Generac Power Systems 75 Testing Rotor Insulation, Megohmmeter, Test Between Parallel Windings

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Section 3

INSULATION RESISTANCE TESTS

TEST BETWEEN PARALLEL WINDINGS:

Connect the tester leads across Stator leads No. 11P and 33. Apply a voltage of 1500 volts. If an insulation breakdown is indicated, clean and dry the Stator. Then, repeat the test between parallel windings. If the Stator fails the second test, replace it.

Figure 3-2. – Stator Leads

TESTING ROTOR INSULATION

To test the Rotor for insulation breakdown, proceed as follows:

1.Disconnect wires from the Rotor brushes or remove the brush holders with brushes.

2.Connect the tester positive (+) test lead to the positive (+) slip ring (nearest the Rotor bearing). Connect the tester negative (-) test lead to a clean frame ground (like the Rotor shaft).

Figure 3-3. – Rotor Test Points

3.Apply 1000 volts. DO NOT APPLY VOLTAGE LONGER THAN 1 SECOND.

If an insulation breakdown is indicated, clean and dry the Rotor then repeat the test. Replace the Rotor if it fails the second test (after cleaning and drying).

THE MEGOHMMETER

GENERAL:

A megohmmeter, often called a “megger”, consists of a meter calibrated in megohms and a power supply. Use a power supply of 1500 volts when testing Stators; or 1000 volts when testing the Rotor. DO NOT APPLY VOLTAGE LONGER THAN ONE (1) SECOND.

TESTING STATOR INSULATION:

All parts that might be damaged by the high megger voltages must be disconnected before testing. Isolate all Stator leads (Figure 3-2) and connect all of the Stator leads together. FOLLOW THE MEGGER MANUFACTURER'S INSTRUCTIONS CAREFULLY.

Use a megger power setting of 1500 volts. Connect one megger test lead to the junction of all Stator leads, the other test lead to frame ground on the Stator can. Read the number of megohms on the meter.

MINIMUM INSULATION

 

GENERATOR RATED VOLTS

 

RESISTANCE

=

__________________________

+1

1000

(in “Megohms”)

 

 

 

 

 

The MINIMUM acceptable megger reading for Stators may be calculated using the following formula:

EXAMPLE: Generator is rated at 120 volts AC. Divide “120” by “1000” to obtain “0.12”. Then add “1” to obtain “1.12” megohms. Minimum Insulation resistance for a 120 VAC Stator Is 1.12 megohms.

If the Stator insulation resistance is less than the cal- culated minimum resistance, clean and dry the Stator. Then, repeat the test. If resistance is still low, replace the Stator.

Use the Megger to test for shorts between isolated windings as outlined “Stator Insulation Resistance”.

Also test between parallel windings. See “Test Between Parallel Windings”on this page.

TESTING ROTOR INSULATION:

Apply a voltage of 1000 volts across the Rotor posi- tive (+) slip ring (nearest the rotor bearing), and a clean frame ground (i.e. the Rotor Shaft). DO NOT EXCEED 1000 VOLTS AND DO NOT APPLY VOLT- AGE LONGER THAN 1 SECOND. FOLLOW THE MEGGER MANUFACTURER'S INSTRUCTIONS CAREFULLY.

ROTOR MINIMUM INSULATION RESISTANCE:

1.5 megohms

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Contents Diagnostic Repair Manual Safety Replacement PartsTable of Contents Section Specifications & Charts Section Exploded Views / Part NumbersElectromagnetic Fields MagnetismElectromagnetic Induction Simple AC Generator More Sophisticated AC GeneratorGenerator Operating Diagram Generator AC Connection System Field BoostLine Breakers 120 Volts only Connection for 120 Volts Only Reconnection for Dual Voltage OutputRotor Assembly Stator AssemblyBattery Charge Components Brush HolderExcitation Circuit Components GeneralAdjustment Procedure Crankcase BreatherVoltage Regulator DescriptionInstall Breather Install oil vapor collector and retainerControl Panel Component Identification Check BreatherCleaning the Generator Effects of Dirt and MoistureInsulation Resistance Testers Drying the GeneratorBrushing and Vacuum Cleaning Stator Insulation ResistanceCloth or Compressed AIR Stator SHORT-TO-GROUND TestsTesting Rotor Insulation Testing Stator InsulationTesting Rotor Insulation MegohmmeterMeters VOMMeasuring AC Voltage Measuring DC VoltageMeasuring Current Measuring AC FrequencyMeasuring Resistance Electrical Units Ohms LAWAmpere VoltOperational Analysis IntroductionCircuit CONDITION- Rest Circuit CONDITION- Priming Circuit CONDITION- Cranking Circuit CONDITION-RUNNING Choke Heater CHCircuit CONDITION- Shutdown Circuit CONDITION- Fault Shutdown Sure Switch LOPBattery Recommended BatteryBattery Cables Engine Controller Circuit BoardSTART-STOP Switch Fuel Primer SwitchAMP Fuse Starter Contactor Relay Starter Motor Troubleshooting Flowcharts Troubleshooting Flowcharts Troubleshooting Flowcharts Troubleshooting Flowcharts Troubleshooting Flowcharts Troubleshooting Flowcharts Troubleshooting Flowcharts Troubleshooting Flowcharts Troubleshooting Flowcharts Troubleshooting Flowcharts Troubleshooting Flowcharts Procedure Test 1- Check NO-LOAD Voltage FrequencyTest 2- Check Engine Governor DiscussionGovernor Adjustment Test 3- Test Excitation Circuit BreakerTest 4- Fixed Excitation TEST/ROTOR AMP Draw If continuity was indicated, go to TestTest 5- Wire Continuity Re-connect Wire 11 and Wire 22 to the Voltage RegulatorSet the VOM to measure AC voltage Set a VOM to its Rx1 scaleTest 7 Test Stator DPE Winding Test 6- Check Field BoostIf field boost checks good, replace the Voltage Regulator Test 8- Check Sensing Leads / Power Windings Across Wires Ohms11S 22S Model OhmsTest 9- Check Brush Leads Test 10 Check Brushes & Slip RingsTest 11- Check Rotor Assembly Tance Tests ProcedureTest 12 Check Main Circuit Breaker Replace the Rotor if it fails the testTest 15 Check Battery Charge Output Test 16 Check Battery Charge RectifierBattery Charge Rectifier BCR is a full wave rectifier Test 13- Check Load Voltage Frequency10. Battery Charge Rectifier Short to GroundTest 19- Test Primer Switch Set a VOM to read battery voltage 12 VDCAlso see Fuel Primer Switch, Test 18 TRY Cranking the EngineTest 20- Check Fuel Pump 13. The LPG Fuel Solenoid FSTest 23- Check Power Supply to Circuit Board Test 22- Check Battery & CablesTest 21- Check 7.5 AMP Fuse Test 24 Check START-STOP Switch 17. Start-Stop SwitchTest 26- Check Starter Contactor Relay Set a VOM to measure DC voltage 12 VDCTest 27 Check Starter Motor Test 26A Check Starter ContactorConditions Affecting Starter Motor Performance Checking the Pinion Tools for Starter Performance TestMeasuring Current TachometerTesting Starter Motor Test 28- Check Fuel SupplyTest Bracket Remove Starter Motor28 LP Gas Carburetion Diagram Discussion LPG ModelsTest 29 Check Wire 14 Power Supply Test 30 Check WireBattery voltage is not measured, proceed to Step Crank the engine. The meter should indicate battery voltageTest 31 Check Fuel Solenoid Gasoline Models Test 32 Check Ignition SparkCylinder Balance Test Conclusion No cylinder is weakest of the two cylindersTest 34 Check and Adjust Ignition Magnetos Test 33 Check Spark Plugs37. Setting Ignition Magneto Armature Air Gap Test 35 Check Valve Adjustment Adjusting Valve ClearanceChecking Flywheel Magnet Flywheel KEYTest 36 Check Carburetion Install Rocker ARM CoverTest 37 Check Choke Solenoid 43. Connector Adjust the regulated pressure on the gauge to 80 psi Down Test / Compression TestRepeat Steps 1 through 8 on remaining cylinder Check CompressionTest 40 Test OIL Temperature Switch Test 39 Check OIL Pressure SwitchIf all steps check GOOD, go to Test Test 42 Check LPG Fuel Solenoid Test 41 Test Choke HeaterShort to Ground 49. Fuel Solenoid Major Disassembly ENCLOSURE/PANEL RemovalStator Removal Rotor RemovalEngine Removal Belt TensioningStarter Removal FLYWHEEL/MAGNETO Removal Page Section Exploded Views / Part Numbers Part NO. QTY Description Enclosure Drawing No E1011-B QTY Description Sheet Metal Drawing No E1012-E QTY Description Flywheel Assy GT-990Control Panel Drawing No E1013-A Wire ASM GRD STD Conn Switch Spdt ON-MOM-ONSwitch 6A Spdt Not Shown PANEL, TOP ControlTwin Engine Drawing No E1014-B ASSEMBLY, Crankcase RV ASSEMBLY, BreatherASSEMBLY, Head #1 ASSEMBLY, OIL Fill CAPLP Regulator Drawing No E1530 CASTING, Twin Regulator Housing Washer Flat M4SOLENOID, Twin Regulator SPRING-SOLENOID PlungerSpecifications & Charts Generator Specifications Nominal Resistances of Generator Windings AT 68FEngine Speeds and Voltage Specifications Page Electrical Data Electrical Data PO BOX 297 WHITEWATER, WI

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