Generator Circuit Breaker: Can MV Cubicle Replace GCB's Function?

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The issue is the capability of the circuit breaker to break faults 'near' the generator and 'far' from the generator. The short circuit fault current is composed of several components: Initial symmetrical current, Peak current, Steady state current and dc offset current. Near the generator, at the inception of the fault and depending on where on the voltage curve you hit the fault, you could get a very substantial dc offset imposed on the fault current. The effect is to raise the peak curent and off set the sine wave above the zero line. The peak current is calculated by multiplying the initial symm current by a factor composed of the square root of 2 multiplied by 2 (if fault inception leads to full offset) and a factor which has a contant component added to the natural log with a negative exponent of system R/X. What this means is that near the generator or generator transformer R is small relative to X therefore you get the highest peak current. As you move away (get far from the generator) the peak drops. The dc component also decays at a rate governed by the negative exponent, comprising R/X multiplied by the time elapsed after the fault, of the natural log. So as R or t increases the short circuit current is not so much upwards modified by the dc offset and becomes essentially symmetrical. If you look at the breaker rating plate you will see a figure for symmetrical breaking current and assymetrical breaking current. The symmetrical current plus the dc offset gives you the assymetrical current, which is not symmetrical around the zero. So near a generator the breaker will be required to break mostly assymetrical sc currents while further away it will be breaking steady state sc currents which are symmetrical.