R·A·V-L-A
SERIES
DYNAMIC CHARACTERISTICS
Fig. 1 Shows the dynamic characteristics of Varistor, Gas Arrester & R·A·V.
SURGE PROTECTIVE DEVICES
Gas Arrester
ZnO Varistor
R·A·V
Fig. 1
(V)
200V/div
Non Suppression Time
Surge Wave
Voltage
Voltage
Transposition
Time
(V)
200V/div
(V)
200V/div
Voltage
Absorbed Surge Wave
Time
Time
Beginning Point of
Suppression
Varistor Operating Arrester Operating
Fig. 2
FEATURES
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.
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.
Varistors
GAS ARRESTERS
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
Voltage (V)
Gas Arresters
10
-6
10
-5
10
-4
10
-3
Current (A)
10
0
10
1
10
2
10
3
149
SURGE PROTECTIVE DEVICES
OKAYA [ Okaya Electric America, Inc. ]
