LABORATORY OF ELECTROMAGNETIC COMPATIBILITY
WARSAW UNIVERSITY OF TECHNOLOGY
DEPARTMENT OF HIGH VOLTAGE AND ELECTROMAGNETIC COMPATIBILITY
Investigations of Surge Protective Devices (SPD) for low voltage supply installations
1. Foreword
There are several types of Surge Protective Devices (SPD’s) which are also called
Overvoltage protectors, Surge arresters, Suppressor diodes or Transzorbers (Transient
Zenner Absorber) having a common task, which is limitation of overvoltages (interference
voltages) mainly caused by lightning or switching.
They usually have non-linear voltage - current characteristic:
- high impedance for nominal (working voltage) of the system,
- low impedance for voltages exceeding maximum rated voltage of the system.
SPD’s have at least one non-linear component and are installed at the input of power or
signal line to shortcut the surge current to the earth. There are classified following types of
SPD:



Voltage switching type SPD – that has high impedance when no surge is present,
but can have a sudden change in impedance to a low value in response to a voltage
surge. Common examples of components used as switching devices are spark
gaps, gas tubes, thyristors (silicon controlled rectifiers) and triacs. These SPD’s are
sometimes called “crowbar type”.
Voltage limiting type SPD’s that has high impedance when no surge is present, but
will reduce it continuously with increased surge current and voltage. Common
examples of used as non-linear devices are varistors and suppressor diodes. These
SPD’s are sometimes called “clamping type”.
One-port SPD’s – connected in shunt with the circuit to be protected. A one port may
have separate input and output terminals without specific series impedance between
these terminals.
Two-port SPD with two sets of terminals, input and output. A specific series impedance is
inserted between terminals.
b)
a)
3
5
c)
4
1
d)
2
5
1
4
2
1 4
5
Fig. 1a. a) Switching components of SPD’s, b) limiting components of SPD’s, c) serial connection of
switching and limiting components, d) parallel connection of switching and limiting components: 1varistor, 2 - gas tube, 3, - gap, 4 - avalanche diode, 5 – thyristor.
a)
b)
2
1
f)
c)
SPD
h)
5
2
1
e)
2
4
3
1
g)
d)
i)
5
2
1
1
SPD
5
Fig.1 b. a), b), c), d) one-port SPD connected in shunt with the circuit, e) one-port SPD used on low
voltage a.c. power lines, f) on-port SPD diagram, g),h) two-port SPD’s, i) two-port SPD diagram; 1 –
varistor, 2 - gas tube, 3 – gap, 4 – avalanche diodes, 5 – series impedance
There are defined the following parameters of SPDs:



Maximum continuous operating voltage Uc, maximum r.m.s or d.c. voltage which
may be continuously applied to the SPDs mode of protection.
Continuous operating current Ic – it is current flowing through each mode of
protection of the SPD when energized at maximum continuous operating voltage Uc.
Voltage protection level Up, which characterizes the performance of the SPD in
limiting the voltage across its terminals, which is selected from a list of preferred
values and is the highest value of limiting voltage during the application of impulses
with specified waveshape and amplitude.
Ratio of Up/Uc depends on technology, material properties and dimensions (diameter d) of
varistors and their nominal discharge current In.
Important parameters of SPD are maximum discharge current I m > In (defined by wave
shape of 8/20 s) and impulse current Iimp. Impulse current Iimp is defined by a peak current
value (manufacturers often described it by 10/350 s waveshape) and the charge Q.
Single SPDs or their combinations are installed at the entrance of supply installation or at
the supply input of protected device. In majority of practical cases there is need to install
two or more stage setup of SPDs, which are selected according to the lightning protection
standards ( PN-EN (IEC) 62305 – series).
The proper selection of SPDs requires voltage coordination to reduce step by step
overvoltages to the level corresponding with surge withstand of the protected equipment.
R1
SPD 1
L1
R2
SPD 2
L2
R3
SPD 3
L3
SPD 4
Urządzenie
chronione
SPD 1 = Uobn (SPD 2) = Uobn (SPD 3)
Fig.2. Example of coordinated setup of different types SPDs: SPD1 – switching type, SPD2
– SPD4) – limiting type.
During the Lab class is used surge current generator producing current surges having
wave form 8/20 s, digital oscilloscope TDS Tektronix with USB input for recording the
current and voltage wave-shapes as well as low inductance ohmic current shunt.
2. Program of tests
2.1 Measurements of voltage-current characteristics of individual SPDs for low voltage
supply installations.
At the output of surge current generator shall be connected the tested SPD. The surge
current having the parameters indicated by the teacher is generated into the circuit show in
Fig.3.
Using digital oscilloscope shall be recorded and stored in USB the following waveforms;
- Current waveform recorded as voltage drop at the current shunt,
- Voltage waveform across the tested SPDs using the high voltage probe with ratio
1:100.
Measurements shall be performed for generator charging voltages of surge current
generator having three different values: i.e. 1,5 kV, 2,0 kV and 2,5 kV for two types SPD –
switching type and limiting type.
The characteristic values of surge current and voltage shall be measured using cursors of
the oscilloscope and stored in the external memory (USB should be delivered by students).
Fig.3 Circuit for single SPD characteristics measurements.
2.1 Measurements of voltage-current characteristics of two stage configuration of SPDs for
low voltage supply installations.
Two stage SPDs setup shall be connected as shown in Fig. 4.
Fig.4. Circuit for two-step SPD configuration.
Using digital oscilloscope shall be recorded and stored in USB the following waveforms;
- Current waveform recorded as voltage drop at the current shunt,
- Voltage waveform recorded in point 1,2,3 in Fig.4 using the high voltage probe with
ratio 1:100.
Measurements shall be done for surge current generator charging voltages 2,0 kV.
The characteristic values of surge current and voltages in points 1,2,3 shall be measured
using cursors of the oscilloscope and stored in external memory (USB should be delivered
by students).
3. Elaboration of test results
The final report shall include:
- Description of measurement methodology and set-up of test arrangement,
- Tests results in tables with description as well voltage current characteristics for single
SPDs
- Printed waveforms (oscillograms)
- Description of results with comments and final conclusions.