Varistor Metal Oxide Varistor Products Page 116 Varistor Metal-Oxide Varistor Products

2017 Littelfuse, Inc. Specifications are subject to change without notice. Revised: 09/14/17 Metal-Oxide Varistors (MOVs) Radial Lead Varistors > C-III Varistor Series NUMBER OF SURGES (RATED FOR 120 PULSES) 0 100 50 150 250 300 200 600 550 500 450 400 350 300 CLAMPING VOLTAGE AT 750A V175LA20C 750A (8/20 s) AC Bias Reliability The C-III Series MOVs were designed for use on the AC line. The varistor is connected across the AC line and is biased with a constant amplitude sinusoidal voltage. It should be noted that the definition of failure is a shift in the nominal varistor voltage (V N ) exceeding +/-10%. Although this type of varistor is still functioning normally after this magnitude of shift, devices at the lower extremities of V N tolerance will begin to dissipate more power. Because of this possibility, an extensive series of statistically designed tests were performed to determine the reliability of the C-III type of varistor under AC bias combined with high levels of temperature stress. To date, this test has generated over 50,000 device hours of operation at a temperature of 125C, although only rated at 85C. Changes in the nominal varistor voltage, measured at 1mA, of less than 2% have been recorded, as displayed in the diagram at right. Transient Surge Current/Energy Transient Capability The transient surge rating serves as an excellent figure of merit for the C-III varistor. This inherent surge handling capability is one of the C-III varistor's best features. The enhanced surge absorption capability results from improved process uniformity and enhanced construction. The homogeneity of the raw material powder and improved control over the sintering and assembly processes are contributing factors to this improvement. In the low power AC mains environment, industry standards (UL, IEC, NEMA and IEEE) all suggest that the worst case surge occurrence will be 3kA. Such a transient event may occur up to five times over the equipment life time (approximately 10 years). While the occurences of five 3kA transients is the required capability, the rated, repetitive surge current for the C-III Series is 20 pulses for the 20mm units and 10 pulses for the 14mm Series. As a measure of the inherent device capability, samples of the 20mm V130LA20C devices were subjected to a worst case repetitive transient surges test. After 20 pulses, each of 3kA, there was negligible change in the device characteristics. Changes in the clamping voltage, measured at 100A, of less than 3% were recorded, as shown in the upper diagram at right. Samples of the 20mm Series V175LA20C were subjected to repetitive surge occurrences of 750A. Again, there was negligible changes in any of the device characteristics after 120 pulses, as shown in the lower diagram at right. In both cases the inherent device capability is far in excess of the expected worst case scenario. 300 250 200 150 100 0 100 200 300 400 500 600 700 800 900 1000 1100 TIME (HOURS) V NOM AT 1mA (V) V130LA20C 500 450 400 350 300 NUMBER OF SURGES CLAMPING VOLTAGE AT 3kA V130LA20C 3kA (8/20 s) (RATED FOR 20 PULSES) 0 10 5 15 25 30 20 High Temperature Operating Life 125C for 1000 Hours at Rated Bias Typical Repetitive Surge Current Capability of C-III Series MOVs Figure 12 Figure 13 Figure 14

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