CONDITIONS FOR SUCCESSFUL INTERRUPTION: 3) The circuit-breaker must pass the dielectric interrupting mode Tarc Interruption 2) The circuit-breaker must pass the thermal interrupting mode 1) After contact parting there must be current zeros present Contact parting Current Recovery voltage 2) The circuit-breaker must pass the thermal interrupting mode 1) After contact parting there must be current zeros present Contact parting Current Recovery voltage Contact parting 1) After contact parting there must be current zeros present Current Current

THERMAL INTERRUPTION Current time Voltage Current at failed thermal interruption Arc voltage after failed thermal interruption Electric conductivity after failed thermal interruption Current Voltage time Post arc current Rising voltage after clearing thermal interruption Electric conductivity at successful thermal interruption

DIELECTRIC INTERRUPTION Current at failed dielectric interruption Insufficient voltage withstand capability for successful interruption. Dielectric failure Rising voltage after clearing thermal interruption Current Voltage time Insufficient voltage withstand capability for successful interruption. Dielectric failure Rising voltage after clearing thermal interruption Voltage withstand capability for successful interruption Rising voltage after clearing thermal interruption

CONDITIONS FOR INTERRUPTION Conditions for successful interruption: 1) After contact parting there must be current zeros present 2) The circuit-breaker must pass the thermal interrupting mode 3) The circuit-breaker must pass the dielectric interrupting mode Conclusion: The interrupting performance is strongly related to the arcing time

LIMITATIONS FOR SUCCESSFUL INTERRUPTION Random interruption Voltage Current Dielectric limit Additional performance by controlled interruption ??? ? Thermal limit

LIMITATIONS FOR SUCCESSFUL INTERRUPTION Random interruption Voltage Current Possible upgrading area by means of controlled switching No thermal interrupting stress

INCREASED DIELECTRIC PERFORMANCE Approach: Controlled reactor switching has become an accepted method for making circuit-breakers reignition free

SOLVING AN INHERENT PROBLEM Recovery voltage phase R phase Y phase B Voltage withstand capability RRDS

DE-ENERGISING A GROUNDED REACTOR BANK Controlled contact partings

SOLVING AN INHERENT PROBLEM Supply side voltage Load side voltage Voltage across CB Current Contact travel Trip coil current Reignition 4 ms

SOLVING AN INHERENT PROBLEM Supply side voltage Load side voltage Voltage across CB Current Contact travel Trip coil current 9 ms

RRDS Rate of Rise of Dielectric Strength at opening Voltage withstand characteristic of the circuit-breaker contact gap at opening, RRDS Contact separation Instant 2 RRDS at min. arcing time Uacross CB Tarcmin Typical: TARCMIN  4 ms (Shorter arcing times will result in re-ignition) Window allowing Reignition-free operation SAFE contact parting area Uacross CB Contact separation Instant 1 Uacross CB Uacross CB Current REACTOR CURRENT INTERRUPTION SESWGBTA 1999-05-11 SWITCHSYNC.PPT USource

DE-ENERGISING OF CAPACITIVE LOAD + UB - Interruption + _ ~ I US UC UC US Bus voltage Load side voltage US = UC I time A discharged capacitor is similar to a momentary short-circuit when connected to a power source. If made when the source voltage is high, the connection results in voltage and current transients that may cause serious problems. Depending on the network configuration, the voltage surge may cause breakdown somewhere in the high voltage network, and low voltage equipment may suffer insulation damage or malfunction. With back-to-back capacitor banks, the inrush current may be steep and high enough to threaten the mechanical integrity of both capacitors and breaker. Synchronising the breaker to energise a capacitive load at source voltage zero will eliminate harmful transients. It is possible to use a three-pole operated circuit-breaker with staggered poles, together with a simple Switchsync model. The voltage measurement shown are from a commissioning test of a 72.5 kV capacitor bank by NESA in Denmark.

COMPARISON OF RECOVERY VOLTAGES Inductive and capacitive case Voltage across contacts Time T/2 = 10 ms at 50 Hz Capacitive current case Inductive current case  200 s Recovery voltages SESWGBTA 1999-05-11 SWITCHSYNC.PPT

COMPARISON OF RECOVERY VOLTAGES T/2 = 10 ms at 50 Hz Capacitive current case Inductive and capacitive case Inductive current case  200 s Inductive case Voltage across contacts Time Typical RRDS starting at minimum arcing time (0 ms) Typical RRDS starting at minimum arcing time (0 ms) Recovery voltages Typical RRDS starting several ms prior to current zero resulting in proper interruption SESWGBTA 1999-05-11 SWITCHSYNC.PPT

RECOVERY VOLTAGE VERSUS TYPICAL RRDS, capacitive case Time Voltage across contacts T/2 = 8,33 ms at 60 Hz T/2 = 10 ms at 50 Hz Typical RRDS starting some ms before current zero Upgrading potential at 60 Hz Typical RRDS starting at minimum arcing time (0 ms) T/2 = 7,58 ms at 66 Hz SESWGBTA 1999-05-11 SWITCHSYNC.PPT

Test circuit for determination of RRDS (“Cold characteristic”) 0 kV

Test circuit for determination of RRDS (“Cold characteristic”) 0 kV 0 kV

Test circuit for determination of RRDS (“Cold characteristic”) 0 kV 0 kV

Test circuit for determination of RRDS (“Cold characteristic”) 0 kV 0 kV

Test record from “Cold characteristic test” Contact parting Supply side voltage Load side voltage Limit of voltage withstand vs. time or distance Voltage across CB (160 Hz) Current Contact travel

Test record from “Cold characteristic test” Limit of voltage withstand vs. time or distance

Plot of RRDS vs. time for a certain condition

Plot of RRDS compared to a 50 Hz recovery voltage starting at minimum arcing time

Plot of RRDS compared to recovery voltages of 50 and 60 Hz and at minimum arcing times

Plot of RRDS compared to recovery voltages of different frequencies and at minimum arcing times

Plot of RRDS compared to recovery voltages of different frequencies and at minimum and prolonged arcing times

Plot of RRDS compared to recovery voltages of different frequencies and at minimum and prolonged arcing times

Plot of RRDS compared to recovery voltages of different frequencies and at minimum and prolonged arcing times About 15 % increased performance can be reached by pre-setting the arcing time by some ms.

Impact of missing arcing How to compare “Cold characterisic” with cap. Switching performance?

Impact of missing arcing How to compare “Cold characterisic” with cap. Switching performance? “Cold characteristic” determined RRDS fits well to reactor switching performance

Impact of missing arcing How to compare “Cold characterisic” with cap. Switching performance? “Cold characteristic” determined RRDS fits well to reactor switching performance “Full-scale” capacitive current switching tests show equal performance

IMPACT OF CONTROLLED INTERRUPTION OF CAPACITIVE CURRENTS Controlling the contact parting instant at interruption of capacitive loads can: - compensate for a lower gas density.

IMPACT OF CONTROLLED INTERRUPTION OF CAPACITIVE CURRENTS Controlling the contact parting instant at interruption of capacitive loads can: - compensate for a lower gas density. - compensate for lower contact speed.

IMPACT OF CONTROLLED INTERRUPTION OF CAPACITIVE CURRENTS Controlling the contact parting instant at interruption of capacitive loads can: - compensate for a lower gas density. - compensate for lower contact speed. - improve the "safety" against restrikes by increasing the voltage withstand margin and taking care of scatter in the early stage.

IMPACT OF CONTROLLED INTERRUPTION OF CAPACITIVE CURRENTS Controlling the contact parting instant at interruption of capacitive loads can: - compensate for a lower gas density. - compensate for lower contact speed. - improve the "safety" against restrikes by increasing the voltage withstand margin and taking care of scatter in the early stage. - can make a circuit-breaker capable to operate in networks with higher frequencies if the performance at random switching is not good.

IMPACT OF CONTROLLED INTERRUPTION OF CAPACITIVE CURRENTS Controlling the contact parting instant at interruption of capacitive loads can: - compensate for a lower gas density. - compensate for lower contact speed. - improve the "safety" against restrikes by increasing the voltage withstand margin and taking care of scatter in the early stage. - can make a circuit-breaker capable to operate in networks with higher frequencies if the performance at random switching is not good. - compensate for ageing represented by contact burn-off.

IMPACT OF CONTROLLED INTERRUPTION OF CAPACITIVE CURRENTS Controlling the contact parting instant at interruption of capacitive loads can: - compensate for a lower gas density. - compensate for lower contact speed. - improve the "safety" against restrikes by increasing the voltage withstand margin and taking care of scatter in the early stage. - can make a circuit-breaker capable to operate in networks with higher frequencies if the performance at random switching is not good. - compensate for ageing represented by contact burn-off. If restrike-free perfomance at capacitive current switching is a limiting factor, controlled interruption is a useful tool for uprating.

IMPACT OF CONTROLLED INTERRUPTION OF CAPACITIVE CURRENTS Controlling the contact parting instant at interruption of capacitive loads can: - compensate for a lower gas density. - compensate for lower contact speed. - improve the "safety" against restrikes by increasing the voltage withstand margin and taking care of scatter in the early stage. - can make a circuit-breaker capable to operate in networks with higher frequencies if the performance at random switching is not good. - compensate for ageing represented by contact burn-off. If restrike-free perfomance at capacitive current switching is a limiting factor, controlled interruption is a useful tool for uprating. Pre-set arcing time will not be longer than average: reduction of contact wear

IDEAL CASES FOR ADAPTING CONTROLLED OPENING OF CAPACITIVE LOADS FREQUENT OPERATIONS REINSERTION OF LINE SERIES CAPACITORS voltage steepness may be high due to power swing SWITCHING OFF HARMONIC FILTER BANKS initial slope of the recovery voltage is steeper and the peak is higher due to the harmonic content. When beeing used in combination with thyristor controlled equipment commutation transients may also be added to the recovery voltage across the circuit-breaker, thus increasing the risk.

APPLICATION WITH CONTROLLED DE-ENERGISING OF GROUNDED CAPACITOR BANK

LIMITATIONS FOR SUCCESSFUL INTERRUPTION Random interruption Voltage Current Possible upgrading area by means of controlled switching Thermal interrupting stress

FUTURE? Controlled fault interruption? Increased electrical life and improved performance compared to random fault interruption? Tarc Blast pressure Pressure required for interruption Pressure at current zero, new CB Normal "arc extinguishing window” >1/2 cycle Narrow window with increased interrupting capability Reduced pressure build-up at current zero in worn CB A discharged capacitor is similar to a momentary short-circuit when connected to a power source. If made when the source voltage is high, the connection results in voltage and current transients that may cause serious problems. Depending on the network configuration, the voltage surge may cause breakdown somewhere in the high voltage network, and low voltage equipment may suffer insulation damage or malfunction. With back-to-back capacitor banks, the inrush current may be steep and high enough to threaten the mechanical integrity of both capacitors and breaker. Synchronising the breaker to energise a capacitive load at source voltage zero will eliminate harmful transients. It is possible to use a three-pole operated circuit-breaker with staggered poles, together with a simple Switchsync model. The voltage measurement shown are from a commissioning test of a 72.5 kV capacitor bank by NESA in Denmark.

WHAT CAN BE REACHED? Increased electrical life compared to random interruption Increased interrupting margins Slightly increased performance A discharged capacitor is similar to a momentary short-circuit when connected to a power source. If made when the source voltage is high, the connection results in voltage and current transients that may cause serious problems. Depending on the network configuration, the voltage surge may cause breakdown somewhere in the high voltage network, and low voltage equipment may suffer insulation damage or malfunction. With back-to-back capacitor banks, the inrush current may be steep and high enough to threaten the mechanical integrity of both capacitors and breaker. Synchronising the breaker to energise a capacitive load at source voltage zero will eliminate harmful transients. It is possible to use a three-pole operated circuit-breaker with staggered poles, together with a simple Switchsync model. The voltage measurement shown are from a commissioning test of a 72.5 kV capacitor bank by NESA in Denmark.

FUTURE? Controlled fault interruption? Infoga tabellen A discharged capacitor is similar to a momentary short-circuit when connected to a power source. If made when the source voltage is high, the connection results in voltage and current transients that may cause serious problems. Depending on the network configuration, the voltage surge may cause breakdown somewhere in the high voltage network, and low voltage equipment may suffer insulation damage or malfunction. With back-to-back capacitor banks, the inrush current may be steep and high enough to threaten the mechanical integrity of both capacitors and breaker. Synchronising the breaker to energise a capacitive load at source voltage zero will eliminate harmful transients. It is possible to use a three-pole operated circuit-breaker with staggered poles, together with a simple Switchsync model. The voltage measurement shown are from a commissioning test of a 72.5 kV capacitor bank by NESA in Denmark.