault Voltage Reach Point Calculated Voltage Change at the Reach Point Remote Bus If calculated voltage change at the reach point is Greater than calculated pre-fault voltage at the reach point, then OPERATE 7

8 External Fault Calculated Voltage Change at the Reach Point Local Bus Dv Di Reach Point Pre-Fault Voltage Actual Voltage Change at the Fault Remote Bus If calculated voltage change at the reach point is Lower than calculated pre-fault voltage at the reach point, then RESTRAIN General Implementation Line Data Reach Other Security Conditions Dv, Di v, i Calculations Dv REACH v PRE + _ In-Zone Fault Directional Supervision 8

9 Implementation Considerations Pre-Fault Voltage Reach Point Voltage Change in Voltage v PRE v REACH Dv REACH Calculated voltage change can be the magnitude of a phasor (hypothetical) Implementation Considerations Pre-Fault Voltage Reach Point Voltage Change in Voltage v PRE v REACH Dv REACH Calculated voltage change can be an edge or a step obtained with a high-pass filter (actual three-decade-old implementation) 9

10 Implementation Considerations Pre-Fault Voltage Reach Point Voltage Change in Voltage v PRE v REACH Dv REACH Calculated voltage change can be a time-domain value obtained via memory (actual modern implementation) CG Fault at 57% of Zone 1 on a 400 kv, 224 km Line 1.9 ms! 10

11 Voltage, kv Voltage, kv CG Fault at 57% of Zone 1 on a 400 kv, 224 km Line margin CG Fault on a 400 kv, 224 km Line Reach = 180% of fault location Reach = 110% of fault location Reach = 85% of fault location 11

12 Need for Speed, 2017 Median Operating (ms) SIR Values Fault Location in Percentage of Reach (%) Traveling-Wave Distance Zone 1 B S F R M LL M tfault = 0 2 M = t 4 t 1 M = LL 2 t 4 t 1 TWLPT LL TWLPT t 1 t 3 t 4 t t 4 t 1 TWLPT < 0.99 pu TRIP t 5 12

13 CG Fault at 78.8 km on a 400 kv, 224 km Line CG Fault at 78.8 km on a 400 kv, 224 km Line Raw Current Current TW 590 ms round trip time or 78.8 km one way distance 13

14 General Implementation Other Security Conditions TW Detection and -Stamping Subsystem t F t 1 Reach Setting + TW21 Directional Supervision Challenges Identifying the first return from the fault Faults close to either of the buses In-zone switching events TW attenuation and dispersion Same TW timing and polarity patterns at multiple buses 14

15 Measuring Voltage Traveling Waves Ideas for Retrofitting CCVTs Primary Voltage Tuning Reactor (a) Data Acquisition and F/O Communications Resistive Divider With Instrumentation Amplifiers (b) Data Acquisition and F/O Communications F/O to TW21 Relay F/O to TW21 Relay History of Distance Elements Electromechanical technology shaped the characteristics we use today Static technology introduced wide design choices Initially limited by processing power, mp technology reverted to speed of electromechanical relays Today s mp relays with very fast sampling and vast processing can implement any distance principle 15

16 Three Types of Distance Principles Apparent impedance elements: Incremental quantity elements: Traveling-wave elements: 1 cycle 2 ms 0.5 cycle 1 2 ms Progress in Distance Element Performance Speed Fast mp TW S mp TD mp Gen 2 Slow mp Gen 1 EM Security Low High 16

17 Conclusions Distance elements are a cornerstone of line protection We have not reached performance limits yet Today we have access to a phenomenal relay technology (ms sampling and processing) We have an obligation to continue to innovate 17