ECONOMICS AND MARKET
NON-DESTRUCTIVE MONITORING OF THE PHYSICOMECHANICAL
PROPERTIES OF ZINC OXIDE VARISTORS
M. A. Krasavina,
E. Z. Kovarskaya,
and S. I. Pugachev
Translated from Novye Ogneupory, No. 8, pp. 59 – 63, August 2007.
Original article submitted February 21, 2007.
Results are presented for a study of the physicomechanical properties of zinc oxide ceramic varistors produced
by the St Petersburg ZAO Zavod Élektrozashchitnykh Ustroistv (ZAO ZÉU) by a non-destructive acoustic
method. With analysis of the results the desirability is demonstrated of using instruments for non-destructive
monitoring in order to improve the quality of the ceramic varistors produced. The effectiveness is also estab
lished of using the method in question for determining the properties of developed larger diameter varistors.
A necessary requirement laid down for modern electrical
equipment for the transmission and distribution of electric
power with a voltage of 6 – 35 kV in electrical engineering
complexes is the provision of electromagnetic compatibility
of the level of insulation, parameters of electrical protection
devices and relay protection devices, and network automa-
tion in a prescribed volume of space, frequency and time
ranges. The importance of resolving this problem is particu-
larly important in connection with ageing of existing equip
ment, extensive introduction of vacuum and elegas
tation equipment, coated insulators (protected) conductors,
microprocessor devices, and the increasing role of nonlinear
Devices for electrical engineering complexes are subject
to the action of thunderstorm and commutation (internal and
temporary) overvoltages. The magnitude of sustained over
should not exceed permissible values con
nected with the level of test voltages.
Comparison of the actual and sustained levels of voltage
acting on the insulation of electrical equipment of electric
networks for a voltage of 6 – 35 kV makes it possible to draw
a conclusion about a requirement for limiting the magnitude
of thunderstorm and commutation overvoltages with the use
of protection equipment, devices for relay protection of net
work automation and effective earthing.
An important link in a system for protection from
overvoltages is an overvoltage limiter (OVL) based on ce-
ramic varistors. Semiconductor resistors with nonlinear
volt-ampere characteristics (VAC) are called varistors. They
have high ohmic resistance with a low voltage, and con-
versely with a high voltage they have low resistance, i.e. high
conductivity. The electrical properties of these elements can-
not be described by Ohm’s law and they are called
“non-ohmic”. Volt-ampere curves are approximated by the
equation I = CU
, where I is current, A; U is voltage, V; C is
a coefficient whose value depends on the type of varistor and
temperature; b is coefficient of nonlinearity, specifying VAC
nonlinearity, for varistors b »1.
Originally varistors were prepared on the basis of silicon
carbide. In subsequent years they were replaced by varistors
based on zinc oxide (ZOV) exhibiting semiconductor proper
ties. In conductivity zinc oxide relates to n-type with a donor
and a specific resistance of 1 W·cm .
The production of zinc oxide varistors is based on use of
a polycrystalline multicomponent system within whose com
position there are oxides of zinc, bismuth (III), antimony (II),
cobalt (II, III), manganese (IV), chromium (III), and others.
The nature of chemical transformations in these systems, the
geometric parameters of grains, the specific nature of the in
teratomic space during thermal action and after their comple
tion may only be described taking account of the physico
chemical properties of the original components, binary, ter
nary, and more complex systems that form the varistor com
Refractories and Industrial Ceramics Vol. 48, No. 4, 2007
1083-4877/07/4804-0306 © 2007 Springer Science+Business Media, Inc.
ZAO Zavod Énergozshchitnykh Ustroistv, OOO Zvuk, St. Peter
sburg State Marine Engineering University, Russia.
Élegas, i.e. sulphur hexafluoride, exhibits high electric strength
and it is used for placing elements of instruments and devices to
which a considerable electric voltage is supplied within it.