What Is A Rectifier and What Does It Do?¾ It has been established that DC electricity will generate corrosion,and corrosion in turn will generate DC electricity. Therefore, it ispossible to prevent corrosion by the use of DC electricity¾ A Direct Current passing from a structure will cause corrosion, anda Direct Current impressed onto a structure will stop corrosion¾ The Rectifier is used to deliver – or impress – a Direct Current ontoa structure¾ The Rectifier has two functions:1.2.To transform incoming line voltage (AC) provided by the utilitycompany to a usable voltage, andTo convert the usable AC voltage to Direct Current (DC) to be usedfor cathodic protection

When Selecting Your Rectifier .¾ Designed for rugged unattended service¾ Cooling options¾ Cabinet options¾ Input – AC Power¾ Output – DC Power keeping possible futurerequirements in mind

What’s the Perfect Rectifier for Me?¾ Constant CurrentMaintains a constant current output by adjusting thevoltage as site conditions fluctuate¾ Auto PotentialAdjusts the rectifier output to maintain a desiredstructure‐to‐soil potential¾ Manual Tap (Constant Voltage)Set it and forget it

Unpacking and Installing your Rectifier¾ Check for freight damage¾ Tighten all loose connections¾ Select a location that’s easilyaccessible¾ Do not install near heat producing equipment¾ Make sure the rectifier is properly grounded

Proper Output Polarity¾ Structure Negative¾ Anode PositiveCP is a “SNAP”

Common Causes of Cathodic Protection System Failures706050403020100RectifierCablesGroundbedAC Power

As with any electrical or mechanical device,rectifier downtime will occur due to unplannedfailure of the equipment.A good maintenance program will help ward offsome component failures, and basictroubleshooting skills will bring the rectifierback on line.

Basic Preventive Maintenance Checks And Services¾ The rectifier enclosure should be maintained¾ Rectifiers must be allowed to cool properly¾ Rectifier enclosure must be properly grounded¾ Check all connections for tightness¾ All rectifier components should be kept clean¾ Basic measurements should be recorded AC input voltage and amperageStack AC input voltageDC output voltage and amperageTransformer tap settings

Rectifier ComponentsTo best understand all components of the rectifier and their relation to oneanother, the best place to start is at the input AC InputInput Lightning ArrestorMain Circuit BreakerPower TransformerRectifier StackFuses or SecondaryBreakersMetersShuntOutput Lightning ArrestorFiltersAccessories

Lightning Arrestors¾ Usually found on theinput and output of therectifier¾ Protects the rectifierfrom extreme voltagesurges¾ Most configurations are aset of gapped points thatan arc current can travelwhen a voltage surge isgreat enough inmagnitude

Main Circuit Breaker¾ Turns the incoming AC onor off¾ Must be placed in each‘HOT’ supply line¾ Provides overloadprotection to the rectifier¾ Contains either a thermalor magnetic tripelement . Or acombination of both

Power Transformer¾ Converts the incomingAC voltage to a ‘usable’voltage¾ Primary – Input¾ Secondary – Output¾ The secondary allows foradjustment of therectifier¾ Most transformers usedin rectifiers are step‐down or ‘bucking’

Rectifier Stack¾ Converts incoming ACto DC output¾ It’s function is to passcurrent in one directionand block it in theopposite direction¾ Selenium¾ Silicon

Rectifier Stack – Silicon¾ Cost effective¾ Very efficient¾ Does not age¾ Longer life¾ Much higher outputrating¾ Easily replaced¾ Must be surge protected¾ Will not show signs of visibledamage

Rectifier Stack – Selenium¾ Can withstand Voltagesurges¾ Can withstand short‐termoverload¾ Becomes less efficient withage¾ Becomes less efficient withheat¾ More difficult to replace¾ If it looks good, it’s‘probably’ good

Fuses & Secondary Breakers¾ Protects the moreexpensive rectifiercomponents. Period.

DC Output Meters¾ Used in the rectifier toindicate the amount ofDC Voltage and/orcurrent at the output¾ Always carry a portablevolt/amp meter whenservicing the rectifier,as rectifier meters havebeen known to giveerroneous readings

Shunts¾ Calibrated device (resistor)used in the DC Circuit formonitoring purposes.¾ DC current can becalculated from themeasured voltage dropacross the shunt

Filters & Accessories¾ All rectifiermanufacturers offervarious accessories toenhance their products FiltersLightsAlarmsAC outletsHour metersRemote monitors

Before We Start Troubleshooting . A Few PrecautionsBe Aware of High Voltages!9 Backhand Rule: Touch the rectifier enclosure with the back of your hand9 De‐energize: If possible, disconnect the power at the source9 One‐Hand Rule: If possible, work within the enclosure with only one hand9 Look Away: When energizing the rectifier, look away or cover your face9 Insulated Hand/Foot wear: Wear them to prevent electrocution9 Work In Pairs: For obvious reasons9 Weather: Do not attempt repairs during inclement weather9 Jewelry: Do not wear jewelry while working on ‘live’ circuits9 Fatigue: Do not work on energized equipment while mentally or physicallyfatigued9 Maintain Constant Vigilance: Know where you are with respect to ‘live’circuits9 Working Knowledge: Have a general understanding of the rectifier circuitoperation and basic troubleshooting skills

And Check For Nests And Other Critters!

Troubleshooting EquipmentDoesn’t have to be elaborate – only functionalProper tools will give the field technician the ability to makeall repairs needed. Recommended tools and equipmentmight be: Digital voltmeterAmp clampHeavy shorting cablesInsulated jumper cablesSpare calibrated shuntLoad resistorAssorted small hand tools

TroubleshootingMost common rectifier problems encountered are:¾ No input – or line – voltage¾ Blown fuses¾ Faulty meters¾ Loose or corroded terminals¾ Open groundbed leads¾ Lightning damage

Most Problems Are Obvious

Some Problems Are Really Obvious

Some Problems Are Really, Really Obvious

And Some Are Tough To Find

Troubleshooting Tips¾ Many rectifier problems are obvious to the experiencedtechnician upon physical examination. Look for looseconnections, signs of arcing, strange odors or discoloration.¾ Carry an inventory of spare parts. The most common being: BreakersFusesDiodesBridge rectifiersWireMiscellaneous connectorsControl boards for auto‐controlled rectifiers

More Troubleshooting Tips No AC line voltage: Do not overlook the possibility thatservice to the rectifier may have been interrupted. Defective Meters: Never trust the rectifier meters.Always verify with a portable voltmeter known to be good. Breaker tripped or blown fuse: If the breaker tripsrepeatedly even with the output reduced, the cause may be ashort circuit in some component (much more on that later).If the breaker trips occasionally for no obvious reason, thecause may be a temporary overload due to groundbedresistance fluctuations, line voltage surges, intermittent shortcircuits due to component breakdown, or the thermal breakermay be affected by sunlight or another heat source.

Even More Troubleshooting Tips Open circuit in a component or connection: Check allconnections for cleanliness and soundness. Check therectifier stack for an open‐circuit condition. The diodes canbe checked with an ohmmeter. (Again, much more on thatlater). Defective transformer: If input voltage is present, checkfor an audible hum. If a hum is present, the primary isprobably working and the secondary is open. Disconnect theAC input and isolate the transformer. Check the resistance ofthe windings with an ohmmeter. The secondary should haveless than one ohm resistance. The primary should have oneto ten ohms resistance. If either is high, the transformershould be replaced.

The Ultimate Troubleshooting TipWhen expected DC voltage is present at the rectifieroutput, there is probably no problem with the rectifieritself – but rather, the problem is within the external(groundbed) circuit.‐In Other Words‐DC Output Voltage Good Rectifier

Troubleshooting ProcedureNo Output Check the input voltage. Us the AC voltage setting of the voltmeter tomeasure across the line side of the circuit breaker (A‐A).Check across the load side of the circuit breaker (B‐B). The measured voltageshould be the same as measured on the line side.Check the input voltage change taps for loose or dirty connections. Verify thatthe tap change bar is in the proper position (C).Check the transformer secondary with your AC voltmeter (D‐E).Measure the AC voltage supplied to the rectifier stack (F‐G). This voltageshould be the same as was measured at the transformer secondary.Measure the DC voltage at the rectifier stack output (H‐I). The stack can beisolated from the rest of the DC circuit by removing either lead at H or I.Check the DC voltage at the rectifier output (J‐K). If DC voltage is present butis much less than expected, the stack will have to be examined. If the DCvoltage is about half of that expected, turn the rectifier off and feel theindividual plates of the stack. If the temperature of the individual plates is notuniform, the stack has an open and is half‐waving. Defective diodes and/orassociated wiring will have to be replaced.If DC voltage is present at the stack but not at the output, check for looseconnections or open leads between the stack and the output. Don’t forgetabout the DC fuse.

Troubleshooting ProcedureMain Breaker Trips Remove the lightning arrestors and try again.If the breaker continues to trip, isolate the breaker from the rectifier byremoving either lead from the load side of the main breaker (B‐B). If thebreaker trips, the breaker is defective. If it holds, the breaker is good.Reconnect and try again.If the breaker continues to trip, isolate the transformer from the DC circuitby removing either secondary tap link bars (D or E). Try again.If the breaker continues to trip, the transformer is shorted and willprobably have to be replaced or adjusted. If the breaker does not trip, theshort circuit is in the DC circuit.Remove either DC lead from the rectifier stack (H or I). If the breakertrips, the rectifier stack will have to be replaced or repaired. If the breakerdoes not trip, the short is still downstream – either in a rectifier outputaccessory, or the groundbed circuit.

Dead-Front Rectifier Troubleshooting

Most Common Cause Of Rectifier FailureApproximately 80% Of All Rectifier Failures Occur At The Rectifier StackRectifier StackEverything Else

Dead Front Stack Check

So To Summarize9Proper Rectifier Selection9Know Your Troubleshooting Procedures9Know your Troubleshooting Equipment9Maintain Constant Vigilance9Have A Plan9Work Your Plan9Good Luck!

Defective transformer: If input voltage is present, check for an audible hum. If a hum is present, the primary is probably working and the secondary is open. Disconnect the AC input and isolate the transformer