Page 70 - Apprentice Manual_Neat

S1-Q19.) Dielectric strength of a generator winding is tested using?

a.) Ammeter
Used to measure current flow.
b.) Digital Multi-Meter
Used to measure potential, flow, resistance of conductors, and several other function (in some cases),
but not insulation strength.
c.) *Insulation Resistance Meter
Correct. This device determines at what voltage the insulation will fail by passing a high
voltage at a small current through the windings. R=E/I. This requires a very high internal
source voltage which the other devices listed in this question do not have.
d.) Torque wrench
Not an appropriate tool for electrical work.

S1-Q20.) The RPM of an AC generator, based on the number of windings, determines what parameter of
that generator?

a.) Voltage output
The voltage is determined by the field strength and number of loops in the winding.
b.) *Frequency
Correct. If a generator has 2 sets of windings for each phase and is spinning at 3600 rpm, the
result will be 60Hz power.
c.) Current output
Current is a function of field and load.
d.) VARs
This is power factor and is determined by the type of load.

S1-Q21.) Which meter(s) would be used to measure phase sequencing?

a.) Two watt meters
There is not enough information given by two watt meters to determine phase rotation.
b.) *Phase rotation meter
Correct. By connecting the phase rotation meters in the proper sequence (phase A – A,
phase B – B, phase C – C), the device will rotate or indicate that the phases are properly
connected. If two of the phases have been crossed, the device will indicate reverse operation.
c.) Clamp-on ammeter
There is no information given by a clamp-on ammeter which would be useful in determining phase
sequence. Current flows the same whether connected properly or in reverse.
d.) Two voltmeters
Potential remains the same whether the phases are connected in forward or reverse. No information
can be for sequence by these devices.

S1-Q22.) When testing a diode using a DVOM in the diode test mode, what would indicate a good diode?

a.) Positive lead closest to the stripe, negative lead on the opposite end yields 0.5V.
This would indicate the reverse bias had broken down and the diode was bad.
b.) Negative lead closest to the stripe, positive lead on the opposite end yields 0.5V.
This is the correct reading for forward bias, but does not indicate the reverse bias condition. No
conclusion could be drawn.
c.) Positive lead closest to the stripe, negative lead on the opposite end yields an open.
This is the correct reading for the reverse bias, but no conclusion could be drawn without testing the
forward bias.
d.) *B and C must both be true or the test is incomplete.
Correct. Individually b and c only tell half the story. Together, they indicate the diode will pass
voltage in the forward bias and block voltage in the reverse bias.

EGSA Apprentice Certification Program Study Guide - Page 62