Thursday, 9 November 2017

Transient Recovery Voltage (TRV)

“The Transient Recovery Voltage refers to the voltage across the pole immediately after arc extinction. Such voltage has a power-frequency component plus an oscillatory transient component.”

In alternating current circuit breakers, the current interruption takes place invariably at the natural zero of the current wave. After a current zero, the arc gets extinguished if the Rate of Rise of Transient Recovery Voltage (RRRV) between the contacts is less than the rate of gain of the dielectric strength. The voltage appearing between the breaker contacts at the moment of final current zero has a great influence on the arc extinction process and consists of voltage of higher natural frequency called restriking voltage superimposed on the power frequency system voltage i.e. recovery voltage as shown in figure below. “Recovery voltage is the voltage which appears across the terminals of a pole of a circuit-breaker after the breaking of current.”


Notice here that, as the most of the portion of power system is inductive, therefore when current reaches zero, the voltage appearing across the contact will be maximum but soon as the current attains some value, the voltage across the contacts then follows the normal sinusoidal nature. Thus transient component of voltage vanishes after a short time and the normal frequency system voltage is established.

Thus we can say that, Transient Recovery Voltage (TRV) is the voltage appearing across the contacts immediately after arc extinction or current zero. Transient Recovery Voltage (TRV) has a power frequency component plus an oscillatory transient component as shown in figure above. The oscillatory transient component in Transient Recovery Voltage is due to the inductane and the capacitance of the power system whereas the power frequency component is due to the system voltage. The oscillatory component of Transient Recovery Voltage vanishes after a few micro seconds and the power frequency component continues. The frequency of transient component of Transient Recovery Voltage is given as


fn = frequcncy of transient recovery voltage in Hz

L = equivalent inductance in henry

C = equivalent capacitance in farad.

In actual systems the waveform of the Transient Recovery Voltage (TRV) has several component frequencies ranging from a few hertz to several thousand hertz, depending upon the values of the circuit parameters.

1 comment:

Ashish kumar Pandey said...