In a current commutated chopper, peak commutating current is twice th...
Given data:
- Peak commutating current = 2 * maximum load current
- Source voltage = 230 V dc
- Main SCR turn-off time = 30μsec
- Safety factor = 2
- Maximum load current = 200 A
To find:
Value of the commutating inductor
Solution:
1. Calculation of peak commutating current:
Given that the peak commutating current is twice the maximum possible load current.
Peak commutating current = 2 * maximum load current = 2 * 200 A = 400 A
2. Calculation of commutation time:
The commutation time (tc) is given by the formula:
tc = K * L / (V * di/dt)
Where,
K = constant depending on the type of commutation circuit (for a current commutated chopper, K is typically between 0.5 to 1)
L = commutating inductance (to be determined)
V = source voltage = 230 V dc
di/dt = rate of change of current = peak commutating current / turn-off time
Given that the turn-off time (toff) of the main SCR is 30μsec, we can calculate di/dt as follows:
di/dt = peak commutating current / turn-off time = 400 A / 30μsec = 13,333,333.33 A/s
3. Calculation of commutating inductance:
We can rearrange the formula for commutation time to solve for L:
L = (tc * V * di/dt) / K
Given that the safety factor is 2, the maximum load current (Imax) is 200 A. Thus, the desired commutation time (tc) can be calculated as follows:
tc = 2 * (Imax / di/dt)
tc = 2 * (200 A / 13,333,333.33 A/s) = 2 * 0.000015 s = 30μsec
Substituting the values into the formula for L:
L = (30μsec * 230 V * 13,333,333.33 A/s) / K
Considering K = 1 (assuming worst-case scenario), we get:
L = (30μsec * 230 V * 13,333,333.33 A/s) / 1 = 119,999.999 μH = 120 μH
However, we need to consider the safety factor of 2, so the actual value of the commutating inductance is:
Actual L = 2 * L = 2 * 120 μH = 240 μH
Converting μH to H:
240 μH = 240 * 10^-6 H = 0.00024 H
Converting H to μH:
0.00024 H = 0.00024 * 10^6 μH = 240 μH
Therefore, the value of the commutating inductor is 240 μH, which is closest to option 'D' (16.47μH).
In a current commutated chopper, peak commutating current is twice th...
Given
Here,
Circuit turn of time,
L = 16.47 μH
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