IEEE Std C62.37.1-2000 pdf download

IEEE Std C62.37.1-2000 pdf download.IEEE Guide for the Application of Thyristor Surge Protective Devices.
If the junction temperature increase, caused by ac heating, is sufficiently high, the maximum value of V(8, measured under ac conditions, can exceed the value of’ measured under impulse conditions. For fixed voltage devices with V,80, values above 10 V, V(80) will generally increase with temperature. The temperature behavior of V(80) depends on where the breakover point occurs in the breakdown region (see Figure 29). If it occurs at the beginning of the breakdown region, giving ‘(80) values typically below a few hundred microamperes, then, at high temperatures, the off-state current will have increased sufficiently to exceed the ‘(B0, value at which the (80 would normally occur. At this temperature and above, the rate of V,801 increase would reduce, finally changing to a negative value, causing V(801 to decrease with increasing temperature.
If V8 occurs toward the end of the breakdown region, giving ‘(80) values typically above 100 mA, then the increase in 17(80) with temperature is reasonably linear. At very high temperatures (30() °C), the off- state current will have increased sufficiently to exceed the (BOI• At this temperature and above, the rate of’ B0) increase would reduce, finally changing to a negative value, causing (8o, to decrease with increasing temperature.
Figure 30 plots an example of peak voltage [(Bo,] per cycle against time for three levels of ac current. The device used had a single-cycle V(801 value of 340 V. For the low current level, where the device does not switch and only operates in the breakdown region, the device temperature rise caused by heating is gradual. This is shown by a slow, progressive voltage rise from 356 V at 0.1 s to 372 V at 1000 s. After 300 s, the voltage is constant, showing that thermal stability has been reached.
Both high and medium currents cause the device voltage to peak and then collapse. In both cases, the heating is substantial, which raises the device junction temperature to a level where semiconductor junction action stops and the device becomes resistive. The high current condition starts at 351 V, and peaks at 383 V in 4 s before collapsing to 4 V. The medium current condition starts at 358 V, and peaks at 381 V in 25 s before collapsing to 2 V.
For the levels and times used for this example, the maximum (8o) was 16% higher than the single-cycle value. In verifying the overvoltage protection, it is important to specify the ac voltage level, the application time, the overall circuit resistance, the device mounting arrangement, circuit connections, and any current- limiting components. The ac voltage and circuit resistance will determine the prospective on-state current, and the resulting losses in the breakdown and on-state conditions. The thermal characteristics of the mounting will influence the medium and long-term temperature rise, which will reflect in the (BO) value. Circuit connections will determine whether single or multiple protectors are activated.
Current-limiting components may activate befbre the end of the specified test time. This will etiectively shorten the test time and could reduce the peak voltage. When fusible current-limiting elements operate, the current flow will stop. When Positive Temperature Coefficient (PTC) resistors switch to a high resistance, the current flow greatly reduces. This condition needs to be evaluated. The low current can cause the thyristor SPD to be biased in the breakdown region. A combination of low current and high breakdown voltage can cause high dissipation, leading to a large voltage rise.
Gated protectors, where the gate is refrence to a fixed voltage, show very little change in until the temperature rise causes the semiconductor properties to be lost and the device turns resistive. In this condition, the gate will also become resistive and short out the gate supply voltage. To avoid excessive gate current flow, a series resistor or fusible element may be used in series with the gate. Alternatively, the circuit component values could be specified so that the protector does not reach a resistive condition.