b) Thời gian chỉnh định: từ 0 đến 99s, bước chỉnh 0,01s; c) Tốc độ thay đổi tần số: từ 0 đến 9,9Hzs, bước chỉnh 0,1Hzs; d) Thời gian trễ: nhỏ hơn 0,1s; đ) Khoá điện áp: lựa chọn từ 55 đến 90% điện áp danh định; e) Các mức chỉnh định: 4 mức theo tần số và 2 mức theo tốc độ thay đổi tần số; g) Tiếp điểm đầu ra: ít nhất 3 tiếp điểm cho mỗi mức. 6. Trình tự phục hồi phụ tải khi tần số tăng trở lại bình thường phải tuân thủ theo mệnh lệnh của Trung tâm Điều độ hệ thống điện có thẩm quyền.
2011-07-24 Generator Protection & Testing Solutions Andreas Schröcker, OMICRON electronics Hanoi: 1st + 2nd of August HCMC: 4th + 5th of August 24 July 2011 Page Chain of Energy Conversion Primary Energy Mechanical Energy Electrical Energy Consumer Source Generator Turbine Consumer Page Generator - How does it work? Mechanical Energy (Turbine) Frequency (Speed) Active Power + - When it is connected to the Network Magnetic Field (Excitation System) Control EMF Voltage Reactive Power Voltage Output Active & Reactive Power (Apparent Power) Page 2011-07-24 Excitation System © VATech Hydro Andritz Page Step Up Transformer Control Room LV Switchgear AC&DC Auxiliary System PT HV Breaker PT Busbar Synch Aux.Transf Gen Breaker CT&PT Governor Turbine Control Systems Gen Protection Excitation Transf Excitation System Generator Page Generator Faults & Abnormal Operations Mechanical Vibration Speed Faults & Abnormal Operations Voltage Electrical Temperature Current Heating Frequency Page 2011-07-24 Fault Categories & Abnormal Conditions that can be detected electrically Major Electrical Faults Short-Circuit in Stator Winding Failure in Excitation System Abnormal Prime Mover (Control) Failure of Prime Mover Over-Frequency Over-Fluxing Dead Machine Energization System Related Feeding an Uncleared Fault Heavy Unbalanced Loading Prolonged or Heavy Overload Loss of Synchronism Over-Frequency Under-Frequency Over-Fluxing Under-Voltage Page Protection Functions ANSI PROTECTION 87G Percentage Differential 87G High-Impedance Differential 50/51 Phase Overcurrent 67 Phase Directional Overcurrent 51V Voltage Dependant Overcurrent 21 Under-Impedance Protection 27 Under-Voltage 59 Over-Voltage 81U Under-Frequency 81O Over-Frequency 40 Loss of Excitation (Impedance) 46 Negative Sequence Overcurrent 32F/32R Low Forward Power / Reverse Power 50N/51N Earth Fault Overcurrent & Sensitive Earth-Fault Page Protection Functions ANSI PROTECTION 59N Residual Overvoltage (90% Stator Earth Fault) 67N Directional Earth-Fault 87N Restricted Earth-Fault 59TN/27TN 100% Stator Earth-Fault 64R Rotor Earth-Fault 24 Over-Excitation, Over-Fluxing, (Volts/Hertz) 68 Out of Step Dead Machine Energization Page 2011-07-24 Protection CTs & VTs Neutral CT Terminal CT Core Balance CT G DYn Starpoint CT Terminal PT Open Delta G 3V0 Starpoint PT Page 10 Testing of Generator Protection Functions Sample Relay: Manufacturer: Type: Function: Siemens 7UM621 Multifunctional Machine Protection Page 11 Connection Diagram Page 12 2011-07-24 SIDE2 (Neutral CT) CT Input, for specific protection function Terminal PT 3V0 Input SIDE1 (Terminal CT) CT Input, for specific protection function Page 13 Application Example Page 14 SIDE1 (Terminal CT) SIDE2 (Neutral CT) Page 15 2011-07-24 Settings Generator / CT / PT INom,Machine,Primary = MVA ×1000 /(√3×kV) A 482.97 A INom,Machine,Secondary = [MVA ×1000 /(√3×kV)]/CTRatio A 0.9659 A © OMICRON Academy Page 16 Generator Differential Protection (Low Impedance) This protection function will be used to protect any short-circuits or faults inside the stator winding Requirement is the availability of x CTs on both sides of the stator (Neutral and Terminal side) Normally used for larger generators (e.g > 2MW) The characteristic depend on CTs (ratio mismatch, error, saturation, ), transformer (losses, excitation current, tap changer, etc.) CT Connections Protected Zone Neutral CT Terminal CT G Power 87G Page 17 Principle: The summation of the currents on each sides, one from the Terminal CT and the other one from the Neutral CT, should be zero (0) in case of an external fault In case of an internal fault, the summation (difference) is not zero (0) and the relay must trip Load/External Fault Neutral CT I2Pri Terminal CT G I1Pri I1Pri + I2Pri = Power I2Sec I1Sec 87G I1Sec + I2Sec = ideally = Relay does NOT Trip Page 18 2011-07-24 Internal Fault Neutral CT Terminal CT G I2Pri I1Pri I2Sec I1Pri + I2Pri ≠ I1Sec 87G I1Sec + I2Sec ≠ Relay Trips © OMICRON Academy Page 19 Note: In case the CT ratios are different, the magnitude correction must be taken care of IGenerator Rated = 900 A Neutral CT -> 1000/1 1000 A Terminal CT -> 2000/1 1000 A G 87G K1 = ? × K1 K2 = ? + × K2 1.0 A 0.5 A Page 20 How to consider the magnitude correction? o Using the nominal current of the Generator for reference K1 = CT RatioNeutral CT/ IGenerator Rated = (1000/1)/900 = 1.11 K2 = CT RatioTerminal CT/ IGenerator Rated = (2000/1)/900 = 2.22 × 1.11 1∠0° A × 2.22 0.5∠180° A 1.11∠0° + 1.11∠180° = o Using the CT at Neutral side for reference K1 = CT RatioNeutral CT/ INeutral CT Nom Cur = (1000/1)/1000 = 1.00 K2 = CT RatioTerminal CT/ INeutral CT Nom Cur = (2000/1)/1000 = 2.00 × 1.00 1∠0° A × 2.00 1.00∠0° + 1.00∠180° = 0.5∠180° A Page 21 2011-07-24 o Using the CT at the Terminal side for reference K1 = CT RatioNeutral CT/ ITerminal CT Nom Cur = (1000/1)/2000 = 0.50 K2 = CT RatioTerminal CT/ ITerminal CT Nom Cur = (2000/1)/2000 = 1.00 × 0.50 1∠0° A × 1.00 0.50∠0° + 0.50∠180° = 0.5∠180° A Page 22 Note: Diff/Bias Operating Characteristic technique will be used in this protection function to protect against CTs differences (e.g saturation, ratio error, etc.) Ideally No Error 200 A G 200 A 1000/1 1000/1 No Error Idiff = A 0.2 A 87G 2000 A No Error G 0.2 A 2000 A 1000/1 1000/1 No Error Idiff = A 2.0 A 87G 2.0 A Page 23 20000 A No Error G 1000/1 20000 A 1000/1 No Error Idiff = A 20 A 87G 20 A Idiff Tripping Area Ideally Ibias 200 A 2000 A 20000 A Ibias = Irestraint; means current increase Page 24 2011-07-24 What happens in reality? 200 A 200 A G 1000/1 No Error 1000/1 10% Error Idiff = 0.02 A 0.2 A 0.18 A 87G 2000 A 2000 A G 1000/1 No Error 1000/1 10% Error Idiff = 0.20 A 2.0 A 1.8 A 87G Page 25 20000 A 20000 A G 1000/1 No Error 1000/1 10% Error Idiff = 2.00 A 20.0 A 87G 18.0 A Idiff Tripping Area 200 A 2000 A 20000 A Ibias = Irestraint; means current increase Page 26 Other factors • • • • • CT ratio error CT phase displacement saturation different burden etc Page 27 2011-07-24 Testing Page 28 Differential Protection (Low Impedance): 87 SIDE2 (Neutral CT) SIDE1 (Terminal CT) Page 29 I-Diff/Bias Characteristic Idiff Idiff>> Slope2 (m2) X3=(Idiff>>/m2)+Base Slope2 Tripping Area Y1= m1×(X2−Base Slope1) Slope1 (m1) Idiff> Ibias Base Slope1 Base Slope2 Ibias = abs(I1)+abs(I2) X2=[(m2×Base Slope2)−(m1×Base Slope1)]/(m2-m1) X1=(Idiff>/m1)+Base Slope1 Page 30 10 2011-07-24 CT & PT Connection: Forward Reverse Protected Area (Instantaneous Trip Time) Protected Area (Delayed Trip Time) Core-Balance CT Neutral CT G DYn 3V0 Vn Ix 3I0 67N Open Delta G Page 151 Directional Using Zero Zequence Voltage for Polarization (Vn = Residual Voltage = 3V0) Example: Setting of the Directional Angle (MTA) = 80° Vc Vc Vn 80° Va 80° Vb MTA Vn 3I0 MTA Va (-Vn) 3I0 Vb 3I0& Polarise = 3V0 (Vn) 3I0& Polarise = -3V0 (-Vn) Page 152 Testing Page 153 51 2011-07-24 Restricted Earth Fault (87N) This function will be used to protect the stator winding, same as differential protection, in case phase CT at neutral side is not available (large generators, e.g G DYn 3V0 Open Delta Vn 59TN Va Open Delta G Vb 3V0 Vc Page 164 Testing Page 165 55 2011-07-24 100% Stator Earth Fault (27TN, 59TN) Note: voltage is required to release the blocking condition minimum power is required to release the blocking condition Page 166 Settings 59TN 27TN Page 167 Testing Page 168 56 2011-07-24 Overexcitation, Overfluxing, Volt/Hz (40) To protect the generator (also step-up transformer) due to very high magnetic flux resulting from low frequency and/or overvoltage Excessive magnetic flux can cause serious overheating and may result in damage to the transformer and generator core Also protection from high induction inside the generator (e.g if a power unit switches off under full-load and the AVR does not respond or not fast enough to prevent voltage increase) High induction can also be caused by frequency reduction (rotating speed) in case of island system Increasing the induction above the nominal value can lead to a saturation of the iron core resulting in high eddy losses and possibly in permanent damaging of the core by "core burning" Page 169 Typical V/Hz limits: V/Hz (pu) 1.25 1.20 1.15 1.10 1.05 Generator 0.2 1.0 6.0 20.0 ∝ Transformer 1.0 5.0 20.0 ∝ E = 4.44×N×f×φm φm ∝ E/f Page 170 G DYn Power PT 40 V/Hz (%) Calculation: VMeasure/VNom 125% 115% Trip fMeasure/fNom Transformer Withstand Curve Generator Withstand Curve 105% t (sec) Page 171 57 2011-07-24 Testing Page 172 Overexcitation: Overexcitation: Volts/Hz (24) Page 173 Settings Page 174 58 2011-07-24 Operating Characteristic U/f = [UMeasured,Secondary×(PTRatio)/kVMachine][fMeasured/fMachine] Time TU/f > TU/f >> U/f 1.40 1.35 1.30 1.25 1.20 1.15 U/f >> 1.10 1.05 U/f > Page 175 Testing Page 176 Rotor Earth Fault (64R) To protect the generator when an earth-fault occurs in the generator, in the exciter circuit A single ground fault in the rotor will not cause a problem (as rotor is isolated), but when a second or multiple ground-faults occur, it will cause problems Particular attention has to be paid to the possible mechanical damages resulting from the asymmetric field caused by this fault This field rotates with the rotor and causes violent vibrations and can damage the rotor's surface or even displace the rotor How to detect this fault? There are a numbers of methods to detect this fault, some of them using a AC voltage, some of them using bridge methods or similar Page 177 59 2011-07-24 Example: Rotor Earth-Fault Excitor AC supply I> R1 R2 slip rings & brushes Page 178 Testing Page 179 Rotor Earth Fault (64R) CT Input is fixed Page 180 60 2011-07-24 Note: XCoupling: Total series reactance (L&C) of the coupling circuit, for reduce the harmonics content in the circuit (if application) RV: Total resistance in the circuit (brush resistance, protection resistance (if applicable) and damping resistance (if applicable) Page 181 Settings Note: Step1 use for warning only Apply 50VAC for testing The pickup current = 0,010A Apply 50VAC for testing The pickup current = 0,025A Page 182 Testing Page 183 61 2011-07-24 Out of Step Protection (68) When the generator loses of synchronization (out of step, pole slip) to the system (number of reasons), serious damaging effects happen because of overloading The protection should separate the generator from the system instantaneous Principle: The voltage and current will be monitored in terms of impedance When the locus of the impedance moves into the protected zone, then this function operates Page 184 Zone Characteristic X X System Angle 4 System Angle 1 R R 4 Trip Trip Generator Mode Motor Mode Page 185 Only Blinder X System Angle R Trip Page 186 62 2011-07-24 Testing Page 187 Out Of Step (78) CT Input is fixed SIDE2 (Neutral CT) Page 188 Settings Page 189 63 2011-07-24 Out Of Step Impedance Characteristic X Note: Characteristic for serious/close faults, for power swing with electrical center being in the generator block until stepup transformer Characteristic 2, for power swing with electrical center being in the network system Zc + Diff Characteristic Zc R Za Characteristic Zb Page 190 Testing Page 191 Dead Machine Energization Protection An accidental energization (connection to the system) when the machine is not running can cause severe damage to the machine because the generator will act as an induction motor The rotor is not designed to operate with this condition, so it easily can lead to severe damage To protect this condition the following logic will be used for tripping the circuit breaker OC Pickup I> U< AND P U Trip DO Page 192 64 2011-07-24 Testing Page 193 65 ... Power Protection This function is not required for the generator protection scheme, but will be used for interlocking of other protection functions (supervision, signaling) But e.g if the generator. .. generator protection scheme However it is used for interlocking of the other protection functions (signaling) G Power DYn PT t Operation 27/59 T> T>> T>> > U e.g to protect the generator e.g as system backup protection