CONDITIONS FOR SUCCESSFUL INTERRUPTION

2003-04 FLORIDA WORKSHOP.PPT

CONDITIONS FOR SUCCESSFUL INTERRUPTION:

Current Contact parting

1) After contact parting there must be current zeros present

Current

2) The circuit-breaker must pass the thermal interrupting mode


Contact parting Current

Recovery voltage

3) The circuit-breaker must pass the dielectric interrupting mode

Tarc

Interruption

2) The circuit-breaker must pass the thermal interrupting mode


Contact parting Current

Recovery voltage


THERMAL INTERRUPTION

Post arc current

Rising voltage after clearing thermal interruption

Electric conductivity at successful thermal interruption

Current

Voltage

time

time

Current at failed thermal interruption

Arc voltage after failed thermal interruption

Electric conductivity after failed thermal interruption


DIELECTRIC INTERRUPTION

Current

Voltage

time

time

Current at failed dielectric interruption

Insufficient voltage withstand capability for successful interruption.

Dielectric failure


Insufficient voltage withstand capability for successful interruption.

Dielectric failure



Voltage withstand capability for successful interruption


CONDITIONS FOR INTERRUPTION

Current

Recovery voltage

Contact parting

Interruption

Tarc

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


Additional performance by controlled interruption ???

LIMITATIONS FOR SUCCESSFUL INTERRUPTION

Random interruption Voltage

Current

Dielectric limit

Thermal limit

? ?

? ?

?

?


Possible upgrading area by means of controlled switching



Current 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

Recovery voltage phase Y

Recovery voltage phase B

Voltage withstand capability RRDS


DE-ENERGISING A GROUNDED REACTOR BANK

Controlled contact partings



Reignition

Supply side voltage

Load side voltage

Voltage across CB

Current

Contact travel

Trip coil current

4 ms



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

Tarcmin

Typical: TARCMIN ≥ 4 ms (Shorter arcing times will result in re-ignition)

Window allowing Reignition-free operation

SAFE contact parting area

USource

Current

RRDS at min. arcing time

Uacross CB

Voltage withstand characteristic of the

circuit-breaker contact gap at opening,

RRDS

REACTOR CURRENT INTERRUPTION

Uacross CB Uacross CB Uacross CB

Contact separation Instant 1

Contact separation Instant 2


DE-ENERGISING OF CAPACITIVE LOAD

+ +

_ _

~

I

US UC

US = UC

I

time

+ UB -

Interruption

UC

US Bus voltage

Load side voltage


T/2 = 10 ms at 50 Hz

Capacitive current case

Recovery voltages

Inductive current case

≈ 200 µs

COMPARISON OF RECOVERY VOLTAGES Inductive and capacitive case

Volta

ge a

cros

s co

ntac

ts

Time 0


Recovery voltages

COMPARISON OF RECOVERY VOLTAGES

Volta

ge a

cros

s co

ntac

ts

Time 0

Typical RRDS starting several ms prior to current zero resulting in proper interruption

Inductive current case

≈ 200 µs

Inductive case

Typical RRDS starting at minimum arcing time (0 ms)

T/2 = 10 ms at 50 Hz

Capacitive current case

Inductive and capacitive case




T/2 = 8,33 ms at 60 Hz

T/2 = 10 ms at 50 Hz Time

0

Volta

ge a

cros

s co

ntac

ts

RECOVERY VOLTAGE VERSUS TYPICAL RRDS, capacitive case

Typical RRDS starting some ms before current zero

T/2 = 7,58 ms at 66 Hz

Upgrading potential at 60 Hz


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

TB

U_LS

WB-Q14 WB-Q10 X3

S1 CH1

Uch +

-

shunt1

Cd

S1- G U_SS

W2

Rs ext

AB

S1-LF

Rf ext

shunt2

Synthetic test circuit Test cell

0 kV


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

TB

U_LS

WB-Q14 WB-Q10 X3

S1 CH1

Uch +

-

shunt1

Cd

S1- G U_SS

W2

Rs ext

AB

S1-LF

Rf ext

shunt2

Synthetic test circuit Test cell

0 kV 0 kV


Test record from “Cold characteristic test”

Supply side voltage

Load side voltage

Voltage across CB (160 Hz)

Current

Contact travel

Contact parting

Limit of voltage withstand vs. time or distance


Test record from “Cold characteristic test”

Limit of voltage withstand vs. time or distance


Plot of RRDS vs. time for a certain condition

0

0,5

1

1,5

2

2,5

3

3,5

0,0 5,0 10,0 15,0 20,0 25,0

"Arcing time" (ms)

Vol

tage

(p.

u.)

Withstand voltage

Breakdown voltage p.u.

RRDS COLD CHARACTERISTICAGED CB P=0.43 MPa(abs) Opening speed = 1.09 x m/s


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

0

0,5

1

1,5

2

2,5

3

3,5

0,0 5,0 10,0 15,0 20,0 25,0

"Arcing time" (ms)

Vol

tage

(p.

u.)

Withstand voltage

Requirement for 50 Hz




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

0

0,5

1

1,5

2

2,5

3

3,5

0,0 5,0 10,0 15,0 20,0 25,0

"Arcing time" (ms)

Vol

tage

(p.

u.) Withstand voltage






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

0

0,5

1

1,5

2

2,5

3

3,5

0,0 5,0 10,0 15,0 20,0 25,0

"Arcing time" (ms)

Vol

tage

(p.








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

0

0,5

1

1,5

2

2,5

3

3,5

0,0 5,0 10,0 15,0 20,0 25,0

"Arcing time" (ms)

Vol

tage

(p.


Requirement for 60 HzRequirement for 66 HzPossible upgrading for 66 HzRequirement for 50 HzBreakdown voltage p.u.



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

0

0,5

1

1,5

2

2,5

3

3,5

0,0 5,0 10,0 15,0 20,0 25,0

"Arcing time" (ms)

Vol

tage

(p.


Requirement for 60 HzRequirement for 66 HzPossible upgrading for 66 HzRequirement for 50 HzBreakdown voltage p.u.


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?



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



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.



Controlling the contact parting instant at interruption of capacitive loads can: - compensate for a lower gas density. - compensate for lower contact speed.



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.




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.





frequencies if the performance at random switching is not good. - compensate for ageing represented by contact burn-off.





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.





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


Possible upgrading area by means of controlled switching



Current Thermal interrupting stress


FUTURE? Controlled fault interruption?

Increased electrical life and improved performance compared to random fault interruption?

Reduced pressure build-up at current zero in worn CB

Pressure at current zero, new CB

Normal "arc extinguishing window” >1/2 cycle

Tarc

Blast pressure

Pressure required for interruption

Narrow window with increased interrupting

capability


WHAT CAN BE REACHED?

Increased electrical life compared to random interruption Increased interrupting margins Slightly increased performance


FUTURE? Controlled fault interruption?

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CONDITIONS FOR SUCCESSFUL INTERRUPTION

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