** Important **

This article explains the procedure for testing a Mecc Alte ECP alternator. it is NOT SUITABLE for unqualified persons to undertake this work. If you are not technically qualified to do so, you should not attempt to perform these procedures as they could lead to serious injury or death.

MAIN STATOR WINDING.

Remove customer’s output cables and disconnect any earth-neutral connections.

Disconnect AVR connections. 

Disconnect radio interference suppression unit if fitted.

Megger main stator winding to earth. Insulation resistance must be above 1MW @ 500 Volts.

Test auxiliary stator winding for continuity two red leads connected to AVR. If auxiliary is open circuit the machine may be operated by linking terminals plus and zero on the AVR. However this will eliminate overload protection device. If in doubt consult Mecc Alte UK.

Refer to handbook for resistance (nominal 1-1.5W).

If necessary, run machine with field leads disconnected or the fuse removed, and check voltage balance across phases or between phases and neutral. Any major imbalance would indicate a blown stator. Residual voltage should be greater than 50volts. Lower voltages could indicate an open circuit exciter stator or a fault in the rotor see paras 2/4.

Split neutral point and megger test insulation between phases.

EXCITER FIELD.

Check for continuity nominal resistance 13-20W. (Yellow and Blue Leads)

Check insulation resistance to earth.

AVR.

Test AVR fuse. If necessary separately excite machine, remove yellow and blue leads from AVR. With a 12 Volt battery connect positive to yellow lead of exciter field and negative to blue lead of exciter field. Remember to only run like this for short period of time. Connect a 33W resistor in series to limit field current if required to run for longer period.

If machine operates OK separately excited. AVR is faulty.

Ensure engine speed is within acceptable limits i.e. 1410 to 1560 RPM for correct operation

ROTOR AND EXCITER ARMATURE.

Disconnect main rotor leads from rotating rectifier assembly (Marked + red and – blue).

Measure rotor resistance (refer to handbook) megger rotor winding to earth as above.

Short together all rectifier plates or disconnect three-phase input from exciter. Megger exciter winding to earth.

Test volt drop across each diode this should be approximately 0.5 Volts. Or a resistance meter should show continuity in one direction and very high resistance in the other.

Check VDR (red button component across main rotor leads) this should show very high resistance in normal operation.