Figure 1-35.-Power sensing.

rheostat A/R1, thus disabling the power-sensing system.

A power-sensing network has been provided in one

If the leads from current transformer A/CT1 to resistor

phase of the generator output (fig. 1-35) for simplicity;

A/R1 are reversed, the phase relationship of the voltage

consider first the power-sensing circuit of generator A.

across resistor A/R1 would be 180 out of phase with

This circuit consists of current transformer A/CT1 and

the secondary of transformer A/T1. Therefore, with

real power-sensing rheostat A/R1. Note that power

increasing load, the regulator would try to raise the

transformer A/T1 is connected from neutral to line C,

output frequency of the generator. This is known as

and, therefore, the voltage across the primary of

frequency compounding.

transformer A/T1 will be in phase with the current in line

C at unity power factor. Transformer A/T2, which is the

frequency-sensing transformer, is in parallel with power

PARALLEL OPERATION

transformer A/T1, and, therefore, the voltage output of

the secondary of transformer A/T2 is in phase with the

voltage in the primary of transformer A/T1. Then, at

Refer to figure 1-35 and note that generator B has a

real power-sensing system exactly as generator A. Note

unity power factor, the voltage across the secondary

windings A/T2 will be in phase with the current in line

also that not only is current transformer A/CT1

C. Real power-sensing rheostat A/R1 is actually the load

connected across its load rheostat A/R1, but when circuit

resistor for current transformer A/CT1. Therefore, when

breaker CB3 is closed, it also is connected across real

power-sensing rheostat B/R1. Consider what would

a load is applied to the output of generator A, a voltage

happen if generator A were to supply the greater amount

will be impressed across rheostat A/R1, and this voltage

of real power to the load. There would be a difference

will be in phase with the voltage across the secondary

winding of transformer A/T1. The voltage from

in potential between current transformers A/CT1 and

B/CT1. Due to the difference in potential, a current will

transformer A/T2 and the voltage across resistor A/R1

flow in resistors A/R1 and B/R1 connected in parallel.

will add, and the sensed voltage will be an increased

The current will be in phase with the voltage out of

voltage to rectifier A/RD1. This would represent an

secondary of transformer A/T1 and 180 out of phase

increased output frequency; thus, the regulator would

with the secondary voltage of transformer B/T1. Hence,

decrease the speed of the motor and thus reduce the

output frequency of the generator. This is known as a

the regulator of generator A will decrease its output

frequency droop. To eliminate this droop in singular

frequency, and the regulator of generator B will raise its

output frequency. This will permit the generator to

operation, a shorting bar or relay contact is placed across

Figure 1-35.-Power sensing.

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