I found solution. Need remove maxOccurs="unbounded" from xs:sequence
Now schema look like this:
<xs:complexType name="Element" abstract="true">
<xs:sequence>
<xs:element name="resistor" type="vs:Resistor" maxOccurs="unbounded"/>
<xs:element name="capacitor" type="vs:Capacitor" maxOccurs="unbounded"/>
<xs:element name="inductor" type="vs:Inductor" maxOccurs="unbounded"/>
</xs:sequence>