IEEE Std C37.012 pdf free download

IEEE Std C37.012 pdf free download.Application of Capacitance Current Switching for AC High-Voltage Circuit Breakers Above 1000V.
After interruption of the current, the source voltage u will be more or less unaffected. There is only a minor decrease in amplitude, associated with the disappearance of the capacitive load. The transition to the new amplitude value is associated with a slight oscillation, the frequency of which is determined by L and C’.
From the moment the current is interrupted, the charge of the capacitor bank C1 is trdpped. The voltage UL will therefore remain constant at the value it had at current zero (namely the peak value of the source voltage).
Together with the low current amplitude to be interrupted, the low initial rate-of-rise of the recovery voltage makes it extremely easy for the circuit breaker to interrupt. Some circuit breakers may interrupt even if the current zero would occur immediately after contact separation. 1-laIf a cycle after current zero, the recovery voltage has risen to an amplitude of no less than twice the peak value of the source voltage. Because the voltage peak occurs earlier, a rated frequency of 60 lIz is more severe than 50 lIz. The circuit breaker may then not be able to withstand the high value of the recovery voltage across a relatively small contact gap. Dielectric breakdown may occur between the contacts and current would start to flow again.
Figure 4 shows current and voltage wave shapes in a case where voltage breakdown occurs relatively close to the recovery voltage peak. The load side voltage recovers through an oscillation, the amplitude of which ideally (without damping present) reaches 3 times the source voltage peak u. The oscillation frequency of the current and voltage after the breakdown is determined by L and C1 (assuming C1 >> C’,). The circuit breaker may easily interrupt the current again at one of its current zeros, with the result that the voltage across the capacitor may attain a new constant value, perhaps higher than before. Further breakdowns associated with even higher overvoltages across the load may then occur (see also Figure 5).
Restnkes will lead to overvoltages across the capacitive load (max. 3 p.u. for a single restrike, where I p.u. is the peak value of the phase-to-ground voltage) while reignitions will not produce any overvoltages (theoretically max. 1 p.u.). Reignitions are acceptable, but they may cause power quality problems. as they represent a temporary short-circuit.
In reality, there are no restrike-free circuit breakers. It would take an infinite number of test shots to verif’ this. For this reason the concept of restrike classification using specified test procedures was introduced in IEEE Std C37.04a-2003.
Vhen interrupting small capacitive currents, some circuit breaker types may exhibit current chopping. Current chopping is an interruption prior to the natural power frequency current zero of the circuit connected to the circuit breaker. Ditierent types of circuit breakers have varying degrees of current chopping.
The effect of current chopping is that the trapped charge on the capacitive load will not be at its peak. This case results in a lower recovery voltage peak and a lower stress on the contact gap of the circuit breaker.IEEE Std C37.012 pdf download.