Guardian Technologies 4270 manual Measuring AC Frequency, Measuring Current, Measuring Resistance

Section 4

MEASURING ELECTRICITY

MEASURING AC FREQUENCY

The generator's AC output frequency is proportional to Rotor speed. Generators equipped with a 2-pole Rotor must operate at 3600 rpm to supply a frequen- cy of 60-Hertz.

Correct engine and Rotor speed is maintained by an engine speed governor. For models rated 60-Hertz, the governor is generally set to maintain a no-load frequency of about 62-Hertz with a corresponding output voltage of about 125 VAC line-to-neutral. Engine speed and frequency at no-load are set slight- ly high to prevent excessive rpm and frequency droop under heavy electrical loading.

MEASURING CURRENT

To read the current flow, in AMPERES, a clamp-on ammeter can be used. This type of meter indicates current flow through a conductor by measuring the strength of the magnetic field around that conductor. The meter consists essentially of a current trans- former with a split core and a rectifier type instrument connected to the secondary. The primary of the cur- rent transformer is the conductor through which the current to be measured flows. The split core allows the instrument to be clamped around the conductor without disconnecting it.

Current flowing through a conductor may be mea- sured safely and easily. A line-splitter can be used to measure current in a cord without separating the con- ductors.

Figure 4-2. – Clamp-On Ammeter

Figure 4-3. – A Line-Splitter

NOTE: If the physical size of the conductor or ammeter capacity does not allow all lines to be measured simultaneously, measure current flow in each individual line. Then, add the individual readings.

MEASURING RESISTANCE

The volt-ohm-milliammeter may be used to measure the resistance in a circuit. Resistance values can be very valuable when testing coils or windings, such as the Stator and Rotor windings.

When testing Stator windings, keep in mind that the resistance of these windings is very low. Some meters are not capable of reading such a low resis- tance and will simply read “continuity”.

If proper procedures are used, the following condi- tions can be detected using a VOM:

•A “short-to-ground” condition in any Stator or Rotor winding.

•Shorting together of any two parallel Stator wind- ings.

•Shorting together of any two isolated Stator wind- ings.

•An open condition in any Stator or Rotor winding.

Component testing may require a specific resistance value or a test for “infinity” or “continuity.” Infinity is an OPEN condition between two electrical points, which would read as no resistance on a VOM. Continuity is a closed condition between two electrical points, which would be indicated as very low resistance or “ZERO” on a VOM.

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