OTHER ELECTRICAL MEASURING DEVICES
Test Instruments & Measuring Devices
Power Factor Meter
A power factor meter is a type of electrodynamometer movement when it is made with two
movable coils set at right angles to each other. The method of connection of this type of power
factor meter, in a 3f circuit, is shown in Figure 14. The two stationary coils, S and S1, are
connected in series in Phase B. Coils M and M1 are mounted on a common shaft, which is free
to move without restraint or control springs. These coils are connected with their series resistors
from Phase B to Phase A and from Phase B to Phase C. At a power factor of unity, one
potential coil current leads and one lags the current in Phase B by 30°; thus, the coils are
balanced in the position shown in Figure 14. A change in power factor will cause the current
of one potential coil to become more in phase and the other potential coil to be more out of
phase with the current in Phase B, so that the moving element and pointer take a new position
of balance to show the new power factor.
Figure 14 3f Power Factor Meter Schematic
Ground Detector
The ground detector is an instrument which is used to detect conductor insulation resistance to
ground. An ohm meter, or a series of lights, can be used to detect the insulation strength of an
ungrounded distribution system. Most power distribution systems in use today are of the
grounded variety; however, some ungrounded systems still exist.
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