Brochure/Catalogue
What are overvoltages?
What are overvoltages?
Surges are extremely high voltages that damage or
even completely destroy insulation and hence impair or
completely disrupt the function of electrical and electronic
components of all kinds.
Every electrical component is provided with insulation to
isolate the electrical voltage from earth or other voltage-
carrying parts. The insulation strength is dependent on
the rated voltage and the type of electrical component,
as stipulated by the IEC/VDE regulations. It is tested by
applying the prescribed voltages for a dened period of time.
If the test voltage is exceeded in operation, the safety effect
of the insulation is no longer guaranteed. The component
can be damaged or completely ruined. Surges are voltage
pulses that are higher than the test voltage, and these could
detrimentally affect an electrical component or system. This
means that components with a high rated voltage may be
capable of withstanding a surge voltage. But components
with a lower rated voltage would be very much at risk from
the same surge. An overvoltage allowable in an electric
motor can spell disaster for an electronic circuit!
Permanently higher voltages also occur with the 50/60 Hz
mains frequency. These voltage can be coupled and can also
occur as a result of faulty switching operations. The resulting
continuous interference voltages are another reason for
installing overvoltage protection.
Individual surge pulses, which have a high frequency
because of their physical formation, have a current rise that
is about ten thousand times steeper compared with 50 Hz
voltage. If the current rise time in the 50/60 Hz range is
5 ms, then for an overvoltage it is around 1 µs.
These surges are designated as “transient” voltages.
This means that they are short-lived, temporary oscillations.
Their shape and frequency depends on the impedance of
the circuit.
Time in µs
25,000
20,000
15,000
10,000
5,000
01
2345
5,000 10,000
Voltage in V
350
300
250
200
150
100
50
0
Rising edge of the surge pulse / mains voltage
Surge pulse
Mains voltage 50 Hz
Edge behaviour between a 50 Hz sine wave and surge pulse
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