Transient Recovery Voltages (TRVs) for High Voltage ...

1 Transient Recovery Voltages ( trvs )for high Voltage circuit BreakersCalgary, October 16th2008 Denis DufournetIEEE FellowChairman IEC TC17 Senior Expert Areva T&D> Transient Recovery Voltages , October 200822 IntroductionXImportance of TRV The TRV is a decisive parameter that limits the interrupting capability of a circuit breaker . The interrupting capability of a circuit breaker was found to be strongly dependent on TRV in the 1950 s. Standard requirements for TRV were first introduced in1971: in (IEEE Std.)

2 327) and IEC 56. When developing interrupting chambers, manufacturers must check and prove the withstand of trvs specified in the standards for different test duties. Users must specify trvs in accordance with their applications. Test laboratories must define test circuits that meet the TRV requirements. > Transient Recovery Voltages , October 200833 ContentXGeneral considerations on trvs , types of TRV, current asymmetry and circuit - breaker influence on TRVXT erminal fault First pole to clear TRV ratings Arcing times & trvs Special case of Generator circuit -breakersXShort-line faultXITRV (Initial TRV)XOut-of-phaseX(Long) Line faultsXApplication considerationsXSelection of circuit breakers for TRV> Transient Recovery Voltages , October 200844 General considerations on Transient Recovery Voltages ( trvs )

3 > Transient Recovery Voltages , October 200855 TRV for high - Voltage circuit BreakersXThe Recovery voltageis the Voltage which appears across the terminals of a pole of circuit breaker after current interruption. XsUABR ecoveryvoltageCurrentTransient Recovery Voltage Power frequency Recovery voltageRecovery Voltage > Transient Recovery Voltages , October 200866 TRV for high - Voltage circuit BreakersXCurrent Interruption Process (in gas blast circuit breakers)Two contacts are separated in each interrupting chamber.

4 An arc is generated, it is cooled and extinguished when current passes through zero. > Transient Recovery Voltages , October 200877 TRV for high - Voltage circuit BreakersXDuring the interruption process, the arc loses rapidly its conductivity as the instantaneous current approaches zero. XDuring the first microseconds after current zero, the TRV withstand is function of the energy balance in the arc: thermal phase of , the Voltage withstand is function of the dielectric withstandbetween contacts: dielectric phase of interruption.

5 XThe breaking operation is successful if the circuit breaker is able to withstand the TRV and the power frequency Recovery TRV is the difference between the Voltages on the source side and on the load side of the circuit circuit breakers: within a few microseconds after current zero, arc resistance (Rarc)reaches 1 million ohms in a few microsecondsand current stops flowing in the (kV)I (A)> Transient Recovery Voltages , October 200888 TRV for high - Voltage circuit BreakersXThermal Restrike During tens of microseconds around current zero, the evolution of arc resistance is function of the energy balance in the arc the difference over time between the power input (Uarcx I = Rarc.)

6 I2) and the power loss by gas cooling. If the gas blast is not sufficient,the arc resistance stop increasing after current zero, it decreases to a low value, as a consequence the interval between contacts becomes conductive again. This type of restrike is called a thermal restrike. Arc model: Rarc= arc resistance Ploss= dissipated power = arc time constant Uarc= arc Voltage I = currentlossarcarcarcPIURdtdR =1> Transient Recovery Voltages , October 200899 TRV for high - Voltage circuit BreakersXThe nature of the TRV is dependent on the circuit being interrupted, whether primarily resistive, capacitive or inductive, (or some combination).

7 XWhen interrupting a fault at the circuit breaker terminal (terminal fault) in an inductive circuit , the supply Voltage at current zero is maximum. The circuit breaker interrupts at current zero (at a time when the power input is minimum) the Voltage on the supply side terminal meets the supply Voltage in a Transient process called the TRV. TRV frequency is withL = short- circuit inductanceC = supply 21> Transient Recovery Voltages , October 20081010 TRV for high - Voltage circuit BreakersCurrent and TRV waveforms during interruption of inductive currentCURRENTTRANSIENT RECOVERYVOLTAGE Supply Voltage > Transient Recovery Voltages , October 20081111 TRV for high - Voltage circuit BreakersTRV and Recovery Voltage in resistive, inductive and capacitive circuits-2-1,5-1-0,500,511,522,500,0050, 010,0150,020,0250,030.

8 035 RESISTIVE CIRCUITINDUCTIVE circuit (with stray capacitance)CAPACITIVE circuit > Transient Recovery Voltages , October 20081212 TRV for high - Voltage circuit BreakersXCombination of the former basic cases are possibleXExample #1: the TRV formainly active load current breakingis a combination of trvs associated with the inductive and resistive components of the circuit . They are specified for high - Voltage switches only as circuit -breakers are able to interrupt with more severe trvs (in inductive circuits).> Transient Recovery Voltages , October 20081313 TRV for high - Voltage circuit BreakersExample #2.

9 circuit with capacitive and inductive a circuit with a low short- circuit power, the Recovery Voltage during interruption of a capacitive loadis the sum a (1 cos) wave-shape on the load side and a Voltage oscillation on the supply side due a Transient across the short- circuit (inductive) reactance at the time of initial Voltage jump tends to increase the minimum arcing time and therefore to increase the shortest duration between contact separation and the instant of peak Recovery standards, the Voltage jump is limited in amplitude in order to test with the more severe condition.

10 > Transient Recovery Voltages , October 20081414 TRV for high - Voltage circuit BreakersXFault interruptions are often considered to produce the most onerous trvs . Shunt reactor switching is one of the exceptions. XTRVs can be oscillatory, triangular, or exponentialand can occur as a combination of these forms. XThe highest TRV peaks are met during capacitive currentand out-of-phase current interruption,XTRVs associated with the highest short- circuit currentare obtained during terminal faultand short-line-fault general, a network can be reduced to a simple parallel RLC circuit for TRV calculations.