HF OPERATORS

1. HF OPERATORS Notes on Lightning by John White VA7JW NSARC HF Operators

2. LIGHTNING THUNDER NSARC HF Operators

3. 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 NSARC HF Operators

4. 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. NSARC HF Operators

5. 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 NSARC HF Operators

6. Annual Thunderstorm Days in America • Numbers are storm days • Florida is Worst - ( Adam AB4OJ/VA7OJ will vouch for that) Don White Consultants NSARC HF Operators

7. Annual Thunderstorm Days in Canada • We are lucky, only ~ 5 days per year IEEE ANSI/IEEE Std 142-1982 NSARC HF Operators

8. Number of Discharges • World wide distribution of Lightning Discharges • Our part of the world 10 to 30 • Central Africa 5400 ! Don White Consultants NSARC HF Operators

9. Strikes vs Tower Height • Lower Mainland @ 5 thunderstorm days per year = low risk • Until you get hit of course NSARC HF Operators

10. 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 NSARC HF Operators

11. Strike Current Waveform • Example for a Typical Strike • Rise Time ~ 5 seconds • Crest ~ 25 kA • Fall time ~ 50 seconds to half of crest value NSARC HF Operators

12. Lightning Parameters NSARC HF Operators

13. Current Distribution • Percentage exceeding a given current • 50 % will exceed 10,000 amps Don White Consultants NSARC HF Operators

14. 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! NSARC HF Operators

15. 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 NSARC HF Operators

16. 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 NSARC HF Operators

17. A Simple Calculation • Strike current = 20,000 A • for 10 usec • Voltage along feedline = 2000 V • bye bye coax • Voltage across ground rod = 200 V • 4 MW for 10 usec • Voltage at top of ground rod = 200,000 V • Side flashing may occur • This is called GROUND RISE • This 200 kV will diminish exponentially with distance from the ground point • Voltage gradient immediate vicinity is dangerous • See cow > ANTENNA Feed line & Tower 0.1 ohms 0.01 ohms Rod 10 -100 ohms Earth NSARC HF Operators

18. 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 NSARC HF Operators

19. 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. NSARC HF Operators

20. 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 NSARC HF Operators

21. 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 50 sec, fusing current ~ 800 kA Don White Consultants NSARC HF Operators

22. 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) NSARC HF Operators

23. 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?) NSARC HF Operators

24. 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 NSARC HF Operators

25. 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 NSARC HF Operators

26. Wire Inductance • 1 foot of #6 AWG copper • Inductance = 0.26 H per foot • Resistance = 0.0004 ohm per foot • 2 S rise time • Resistive Voltage drop / foot at 20 kA = 8 volts / foot • Inductive voltage drop / foot at 10 kA/s = 2600 volts / foot • The impedance to ground is clearly limited by L K7MEMCalculator NSARC HF Operators

27. 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! NSARC HF Operators

28. 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 NSARC HF Operators

29. Tower Grounding • Grounded plate at base of tower • Coax protected with arrestors • Copper strap tying off to the system ground NSARC HF Operators

30. 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 NSARC HF Operators

31. 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 Don White Consultants NSARC HF Operators

32. 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 NSARC HF Operators

33. 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 NSARC HF Operators

34. 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 NSARC HF Operators

35. 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 NSARC HF Operators

36. 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 NSARC HF Operators

37. 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 General Semi NSARC HF Operators

38. System Approach • Combination MOV - Gas Tube protector for Lines NSARC HF Operators

39. Comparison’s • Comparison of common arrestors • Use Gas Tubes and then MOV’s closer to threat • Use Diode clamps closer to protected equipment NSARC HF Operators

40. 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 MFJ $35 RF Parts $55 NSARC HF Operators

41. Cable Suppressors • For use on rotors or other control lines • Internal arrestor devices not known • Place on Grounded Entrance Plate Array Solutions $46 DX Engineering $133 NSARC HF Operators

42. NSARC Antenna Protection • Copper Plate • Connected to Building ground System (big bare copper wire) • In Roof Top Equipment Room NSARC HF Operators

43. NSARC Rotor Protection • Copper Plate • Connected to Building ground System (green wire) • In Roof Top Equipment Room NSARC HF Operators

44. Home System NSARC HF Operators