Critical Rate of Rise of Voltage
It depends on the junction temperature higher the junction temperature lower the critical rate of rise of voltage. It is also known as static dv/ dt. The switching from the off state to the on state with gate open is known as forward dv/ dt rating. A high value of dv/dt at which a thyristor just gets tumed on is called critical rate of rise of voltage. If the applied rate of rise of voltage is more than its critical value thyristor gets tumed on. This false triggering is because of the capacitance passed by the large of junctions J2. When the rate of rise of the applied voltage dv/ dt is very large the capacitive charging current Ddv/ dt may becomes large enough to trigger the device. This is not likely to damage the device but an unintended triggering may lead to either high di/ dt through the SCR or large shortest circuit current which may lead to the failure of the device.