Bergey Excel 10, Bergey Excel 5 and XL.1

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Bergey Excel 10, Bergey Excel 5 and XL.1-48: Turbine Circuit Diagnostics
These three tests will verify the health of the alternator and turbine side circuit. They should all be
completed and in numerical order.
NOTE: As always, never leave the site with the turbine connected to a dead short. The proper
decommissioned state is to leave the turbine free-wheeling.
REQUIRED TOOLS: Standard hand tools
Volt meter
Megger (i.e. insulation tester) with 500V scale
TEST 1: Open-Circuit Voltage
1. Deactivate the controller (i.e. grid-tied inverter, battery control etc.).
2. At the controller, measure the phases-to-phase voltage, AC-volts, between all three pairs from
the turbine(i.e. phaseA to phaseB, phaseA to phaseC, phaseB to phaseC).
a. These three voltages should be within a couple of volts of one another. If so, move on
to the TEST 2.
b. If one or two of these readings are off, there is bad connection somewhere towards to
the alternator. Check the circuit for and repair: loose connections, blown fuses, etc.
NOTE: Connections need to be good, solid, corrosion free metal-on-metal
contact. Make sure someone didn’t push the cable in too far and clamp
on the cable insulation.
TEST 2: Short Circuit
1. Begin this test after the system passes the Open-Circuit Voltage test.
2. Turn off the tower disconnect.
3. With the controller still deactivated, disconnect the three turbine cables from the controller and
short them together.
NOTE: The short must be a good solid electrical connection between all three phases,
and the short must remain isolated from earth ground.
4. Listen to the turbine as you turn on the tower disconnect.
a. The turbine should come to a smooth stop. If so, move on to the TEST 3.
b. If the turbine growls, or shakes the tower, there is a discontinuity somewhere in the
circuit between (AND INCLUDING!) the short circuit that you applied and the alternator.
Check for and repair: loose connections, blown fuses, damaged wire, etc.
i. To further isolate the location of the problem, turn the tower disconnect off.
ii. Install a short in the bottom of the tower disconnect.
iii. Listen to the turbine and turn the tower disconnect back on.
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Bergey Excel 10, Bergey Excel 5 and XL.1-48: Turbine Circuit Diagnostics
1. If the growl goes away, you know the discontinuity is in the circuit
somewhere between (AND INCLUDING!) the new short location and the
original short location.
2. If the growl persists, the discontinuity is between the new short location
and the alternator. Check for and repair: loose connections in the
tower disconnect. Up the tower, check for and repair: problems in the
brush/slip ring area, loose connections tower terminal block, etc.
Consult the tower installation manual for further turbine inspection
procedures.
TEST 3: Ground Fault
1.
2.
3.
4.
Begin this test after the system passes the Open Circuit Voltage and Short Circuit tests
Repeat Step 2 and Step 3 of TEST 2, to apply a short to the turbine.
Listen to the turbine and turn on the tower disconnect, it should come to a smooth stop.
Test for ground faults using a megger, or insulation tester, set to the 500V scale.
a. Connect the common probe to earth ground.
b. Test one of the phases to ground (they should all give the same reading at this point due
to the applied short), you should see 50MΩ (megaohm) or higher on the 500V scale.
c. On some systems, readings as low as 40MΩ or even 30MΩ may be fine. This depends
on the controller, if the controller is not faulting due to ground fault then these readings
are fine.
d. If the reading is below 30MΩ, there is a ground fault somewhere in the circuit. Isolate
different portions of the circuit and test them independently to determine the
component needing repair. For example:
i. Turn off the tower disconnect, you’ve essentially chopped the system in half.
ii. Test the bottom terminal of the disconnect, this is testing the “wire run half” of
the circuit.
iii. Test the top terminal of the disconnect, this is testing the “up tower half” of the
circuit.
NOTE: Most meggers don’t respond well to voltages produced by the
turbine. To test the top terminals of the disconnect, turn the
disconnect back on, until the turbine stops. Then turn the
disconnect back off and take your megger reading quickly
before the turbine starts spinning.
iv. Continue isolating pieces of the circuit until the ground faulted component is
discovered.
e. Repair/Replace the damaged circuit component.
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