R·A·V-L-A SERIES SURGE PROTECTIVE DEVICES Structure Power surges, both voltage and current, are occurring continually in today's power systems. Whether they occur naturally, such as from lightning and static electricity; or are man made, such as inductive surges from motor, transformers, solenoids, etc. power surges are a fact of life. These power surges have a very high voltage and current level as compared to electrical noise. Recent developments in electronic designs have tended toward smaller and higher density packaging of circuitry. This results in a greater susceptibility to surges. Once attacked by a surge, electronic circuits FDQEHGHVWUR\HGLQDVVKRUWDVȝVHF7KHGHVLJQHU of electronic equipment must be aware of, and be able to deal with, power surges in product design. OKAYA's R·A·V surge absorbers are designed to assist in dealing with the problem of power surges. The R·A·V series is a unique new approach which combines the features of two well known technologies. Combining the high speed capabilities of Metal Oxide Varistor (MOV) with the large power handling capability of Gas Arrester, OKAYA has developed a product which can clamp power surges faster than gas arrester alone and handle large power surges far beyond the capability of MOV. Symbol Lead terminal Cap Electrode of Arrester Varistor Ceramic Tube Inert Gas Circuit FEATURES The R·A·V Surge Absorber is applicable for the protection of many types of electrical equipment. The R·A·V has the following features: 1) Large capacity surge protection 2) Fast response time 3) Good endurance to repetitive lightning 4) High clipping performance 5) Low internal capacitance 6) No environmentally hazardous materials OPERATING PRINCIPAL Surge Wave The R·A·V connected between lines will shunt the surge from one side of the line to the other. The high speed varistor quickly shunts the surge until the slower, but more powerful gas arrester takes over. This allows the gas arrester to handle the high energy portion of the surge and protect the MOV from damage. This interaction of the R·A·V assures safe handling of the power surge and long life stability to the MOV. (V) Voltage Absorbed Surge Wave Surge Absorbed Area Varistor Operating 148 Arrester Operating Time ȝV SURGE PROTECTIVE DEVICES DYNAMIC CHARACTERISTICS Fig. 1 Shows the dynamic characteristics of Varistor, Gas Arrester & R·A·V. Gas Arrester ZnO Varistor R·A·V Fig. 1 (V) 200V/div (V) 200V/div (V) 200V/div Non Suppression Time Absorbed Surge Wave Time Time ȝVGLY Fig. 2 ȝVGLY Beginning Point of Suppression Voltage Voltage Voltage Surge Wave Transposition Time ȝVGLY Varistor Operating Arrester Operating FEATURES Lightning surges have precipitous dv/dt values and huge electrical charge. Surge absorbers must assimilate this surge. This limiting voltage capability varies depending upon the type of absorber. The voltage and current curves in Fig. 2 characterize varistors and gas arresters. Varistor voltage is specified by the manufacturer at low current (ie, 0.1-1.0 mA). The clamping voltage of the Varistor at higher current (ie, 1.0 Amp)can be several times higher and will increase as the current goes higher (See Fig. 2). Varistors have a very fast response time (ie, 50 nsec.) and will clamp at rated voltage for low currents or short periods of time. However, as a power surge increases in either current or duration, the Varistor clamping voltage can rise to unsafe levels, ultimately failing when its maximum energy level is exceeded. Although the Varistor may survive most power surges, each time it absorbs a power surge, damage occurs to the Varistor. Ultimately the MOV is rendered inoperative and unable to perform its suppression task. Varistors GAS ARRESTERS Voltage (V) The rated voltage of the Gas Arrester is defined as a DC breakdown Voltage (Ez). In contrast to the Varistor, as the surge current increases this voltage decreases. Therefore, once the Gas Arrester is triggered, the voltage level is maintained at a safe level, regardless of the increase in current or duration of the power surge. Typically the trigger response time LVȝVHF Gas Arresters 10-6 10-5 10-4 10-3 Current (A) 100 101 102 103 149 SURGE PROTECTIVE DEVICES R·A·V-L-A SERIES SURGE PROTECTIVE DEVICES The electrical characteristics of gas arresters are QRUPDOO\PHDVXUHGE\WKHHOHPHQWSHUIRUPDQFH expressed in terms of the DC breakdown voltage. :KHQVXFKGHYLFHVDUHXVHGDVVXUJHDEVRUEHUV KRZHYHUWKHPRUHLPSRUWDQWYDOXHLVWKHVXUJHILULQJ potential voltage (Vf: the voltage at which surge GLVFKDUJHEHJLQV)RUH[DPSOHHYHQLQWKHFDVHRID JDVDUUHVWHUZLWK'&EUHDNGRZQYROWDJHRI9WKH9I value at 19ȝVLQGLFDWHVDVXUJHILULQJSRWHQWLDORI about 500V (See Fig.3). The surge cannot be discharged until the voltage rises to this value. This characteristic forms the chief failing of gas arresters. :LWKWKH5Â$Â9VXUJHDEVRUEHUKRZHYHUWKHVDPH 90V type permits the discharge operation to begin at a 9IDW9ȝVRIDERXW9$VDUHVXOWWKH GLVFKDUJHRSHUDWLRQEHJLQVDWDOHYHO9ORZHUWKDQ the gas arrester. R·A·V CHARACTERISTICS Power surges resulting from indirect lightning strikes occur with precipitous speed. The dv/dt of the ULVLQJZDYHIRUPZLOOH[FHHGYȝVHF$VDUHVXOWD surge absorber without excellent response performance will be unable to protect equipment from damage. The element performance of gas arresters and other general surge absorbers is evaluated by PHDQVRIWKH9ROWDJH7LPHFKDUDFWHULVWLFFXUYHZKLFK expresses the relationship between the rise time of the voltage and the firing potential voltage of the device at the time of the surge rise. The accompanying graph shows an example of V-T characteristics. Fig. 3 7KHȝVHFWHVWLVXVHGWRGHWHUPLQHWKHSHDN VXUJHYROWDJHWKH'87FDQZLWKVWDQG7KHȝVHF test is used to determine the maximum discharge current the DUT can withstand. These wave forms are GHULYHGIURP,((($16,7KLV standard defines the open circuit and short circuit current waveforms which can be expected to occur on $&SRZHUOLQHVRI9ROWVRUOHVV There are two standard tests which are used to classify surge absorbers. Each test uses a signal pulse which is imposed on the device under test (DUT). This pulse is described by two sets of numbers ȝVHFDQGȝVHF7KHILUVWQXPEHULQHDFK set is the duration of the rise time of the signal LPSRVHGRQWKH'877KHVHFRQGQXPEHULVRIWKH duration of the fall time of the signal imposed on the DUT. 150