2/9/2016
Surge superimposed on AC Mains propagating
into a product
This surge is of short duration. It
has very high amplitude (few
kilovolts)
Simple concepts of surge flow
and surge protection
Live
230 V AC
50 Hz
Critical load to
be protected
230 V AC
50 Hz
Power Flow
Neutral
Nihal Kularatna
The University of Waikato
Hamilton
New Zealand
Earth connection
Simple electrical system and 230 V AC power flow with a
surge superimposed
AC power flow into a product
Surge protectors duty?
Surge protector’s duty is to absorb energy in the surge
and limit the high voltage superimposed on load rail
Live
Live
230 V AC
50 Hz
Power Flow
Critical load to
be protected
230 V AC
50 Hz
Power Flow
Neutral
Surge
protector
Critical load to
be protected
230 V AC
50 Hz
Neutral
Earth connection
Earth connection
Simple electrical system and 230 V AC power flow with a
surge superimposed and surge protector blocking energy
flow
Simple electrical system and 230 V AC power flow
A good surge protector is expected to absorb surge energy and pass only
a safe amount to the critical load
2/9/2016
Simple circuit theory works inside the surge
protector also
Real world case of a SPD in a system
Surge energy related current flow should occur
within the surge protector device (SPD)
Live
Live
230 V AC
50 Hz
Power Flow
Critical load to
be protected
230 V AC
50 Hz
Surge
protector
Neutral
Z1
Z2
Neutral
Earth
Surge protector
Earth connection
• Practically:
•
Simple electrical system and 230 V AC power flow with a
surge superimposed and surge protector blocking energy
flow
Ultimate aim of a SPD is to create a short circuit current(s) within the SPD
--- to absorb the surge energy into the SPD
All what works is the ohm’s law
High series impedance
for surge voltage source
•
•
•
Connection wires contribute a lot of useful resistance and series inductance to
Z1
When bundled conductors are used their shunt resistances and shunt
capacitances form part of the Z2
All what we do inside a SPD is to artificially increase Z1 value and artificially
decrease the Z2 value
In this process we make sure that Z1 does not show high impedance to 50 Hz
energy flow. Z2 acts vice versa.
Let us go back to simple ohms law and circuit
theory
V=IR (or IZ) works , as always …
For an (ideal) inductor following relationship works
Live
Z1
vL  L
Z2
Neutral
Critical
load
Critical
load
di
dt
All what we do in a SPD
design is to create a set
of impedances using nonlinear devices, inductors
and capacitors
For an (ideal) capacitor following relationship works
Earth
t
Surge protector
Low shunt impedance to
surge current
1. A surge protector should create two sets of impedances within the SPDOne high series impedance and a low shunt impedance.
2. For 230 V AC power flow these should work in an opposite way..
vC 
1
idt
c 0
At a constant frequency of f hertz, inductor and capacitor impedance are
given by
1
Z L  2 fL ; Z C 
2 fC
2/9/2016
More on Ohm’s law in SPDs
Live
Surge source and a critical load in a loop
Z1
Z2
Neutral
Earth
Rp,Lp (due to long lines )
Critical
load
Surge protector
Rsurge
Parasitic impedances in the
connecting paths
t
•
•
•
•
•
•
surge   v surgeisurge dt
Surge source superimposed on theE230
V
Ac mains line is an additional energy
0
source.
This is however very short duration (in the order of 20 to 100 µs only)
Power line cycle time is 20 ms or 16.66 ms
To damage something there should be an electrical current flow in an electric circuit.
Ohms law tells us that lower the total impedance higher the current in the closed path
Energy dissipated in the path is given by
RL
Critical load to
be protected
Vsurge
t
E
surge


v surge i surge dt
0
All what we do in a SPD is to absorb most part of the surge energy into the
components within the SPD.
What are the difficulties in designing a SPD
•
•
•
•
•
•
•
•
Surge is very random, transient and unpredictable activity
Surge voltage can be having a peak value of 1 to 20 kV or higher
Waveform shape is very unpredictable, and hard to predict in the real world
Components we should use within a SPD should work safely at short-term very high
voltages
Most surge absorbing type non linear devices (NLD) are having only transient energy
ratings
Surge waveforms cannot be easily generated
An SPD should be designed to pass 50/ 60 Hz power/energy into the load and it should
absorb or block surge energy flow into the critical load
Surge can be superimposed as three components
• Line to neutral induction (differential mode)
• Line/ neutral to earth terminal (common mode)
Difficulty arises due to all above and our inability to apply the ohm’s law in
a SPD
A simple voltage divider is created by the
total elements in the loop
Simple capacitor charging curve
2/9/2016
Can SCs absorb high voltage transients like lightning
surges induced on power supplies?
•We have tested several types of SCs for their surge absorb capability using a LSS
•Most SCs can absorb transient HV surges of several 100 micro second durations
•Simple circuit concepts work here…
VDC
Short duration pulse voltage
Capacitor voltage curve
Voltage at capacitor at the
end of pulse duration
time
Chragetime  5  5 RC
Transient Voltage Surge Suppressors
• Different kinds of TVSS circuits
Figure 3: Comparison of TVSS solutions