Internal Arc Calculations
Requirements for the strength of the cabinet:
In order to guide the design of the switchgear cabinet, the maximum pressure at critical locations and the time at which the maximum pressure occurs are derived by using HONERWELL's pressure transducers for data collection during the test.
The pressure data are as follows:
When the combustion arc pressure release is smooth in the center cabinet
31.5KA/1s IAC test, handcart room test, switch compartment door maximum pressure 0.102Mpa @11.2ms. handcart room pressure relief cover is slightly farther away relative to the handcart room door, but due to the handcart room internal arc fault ignition assurance point and the handcart room door plate between the circuit breaker handcart block, so the shock wave through the side of the refraction to the handcart room door plate, the handcart room door plate, hinged door lock needs to be Reinforcement, especially in the impact route of the hinge door lock, i.e., the hinge door lock in the lower left-right position.
31.5kA/1s cable room internal arc test, switchgear top pressure relief plate 0.0877Mpa @ 18.2ms, this is due to the cable room arc inducing point is very far from the cover plate, so the journey is long, open time is long. And if the pressure relief channel is not smooth, it needs several refractions and reflections, it will prolong the pressure release time.
40KA/1s IAC test, the maximum pressure of the cover plate after the cable room 0.229Mpa@8ms. cable room internal arc fault, due to the pressure relief path is long, need to be more than 12ms pressure relief cover plate open, the cable room cover plate is close to the center of the arc explosion distance, the pressure of the shock wave by the huge, so the cable room cover plate needs to have a very high strength, and at the same time, if the front cabinet and the front cabinet directly connected, then the effect to the front lower door is very high. At the same time, if the front cabinet is directly connected to the front of the lower door pressure is also huge, the door, door locks, hinges must have sufficient strength.
Arc distance control
According to the power formula, refer to the relevant literature, to 13 volts per centimeter arc strength calculation, you can initially calculate the arc length as shown in the table below;
For 650mm wide switchgear, the maximum power of internal arc fault is 129MW, the test current is 40kA, the calculated arc voltage is 1862V, and the arc length is 1862/13=143cm=1.43m. The same calculation 800mm wide switchgear, internal arc fault current 31.5kA, arc length 1.68 meters, 1000mm wide switchgear arc length 1.92 meters.
Obviously the arc length and the width of the switchgear is proportional to the relationship, or and phase spacing.
Here is another theory, the arc voltage and short-circuit current related to the formula is as follows:
-------- Equation 1
Where Varc = arc voltage, g = net distance between the two electrodes (in meters), Iarc = arc current (A)
The arc length, i.e., the electrode spacing, calculated using this method is as follows:
It can be seen that the arc length in the wider the switchgear, the larger the relative space compartment, the longer the arc length, even if the arc current is not large, but the energy generated is very large, therefore, the design of the switchgear need to give full consideration to limiting the length of the arc, such as a switchgear phase to phase and to the ground completely GPO-3 arc-resistant insulating panels are completely blocked, the test has proved that the partition prevents the arc of the length of the arc propagation, the arc energy Significantly reduced.