Special Requirements of IEEE C for Generator Circuit Breaker Applications

Transcription

1 Special Requirements of IEEE C for Generator Circuit Breaker Applications November 20, 2009 Schutzvermerk / Copyright-Vermerk Siemens AG 2009

2 Generator Circuit Breaker Applications What is different about generator circuit breakers? Applicable standards Special considerations Vacuum versus SF6 technology Questions. Folie 2

3 Generator and Distribution Circuit Breakers Generator circuit breaker Distribution circuit breaker Folie 3

4 Circuit Breakers for Distribution Requirements Standards: IEEE C37.04 IEEE C37.09 IEEE C37.10 X/R ratio: Time constant of dc decay: Rating structure for HV circuit breakers Tests for HV circuit breakers Application guide for HV circuit breakers. 17 (60 Hz). 45 ms. TRV typical values (15 kv, class S1 cable): Peak voltage (uc) = 25.7 kv Time-to-peak (t3) = 66 µs RRRV 0.39 kv/µs. Duty cycle: Folie 4 O t CO t CO t = 0.3 s for reclosing / 15 s for non-reclosing t = 3 minutes.

5 Circuit Breakers for Generation Requirements Standards: IEEE C Generator circuit breaker. X/R ratio: Time constant of dc decay: 50 (60 Hz). 133 ms. TRV typical values (15 kv, 100 MVA machine): Peak voltage (E2) = 1.84 V = 1.84 x 15.0 = 27.6 kv Time-to-peak (T2) = 0.62 V = 0.62 x 15.0 = 9.3 µs RRRV 3.5 kv/µs. Duty cycle: CO 30 min CO. Folie 5

6 Notes on TRV Representation IEEEC37.04 for distribution circuit breakers expresses TRV in terms harmonized with IEC with peak voltage uc, and time-to-peak t3. IEEE C still uses old TRV expressions with peak voltage E2 and time-to-peak T2. Peak voltage is not changed, but t3 is approximately 0.88 x T2. The physics are not changed, just the representation. Folie 6

7 IEEE C Scope IEEE Standard Rating Structure for AC High-Voltage Circuit Breakers 1. Scope This standard establishes a symmetrical current rating structure and construction requirements for all indoor and outdoor types of ac high-voltage circuit breakers rated above 1000 V. It is only applicable to three-pole circuit breakers used in three-phase systems and single-pole circuit breakers used in single-phase systems. This standard does not cover circuit breakers used at frequencies other than 50 Hz or 60 Hz, or generator circuit breakers that are covered in IEEE Standard C Folie 7

8 IEEE C Scope IEEE Standard for AC High-Voltage Generator Circuit Breakers Rated on a Symmetrical Current Basis 1. Scope This standard applies to all ac high-voltage generator circuit breakers rated on a symmetrical current basis that are installed between the generator and the transformer terminals... Note: Since no other national or international standard on generator circuit breakers exists, this standard is used worldwide. Folie 8

9 IEEE C the International Standard for Generator Circuit Breakers IEEE C Revision PAR (Project) PAR approved by IEEE-SA Standards Board, March, 2009 Joint development with IEC SC 17A (HV Switchgear and Controlgear) IEEE WG chair is convenor (WG chair) of IEC working group. IEC has no standard for a generator circuit breaker. The IEEE and IEC intent has been that IEEE C would be the global standard. IEC SC 17A WG 52 WG scope: Joint IEC/IEEE revision of IEEE C37.013: IEEE Standard for AC High- Voltage Generator Circuit Breakers Rated on a Symmetrical Current Basis Folie 9

10 X/R Ratio Determines %dc Component X/R = 17, τ = 45 ms X/R = 50, τ = 133 ms %dc vs Contact Part for X/R = 17 and X/R = %dc Component Folie 10 Contact Part time (ms) X/R = 17 X/R = 50

11 X/R Ratio Effect on Asymmetrical Interrupting Current (Isc = 1.00) Instantaneous (total) current dc component S-factor (C ) dc component (in decimal form) (multiply by 100 for %dc component) (C ) Folie Symmetrical current (ac component) Time (in degrees)

12 X/R Ratio Effect on Asymmetrical Interrupting S = I I total symmetrical = 1+ 2(% dc /100) S factor (from IEEE C ) Ratio of rms asymmetrical current to rms symmetrical current Assume contact part time of 55 ms, and 50 ka symmetrical current X/R = 17 %dc = 29.5 S = I = 54.2 ka X/R = 50 %dc = 66.1 S = I = 68.5 ka over 26% higher Folie 12

13 Short-Circuit Currents Consider system shown: Transformer 1,000 A full load (self-cooled) impedance = 10% Generator 1,000 A full load Xd (subtransient reactance) = 20% For fault at F2, circuit breaker sees transformer fault current, roughly 1,000 A / 0.10 = 10 ka For fault at F1, circuit breaker sees generator fault current, roughly 1,000 A / 0.20 = 5 ka G F1 F2 Note: Fault current for generator source fault is only about 50% of fault current for system (transformer) source fault Folie 13

14 Generator Circuit Breaker Ratings Characteristic Maximum voltage Dielectric 60 Hz / BIL Short-circuit current Transformer source Generator source %dc component Delayed current zero* TRV parameters Peak voltage (1.84 V) RRRV transformer source RRRV generator source * Higher values may be available Folie 14 Unit kv kv/kv ka ka % ms kv kv/µs kv/µs Drawout (Metal-Clad) / / / / / / / 1.8 Fixed- Mounted / / 63 / / 31.5 / / 65 / / 30 / / 4.5 / / 1.8 / 1.8

15 Generator Circuit Breakers Folie 15

16 Generator Circuit Breakers Folie 16

17 Out-of-Phase Switching Circuit Breakers for Standard Applications: IEEE C37.04 (clause 5.12): Out-of-phase switching is optional, not required for general purpose circuit breakers If a rating is assigned, the preferred rating is 25% of the rated symmetrical interrupting rating, with recovery voltage of (250% rated voltage / 1.732). Therefore, out-of-phase ratings are not typically assigned to general purpose circuit breakers rated per IEEE C37.04 and tested to IEEE C Folie 17

18 Out-of-Phase Switching Circuit Breakers for Generator Switching Applications: IEEE C (clause 6.2.9): Out-of-phase switching is optional, not required for generator circuit breakers If a rating is assigned, the assigned rating is shall be 50% of the rated symmetrical interrupting rating (transformer or system source). Out-of-phase switching recovery voltage values are based on a maximum out-of-phase condition of 90 degrees between generator and system. This is reasonable as more extreme angles would result in damage to the machine. The likelihood of out-of-phase switching is influenced by generator inertia, i.e., low-inertia machines are more likely to be subject to out-of-phase switching conditions. Generator circuit breakers should have an assigned out-of-phase switching rating. Folie 18

19 Other Differences Reclosing: Reclosing duty not required for generator circuit breakers. Short-time current duration: Normal circuit breakers 3 seconds (metal-clad switchgear = 2 seconds) Generator circuit breakers 1.0 second (typically test to 3 seconds). Closing & latching rating: Normal circuit breakers Peak current 260% of symmetrical short-circuit (60 Hz) With X/R = 17, real peak is 259.3% Generator circuit breakers Peak current 274% of symmetrical short-circuit (60 Hz) With X/R = 50, real peak is 274.2%. Folie 19

20 Delayed Current Zero Example C Current (unitized) Time (ms) Folie 20

21 Delayed Zero Test Example 20.6 ms 30.0 ms 40.1 ms 57.7 ms Folie 21

22 Generator Circuit Breaker Technologies Vacuum Well-suited to smaller units (up to 6,000 A or so) Most economic for small units Derived from proven distribution unit operators and interrupters High experience-base Very low arc voltage (20-50 V) Little affect on X/R ratio Lower arc voltage = less arc energy = lower contact erosion SF 6 Only option for very large units VERY expensive Unlike distribution products Lower experience-base SF 6 low arc voltage (several 100 V) Somewhat higher impact on X/R ratio Higher arc voltage = higher arc energy = greater contact erosion Extremely rapid recovery of dielectric strength between contacts after interruption good for extreme TRV levels Less able to cope with high TRV levels Folie 22