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