a presentation to the qcwa chapter 70 about lightning and grounding

A presentation to the QCWA Chapter 70 about Lightning and

Grounding

Many of the following slides courtesy of

Todd Sirola C.O.O.SAE Inc.

Todd provided a presentation to the CCBE last fall on the following topics

Threats To EquipmentGrounding FundamentalsElectrical Protection SystemsCase Studies

How do we get lightning?

• We need convection, cumulo-nimbus clouds, the ones with the anvil shape, the result of a collision of warm and cold air masses

• Ice pellets and grauple• Super cooled water droplets above the

freezing level• Earth has a positive charge, the bottom of the

cloud negative charge• Air is a great insulator so the charges build up

Capacitor Analogy

And then, BOOM!

• At some point the charge is large enough to overcome the insulator

• The leaders build out slowly at relatively low current in both directions

• Once they join the current flows. Upwards of 400,000 amps peak

• Power levels in excess of 1 Gigawatt may be encountered

• Systems need to be engineered with this in mind

• lightning can, and often does, strike the same spot more than once--even the same person. U.S. park ranger Roy Sullivan reportedly was struck seven times between 1942 and 1977.

• Take especially swift action if your hair stands on end, as that means charged particles are starting to use your body as a pathway.

Just remember

Lightning energy and power system ground faults will find a path to earth.

The key is to design an electrical protection

system to ensure it doesn’t damage equipment.

09/03/93 - 29.6 kA strike - Sandia National Labs

Evidence in Nature

Electrical representation of a tree

Roots

Branches

Trunk

Types of Lightning

• Cloud to Cloud (CC)• Cloud to Air (CA)• In Cloud• Cloud to Ground (CG)• Peak or Positive Giant• Blue Streak • Red Sprite

A plug for Todd, he can provide

Design, Supply and Install Professional Engineering SupportGrounding System AuditsSystem Resistance (R-Value) TestingSoil Resistivity TestingForensic AnalysisEducational and Training Seminars

What are the threatsLightning

• Direct• Induced

• AC mains• Telecom twisted pair

Electric power systems• Switching operations• Power system ground faults

A typical Ham installation

Definition of Grounding

An engineered , low impedance path to earth.

Definition of Soil Resistivity

A measurement of the electrical resistance of a unit volume of soil. The commonly used unit of measure is the ohm-m.

Factors Influencing Soil Resistivity

Soil Type (chemical makeup)• natural elements (clays, quartz)• foreign elements (salts, fertilizer)

Moisture Content

Temperature

Soil Type

Soil Type Resistivity (ohm-m)

Clays 10-150Sandy Clays 150-600Pure Sand 600-5000Gravel 5000-30,000

Shale/Slate 400-1,000Limestone 1,000-5,000Sandstone 5,000-50,000Granite 1,000-80,000

Moisture Content

Temperature

Temperature Resistivity (ohm-m)

20 0 C 72 10 0 C 99 0 0 C 130 0 0 C (ice) 300 -5 0 C 790 -15 0 C 3,300

Ground Resistance Formula

R = X fR = ground resistance = soil resistivityf = a function determined by

the shape and size of the

electrode

Electrical Protection Systems

Outside Ground Electrodes• Low R value, Low Impedance, High

capacitance, • High energy dissipation

Inside/Equipment Grounding• Single point

Surge Protection Devices (SPD’s)• AC system, Incoming telecom, Transmission

lines

Structural Lightning Protection• Lightning rods, Down conductors

Proactive Lightning Detection

What makes a good outside grounding system?

Low Impedance• Low Resistance• Low Inductance• High Capacitance

High Energy Dissipation

Proper Orientation

Corrosion Resistance

Theft Resistant

Low Impedance Grounds

Z = V / I or

Z = [ R2 + (2ƒL - 2ƒC-1)2 ] 1/2

Lower ResistanceLower Inductance

Increase Capacitance

Low Impedance Grounds

• Increase electrode surface area• Use a capacitive enhancement

product• Increase conductor size• Minimize bends• Maximize bending radius• Eliminate 90º bends• Decrease # of connections

The Trouble with “T” Connections

Lightning travels in straight lines.90 degree connections offer much higher impedance than a straight horizontal conductor.

Weaknesses of Conventional Grounding Systems

• Poor lightning protection• Higher surge impedance• Seasonal fluctuation of R value• Subject to corrosion• Multiple connections

How can I lower Ground Resistance?

Add more rods?

How can I lower Ground Resistance?

Rods must be spaced appropriately ortheir benefit is diminished.

#Rods *Multiply By

2 1.16 4 1.36 8 1.68 16 1.92

24 2.16

*Multiplier if rods are spaced one length apart.

How can I lower Ground Resistance?

Conductive Concrete

Horizontal Electrode Construction

Vertical Electrode Construction

What about inside the shack

Or how to keep Greg on the air

Single Point Grounding

Buildings should be converted to single point grounding. This method eliminates current loops and creates an environment in which it is easier to protect equipment against power surges from whatever source.

Single Point GroundingTypical Radio Site Layout

Single Point GroundingTypical Radio Site Layout

Single Point Grounding

Single Point Grounding

Single Point Grounding

Materials used for inside grounding

• Green insulated grounding conductor • Rated double holed compression lugs with

stainless steel hardware• Copper ground bars with insulated

mounting brackets• NON-Metallic mounting clips• Parallel Compression Connectors

Label all conductors at both ends with permanent identification labels

Surge Protection

Surge Protection is required for all metallic conductors that enter the building:

• Telephone lines• Intranet Line• AC Power Systems• Transmission lines

Surge Protection

Types of Surge Protection

Voltage Limiting Devices

• Gap devices e.g. air gap carbon arrestors and gas tubes

• silicon avalanche diodes, metal oxide varistors.

Current Limiting Devices

• Fuse links

• Circuit breakers

• Heat coilsOther

• Quarter Wave Stubs• Neutralizing transformers• Isolation transformers• Dielectric fiber optics

Case Studies

CKVR Television, Barrie OntarioTower located at the studioComplex on top of the hill overlooking Barrie

Case Study: CKVR - Barrie Broadcast Tower

The protection system included a comprehensive approach to eliminating damage due to lightning and electrical surges.

• Outside grounding electrodes• Inside single point grounding• LSC2000 Lightning Strike Counter• ESID storm monitor linked directly to a stand-by Generator

CKVR - Barrie Broadcast Tower Outside Grounding

A total of 378 m of horizontal electrode was installed at the tower center and each of the guy anchors. The overall ground resistance of the system is 0.9 ohms.

CKVR - Barrie Broadcast Tower Outside Grounding

Guy Anchor GroundingCompound Grounding

CKVR - Barrie Broadcast Tower Inside Grounding

SAE Inc. installed a Master Ground Bar (MGB) in the equipment building.

MGB

CKVR - Barrie Broadcast TowerLightning Strike Counter

Sensor Unit

Counter Unit

CKVR - Barrie Broadcast TowerESID - Generator Installation

The ESID detects storms in the area and automatically switches the site to generator power.

ESIDGenerator

Is there any science to this?

• It’s a lot of money to spend on the off hand chance it might take a lightning hit.

Case Study:CKVR - Barrie Broadcast Tower

On June 11, 2000 a severe storm rolled through Barrie. Lightning knocked out a substation at 6:21 am cutting off power to the surrounding area. Fortunately at 5:08 am the ESID had identified the storm activity and switched the site to generator power. The site remained on generator until 9:40 am when the storm had passed.

CKVR was never off the air.

Case Study:CKVR - Barrie Broadcast Tower

During the same storm the LSC2000 registered 3 direct strikes to the tower. Global Atmospherics data confirmed the times and provided peak currents: 4:55 am 20 kA 5:10 am 35 kA 5:59 am 59 kA

The grounding system absorbed the energy of the strikes and no damage occurred to any of the sensitive broadcasting equipment.