Question

The asymmetrical short-circuit current in series R–L circuit for a simulated solid or “bolted fault” can be considered as a combination of symmetrical (ac) component that is a _____, and dc-offset current that decays _____ and depends on _____.

Short answer

Therefore, the asymmetrical short-circuit current in series R–L circuit for a simulated solid or “bolted fault” can be considered as a combination of symmetrical (ac) component that is asinusoidal, and dc-offset current that decaysexponentially and dependson the instant of short circuit.

Step-by-step solution

Apply the Kirchhoff’s voltage law.

Consider the RL circuit below,

Apply KVL to the circuit above.

Here, i ( t ) is the loop current, R is the resistance, e ( t ) is the supply voltage and L is inductance.

Determine the answer.

Initially the switch is open, so current is zero.

Now, switch is closed and fault current is flowing through the circuit, considering fault impedance zero that is bolted.

The solution of current is divided into ac and dc.

Here, V is a peak voltage of supply, Z is series impedance, T is time period of switch, $\alpha$is phase between i ( t ) and e( t ) , is phase between e ( t ) and i_ac ( t ) .

So, from equation (1), i ( t ) is sinusoidal, exponential and fault current is appeared when switch is closed.

Therefore, the asymmetrical short-circuit current in series R–L circuit for a simulated solid or “bolted fault” can be considered as a combination of symmetrical (ac) component that is a sinusoidal, and dc-offset current that decays exponentially and depends on the instant of short circuit.