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HF OPERATORS - • - • - - • - - •• • ••• - • - - • •• - • ••• • -• Notes on Lightning by John White VA7JW va7jw@shaw.ca 10 April 2013 Revision 4 NSARC HF Operators 1 LIGHTNING - • - • - - • - - •• • ••• - • - - • •• - • ••• • -• THUNDER 10 April 2013 Revision 4 NSARC HF Operators 2 Generation of Lightning - • - • - - • - - •• • ••• - • - - • •• - • ••• • -• Thunderstorms Cold front - air aloft sinks Warm air at ground rises Vertical air flow, up and down Friction between water droplets Droplets become charged Charges separate within cloud High voltages develop Within, cloud to cloud Cloud to Earth Air breakdown occurs LIGHTING DISCHARGE 10 April 2013 Revision 4 NSARC HF Operators 3 Some Facts - • - • - - • - - •• • ••• - • - - • •• - • ••• • -• Average duration 50 microseconds Average speed of Lightning stroke 20,000 mph Average Temperature 30,000 degrees C Average Length 3 km Average Energy 300,000,000 joules Average Power 10,000,000,000,000 watts (10 terawatts) Average number of strokes per flash, 4 200 thunderstorms in progress world wide any time 100 flashes per second worldwide any time Astraphobia – fear of thunder and lightning Reference “Lightning and Lightning Protection”, William Hard and Edgar Malone. Don White Consultants publisher 1979. and other internet sources. 10 April 2013 Revision 4 NSARC HF Operators 4 Forms of Lightning - • - • - - • - - •• • ••• - • - - • •• - • ••• • -• Cloud to Ground – our major concern ! Cloud discharge to ground Within a cloud Discharge in a cloud Cloud to cloud Discharge between clouds Heat lightning Intracloud, far away Thunder not audible Sheet Lightning Intracloud, diffuse Cloud to air Bolt-from-the-blue Don White Consultants 10 April 2013 Revision 4 NSARC HF Operators 5 Annual Thunderstorm Days in America - • - • - - • - - •• • • • • - • - - • •• - • ••• Numbers are storm days Florida is Worst - ( Adam AB4OJ/VA7OJ will vouch for that) • -• Don White Consultants 10 April 2013 Revision 4 NSARC HF Operators 6 Annual Thunderstorm Days in Canada - • - • - - • - - •• • •••- • We are lucky, only ~ 5 days per year - • •• - • ••• • -• IEEE ANSI/IEEE Std 142-1982 10 April 2013 Revision 4 NSARC HF Operators 7 Number of Discharges - • - • - - • - - •• • • • • - • - - • •• - • World wide distribution of Lightning Discharges Our part of the world 10 to 30 Central Africa 5400 ! ••• • -• Don White Consultants 10 April 2013 Revision 4 NSARC HF Operators 8 Strikes vs Tower Height - • - • - - • - - •• • • • • - • - - • •• - • ••• • - • Lower Mainland @ 5 thunderstorm days per year = low risk Until you get hit of course 10 April 2013 Revision 4 NSARC HF Operators 9 Thunder - • - • - - • - - •• • • • • - • - - • •• - • ••• • Sound of the explosion along the superheated lightning channel -• 30,0000 degrees Superheated air, gas pressures 10 to 100 atmospheres Shockwave is what we hear Rumblings are primarily due to the various distances between observer and tortuous path of the lightning discharge Speed of sound is ~ 1000 ft per second count the seconds between the flash and the onset of thunder to determine your distance to strike; seconds = thousands of feet 10 April 2013 Revision 4 NSARC HF Operators 10 Strike Current Waveform - • - • - - • - - •• • ••• - • - - • •• - • ••• • -• Example for a Typical Strike Rise Time ~ 5 seconds Crest ~ 25 kA Fall time ~ 50 seconds to half of crest value 10 April 2013 Revision 4 NSARC HF Operators 11 Lightning Parameters - • - • - - • - - •• Parameter • ••• - • - - • •• - • ••• • -• Percentage of Strokes EXCEEDING Value indicated 90% 50% 10% Max Observed Crest (peak) Current 2 to 8 kA 10 to 25 kA 40 to 60kA 230 kA Rate of Rise to Crest 2 kA/us 8 kA/us 25 kA/us 50 kA/us 0.3 to 2 us 1 to 4 us 5 to 7 us 10 us 0.1 to 0.6 ms 0.5 to 3 ms 20 to 100 ms 400 ms Time between Strokes 5 to 10 ms 30 to 40 ms 80 to 130 ms 500 ms Total Stroke Duration 0.01 to 0.1 s 0.1 to 0.3 s 0.5 to 0.7 s 1.5 s Time to Crest Duration of Single Stroke 10 April 2013 Revision 4 NSARC HF Operators 12 Current Distribution - • - • - - • - - •• • • • • - • - - • •• Percentage exceeding a given current -• ••• • -• 50 % will exceed 10,000 amps Don White Consultants 10 April 2013 Revision 4 NSARC HF Operators 13 Strike Current Spectrum - • - • - - • - - •• • ••• - • - - • •• - • ••• • -• Most Energy concentrated DC to 1 kHz. Destructive energy range < 1 kHz Not energy > 1MHz that destroys radio installations It will sound loud on radio though! 10 April 2013 Revision 4 NSARC HF Operators 14 Primary Protection - • - • - - • - - •• • ••• - • - - • •• - • ••• • -• Cloud to Ground discharges of concern to us Need to direct the lightning current to earth as directly as possible Protection of Life and Property Fire Protection Shock Protection Equipment Protection 10 April 2013 Revision 4 NSARC HF Operators 15 Ground - • - • - - • - - •• • • • • - • - - • •• - • ••• Cloud to Ground Strike current seeks earth ground • -• the strike point directly to surface or via tree, tower, antenna etc. Current flows outwards from strike point through earth Earth ground is not a good conductor Thousands of amperes flow through ohms of resistance Thousands of volts per foot exist outwards from strike point 10 April 2013 Revision 4 NSARC HF Operators 16 Ground Rise - • - • - - • - - •• • ••• Strike current = 10,000 A - • - - • •• - • ••• • -• ANTENNA Tower System = 1000 V Voltage across ground rod = 100 V Voltage at top of ground rod = 100,000 V 0.1 ohms 0.01 ohms Rod 10 -100 ohms Earth Side flashing may occur This is called GROUND RISE Feed line & Tower This 100 kV will diminish exponentially with distance from the ground point Voltage gradient immediate vicinity is dangerous See cow > 10 April 2013 Revision 4 NSARC HF Operators 17 Station Grounds - • - • - - • - - •• • ••• - • - - • •• - • ••• • -• Multiple grounds exist out of necessity Electrical - AC Power “green wire” power safety Lightning - Towers, feed lines Signal – chassis, shields, coax, Antenna RF – ground planes, counterpoises 10 April 2013 Revision 4 NSARC HF Operators 18 Unsafe Ground System - • - • - - • - - •• • • • • - • - - • •• Multiple unconnected Grounds > Problem -• ••• • -• Lightning currents flowing in each ground system not equal Dangerous voltages will develop between equipments due to different ground system impedances Extreme shock hazard. 10 April 2013 Revision 4 NSARC HF Operators 19 Safer Ground System - • - • - - • - - •• • • • • - • - - • •• Multiple, Connected Grounds much Safer -• ••• • -• Connecting all grounds together creates an EQUIPOTENTIAL environment Voltage drop between ground systems ideally ZERO if wire has zero resistance Ground rise will be same everywhere and differential voltages will be minimal Multiple ground points leads to lowering resistance to ground thus lowering of Ground Rise overall 10 April 2013 Revision 4 NSARC HF Operators 20 Wire Sizing - • - • - - • - - •• • • • • - • - - • •• - • ••• • - • What Gauge wire is needed to carry a strike current Wire Melt, called FUSING as in blowing a fuse, is the issue #6 is typical code For 70 sec, fusing current ~ 500 kA Don White Consultants 10 April 2013 Revision 4 NSARC HF Operators 21 Bonding - • - • - - • - - •• • ••• - • - - • •• - • ••• Objective is to create an EQUIPOTENTIAL AREA • -• Bonding means an electrical connection between equipments mechanically connected hardware is not bonding. Independent, random unconnected ground systems where conductivity is not assured is unacceptable All grounds and equipments must be electrically connected voltage differences are small and shock hazard is suppressed lower impedances are achieved large currents are distributed over many paths lowering voltages “All grounds … . must be bonded together in order to protect life and property (ARRL 2010 Handbook pg 28.7) 10 April 2013 Revision 4 NSARC HF Operators 22 Grounding Impedance - • - • - - • - - •• • ••• - • - - • •• - • ••• • -• Grounding is not just a simple Resistance problem The rate of rise of current, kA / microsecond, is same as a High Frequency Signal and must be treated the same way. LOW IMPEDANCE to Ground is the requirement DC resistance can be achieved with large diameter copper INDUCTANCE of the ground system is the limiting factor (how could the inductance of straight wires be of any consequence?) 10 April 2013 Revision 4 NSARC HF Operators 23 Inductance - • - • - - • - - •• • • • • - • - - • •• - • ••• • - • Conductors carrying the rapidly increasing strike current generate a rapidly changing magnetic field. A changing magnetic field produces a back EMF that opposes the applied voltage thus constraining the rate at which the current can rise. This is Inductance Current cannot rise instantly in the presence of inductance 10 April 2013 Revision 4 NSARC HF Operators 24 Inductive Voltage - • - • - - • - - •• • • • • - • - - • •• - • ••• • - • Relationship between Voltage and Current for an inductance V is the voltage developed across and inductor L is the inductance value i is the current t is time di/dt is the rate of change of current with time, i.e amps per sec 10 April 2013 Revision 4 NSARC HF Operators 25 Wire Inductance - • - • - - • - - •• • ••• 1 foot of #6 AWG copper - • - - • •• - • ••• • -• K7MEMCalculator Inductance = 0.26 H per foot Resistance = 0.0004 ohm per foot 8 S rise time Resistive Voltage drop / foot at 10 kA = 4 volts / foot Inductive voltage drop / foot at 10 kA/8s = 325 volts / foot The impedance is clearly limited by L 10 April 2013 Revision 4 NSARC HF Operators 26 Voltage Flashover - • - • - - • - - •• • ••• - • - - • •• - • ••• • -• A 50 foot vertical run of coax from feed point to ground could develop 130 kV (ignoring Ground rise) Very difficult to make all ground and bonding systems run in a straight line 90o corners and bends in cable runs INCREASE inductance Higher yet voltages are developed High voltage will flash over from cable to cable or equipments or other structures – whichever forms the lowest impedance to earth! 10 April 2013 Revision 4 NSARC HF Operators 27 Magnetic Field - • - • - - • - - •• • • • • - • - - • •• - • ••• • - • Mechanical forces develop between conduction paths due to their magnetic fields 2 Conductors carrying 20,000 amps Side x side, 1 cm separation Force between conductors ~ 500 lbs / foot Cable bundles burst, wires break, cables straps rupture, brackets break, cables deform etc. ARRL Handbook 2010, sec 28.1.8 10 April 2013 Revision 4 NSARC HF Operators 28 Tower Grounding - • - • - - • - - •• • •••- • Grounded plate at base of tower Coax protected with arrestors Copper strap tying off to the system ground 10 April 2013 Revision 4 NSARC HF Operators - - • •• - • ••• • -• 29 Secondary Protection - • - • - - • - - •• • ••• - • - - • •• - • ••• • -• Primary Protection Diversion of high currents and voltages to ground Secondary Protection Limiting dangerous Voltages to non destructive values Divert excessive Currents to non destructive values Lightning Arrestor Devices Placed on cables and equipments 10 April 2013 Revision 4 NSARC HF Operators 30 Cone of Protection - • - • - - • - - •• • ••• - • - - • •• - • ••• • -• A Rule of Thumb (old theory) You are protected from a strike if a tall structure is close by. Distance out (radius) = height. Defines a cone Theory - Safe inside from a “hit” Your Tower / Antenna probably IS the Air Terminal ! A big tree might help but don’t depend on it 10 April 2013 Revision 4 Don White Consultants NSARC HF Operators 31 Arrestors - • - • - - • - - •• • • • • - • - - • •• - • ••• • - • Coax’s, Rotor Cables, any wires, to outdoor antennas are prime conduits for destructive energy to enter house / shack. Arrestors are placed across cables to ground Zero current flow to ground under normal conditions Does not shunt your signal to ground Elevated voltages to ground will cause conduction to ground to divert harmful current and limit excessive voltages Don White Consultants 10 April 2013 Revision 4 NSARC HF Operators 32 Arrestor Requirements - • - • - - • - - •• • • • • - • - - • •• - • ••• Designed for TRANSIENT performance, the strike. • -• NOT for continuous application of high voltage or current Excessive power dissipation will cause failure Industry Standard test waveform is 8 x 20 s Rises to peak in 8 s and falls to 50% in 20 s Arrestors pass currents / clamp voltages for the 8 x 20 s test without self destructing Don White Consultants 10 April 2013 Revision 4 NSARC HF Operators 33 Gas Tubes - • - • - - • - - •• • • • • - • - - • •• - • ••• • - • Gas filled ceramic or glass cylinder Metal ends for circuit connection Often in a fuse-like holder, replaceable Fire on transient, divert current, clamp voltage to safe level Don White Consultants 10 April 2013 Revision 4 NSARC HF Operators 34 Gas Tubes - • - • - - • - - •• • • • • - • - - • •• - • ••• • Available with various firing and clamping voltages and current ratings -• Operating voltage up to 250 VDC Transient strike voltage 500 VDC Clamp voltage 100 V High current conduction Don White Consultants 10 April 2013 Revision 4 NSARC HF Operators 35 Varistors - • - • - - • - - •• • ••• - • - - • •• - • ••• • -• Commonly called MOV - Metal Oxide Varistor A resistor that changes value when voltage is applied Resistance decreases with increasing voltage Clamps excessive voltage Conducts high surge currents to ground Don White Consultants 10 April 2013 Revision 4 NSARC HF Operators 36 Surge Rated Zener Diodes - • - • - - • - - •• • ••• - • - - • •• - • ••• • -• Low Operating Voltage Applications High surge current rating 100A / 10 s Clamps voltage to rated Zener Voltage Used singly or back to back Power supply rails, AC signal lines Vsig = +/1 15V Vpwr = +15V Vz = 24V Vz = 24V Vz = 24V General Semi 10 April 2013 Revision 4 NSARC HF Operators 37 System Approach - • - • - - • - - •• • • • • - • - - • •• - • ••• Combination MOV - Gas Tube protector for Lines 10 April 2013 Revision 4 NSARC HF Operators • -• 38 Comparison’s - • - • - - • - - •• • ••• - • - - • •• - • ••• • -• Comparison of common arrestors TYPE GAS TUBE MOV DIODE SURGE CURRENT > 20 kA to 70 kA 100 A NUMBER of SURGES > 20 @ 20 kA 1000 @ 100A infinite @ 50 A RESPONSE TIME 5 uS 1 nS 1 uS Use Gas Tubes and then MOV’s closer to threat Use Diode clamps closer to protected equipment 10 April 2013 Revision 4 NSARC HF Operators 39 Coax Surge Suppressors - • - • - - • - - •• • • • • - • - - • •• Placement in series with Coax Typically gas tube Place on grounded Service Entrance Plate Alpha Delta $50 -• ••• • -• DX Engineering $55 R&L Electronics $45 RF Parts $55 10 April 2013 Revision 4 MFJ $35 NSARC HF Operators 40 Cable Suppressors - • - • - - • - - •• • • • • - • - - • •• For use on rotors or other control lines Internal arrestor devices not known Place on Grounded Entrance Plate Array Solutions $46 10 April 2013 Revision 4 NSARC HF Operators -• ••• • -• DX Engineering $133 41 NSARC Antenna Protection - • - • - - • - - •• • ••• - • - - • •• - • ••• • -• Copper Plate Connected to Building ground System (big bare copper wire) In Roof Top Equipment Room 10 April 2013 Revision 4 NSARC HF Operators 42 NSARC Rotor Protection - • - • - - • - - •• • ••• - • - - • •• - • ••• • -• Copper Plate Connected to Building ground System (green wire) In Roof Top Equipment Room 10 April 2013 Revision 4 NSARC HF Operators 43 Home System - • - • - - • - - •• • ••• - • SYSTEM GROUNDING - - • •• - • ••• • -• 1. TOWER TO BE GROUNDED 2. TOWER COAX TO BE GROUNDED ORANGE WIRING OWNER INSTALLED 3. ENTRANCE PLATE TO BE GROUNDED GREEN WIRING EQUIPMENT INSTALLED 4. RADIO TO BE GROUNDED TO ENTRANCE PLATE 5. RADIO IS GROUNDED TO ELECTRICAL SYSTEM BY LINE CORD CODE 6. ELECTRICAL SYSTEM IS GROUNDED AT SERVICE ENTRANCE BY CODE 7. SERVICE ENTRANCE IS GROUNDED BY CODE DIPOLE 8. GROUND SYSTEMS TO BE TIED TOGETHER TOWER Panel Service Entrance Eqpt RADIO Branch Circuit Plug Socket Line Cord ENTRANCE PLATE Surge Supressors COAX COAX Eqpt GROUND RODS GROUND RODS SERVICE ENTRANCE GROUND SYSTEM (Hydro) 10 April 2013 Revision 4 NSARC HF Operators 44
