To successfully carry out the various test procedures suggested in this manual, certain test instruments are essential. The following lists detail the basic requirements in this respect.
It should be noted that in addition to these instruments a comprehensive kit of tools is also essential. For fault finding purposes this need not include any specialised tools.
Item 1 – Multimeter
It is essential that all test instruments be regularly checked for safety, and any connection leads, probes or clips checked to ensure that they are suitable for the voltage levels being tested. Never attempt to test a “LIVE” generator unless there is another competent person present who can switch off the power supply or shut down the engine in an emergency. The Multimeter is a comprehensive test instrument for measuring voltage, current and resistance.
Never expose “LIVE” connections unless you have created a safe working area around you. Make sure you have made all other persons in the immediate area fully aware of what you are doing.
Do not attempt to carry out tests on medium or high voltage generators without using specialised instruments and probes, with suitable protection equipment and procedures for grounding (earthing) the output terminals.
Item 2 – Tachometer or Frequency meter
This instrument is for measuring the shaft speed of the alternator and should be capable of measuring speeds between 0 and 5000 revolutions per minute, (RPM). An alternative to the tachometer is the frequency meter. However the alternator must be generating its normal output voltage for this instrument to be accurate.
Item 3 – Megger (Insulation test meter)
This instrument generates a voltage of 500V or 1000V, and is used to measure the resistance value of the insulation to earth (ground). It may be an electronic push button type, or a hand cranked generator type.
Item 4 – Clip-On Ammeter (Clampmeter)
Used to measure AC current, it consists of a pair of callipers, which are clamped around the conductor, and by means of a transformer action, gives an indication of the amperes flowing in the conductor. Useful ranges to have on this meter are
AC Amps 0-10-50-100-250-500-1000
Item 5 – Kelvin Bridge – low resistance meter
This instrument is used to measure resistance values below 1.0 ohm. They are bulky, and expensive, but are the only means of accurately measuring very low resistances, such as main stator and exciter rotor windings.
However, there are other methods of testing low resistance windings, and these are included in the various test procedures, i.e. Test Method A. This section will enable the main generator windings to be tested while running the generator at normal speed without load.
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