GENERATOR PROTECTION @ MULTILIN GE Power Management Tecnology Center Haver, BA USAGenerator Protection General Considerations * Severe faults * Can cause damage to: — Insulation — Windings — Core * Can cause mechanical shock to: — Shatts — Couplings Generator Protection Topics « Stator Windings — Phase Faults — Tum-to-Tum Faults — Ground Faults * Rotor — Ground Fa © System Back-up — Phase Faults — Ground Faults ‘+ Abnormal Operating Conditions — Loss of Excitation — Unbalanced Stator Current — Overexcitation — Abnormal Frequency — Reverse Power Pe+ References + IEEE Guide for AC Generator Protection - C37.102 + IEEE Guide for Generator Ground Protection - C37.101 + IEEE Guide for Abnormal Frequency Protection for Power Generating Plant - C37.106 + IEEE Tutorial on the Protection of Synchronous Generators - 95 TP 102 + Generator Protection - GEK-75512 + Generating Station Protection - GET-6497 + Art and Science of Protective Relaying - Chapter 10 + Loss of Excitation - GER-3183 + Negative Sequence - GER-3181 + Out of Step - GER-3179 + HSR - System and Machine Considerations - GER-3224 + Performance Assessment of a New Digital Subsystem for Generator Protection - (Paper) ital Protection System PRO's CON's + Economy - Material and Labor + Redundancy + Enhanced Protections + Field Experience - Frequency Tracking = Configurable Inputs / Outputs + Peripheral Functions - Self Tests - Present Values - Communications - Sequence of Events Recording = Fault Report / Oscillography + Physical Size Pa) aus CONTROL PACKAGE @ (9) oe crs (PTs 3€ 600 VOLTS & BELOW OTHER TYPES OF GROUNDING MAY BE APPLICABLE RECOMMENDED MINIMUM PROTECTION FOR SMALL GENEATOR 1. 0-600 kVA, BELOW 5 kV 2 500-1000 kVA, BELOW 24kV Time Overcurrent Relay With Voltage Restraint (Type IFCV) 51G Time Overcurrent Ground Relay (Type 1FC53)O DISTRIBUTION ‘TRANSFORMER OVERVOLTAGE RELAY OVERVOLTAGE RELAYU Device SIV 51g 32 87 86 Bus GROUNDING MAY BE APPLICABLE RECOMMENDED PROTECTION FOR SMALL GENERATOR 1, 0-800 kVA, BELOW 8 KV 2. 600-1000 KVA, BELOW 24 kV Time Overcurrent Relay With Voltage Restraint (Type IFCV) Time Overcurrent Ground Relay (Type 1FC53) Phase Balance Relay (Type SGC) ‘Anti-Motoring Relay (Type ICW or GGP) Differential Relay (Type 1JD or CFD) Auxiliary Lockout Relay (Type HSA) PsSELF BALANCE DIFFERENTIAL,MINIMUM PROTECTOR FOR LARGE GENERATOR 1. 0-600 kVA, ABOVE 5 kV 2, 600-1000 kVA, ABOVE 2.4KV 3, ABOVE 1000 kVA, ANY VOLTAGE Device 51V__ Time Overcurrent Relay With Voltage Restraint (Type IFCV) 51G Time Overcurrent Ground Relay (Type IFC53) | 48 Phase Balance Relay (Type SGC) 40 Loss of Excitation Relay (Type DS2820A100 or CEH) 87 Differential Relay (Type IUD or CFD) > 86 Auxiliary Lockout Relay (Type HSA) PBRECOMMEND GENERATOR PACKAGE Device 51V_ Time Overcurrent Relay With Voltage Restraint (Type IFCV) 51G Time Overcurrent Ground Relay-Generator Neutral Grounded (Type IFC53) 50GS _Instantaneous Overcurrent Ground Relay-Generator Neutral Ungrounded (Type HFC) 32 Anti-Motoring Relay (Type ICW or GGP) 40 Loss of Field Relay (Type DS2820A100 or CEH) 46 Phase Balance Relay (Type SGC) 64F Field Ground Relay (Type PUG) 60V Loss of Potential Relay (Type CFVB) 59 ‘Overspeed Relay (Type IFV71) 87 Differential Relay (Type WWD or CFO) 87G _ Sensitive Ground Differential Relay (Type FD) 86 Auxiliary Lockout Relay (Type HSA) PaPhase Fault Stator Winding Protection Variable Slope % Diff Relay Generator Stator C2 ‘Winging ) Phase Fault Stator Winding Protection ~ Variable Slope % Diff Relay * Variable slope minimizes chance of misoperation during external fault * Use identical CT's * Consequences of phase faults severe, but are very rare; Isolated phase bus * Detects all phase and some ground faults * High R grounded fault currents too low! * Simultaneous tripPhase Fault Backup Stator Windings Overall differential Primary protection for transformer and buswork Backup for generator Less sensitive and slower than generator differential (CFD) Simultaneous trip panStator Winding Turn-Turn Faults Split Phase Protection Using Separate Bushing CT’s + Hydro machines have — Multiple turns per slot — Multiple circuits per phase * Differentially connected 50/51 relay “compares” current In each circuit * Difference indicates tum-to-tumn fault + 50 must be set insensitively due to — Normal unbalance — CT mismatch Stator Winding Turn-Turn Faults Split Phase Protection Using Single Window CT * Single CT per phase eliminates CT mismatch problems * Differential current caused by differential flux «50 can be set more sensitively ‘ Detects some phase and ground faults + Simultaneous tripGenerator Grounding St re Ts eg * Zee Sequence Capacv Retctnce wal} El}e PERERA ci yd Generator Grounding * ho Vug = Vig: Veu = 5.4V, #10 TD =>4 sec #10 TD (4 sec) coordinates with system relays. + Vo = >0 for fault at N ‘+ Relay protects 95-97% of winding * Simultaneous tripping Stator Winding Ground Fault Protection (cont'd) Also Ip = 0 for fault at N Need to clear in case another occurs; then machine is solidly grounded! Normally Ves # 0 * Fault at N= >Vyo: ‘ould use third harmenic undervoltage relay to protect remaining 3-5% * Many other methods used PasG Coordination - Stator Ground Relay Capacitance Between Wingings 4 sk ‘SLG a je Te) TT Fw * SLG fault on system causes zero sequence voltage * Voltage can couple to generator side through capacitance between GSU windings ‘* 1AV must coordinate with system ground fault protection (if system relaying is overcurrent) P16Coordination - Stator Ground Relay Coordination - Stator Ground Relay PT secondary fault may be detected before fuse can blow Could remove generator for PT fault — very bad! Solution: Ground one phase instead of neutral Line-line voltage across fuse during phase A or phase C fault Then fuse and IAV probably coordinate patRotor ield Ground Protection Exciter mt Rotor Field Ground Protection * Ifinsulation between field and rotor breaks down, ground fault occurs © Shorts part of windings = > unbalanced flux * Detect with instantaneous DC relay with timer © Timer prevents operation due to transients caused by fast excitation response ‘+ Recommend simultaneous trip — sequential sometimes used, some alarm PagLoss of Excitation Protection * Loss of field — short or open * No magnetic field * Rotor still driven; so power produced * Generator derives excitation from system — Induction generator * Problems! — Rotor overspeeds — Draws Vars, --Voltage pulsates — Current pulsates (2¥2x Normal) * Z looking into generator varies! pagLoss of Excitation Protection Loss of Excitation Characteristics for a Tandem Compound Generator er Unit impedance Loss of Excitation Protection Stable Transient Swing-Generator Initially Operating at 0.95 Leading Power Factor i un Feu an ar el t Oat 1 a C ln Max Time ¥ wd bee —f Per Unit Impedance P20“) Generator Protection Using Two Loss of Excitation Relays, One CEH52A Relay x I 2 Diameter = 10PU LL (No Times Delay) Diameter = (Ys sec Time] x | Delay) ‘ Utilizes 2 offset MHO characteristics ‘¢ Results in simultaneous or generator tripUnbalanced Stator Current Protection 8B ee at po —| le Lemna te Leh #le * Unbalanced currents caused by: - = Yreymmetrical faults + Result in Ig and lp Unbalanced Stator Current Protection Rotor End Section of Generator Including Retaining Ring Retaining Ring ‘* Generators hate lp * Icauses: = 120H2 rotor currents — Excessive heating in retaining ring, slot wedges and field windingoO Unbalanced Stator Current Protection ‘Table | ANSI Requirements for Unbalanced Faults on Synchronous Machines Permissible 17t ‘Types of Synchronous Machine (lz in Per Unit) Sallent pole generator" 40 ‘Synchronous condenser* 30 Cylindrical rotor generators** Indirectly cooled 30 Directly cooled (0-800 MVA) 10 Directly cooled (801-1600 MVA) See Next Slide ANSI C-s0:12 ANSI C50: Negative-Sequence Fault Current Capability for Directly Cooled Generators (per ANSI C50.13) eta ft 10, -(00625)(MVA - 800) tin Per Unit “400 00 7200 7600 Generator MVA RatingUnbalanced Stator Current Protection Table I! Continuous Unbalanced Current Capability Permissible lp ‘Type of Generator and Rating (percent) Salient Pole With connected amortisseur windings 10 With non-connected amortisseur windings 5 Cylindrical Rotor Indirectly cooled 10 Directly cooled to 960 MVA 8 961 to 1200 MVA 6 1201 to 1500 MVA 5Unbalanced Stator Current Protection <$ Negatve sequence ET) Tee orcaeey = ‘Compare Electromechanical (INC) ‘and Static (SGC) Unbalanced Stator Current Protection Typical Time-Current Curve for Electromechanical INC Relay 121 Generate Capadites — Relay Charactratics for Aanous Time Olt Setings + Minimum sensitivity ~0.6 PU B88 88 ‘© Relay curves cross generator capability curves * Designed to detect unbalanced, uncleared system faults “Time (seconde) £88. e7a1otsa0 2456 810 eu) P25,Unbalanced Stator Current Protection Generator Negative Sequence Currents with Open Conductor ‘Open Conductor X=02PU. Number of Lines (PU) 1 06 2 0.09 3 0.05 * INC sensitivity inadequate for open conductor * Coordination with capability curves difficult Unbalanced Stator Current Protection Characteristics of the SGC Static Negative ‘Sequence Time Overcurrent Relay aes 3 888 “Time In Seconds a aos 1 228 1 295 0 er Unt P26Unbalanced Stator Current Protection oo) Application of the SGC Relay on an 800 MVA 2-Pole Directly Cooled Generator “Time tn Second & ange oy —l ‘Open Conductor Range oy O2b tee systema af ) ‘+ Generator trip if auxillaries permit © Simultaneous trip, if notOverexcitation Protection * Regulator left in service during startup and shutdown © ITE constant and f |, then 1 + Flux enters non-laminated parts of generator and transformer magnetic core, :.Severe overheating ‘© Trip generator and field breakers 5 Overexcitation Protection General Guide for Permissible Short-Time Overexcitation of Generator Step-up Transformers x TTS eodeo] 7 ree ea Bas 7° een a: Ath sore, 15 L ui " tf one Ton 1 2845 10 2345 10 20904050 100 ‘Time (Minutes) P20) Overexcitation Protection STV Volts/Hz Relay ' (s 7 p= \_s™%) % v= T> damicR © Simultaneous trip amicr > 1 v= kt KSTurbine Abnormal Frequency Protection ) + Overspeed caused by load rejection * Not a problem, operator or automatic control can fore normal speed Underspeed caused by loss of generation Load shedding takes long time to restore normal speed Possibility of turbine damage most critical P30Turbine Abnormal Frequency Protection ‘Turbine Off-Frequency Limits 0.5 Hz Frequency Bands * Vibrations caused — different modes for different frequencies * Blade covers and tie wires can crack + Generator trip Turbine Abnormal Frequency Protection Failure modes are different for different bands. Failure modes are dependent on cumulative time within band Detect cumulative time within bands using “N” Generator trip or PatTurbine Abnormal Frequency Protection Three Step Under Frequency Protective Scheme Using One Relay and One Timer Per Step Fa [ i F,, Fyand F, — Frequency el Ty Tpand T — Timers wtReverse Power Protection Caused when energy supply to prime mover Is cut off Generator drives turbine = >Motor! Heating due to “windage” losses in turbine and slip frequency currents Heating causes abnormal contraction and expansion of parts, Maximum time turbine can operate Power directional relay (GGP 53C) set between 0.5 and 3.0% (setting a function of load and turbine idling losses) Time delay (30 sec) ‘Turbine trip PasBackup Protection for System Faults O ‘« I system relays are distance relays — Use CEB, overeach longest fi | simultaneous trip * If system relays are overcurrent — Use IFCY, voltage restrained overcurrent relay, generator trip out of station, TD <1 sec, Backup Protection for System Faults Problem-Setting of CEB Backup Relay ces Prose * Large CEB setting may result ‘* Danger of tripping on load or swing * If false tripping possible, set to detect only bus fault ) and use redundant transmission line relaying Pst