Calculations of Protective Relay Setting

ABSTRACT CALCULATIONS OF PROTECTIVE RELAY SETTINGS FOR A UNIT GENERATOR FOLLOWING CATASTROPHIC FAILURE by Jaime Anthony Ybarra December 2011 After a catastrophic failure of a unit generator system the major components may need to be replaced Many times exact replacement of the failed or damaged components may not be possible In such a case components with electrical characteristics as close to the original may be used Therefore new protective relay settings must be calculated In this thesis, we will examine a type of generator protection relays, evaluate new settings and develop a one-line diagram for a 25 MVA generator system A methodology for the development of a safe and reliable protections scheme for a unit generator system is also presented CALCULATIONS OF PROTECTIVE RELAY SETTINGS FOR A UNIT GENERATOR FOLLOWING CATASTROPHIC FAILURE A THESIS Presented to the Department of Electrical Engineering California State University, Long Beach In Partial Fulfillment of the Requirements for the Degree Master of Science in Electrical Engineering Committee Members: Hassan Mohamed-Nour, Ph.D (Chair) Mohammad Talebi, Ph.D Hen-Geul (Henry) Yeh, Ph.D., P.E College Designee: James Ary, Ph.D By Jaime Anthony Ybarra B.S., 1999, California State University, Long Beach December 2011 UMI Number: 150766 All rghts reserve INFORMATION TO ALL USER The qualty of this reproduction is dependent on the quality of the copy su In the unlikely event that the author did not send a complete man and there are missing pages, these will be noted, Also, if material had to be a note will indicate the deleti UMI 150766 Copyright 2012 by ProQuest L All rghts reserved This edition of the work is protected a unauthorized copyng under Title 17, United States C ProQuest LLC 789 East Eisenhower Parkws P.O Box 134 Ann Arbor, Ml 48106-1 TABLE OF CONTENTS Page LIST OF TABLES v LIST OF FIGURES vi CHAPTER INTRODUCTION GENERATOR COMPONENTS AND PROTECTION SCHEME The Transformer Short Circuit Per Unit Quantities One Line Diagram Relay and Control Symbols Elementary Diagrams 10 11 14 15 UNIT GENERATOR PROTECTION RELAYS Volt/Hertz relay (24) Synchronizing Check Relay (25) Under Voltage Relay (27) Directional Reverse Power Relay (32) Loss of Excitation (Field) Relay (40) Negative Sequence or Unbalance Relay (46) Stator Temperature Relay (49) Inadvertent Energization Protection Relay (50) Voltage Controlled Over Current Relay (51V) Over Voltage Relay (59) Voltage Balance Relay (60) Sudden Pressure Relay (63) Field Ground Relay (64F) Oil Level Relay (71) Out Of Step Relay (78) Frequency Relays (81) Lock Out Relay (86) iii 18 18 20 20 21 21 23 24 25 25 26 26 27 27 27 28 29 31 CHAPTER Page Differential Relay (87) 31 SETTINGS CALCULATIONS AND EXPERIMENTAL RESULTS Preliminary Calculations 33 34 Typical Relay Settings Calculations and Verification with Experiment 5 CONCLUSIONS 52 REFERENCES 54 iv LIST OF TABLES Page Sample Generator Parameters 33 Sample Unit Transformer Parameters 34 Relay Volt/Hertz Experimental Test Result 37 Under Voltage Test Result 38 Reverse Power Test Result 39 Zone Test Result 41 Loss of Excitation Zone Reach Test Result 41 Current Unbalance Pickups for A, B and C Phases 42 Voltage Controlled Over Current Test Results 43 Over Voltage Relay Test Result 44 Relay Reverse and Forward Reach Z Test Results 46 Relay Right Blinder Reach Z Test Result 46 Left Blinder Reach Z Test Result 47 Equipment Summary Table 48 Relay Settings Summary Table 49 v LIST OF FIGURES Page Graphical representation of phase power generation Basic structure of a cylindrical rotor Brushless excitation system Wye connected windings Phase fault with DC component offset Short circuit waveform showing the three transient periods Typical electrical symbols 12 Waveform output with polarities in phase 13 Waveform output with polarities reversed 14 Unit connected generator protection with typical relays 16 Basic elementary diagram 17 Various volts/hertz limit curves 19 Generator, transformer and relay plot for volts/hertz relay plot 20 zone protection diagram 22 Typical negative sequence relay curve 24 Out of step protection zone 29 Representation of differential protection 31 vi FIGURE Page 18 Experimental setup 36 19 RMS TIME vs VOLTS of volt/hertz relay (24) operation 37 20 Under voltage (27) relay operation graph 38 21 phase vector diagram of reverse power relay (32) 39 22 Zone reach impedance and phase angle relationship 40 23 Loss of excitation zone reach test 40 24 Loss of excitation zone reach test 41 25 Unbalance A, B and C phases 42 26 Voltage control relay (51C) results 43 27 Voltage controlled relay (51C) RMS trip graph 44 28 Over voltage relay (59) result plot 44 29 Loss of Synchronization protection boundaries 45 30 Forward reach results 45 31 Reverse blinder result 46 32 Right blinder result 46 33 Left blinder result 46 34 Sample system one line 50 vii CHAPTER INTRODUCTION A generator system is designed to provide electric power to customers reliably Failure of any electric component such as the generator, unit-transformer or auxiliary transformers can lead to catastrophic damage If any of these components are damaged beyond repair then they must be repaired or replaced However, due to age and customized engineered system components exact replacements may not be available or the time for new components to be manufactured may not be economically viable The generator owner or user may have to purchase readably available equipment with capabilities as close as possible to original components If this is the case new protective device settings must be calculated to properly protect the generation In the event of the replacement of any of the components the following basic steps are recommended: Calculate the new capabilities of the generation system Calculate protective device settings based on new system Develop or update electric system single line diagrams (one-lines) to describe the basic layout of the electrical system as well as basic information of the major components Verify that the relays will operate as programed or set with simulation of fault conditions inherent to that protective device constant then raised above the threshold before trip Phases B and C the current is ramped up to trip, Note phase lower than other phases FIGURE 25 Unbalance A9 B and C phases TABLE Relay Current Unbalance Pickups for A9 B and C Phases PickupCurrent A PHASE (Amps) 0.90 PickupCurrent B PHASE (Amps) 0.91 PickupCurrent C PHASE (Amps) 0.91 CalcPickup A PHASE (Amps) 0.88 CalcPickup B PHASE (Amps) 88 CalcPickup C PHASE (Amps) 0.88 MinRange A PHASE (Amps) 0.84 MinRange B PHASE (Amps) 0.84 MinRange C PHASE (Amps) 84 MaxRange A PHASE (Amps) 0.93 MaxRange B PHASE (Amps) 0.93 MaxRange C PHASE (Amps) 93 Error A PHASE (%) 2.46 Error B PHASE (%) 3.54 Error C PHASE (%) 3.60 Pass/Fail Pass Pass Pass Voltage controlled relay (51C): Set relay to pickup up the voltage control unit at 75% of rated voltage and the overcurrent pickup at 50% of the generator full-load current 51C OC pickup = 18 x 50 - 09A 51C undervoltage element pickup = 69 28 * 75 = 52V 42 Time Vs Current Multiples of Ptctajp FIGURE 26 Voltage control relay (51C) results TABLE Voltage Controlled Over Current Test Results Multiplier Applied ExpectedJTime Error MinRange Time (Seconds) (Amps) (Seconds) (Seconds) (X Pickup) (%) 6.00 3.7197 0.91 3.7539 3.55 0000 10.00 19 0000 1.3598 1.3573 1.28 14.00 0, 7666 0.71 7620 0000 -0.61 Note that OC unit does not occur until voltage drops, FIGURE 27, Voltage controlled relay (51C) RMS trip graph, 43 MaxRange (Seconds) 3.89 1.44 0.82 Pass/Fail Pass Pass Pass Over Voltage Relay (59): For our experiment set the over voltage threshold to 110% of the nominal line to neutral voltage 1.10 x 69 28= 10 x 69 28 = 76 2V Figure 28 Over voltage relay (59) result plot TABLE 10 Over Voltage Relay Test Result Pickup (Volts) 76.70 ExpectedPU (Volts) 76.21 Error 0.64 MinRange (Volts) 72.40 IVfaxRange (Volts) 80.02 Pass/Fail Pass Loss of synchronization relay (78) For our example the Xsystem = 00 with p = 90 and = 120 with the assumption that no stability studies are available and there is no information on the system d (blinder distance) = (3 25 + 02 + 0)/2 x tan(30) = 23 fl or 2fortests MHO unit diameter = (2 x 25 + x 02) = 03 Q with impedance angle of 90 and a time delay of 50 ms> Theforwardreach (lower circle portion) is2x3 s 25 :=:: s and the reverse reach is L x 02 = 53 for our experiment use Again using the fact that I = Volts/Z we calculate thefollowingvalues, a, Forward reach current I = 69 28/6 = 10, 65A 44 b Reverse reach current I = 69, 28/1 = 46, 19A note that this is exceeds typical phase test equipment Since we are interested in the current and the impedance is fixed we can use a lower voltage to calculate a suitable I Use 20V and calculate I 20V/1 = 13 3A c Right Blinder the current phases are rotated as to allow the impedance vector approach from right to left as in b above 20V/1.2 = 16 67A d Left Blinder the current phases are rotated to allow the impedance to approach from left to right I is 20V/1.2=16 67A The protection zone are bound by these values (see Figure 29), 90 Reverse reach 180 11 9.0 7,0 _JV "^< s.o f6 Right Blinder .,_ ***** i 7§ 9.0 110 Left Blinder Relay will trip inside circle and Forward reach inside left and ~ — right Blinder lines, —J 270 FIGURE 29, Loss of Synchronization protection boundaries, Reverse and forward reach experimental results Voltage A j Voltage B j [ f ™ blF* Voltage c j Current B | Cur rent A j | 20.000V* f"""" 240.0 13J?? A r pESoW [^SOOOHT FIGURE 30 Forward reach results 45 Current C I f nJffK [ mor Voltage A J Voltage e l Voltage C J [ "™5S5So'v | p ™ l o ^ v " f" o.o* i [ P'OSOOOHZ"* H^oX - f 1337? A" j *""* 13.377 A [~"T£o Current € Current B Current A v 210,0 * j [ 13.37? A ["~5bo.or W Hz [ lo~OQOHz" FIGURE 31 Re¥erse reach results, TABLE 11 Relay Reverse and Forward Reach Z Test Results Volts Current (Amps) 13.38 Current Angle (Degrees) 90.00 Angle ZJREV (Ohms) 1.50 Z^FWD Ideal Z REV (Ohms) 1.50 IdealJZJWD (Volts) (Amps) (Degrees) (Ohms) (Ohms) 20.00 10.69 270 00 6.483 6.500 Volts (Volts) 20.00 Voltage B j VoltageAj Votlage C J 16.712 A 0.0« 60.000 Hz oo.ooo Hz 240.0 j 60.000 Hz -0.33 -0.26 Current B Current A %error I Current C 16.712A pgo^SflMHT FIGURE 32, Relay right blinder result TABLE 12, Relay Right Blinder Reach Z Test Result Volts (Volts) 20.00 Angle (Degrees) 0.00 Current (Amps) 16.71 | 20.000 V | 0.6 * | 60.000 Hz Voltage C I VoftageBJ Voltage A r 20.000 V j 20.000 V 10,012 A r'^oooHir I 1*0.000 Hz j 00.000 Hz m m tsar FIGURE 33 Left blinder result 46 -0.27 Current I Current A f %error IdeaLZ (Ohms) 1.20 ZJ78R1 (Ohms) 1.20 Current C | 16.612 A f ISJUA [ 300.0 * [ 00.0 * psbSoo HT | 60,000 Hz TABLE 13 Left Blinder Reach Z Test Result Volts (Volts) 20.00 Current (Amps) 16.61 Angle (Degrees) 180 00 Z_78R2 (Ohms) 1.20 ldeal_Z (Ohms) 1.20 %error 0.33 The settings results can then be summarized on a table which can be provided to the personnel programing and setting the relays Note that all CT ratios are based on 5A secondary and PT are based on 120V secondary Only settings that required calculations are on Table 14 Settings that require curve selection and not included 47 TABLE 14 Equipment Summary Table Generator Data MVA Xd X'd X"d X2 Voltage ( k V ) Power Factor (pf) PT Ratio PT Configuration D/Y CT Ratio Generator Differential CT Ratio Unit Differential Generator Grounding transformer ratio Grounding transformer resistor 25 1.15 196 136 129 14.40 85 120:1 Y 240:1 240:1 60:1 25Q Unit Step up Transformer Data MVA Primary Voltage ( kV ) (adjust tap for +4%) Secondary Voltage ( kV ) Transformer nameplate impedance Primary Full Load Amps Secondary Full Load Amps CT Ratio Phase Primary CT Ratio Phase Secondary Grounding method 30.0 13.8 36.0 8% 1255 481 300:1 120:1 Solid Auxiliary Transformer Data MVA Primary Voltage (kV ) Secondary Voltage (kV ) Nameplate impedance CT Ratio Primary CT Ration Secondary Grounding method 14.4 480 5% 25:1 800:1 Solid 48 TABLE 15 Relay Settings Summary Table Relay Function 25 Over Excitation 27 Under Voltage Trip 32 Reverse Power 40 Loss of Field (Negative offset MHO) Zone Diameter Zone Offset Zone Diameter Zone Offset 46 Current Unbalance Relay 51V Voltage controlled Over Current Relay 59 Over Voltage Trip 78 Loss of Synch Relay Left and right binders MHO diameter Forward reach Reverse reach 49 Pickup 105% 62.4V 21A@120V seconds 50 seconds 16.59ft -1.62ft 19.07 ft -1.62ft 7%, K=9 2.09A @ 52V 76.2V minute linear reset Inverse time curve 10 seconds 1.2ft 8.03ft 6.5 ft 1.5 ft Delay 50 milliseconds 36KV 600A ) O GFCT ( FIGURE 34 Sample system one-line * j ' ' I* 13.8KV-480V CHAPTER CONCLUSIONS A procedure for protective relay settings for a 25MVA generator has been presented An AC generator system that has experienced catastrophic failure may have one or more major components repaired or replaced Due to either obsolescence or long delivery time exact replacements may not be available therefore recalculations and verification of new relay settings are necessary The following conclusions are drawn from the presented study Basic knowledge of generators, transformer, characteristic of short circuits and the variables that are used to express how the magnitudes will manifest during a fault are important for the engineer to understand prior to integrating replacement electrical components into the repaired system In order to develop settings for relays that will be protecting replacement components that may not have the same electrical characteristics, thorough familiarity with the protective relays, magnitude sensing devices and there unique functions are necessary In order to achieve the highest reliability the new system should be based on available standards and the consequences of omitting a protective relay must be carefully evaluated 51 Once replacement components have been obtained and installed, develop or update one-line diagrams which will represent the generator, transformers and circuit breaker system In order to reduce the chance of settings errors all electrical information needs to be gathered and documented prior to placing the generation system back online Once electrical and control diagrams have been developed calculations to convert primary quantities into secondary quantities are performed to set all relays Prior to a generator system being place back into service A phase power systems simulator is used to verity the proper operation of the protective relays and all results documented This procedure may be applied to a unit configured AC generator 52 REFERENCES 53 REFERENCES [I] IEEE Power & Energy Society "IEEE guide for AC generator protection." IEEE Std C37.102-2006 (Revision of IEEE Std C37.102-1995), 2006 [2] IEEE Power & Energy Society " IEEE guide for generator ground protection." IEEE Std C37.101-2006, 2007 [3] IEEE Power & Energy Society "IEEE standard for electrical power system device function numbers, acronyms, and contact designations." IEEE Std C37.2- 2008, 2008 [4] IEEE Power & Energy Society "IEEE guide for abnormal frequency protection for power generating plants." IEEE Std C37.106-2003, 2004 [5] IEEE Power & Energy Society "IEEE standard for cylindrical-rotor 50 Hz and 60 Hz synchronous generators rated 10 MVA and above.",IEEE Std C50 13-2005, 2006 [6] IEEE Power & Energy Society "IEEE recommended practice for electric power distribution for industrial plants." IEEE Std 141-1993, 1994 [7] IEEE Power & Energy Society "IEEE recommended practice for protection and coordination of industrial and commercial power systems." IEEE Std 242-2001 (Revision of IEEE Std 242-1986) [IEEE Buff Book], 2001 [8] IEEE Power & Energy Society "IEEE recommended practice for grounding of industrial and commercial power systems." IEEE Std 142-2007 (Revision of IEEE Std 142-1991), 2001 [9] Donald Reimert Protective Relaying for Power Generation Systems Boca Raton, FL: CRC Press, 2006 [10] ABB Power T&D Company Inc Electrical Transmission and Distribution Reference Book Raleigh, NC: ABB Power T&D Company Inc, 1997 [II] IEEE Power & Energy Society "IEEE Standards Dictionary: Glossary of Terms & Definitions." New York, NY: IEEE, 2009 54 [12] IEEE Power & Energy Society IEEE Tutorial on the Protection ofSynchronous Generators (Publication 95 TP 102) Piscataway, NJ: IEEE, 1995 [13] Megger Inc Instructional Manual for MPRT Protective Relay Test System, 710000 Dallas, TX: Megger Inc., 2010 [ 14] Megger Inc Instructional Manual for A VTS 4.0 Advanced Visual Test Software Dallas, TX: Megger Inc., 2010 [15] Schweitzer Engineering Laboratories Instruction Manual for SEL-700G Generator Protection Relay, 20110324 Pullman, WA: Schweitzer Engineering Laboratories, 2011 55 [...]... CHAPTER 3 UNIT GENERATOR PROTECTION RELAYS A wide variety of relays are required to protect a generator system Each type of relay will protect the system from a particular type of abnormality If electro-mechanical relays are used it may require up to 3 relays of a single type to protect each phase of a 3 phase system However, with the advent of microprocessor based relays many fiinctions if not all are... recalculation of protective relay settings of a generator protection system with replacement components that do not have the same ratings or capabilities as the original and will require new protective relay settings calculations Chapter 2 will discuss generating system component and electrical fundamentals as well as the symbols used to describe an electrical system Chapter 3 will describe protective relay. .. for use in the relay Time delays are of 1 seconds for Zone 1 and 5 seconds for Zone 2 are suggested Zone 1 (inner circle) is commonly set to 1 0 pu of impedance Z The offset of the inner and outer circle X is the negative quantity of the half the transient reactance The diameter of the outer circle is equal to the direct access transient with the offset being equal to that of the Zone 1 offset Note that... instead of providing it to the system Heavy currents will also be induced into the rotor teeth and wedges which will cause thermal damage to the generator if allowed to operate in this condition Common causes of excitation loss can be operator error, excitation system failure, accidental tripping of the field breakers or flashover of the exciter commutator A type of 40 relay is called an offset MHO relay. .. similar transformer curve can be obtained and the relay set to protect both (see Figure 12) 19 130- t 120- RELAY CHARACTERISTIC too 01 TIME (MINUTES) FIGURE 13 Generator, transformer and relay plot for volts/hertz relay plot [1] Synchronizing Check Relay (25) A 25 sync check relay is used to check whether or not two separate portions of a system are of similar phasor quantities such as phase, frequency... operation of the 50 for a period of time so that it will not operate if there are short term instabilities in voltage or frequency levels and arm the 50 relay when the generator is taken out of service Voltage Controlled Over Current Relay (51V) Voltage Controlled Over-Current relay is used to provide protection against a prolonged fault contribution by the generator The basic operation of the relay is... This many relays are required due to the large capital investment of not only the generator and transformer, but the stability of the system The following sections will describe the typical types of relays used in generator protection Not all relays are used in every instance, but a thorough review is necessary to allow the protection engineer to decide if the application warrants the inclusion of a certain... the pickup of the over-current unit is not activated until there is a voltage drop due to a short circuit out in the system The further the fault is from the generator the lower the magnitude of the voltage drop 25 The relay received its input from potential transformers and works in conjunction with the 60 relay If a 60 relay detects a blown fuse it will block the operation of the 51V relay due to... 51V relay due to voltage input being lost due to the blown fuse Typical settings for the overcurrent unit is 50% of the full load current if the activation voltage level is 75% of the rated voltage Over Voltage Relay (59) The over voltage relay is used to senses above normal voltage magnitude Another important use of an over voltage relay is for ground fault protection in impedance grounded generators... FIGURE 5 3 Phase fault with DC component offset [12] 8 A"' d Subtransicnt reactance: Is the reactance of a generator at the initiation of a fault and is used in calculations of the initial asymmetrical fault current (see Figure 6) The current continuously decreases lasting approximately 0.05 s after an applied fault [1] vY"d Transient reactance: Is the reactance of a generator between the subtransienl ... _ Base relay "" 40 ~~ l — 69 - _69.287_ ^Base relay ~~ A * JCA "~" ^ Typical Relay Settings Calculations and Verification with Experiment The following are the calculations for relays settings... offset MHO relay Zone offset (relay) = - 098 x 16 59 = - 62 Q Zone diameter Zeasejeiay = 16.59 O Zone diameter (relay) = | - 15 x 16 59 | = 19 07 O or 19 Zone offset (relay) = Zone offset (relay) ... 27 28 29 31 CHAPTER Page Differential Relay (87) 31 SETTINGS CALCULATIONS AND EXPERIMENTAL RESULTS Preliminary Calculations 33 34 Typical Relay Settings Calculations and Verification with Experiment