Transient Recovery Voltages (TRVs) for High-Voltage Circuit Breakers Part 2

Transcription

1 Transient Recovery Voltages (TRVs) for High-Voltage Circuit Breakers Part Denis Dufournet Chair CGRE WG A3.8 & EEE WG C37. San Antonio (USA), 9/9/3 GRD

2 nitial Transient Recovery Voltage

3 nitial Transient Recovery Voltage (TRV) Due to travelling waves on the busbar and their reflections, a highfrequency voltage appears on the supply side of a circuit breaker after short-circuit current interruption. A B Circuit Breaker Fault to ground This oscillation, which is called nitial Transient Recovery Voltage (TRV) is superimposed to the very beginning of the terminal fault TRV. TRV HV Circuit Breakers P 3

4 nitial Transient Recovery Voltage (TRV) TRV and terminal fault TRV TRV (V B ) Voltage V A Voltage V A at current zero V A -V B TRV HV Circuit Breakers P 4

5 nitial Transient Recovery Voltage (TRV) Standard values of TRV Z b = 6 Ω in general, but 35 Ω for U r = 8 kv TRV HV Circuit Breakers P 5

6 nitial Transient Recovery Voltage (TRV) Compared with the short-line fault TRV, the first voltage peak is much lower, and the time to the first peak is shorter, within the first two microseconds after current zero. f a circuit breaker has a short-line fault rating and SLF tests are performed with a line having a time delay less than.µs, the TRV requirements are considered to be covered. Equivalent circuit for SLF testing TRV HV Circuit Breakers P 6

7 nitial Transient Recovery Voltage (TRV) 3,5 TRV (kv),5,5,5,,5,,5,3,35,4 T(µs) Comparison of TRV for SLF with time delay and TRV (solid line) and SLF with time delay less than. µs (dotted line). TRV HV Circuit Breakers P 7

8 nitial Transient Recovery Voltage (TRV) TRV is proportional to the busbar surge impedance and to the current. TRV requirements can be neglected - for circuit-breakers with a rated short-circuit breaking current less than 5 ka, - for circuit-breakers with a rated voltage below kv, - for circuit-breakers installed in metal enclosed gas insulated switchgear (GS), because of the low surge impedance, - when the capacitance of the liaison to the bus is higher than 8pF (amendment EC 67- in ). TRV HV Circuit Breakers P 8

9 Out-of-Phase

10 Breaking in Out-of-Phase Condition Some circuit-breakers may have to interrupt faults that occur when two systems are connected in outof-phase conditions. At current interruption, the voltage on each side of the circuit-breaker meets the voltage of the supply. n full out-of-phase condition, the recovery voltage is two times the phase-to-ground voltage. The TRV peak is the highest during short-circuit interruption. Fault current is 5% of rated shortcircuit breaking current. TRV HV Circuit Breakers P

11 Voltages During Breaking in Out-of-Phase U (p.u.) 3 TRV Supply voltage - - Load voltage -3,5,7,9,,3,5,7,9,,3,5 Time (s) n case of single-phase fault in full out-of-phase, the pole to clear factor is. TRV HV Circuit Breakers P

12 Voltages during Breaking in Out-of-Phase n standards the out-of-phase factor for single-phase tests is. for effectively grounded systems ( 45kV).5 for non-effectively grounded systems (<45kV). TRV HV Circuit Breakers P

13 Out-of-Phase Angle The standard out-of-phase factor of. for effectively grounded systems and.5 for non-effectively earthed systems cover respectively an out-of-phase angle of 5 for systems with effectively grounded neutral 5 for systems with non-effectively grounded neutral TRV HV Circuit Breakers P 3

14 Three-Phase (Long) Line Fault

15 Three-Phase Line Faults With some three-phase long line faults conditions the TRV may not be strictly covered by the standard TRV withstand capability defined for terminal fault and short-line fault. Such situations can occur, depending on the actual short-circuit power of the source, during interruption by the first-pole-to-clear of threephase line faults. Mutual coupling of lines between the first interrupted phase and the two other phases can increase the line side contribution of TRV on the first pole to clear. The matter has been studied extensively by CGRE WG A3-9. Results are given in CGRE Technical Brochure 48 (-). Studies were made also in Japan and USA (BPA). TRV HV Circuit Breakers P 5

16 Three-Phase Line Faults Examples of three-phase line faults TRV calculations are given in the following slides. The TRV withstand capability demonstrated by terminal fault test duties T, T3 and out-of-phase test duty OP usually cover LLF TRVs. Some standard values of TRV have been revised (or will be revised) to better cover long line faults For rated voltages 45 kv and above, the amplitude factor for test duty T in EC standard was raised from.53 to.76 (k pp =.3). Requirements for short-line-faults are adequate and there is no need to revise them. TRV HV Circuit Breakers P 6

17 Three-Phase Line Faults Mutual Coupling Between Phases The mutual inductance between two phases i and j can be evaluated by the following equation: ' µ D M ij ln D where µ = air permeability = 4 x -7 H/m D ij = center-to-center spacing between conductors (m) D = distance to the image of the other conductor f a three-phase line-fault and a circuit with isolated source is considered to simplify the analysis, there is no 5 or 6 Hz shortcircuit current circulating in the ground path. Therefore only the mutual inductances between phases must be considered to take into account coupling. ij TRV HV Circuit Breakers P 7

18 Three-Phase Line Faults Mutual Coupling Between Phases (Cont d) After current interruption by the first pole to clear (e.g. in phase B) and during line TRV build-up, voltage is the induced voltage in phase B. t is generated by the high short-circuit current still circulating through the two other phases A and C. V ind M ab d dt a The induced voltage is superimposed on the line TRV of the interrupted pole. The next slide shows that when the induced voltage is subtracted from the actual line voltage in phase B (first cleared phase), then a typical triangular wave is obtained with a peak factor less than. t shows clearly that during a 3-phase fault current interruption, the increase of the voltage peak on the first pole to clear is due to coupling between phases. M cb d dt c TRV HV Circuit Breakers P 8

19 Three-Phase Line Faults 4 Currents sc (ka) b - c a d/dt Actual line voltage nduced voltage D/DT (A/us) V (kv) d a /dt d c /dt d =.37 Actual line voltage minus induced voltage Line TRV (kv) t (ms) 5 d =.8 by M.Landry TRV HV Circuit Breakers P 9

20 Three-Phase Line Faults Mutual Coupling Between Phases From EEE C37.-: d d 3 3 d 3 and d are the peak factors for 3-phase and single-phase faults. Z first and Z last : surge impedances for the first and last pole to clear Z Z first last t follows that d d 3 L L 3 L Z Z first last then with L m L L 3 d d L L 3 m Z Z first last where L m represents the part influenced by the other phase currents. This equation gives a physical explanation for the relationship between d 3 and d. TRV HV Circuit Breakers P

21 Three-Phase Line Faults / Effective surge impedances for the first and last clearing poles

22 Three-Phase Line Faults / Effective surge impedances for the first and last clearing poles The equivalent surge impedance for the last clearing pole can be derived from the simple circuit in the middle: Z last Z Z 3 For the first clearing pole, the neutral impedance and two of the other phases are in parallel, as shown in the bottom scheme. Reducing the connection and adding Z results in the effective surge impedance for the first pole: Z first 3Z Z Z Z

23 Three-Phase Line Faults Typical values of surge impedance in EEE C37.- Note: Z eff is the surge impedance for the last pole to clear (Z last ) U r = 45kV Z last = 4 Ω and Z first = 4 Ω

24 Three-Phase Line Faults Example : L3 and L in 735kV/4kA network 4 Vn= 735 kv, Rated sc= 4 ka, kpp=.3, L3 Source TRV parameters: Kaf=.4, RRRV=. kv/us 4 Vn= 735 kv, Rated sc= 4 ka, kpp=.3, L Source TRV parameters: Kaf=.4, RRRV=. kv/us Line & Source TRV Pole- line TRV,TRV slope=.9 kv/us, d=.53 EC Line TRV, L3, Zline= 45 ohms EC -parameter TRV - T3 (38 kv - 6 us) Line & Source TRV Pole- line TRV, TRV slope=.65 kv/us, d=.54 EC Line TRV, L, Zline= 45 ohms EC -parameter TRV - T (99 kv - 86 us) 8 L3 8 L TRV (kv) 6 TRV (kv) t (us) TRV HV Circuit Breakers P t (us) Comparison of first (blue) and last (red) clearing pole TRVs for three-phase L3 and L, with total TRV for first pole (blue) Note: the standard parameter TRV with k pp =.3 is shown in green. n edition. of EC 67- and EEE C37.6, k pp has been increased to.5 for test duty T.

25 Three-Phase Line Faults Example : L3 and L in 4kV/63kA network with % short-circuit power source T T3 TRV comparison for Long Line fault and EC terminal fault and out of phase: Calculations WG 3.9 with % of source short circuit power EC values for T3, T, OP 3phL3_st OP 3phL_st 3phL3_st 3phL3_3rd 3phL_st 3phL_3rd T3 T OP 6 kv 5 3phL3_3rd 3phL_3rd us Comparison with TRV withstand capability demonstrated by T, T3 and OP (out-of-phase) TRV HV Circuit Breakers P 5

26 Three-Phase Line Faults Example 3: L3 and L in 4kV/63kA network with 8% short-circuit power source T T3 TRV comparison for Long Line fault and EC terminal fault and out of phase: Calculations WG 3.9 with 8% of source short circuit power EC values for T3, T, OP 3phL3_st_8% OP 3phL_st_8% 3phL3_st_8% 3phL3_3rd_8% 3phL_st_8% 3phL_3rd_8% T3 T OP 6 kv 5 4 3phL3_3rd_8% 3phL_3rd_8% us Comparison with TRV withstand capability demonstrated by T, T3 and OP (out-of-phase) TRV HV Circuit Breakers P 6

27 Three-Phase Line Faults Example 4: 3-phase SLF with 75% sc (sc= 4 ka) with source having a short-circuit current of 4kA or 3 ka For a given fault current, the TRV (blue curve) is strongly dependent on the short-circuit power of the source. TRV HV Circuit Breakers P 7

28 Three-Phase Short-Line Faults SLF test duties prove the circuitbreaker s capability to interrupt a high short-circuit current with a steep rate-of-rise of recovery voltage (RRRV or du/dt). The short-line fault breaking capability in EC 67- and EEE is demonstrated by single-phase tests performed with a line that has a surge impedance (Z) of 45 Ω. Z = 45 Ω has been chosen to cover the RRRV in all cases of SLF. SLF requirements were first introduced in 97. They were based on a basic study by CGRE SC3 in 963. All types of SLF (-phase and 3-phase) were already considered. The validity of the SLF requirements was confirmed afterwards by almost 4 years of experience. TRV HV Circuit Breakers P 8

29 Three-Phase Short-Line Faults The first peak of TRV seen by the first-pole-to-clear during interruption of a three-phase SLF (U L3 ), could exceed the standard value in some cases. However the following needs to be considered: U L3 is associated with a lower RRRV than standardized and it is recognized that RRRV is the most severe TRV parameter during SLF interruption. The standard RRRV is based on an equivalent surge impedance of 45 Ω that is seldom obtained in practice. CGRE Technical Brochure 48 shows that U L3 decreases significantly when the short-circuit power of the source decreases. A U L3 that exceeds the standard value is only possible in the very low probability of cases where a three-phase fault occurs at a critical distance from the circuit-breaker and when the supply has its full shortcircuit power. TRV HV Circuit Breakers P 9

30 Three-Phase Short-Line Faults The following figure is based on data from CGRE TB 48 t shows that the dielectric phase of TRV seen by the first pole to clear during a three-phase fault is covered by interpolating the withstands demonstrated in the standard test duties (same range of currents). U L (kv) 5 45 Case Ur = 45kV sc = 4kA f =5Hz Test duty L kA st pole 3-phase SLF 36kA Test duty L kA Time (µs) TRV HV Circuit Breakers P 3

31 Three-Phase Short-Line Faults All these considerations supported and still supports the choice made by EC and EEE to require two mandatory SLF test duties L9 and L75 performed single-phase with respectively 9% and 75% of rated short-circuit current (with an option in EC to perform a test duty L6 when arcing times during L75 are significantly longer than during L9). These test duties performed single-phase demonstrate an interrupting window of arcing times of 8 -, the largest possible for any type of fault. Conclusion: there is no need to change the requirements for SLF tests duties L9 and L75 in international standards. TRV HV Circuit Breakers P 3

32 Shunt Reactor Switching

33 Switching of nductive Loads (Shunt Reactors) nterruption of shunt reactors currents nterruption of small inductive currents Current chopping Multiple reignitions Synchronized tripping Breaking tests TRV HV Circuit Breakers P 33

34 Switching of nductive Loads (Shunt Reactors) nterruption of small inductive currents s nterruption of small inductive currents is obtained during switching of shunt reactance, no-load transformers, medium voltage motors. The figure give a representation of a single-phase circuit for small inductive current switching. The load is represented by its inductance L t and its capacitance to ground C t TRV HV Circuit Breakers P 34

35 Switching of nductive Loads (Shunt Reactors) Current chopping When an arc of small intensity is submitted to a powerful blast, it can be unstable as it interacts with the circuit connected at its terminals. Oscillations lead to a premature current zero: current is chopped Current chopping produces an overvoltage on the load side of the circuit-breaker. TRV HV Circuit Breakers P 35

36 Switching of nductive Loads (Shunt Reactors) Voltage (V) Current chopping: Current-Voltage characteristic Current oscillations initiated by a disturbance (arc voltage drop), are - initially damped, - later amplified when the arc acts like a negative impedance Current (A) TRV HV Circuit Breakers P 36

37 Switching of nductive Loads (Shunt Reactors) Chopped current is given by o Ko C with K o chopping number C equivalent capacitance of the circuit f arc voltage and damping are neglected, the overvoltage factor is given by : Lt io S E C with E o voltage at interruption time L t C o inductance of load circuit capacitance of load circuit L TRV HV Circuit Breakers P 37

38 Switching of nductive Loads (Shunt Reactors) Multiple reignitions Current TRV 3 Voltage withstand between contacts When the natural frequency of the TRV is high, reignitions cannot be avoided as the circuit breaker tries to interrupt with short arcing times i.e. with a small distance between contacts. Reignitions occur until the contact distance is sufficient to withstand the TRV. Fast voltage changes can endanger the insulation of transformers in series with the circuit breaker. TRV HV Circuit Breakers P 38

39 Switching of nductive Loads (Shunt Reactors) Multiple reignitions TRV during a test with multiple reignitions Reignitions can produce overvoltages on the supply side and load side TRV HV Circuit Breakers P 39

40 Switching of nductive Loads (Shunt Reactors) The maximum allowable level of overvoltage is less than in highvoltage networks, therefore several techniques were developed to guarantee that the required level of overvoltage is not exceeded: use of varistors phase-to-ground and in parallel to circuitbreakers, breaking with opening resistors (in air blast circuit breakers). synchronized opening of a circuit breaker, where the arcing time is in a given range such that there won t be reignitions or high current chopping. Today the best solution is synchronized opening. TRV HV Circuit Breakers P 4

41 Switching of nductive Loads (Shunt Reactors) Synchronized opening Optimal interval for contacts separation TRV HV Circuit Breakers P 4

42 Switching of nductive Loads (Shunt Reactors) Synchronized Opening Voltage Primary voltage Current Current 3 4 Order given Open command to RPH Order transmitted Comman d by RPH CB Main contact Contacts separation t_d CB Opening time t_arc 5 ms = 6 ms t_arc arcing time t_d RPH delay t = 44 ms 55 ms TRV HV Circuit Breakers P 4

43 Switching of nductive Loads / Standards Standard/Guide for inductive load switching EC 67- nductive load switching EEE C37.5 Guide for the Application of Shunt Reactor Switching Technical Report on controlled switching EC 67-3 Alternating current circuit-breakers with intentionally non-simultaneous pole operation TRV HV Circuit Breakers P 43

44 Transformer Limited Faults

45 Transformer Limited Faults / Content Part Part ntroduction Options for specification (EEE C37.-) TLF TRV for EHV & UHV Circuit Breakers TRV HV Circuit Breakers P 45

46 TLF TRV / ntroduction Severe TRV (Transient Recovery Voltage) may occur when a shortcircuit current is fed or limited by a transformer without any appreciable capacitance between the transformer and the circuit breaker. These faults are called Transformer Limited Faults (TLF). n such case, the rate-of-rise of recovery voltage (RRRV) exceeds the values specified in the standards for terminal faults. TLF TRV EHV-UHV Circuit Breakers - P 46

47 TLF / Options for Specification As explained in EEE C37.- (Guide for the Application of TRV for AC High-Voltage Circuit Breakers), the user has several basic possibilities. Specify a fast TRV for TLF with values taken from standards or guides (e.g. ANS C37.6.),. Specify a TRV calculated for the actual application taking into account the natural frequency of the transformer, and/or (depending on the knowledge of system parameters) additional capacitances present in the substation, sum of stray capacitance, busbar, CVT etc 3. Add a capacitor to reduce the RRRV TRV HV Circuit Breakers P 47

48 TLF / Options for Specification Option : Specify a fast TRV for TLF with values taken from Guides (e.g. ANS C37.6.) ANS Guide C37.6. is assumed to cover the large majority of all cases for this switching duty. TLF TRVs are given for two fault currents: 7% and 3% of rated short-circuit current. They are based on the assumption of a negligible capacitance between the circuit breaker and the transformer. TRV HV Circuit Breakers P 48

49 TLF / Options for Specification Option (Cont d): TRV values in ANS C37.6. TRV HV Circuit Breakers P 49

50 TLF / Options for Specification Explanation on TRV value in ANS C37.6. Case: U r = 36 kv, sc =63kA, TLF =7% sc Load voltage at the time of interruption U S S L. SC S SC L. 93 S L S.7 U U load L SC TRV peak (neglecting the contribution on the supply side) U r U c kaf Uload kaf.93 k pp 3 with k pp =.5 (assumed in ANS C37.6.) and k af =.8 S SC 36 U c kv 3 S Reactance supply Reactance transformer U s s L U load TRV HV Circuit Breakers P 5

51 TLF / Options for Specification Option (Cont d): TRV values in ANS C37.6. Calculation TLF TRV peak - Case 7% rated short-circuit current Ur Ur sqrt(/3) kp kaf kvd Calculated Uc ANS C37.6. rated voltage system peak phase-ground voltage pole-to-clear factor amplitude factor voltage drop across transformer TRV peak TRV peak kv kv pu pu pu kv kv 3,4,5,8,93 5, ,4,5,8,93 97, ,8,5,8,93 348,5 35 TRV HV Circuit Breakers P 5

52 TLF / Options for Specification Option (Cont d) As indicated in ANS/EEE Std C37.6-6, time t 3 is given by the following equation: U r C t3. 6 where U r is the rated voltage in kv, C is equal to the lumped equivalent terminal capacitance to ground of the transformer in pf, and TLF is equal to the transformer-limited fault current in ka. C = TLF (pf) for rated voltages less than 3 kv C = TLF (pf) for rated voltages 3 kv and above For U r 3 kv, time t 3 can be also expressed as follows: TLF t TLF U r t 3 decreases (and RRRV increases) when the fault current increases. TRV HV Circuit Breakers P 5

53 TLF / Options for Specification Option a Check the actual TRV time to peak from the natural frequency of the transformer(s) T f nat where T is the time to TRV peak (=.5 t 3 ) f nat is the natural frequency of the transformer f T is longer than the value in ANS C37.6. it may be crosschecked with available test results. Determination of the transformer natural frequency can be done in several ways as explained in part 3. TRV HV Circuit Breakers P 53

54 TLF / Options for Specification Option b TRV calculation for a given application Calculate the TRV for the given application, taking into account additional available capacitances or additional added capacitances i.e. line to ground capacitors, CVT s, grading capacitors etc. The additional capacitance increases the time to TRV peak (T mod ) and reduces the stress for the circuit breaker according to the following equations where T mod L nat C ( C add ) L kpp U r 3 sc f r sc C nat 4 ( T ) /( L) TRV HV Circuit Breakers P 54

55 TLF / Options for Specification Option b (Cont d) where k pp U r sc is the first pole to clear factor is the rated maximum voltage is the rated short circuit current is the transformer limited fault current f r is the power frequency L is the equivalent inductance of the transformer C nat is the equivalent capacitance of the transformer (/3 of the surge capacitance in case of 3-phase ungrounded fault) C add is the equivalent additional capacitance (/3 of the capacitance added phase to ground in case of 3-phase ungrounded fault) TRV HV Circuit Breakers P 55

56 TLF / Options for Specification Option b (Cont d) : Example Rated maximum voltage : 36 kv Rated short circuit current : 63 ka Based on 3% of rated short circuit current, the required test current is 8.9 ka. TRV parameters as defined in ANS C37.6. T = 37. µs u c = 7 kv The equivalent inductance and capacitance of the transformer are derived using previous equations L = 3.7 mh C nat = 4.54 nf Taking into account additional (equivalent) capacitances present in the substation (sum of stray capacitance, busbar, CVT etc. ) of 3.5nF, the modified time to peak T mod is equal to 49 µs. This T mod would be the shortest time to peak TRV that the breaker has to withstand in service and during testing. TRV HV Circuit Breakers P 56

57 TLF / Options for Specification Option 3 Additional capacitor Test reports may be available for the circuit breaker showing a certain T value which is higher than the T value given in ANS C Such a breaker could be used for this application by adding a capacitor to ground which changes the actual T to a value where a proof for the circuit breaker capability exists. where T test value is the time to peak of tested TRV. f for example, a circuit breaker has been tested with a time T test of 7 µs, a current equal to 3 % of its rated short circuit current of 63kA and a rated maximum voltage of 36 kv, this would require an additional capacitance of.6 nf in order to make the breaker feasible for this application. TRV HV Circuit Breakers P 57 C add T test L C nat

58 Transformer Limited Fault TRV for EHV & UHV Circuit Breakers Denis Dufournet (Alstom Grid) Paper for SH 3 Conference, Seoul, August 3 Paper co-authored by Joanne Hu (RBJ Engineering) and Anton Janssen (Liander) GRD

59 TLF TRV for EHV & UHV Circuit Breakers. ntroduction. TLF TRV Peak Calculation 3. TLF RRRV Calculation 4. Application to EHV Circuit Breakers (Standardization in EEE) 5. Application to UHV Circuit breakers (Standardization in EC) 6. Conclusion TLF TRV EHV-UHV Circuit Breakers - P 59

60 TLF TRV / ntroduction Recent studies on TLF TRVs by CGRE WG A3 /8 for EHV and UHV circuit breakers Technical Brochures 36 (8) and 456 () New Technical Brochure to be published end of 3 EC SC 7A for UHV circuit breakers Standard values in Edition. of EC 67- () EEE WG C37. Application Guide for TRV for AC High- Voltage Circuit Breakers () Different options available to evaluate if a circuit breaker is suitable for an application with TLF condition. TLF TRV EHV-UHV Circuit Breakers - P 6

61 TLF TRV / ntroduction TLF conditions for EHV and UHV circuit breakers UHV Circuit Breaker in UHV/EHV S/S UHV EHV TSF UHV EHV TFF EHV Circuit Breaker in UHV/EHV S/S UHV EHV TSF UHV EHV TFF EHV Circuit Breaker in EHV/HV S/S EHV HV TSF EHV HV TFF TLF: Transformer secondary faults (TSF) and transformer fed faults (TFF) TLF TRV EHV-UHV Circuit Breakers - P 6

62 TLF TRV Peak Calculation Pole-to-clear factor, Amplitude Factor & Voltage Drop Ratio

63 TLF TRV Peak / Pole-to-clear factor The TRV peak is function of 3 factors as shown in the following equation U k p = pole-to-clear factor, k af = amplitude factor, k vd = voltage drop across the transformer, U r = rated voltage Pole-to-clear factor c k p k af On the EHV or UHV side the transformer neutral is effectively grounded. Since the transformer impedance is dominant, poleto-clear factors are between. and.5 at maximum. A conservative value of. was adopted by EC for UHV. For EHV a conservative value of.3 covers the need. k vd U r 3 TLF TRV EHV-UHV Circuit Breakers - P 63

64 TLF TRV Peak / TRV Amplitude Factor From the initial part of a FRA-measurement an equivalent inductance can be determined. n the higher frequency region (some hundreds of khz) the equivalent capacitance can be approached. Transformer 35 MVA, 4 kv L =. H, C = 94 pf R = 65 kω, F =.6 khz Z = 4.6 kω, R/Z = 4.45 kaf =.7 TLF TRV EHV-UHV Circuit Breakers - P 64

65 TLF TRV Peak / TRV Amplitude Factor From L and C values both a TRV frequency can be determined and an equivalent value Z. A representation by a simple single frequency model gives the highest amplitude factor, as the multiple frequencies of a more complicated model tend to decrease the overall amplitude factor. The ratio between the highest peak of the FRA-impedance measurement and this value Z determines the amplitude factor. A ratio R/Z of 5, as found in the example studied by WG A3-8, gives an amplitude factor of.73. EC adopted.7 for UHV circuit breakers. A conservative value of value of.8 could be standardized for EHV circuit breakers. TLF TRV EHV-UHV Circuit Breakers - P 65

66 TLF TRV Peak / Voltage Drop Ratio n EC & EEE standards, the voltage drop ratio is assumed to be.9 for terminal fault test duty T. The voltage drop ratio is function of the ratio of TLF current and the bus short-circuit current minus the contribution from the faulted transformer ( p-net ) Considering the circuit breaker at the primary side, the voltage drop in case of a transformer secondary fault (TSF) is CB p(net) p(tsf) s(tff) Primary side V ptsf pnet Fault s(net) s(tsf) p(tff) Secondary side TLF TRV EHV-UHV Circuit Breakers - P 66

67 TLF TRV Peak / Voltage Drop Ratio Based on the previous equation, the voltage drop can be expressed as function of the ratio TLF fault current divided by rated short-circuit current (in percentage), assuming different possible values of the bus short-circuit current TLF TRV EHV-UHV Circuit Breakers - P 67

68 TLF TRV Peak / Voltage Drop Ratio CGRE WG A3.8 has done a survey of voltage drop values for EHV and UHV. Results for 55kV in Japan (TEPCO) are given below. The maximum value is 7%. First results for EHV show that for TLF currents in the range 5-3% sc, the voltage drop is close to 7% (or voltage factor =.7). Voltage drop in % TLF TRV EHV-UHV Circuit Breakers - P 68

69 3 TLF RRRV Calculation

70 TLF RRRV Calculation The rate of rise of recovery voltage (RRRV) can be calculated from the TRV peak u c and time t 3 Time t 3 is derived from T =½F R,withF R = TRV frequency TRV frequency from measurement (e.g. FRA) and calculation (additional capacitances) TLF TRV EHV-UHV Circuit Breakers - P 7

71 4 Application to EHV Circuit Breakers (Standardization in EEE)

72 TLF TRV for EHV Circuit Breakers TRV peak can be calculated as shown previously with: First pole to clear factor =.3 Voltage drop ratio =.9 (% sc) and.7 (3% sc) Amplitude factor =.8 TRV time to peak and time t 3 n EEE a -cos waveshape is assumed for the TRV t follows that t 3 is.88 T n a first step in EEE, TRV time to peak (T ) from ANS C37.6. could be used Rate-of-rise-of-recovery-voltage (RRRV) RRRV is TRV peak (u c ) divided by t 3 TLF TRV EHV-UHV Circuit Breakers - P 7

73 TLF TRV for EHV Circuit Breakers Application to standard values in EEE TRV peak and RRRV for TLF = 8.9 ka (3% of 63 ka) and rated voltages 45kV to 8kV U r SC TLF u c Time T Time t 3 RRRV kv ka ka kv μs μs kv/μs 45 63, , , 36 63, , , , , ,9 8 63, , ,8 Note: and T is taken from ANS C37.6. TLF TRV EHV-UHV Circuit Breakers - P 73

74 5 Application to UHV Circuit Breakers (Standardization in EC)

75 Standardization of TLF for UHV in EC 67- Transformer limited fault (TLF) is covered in Annex M. Clause M.4 is for rated voltages higher than 8kV The system TRV can be modified by a capacitance and then be within the standard TRV capability envelope. As an alternative, the user can choose to specify a rated transformer limited fault (TLF) current breaking capability. The rated TLF breaking current is selected from the R series in order to limit the number of testing values possible. Preferred values are ka and.5 ka. TRV parameters are calculated from the TLF current, the rated voltage and a capacitance of the transformer and liaison of 9 nf. The first-pole-to clear-factor corresponding to this type of fault is.. Pending further studies, conservative values are taken for the amplitude factor and the voltage drop across the transformer. They are respectively equal to.7 and.9. TLF TRV EHV-UHV Circuit Breakers - P 75

76 Standardization of TLF for UHV in EC 67- TRV Table from EC See paper for detailed calculation of TRV parameters for the case kv.5ka TLF TRV EHV-UHV Circuit Breakers - P 76

77 6 - Conclusion

78 TLF - Conclusion Transformer-limited-faults produce fast TRVs with a high RRRV if there is a low capacitance between the transformer and the circuit-breaker. Options for specification are described in EEE C37.- RRRV is function of the TRV peak and the time to peak (related to the TRV frequency). TRV peak is function of several factors (pole-to-clear, amplitude factor, voltage drop across transformer) that must be properly chosen in standards. CGRE WG A3-8 studied TLF TRVs parameters for TRV peak calculation. and recommended They can be used for the standardization of TLF TRV for EHV circuit breakers by EC and EEE. EC has already standardized TLF TRV for UHV circuit breakers in edition. of EC 67-. TLF TRV EHV-UHV Circuit Breakers - P 78

79 Series Reactor Limited Faults

80 Series Reactor Limited Faults A current limiting reactor is used to reduce a fault current magnitude. t is used also to limit inrush currents in capacitor bank applications. Due to the very small inherent capacitance of a number of current limiting reactors, the natural frequency of transients involving these reactors can be very high. A circuit-breaker installed immediately in series with such type of reactor will face a high frequency TRV when clearing a terminal fault (reactor at supply side of circuitbreaker) or clearing a fault behind the reactor (reactor at load side of circuitbreaker). The resulting TRV frequency generally exceeds by far the standardized values. TRV HV Circuit Breakers P 8

81 Series Reactor Limited Faults Example of a 38 kv Circuit Breaker that clears a 3-phase fault with a current limiting reactor (CLR) on the supply side Equivalent single-phase circuit Calculated TRV: RRRV =.4 kv/µs TRV HV Circuit Breakers P 8

82 Series Reactor Limited Faults f the system TRV exceeds a standard breaker capability, a capacitance can be added in parallel to the reactor in order to reduce the TRV frequency and have a system TRV curve within the standard capability envelope. TRV HV Circuit Breakers P 8

83 Series Reactor Limited Faults The capacitor can also be mounted phase to ground, the effect is similar. This mitigation measure is very effective and cost efficient. EEE C37.- gives a method to calculate by hand the TRV modified by an additional capacitor. n the case of a phase-to ground capacitor, assuming a rated voltage of 38kV, a short-circuit current of the supply of 5 ka and a frequency of 6 Hz, the short-circuit inductance of the source is As the fault current of.5 ka is limited by the short-circuit inductance and the CLR inductance in series: 38 LS LCLR mh 3.5 CLR inductance: Ur 38 LS. 64 mh sc L CLR mh TRV HV Circuit Breakers P 83

84 Series Reactor Limited Faults Equivalent CLR inductance for 3-phase fault.5 L CLR mh TRV frequency with addition of C = nf ftrv.5 L C 5.4 CLR PH G Hz Time to peak TRV 5.4 T s 4.9 µs 6 ftrv Time t 3 T 4.9 t3. 7 µs CLR contribution to TRV peak 3 U CLR.5 LCLR kaf kv TRV HV Circuit Breakers P 84

85 Series Reactor Limited Faults Source-side RRRV (rated value is. kv/µs for 5kA).5..3 kv / µs 5 Source-side contribution to TRV Sum of CLR and source contributions RRRV.3 t kv u c kv 7.8 RRRV 3.35 kv / µs.7 The calculated values of u c and RRRV obtained in a simplified way compare well with those obtained by ATP simulation of the complete system, respectively 77. kv and 3.4 kv/µs. TRV HV Circuit Breakers P 85

86 nfluence of Series Capacitors on TRV CGRE WG A3-8 Study GRD

87 nfluence of Series Capacitors on TRV CGRE studies Current study by CGRE WG A3-8 will be covered in a Technical Brochure (TB) that will be published end of 3. t is part of an extensive study on TRVs in EHV and UHV networks. Following slides are taken from the draft TB. Simulations were performed by Hiroki to (Chairman of CGRE SC A3) and Hiroki Kajino (both of Mitsubishi). Former study made by CGRE WG A3.3*, reported in TB 336. * Convenor is Anton Janssen (NL) TRV HV Circuit Breakers P 87

88 nfluence of Series Capacitors on TRV Case: TRV for a line circuit breaker in case of 3-phase line fault with a series capacitor in the middle of the line in a 55kV system. TRV HV Circuit Breakers P 88

89 nfluence of Series Capacitor on TRV Case : Fault conditions & TRV with series capacitor by-passed or not (4% compensation) The TRV peak is increased due to the trapped charge in the series capacitor. TRV HV Circuit Breakers P 89

90 nfluence of Series Capacitors on TRV Case : 3-phase line fault in 55 kv system with parallel circuit having 4% compensation (Hydro-Quebec lines parameters). Series-capacitor by-passed. Series-capacitor not by-passed Case.: TRV peak is slightly higher than the value for out-of-phase TRV HV Circuit Breakers P 9

91 nfluence of Series Capacitors on TRV Case 3: -phase & 3-phase line faults in 765 kv radial system (Hydro-Quebec parameters) with 4% compensation TRV peak for 3-phase faults exceed the values for T and T3 TRV HV Circuit Breakers P 9

92 nfluence of Series Capacitors on TRV Case 3: nfluence of the degree of series compensation TRV peak increases with the degree of compensation TRV HV Circuit Breakers P 9

93 nfluence of Series Capacitors on TRV Case 3: nfluence of the degree of series compensation TRV peak increases with the degree of compensation TRV HV Circuit Breakers P 93

94 nfluence of Series Capacitors on TRV TRV peak can be up to 4.8 p.u. (Turkey), compared to.5 p.u. for OP, two approaches possible: Circuit breaker with higher TRV withstand capability (e.g. 55kV circuit breaker for a 4kV application). TRV limitation Use of CBs with opening resistors rated at 4 to 6 Ω, Use of surge arresters connected phase-to-ground on the series compensated lines. Use of metal-oxyde varistors connected in parallel with the main contacts of CBs. Fast by-passing of series-capacitors of the faulty line by forced triggering of the protection spark gap, or by closing the by-pass CB. TRV HV Circuit Breakers P 94

95 Annex: Series Capacitor Bank Equipment By-pass varistor Spark gap Damping device By-pass switch When the voltage across the capacitor reaches the limiting value for the capacitor design, a portion or all of the current is by-passed through the capacitor by-pass system which may include, in addition to the series capacitor, a by-pass varistor, a spark gap, and a by-pass switch with its damping device, depending on the specification of the bank. TRV HV Circuit Breakers P 95 Annex from François Gallon tutorial on reactive power

96 Annex: Series Capacitor Bank Equipment Metal-oxide Resistor Capacitor By-pass Switch Triggered Air-gap Composite nsulator Damping Reactor TRV HV Circuit Breakers P 96

97 Harmonization of EC and EEE Standards for High-Voltage Circuit Breakers

98 Harmonization of EC & EEE Standards Harmonization of EC & EEE standards for HV circuit breakers Work done from 995 to. Aim: Common ratings & test requirements for making and breaking capabilities. Done first for capacitive current switching, and later to harmonize TRVs. Previously, common work was done on shunt reactor switching. TRV HV Circuit Breakers P 98

99 Harmonization of EC & EEE Standards ntroduction Proposals to harmonize EC & ANS/EEE standards for highvoltage circuit-breakers in the 98 s C.L.Wagner and H.M. Smith Analysis of TRV rating concepts, EEE Transactions on PAS, Nov. 984, S.Berneryd mprovements possible in testing standards for HV circuitbreakers, Harmonization of ANS and EC testing, EEE Transactions on Power Delivery, Oct Early contributions First harmonized document in EEE C37.5 / EC 633 in 993/94: Shunt reactor Switching Project leaders: D.Peelo & S.S.Berneryd Other by R.Harner, E.Ruoss, A.Bosma & H.H.Schramm. The process gained momentum after a joint meeting of EC SC7A & 7C and the EEE Switchgear Committee in 995. TRV HV Circuit Breakers P 99

100 Harmonization of EC & EEE Standards ntroduction (Cont d) Major advances have been made since 995 towards the further harmonization of EC and ANS/EEE standards for high-voltage circuit breakers, especially for capacitive current switching and short-circuit breaking tests. A first round of harmonization was done in when EEE C37.4 and C37.9 were revised to have Rated voltages 3 kv, 7kV & 45kV (EC adopted 55kV & 8kV) RRRV= kv/µs for circuit breakers with rated voltages 3kV Capacitive current ratings and tests were harmonized first. Harmonization of Transient Recovery Voltages (TRVs) for shortcircuit breaking tests was done in two projects: Harmonization of TRVs for breaking tests of circuit breakers < kv Harmonization of TRVs for breaking tests of circuit breakers kv TRV HV Circuit Breakers P

101 Harmonization of Capacitive Current Switching

102 Harmonization of EC & EEE Standards Capacitive current switching Revision prepared by a common EC-EEE Task Force in 995. ntroduction of class C (low probability of restrike) and class C (very low probability of restrike) and new test requirements. For class C, the number of tests is doubled and tests are performed after 3 interruptions with 6% of rated short circuitcurrent. mplemented by EC SC7A in the first edition of EC 67- (-5), mplemented by the EEE Switchgear Committee in EEE C37.4a (3-7) and C37.9a (5-9) TRV HV Circuit Breakers P

103 Harmonization of TRVs for Circuit Breakers of Rated Voltages Higher than kv & Less than kv

104 Harmonization of EC & EEE Standards Using the input from several Working groups of CGRE SC A3, EC SC 7A started in the revision of TRV requirements for circuitbreakers of rated voltages higher than kv and less than kv. Among the reasons for this revision, there was the need to cover cases of application with TRV stresses that were not covered in edition. of EC 67-, for example Breaking terminal fault currents in systems with low capacitance on the supply side of circuit-breakers; Breaking short-line fault currents in the case of direct connection of the circuit breaker to an overhead line and with rated voltages 5 kv and < 5 kv Breaking transformer-limited faults in the special cases of circuitbreakers intended to be connected to a transformer with a connection of small capacitance; TRV HV Circuit Breakers P 4

105 Harmonization of EC & EEE Standards Cable systems and line systems n order to cover all types of networks (distribution, industrial and subtransmission) and for standardization purposes, two types of systems are introduced: Cable systems Cable systems have a TRV during breaking of terminal fault at % of short-circuit breaking current that does not exceed the envelope derived from Table 4 in Edition. of EC 67-. TRV values are those defined in the former editions of EC standard for high-voltage circuit breakers. Line systems Line systems have a TRV during breaking of terminal fault at % of short-circuit breaking current defined by the envelope derived from Table 5 in Edition. of EC 67-. Standard values of TRVs for line systems are those defined in ANS/EEE C37.6 for outdoor circuit-breakers. TRV HV Circuit Breakers P 5

106 Harmonization of EC & EEE Standards Comparison of TRVs for cable systems and line-systems Envelope of Line system TRV U c Envelope of Cable system TRV t 3 The rate of rise of recovery voltage (RRRV) for line systems is approximately twice the value for cable systems TRV HV Circuit Breakers P 6

107 Harmonization of EC & EEE Standards Harmonization of TRVs between EC and EEE EC TRV Table a t3 kaf ANS TRV Outdoor c.b. ANS TRV ndoor c.b. COMMON TRV TRV Cable-systems TRV Line-systems TRV HV Circuit Breakers P 7

108 Harmonization of EC & EEE Standards Classes of Circuit breakers Circuit-breaker class S circuit-breaker intended to be used in a cable system Circuit-breaker class S circuit-breaker intended to be used in a line-system, or in a cablesystem with direct connection (without cable) to overhead lines TRV HV Circuit Breakers P 8

109 Harmonization of EC & EEE Standards Classes of Circuit breakers Circuit breaker Ur < kv Cable-system Class CS S SLF? No Line-system Class S LS Direct connection to OH line Yes Cable-system Class S LS Direct connection to OH line Yes Short-line fault breaking performance is required only for class S TRV HV Circuit Breakers P 9

110 Harmonization of EC & EEE Standards Examples of TRVs Table Standard values of transient recovery voltage for class S circuit-breakers Rated voltage 4 36 U r kv 7,5 Type of test Terminal fault Terminal fault Terminal fault Out-ofphase Terminal fault Out-ofphase Out-ofphase Out-ofphase First-poleto-clear factor k pp p.u. Amplitude factor k af p.u. TRV peak value u c kv Time t 3 μs Time delay t d μs RRRV a u c /t 3 kv/μs,5,4,6 6 9,34,5,5 3,6 8,5,5,4 4, 87 3,47,5,5 6, 74 6,35,5,4 6,7 9 6,57,5,5 9,9 8 33,4,5, ,75,5, ,56 RRRV: Rate of rise of recovery voltage TRV HV Circuit Breakers P

111 Harmonization of EC & EEE Standards Examples of TRVs Table Standard values of transient recovery voltage for class S circuit-breakers Rated voltage Type of test First-poleto-clear factor Amplitude factor TRV peak value Time Time delay RRRV a U r k pp k af u c t 3 t d u c /t 3 kv p.u. p.u. kv μs μs kv/μs 4 Terminal fault,5,54 45,3 43,5 Short-line fault,54 3, 43,7 Out-of-phase,5, ,7 36 Terminal fault,5,54 67,9 57 3,9 Short-line fault,54 45,3 57 3,79 Out-of-phase,5, ,8 7,5 Terminal fault,5, ,47 Short-line fault,54 9, 93 5,98 Out-of-phase,5, ,99 TRV HV Circuit Breakers P

112 Harmonization of EC & EEE Standards Amplitude factor of TRVs for cable systems and line systems k af (p.u.),9,8,7 Line systems,6,5,4 Cable systems TRV HV Circuit Breakers P,3,, Amplitude factor (k af ) as function of the short-circuit current ( sc is the rated short-circuit current) % sc

113 Harmonization of EC & EEE Standards Short-line-fault requirements Short-line fault tests (SLF) are mandatory for circuit-breakers with rated voltages of 5 kv and above, that are directly connected to overhead lines This requirement was limited in edition. of EC 67- to rated voltages of 5 kv and above. For circuit-breakers rated 48,3 kv, 5 kv and 7,5 kv the tests comprise a test duty L 9 and a test duty L 75. n the voltage range of 5 kv up to and including 38 kv, the test duty L 9 has been deleted and the tolerances on the line length for L 75 have been adapted (7% to 79% SLF). TRV HV Circuit Breakers P 3

114 Harmonization of TRVs for Circuit Breakers of Rated Voltages Equal or Higher than kv

115 Harmonization of EC & EEE Standards The harmonization of TRVs for circuit-breakers of rated voltages equal or higher than kv was prepared by a common EC-EEE Working Group. The most significant change proposed was the adoption by EEE of the two-parameter and four-parameter description of TRVs that is used in EC. Previously, for breaking tests with short-circuit current equal or higher than 6% of the rated value, ANS/EEE specified a TRV with a so-called exponential-cosine waveshape i.e. the envelope of two curves as shown on the next slide. t was also proposed that EC changes some values of TRV parameters and adopts a two-parameter TRV for test duty T3 (at 3% of rated short-circuit breaking current). TRV HV Circuit Breakers P 5

116 Harmonization of EC & EEE Standards Voltage U(kV) 5. u c & E 4-Parameter Reference Line. E 5. u. 5. Exponential - Cosine Envelope t t T t(us) Exponential-Cosine TRV envelope from ANS/EEE and the new four-parameter TRV harmonized with EC TRV HV Circuit Breakers P 6

117 Harmonization of EC & EEE Standards The revisions of EEE standards C37.4 and C37.6 introduce the four-parameter waveshape, as defined in EC 67-, the first segment (from O to u -t ) is tangent to the exponential part of the former waveshape and that third segment is tangent to the peak value of TRV. The choice of parameters ensures that the TRV defined with four parameters covers the old one defined by the exponential-cosine waveshape. The first reference point (u -t ) of the four-parameter envelope is higher than the corresponding point of the exponential-cosine envelope, this fact prompted the EC-EEE WG to recommend having a compromise value, equal to u,75 kppu r 3 where k pp is the first pole to clear factor and U r is the rated voltage. TRV HV Circuit Breakers P 7

118 Harmonization of EC & EEE Standards The recommendations from the WG were approved by EC and lead to amendment to EC 67- published in May. The RRRV for test duty T (at % of rated short-circuit breaking current) was set to 7 kv/µs, for all rated voltages. The TRV peak for test duty T is increased to better cover the cases of long line faults (k af =.76). EEE has approved the same TRV values in EEE C37.4b-8 Amendment : To Change the Description of Transient Recovery Voltage for Harmonization with EC 67- EEE C37.9b- Amendment : To Change the Description of Transient Recovery Voltage for Harmonization with EC 67- n addition, EEE has kept alternative values with a first-pole-to-clear factor of.5 for all rated voltages (to cover three-phase ungrounded faults). TRV HV Circuit Breakers P 8

119 Harmonization of EC & EEE Standards Conclusion Major advances have been made during 5 years (995-) towards the harmonization of EC and ANS/EEE standards for high-voltage circuit breakers. t allows to perform common tests for capacitive current switching, making and breaking short-circuit currents. Harmonization of TRVs is completed with harmonized values in amendment to EC 67-, amendments to EEE C37.4 and 9. TRV HV Circuit Breakers P 9

120 Harmonization of EC & EEE Standards Bibliography D. Dufournet - Harmonization of EC and EEE Standards for High-Voltage Circuit-Breakers and Guidance for Non-standard Duties, CGRE nternational Technical Colloquium, September &3, 7 Wagner C.L., Dufournet D., Montillet G. - "Revision of the Application Guide for Transient Recovery Voltage for AC High- Voltage Circuit-breakers of EEE C37.: A Working Group Paper of the High Voltage Circuit-breaker Subcommittee", EEE Transactions on Power Delivery, January 7, pp Smith K., Dufournet D. - Harmonization of EC and EEE TRV waveforms, Tutorial on Power Circuit-breakers presented at EEE PES General Meeting in Pittsburgh, 8. TRV HV Circuit Breakers P

121 Annexes

122 TRV HV Circuit Breakers P Annex A First-Pole-to-Clear Factor (Symmetrical components)

123 TRV HV Circuit Breakers P 3 Symmetrical Components C.L.Fortescue published a paper in 98 in which he proposed a method to resolveanunbalancedsetofnphasorsintoasystemof n- balanced sequence components and one zero-sequence component. The so-called symmetrical components thus created are commonly used for the analysis of 3-phase electrical systems. A vector for three-phase voltages and corresponding symmetrical components can be written as where a is an operator that rotates any phasor quantity by Subscripts, and refer respectively to the zero sequence, positive sequence and negative sequence components. U U U a a a a U U U T S R T S R U U U a a a a U U U 3 /3 j a e First-Pole-to-Clear Factor Calculation

124 First-Pole-to-Clear Factor Calculation Symmetrical Components llustration of 3 unbalanced voltages V a, V b and V c that are each the sum of balanced components (positive sequence, negative sequence and zero sequence) Positive sequence components Negative sequence components Zero sequence components TRV HV Circuit Breakers P 4

125 First-Pole-to-Clear Factor Calculation Three-phase circuit with a threephase terminal fault. E R S U R U S Figure shows the situation just after interruption by the first pole. T U T Using symmetrical components U U R U U U S T E R U U S T U U a a U avec U a a a U U j /3 e () = positive-sequence reactance = negative-sequence reactance = zero-sequence reactance TRV HV Circuit Breakers P 5

126 TRV HV Circuit Breakers P 6 Replacing U, U and U in () a (4) (3): a (3) (4): a E a a E a E a a a E a a a () (3) (4) a a (5) E E a a a (6) First-Pole-to-Clear Factor Calculation

127 TRV HV Circuit Breakers P 7 From (5): From () and (7): and From (6): From () and (8): (7) E E E (9) (8) () First-Pole-to-Clear Factor Calculation

128 TRV HV Circuit Breakers P 8 f : 3 E U E E U E E U E U E U U U U U R R R R R R 3 3 E U k R pp First-Pole-to-Clear Factor Calculation

129 First-Pole-to-Clear Factor Calculation Application of the basic formula Systems with non-effectively grounded neutral is much larger than, then: Systems with effectively grounded neutral by definition, is equal or lower than 3, then the highest value of k pp is: k pp k pp n the case of UHV systems, the ratio / is close to, as the system is radial and high power transformers have a great influence on this ratio, it follows that k pp is in this case near 6 / 5 =.. k pp TRV HV Circuit Breakers P 9

130 First-Pole-to-Clear Factor Calculation k pp,6,4,,3,8,6,4,,5,5,5 3 k pp,6,4,,8,6,4, / TRV HV Circuit Breakers P /