1-6
BE1-32R, -32 O/U GENERAL INFORMATION
Figure 1-8. Power Factor, Third And Fourth Quadrants
Figure 1-9 (a) shows an underpower tripping application based on the BE1-32 O/U, model A1F with an
overpower setting of 0.5 watts and an underpower setting of 50%. The control circuit for this application is
shown in Figure 1-9 (b). Figure 1-8 (b) shows the operating characteristic in the first and second quadrant. The
relay UNDER contact closes to trip the breaker when the real power flow from the utility drops below 0.25 watts.
Because this contact is preclosed at the instant of breaker closing, the trip circuit must be disabled by a timing
relay (62) until after the breaker has closed.
Figure 1-9. Underpower Tripping
Example 7, Reactive Power (Vars) Detection
This example illustrates a directional power relay configured to distinguish between real and reactive power.
Real power (watts) is supplied to the synchronous generator by the prime mover, and reactive power (vars) is
supplied to the field by the exciter. When field excitation is significantly reduced and the connected system can
provide sufficient reactive power to maintain the generator's terminal voltage, reactive power flows into the
machine and causes it to operate as an induction generator with essentially the same kW output. This situation
causes two major problems. First, the additional reactive loading of the faulty generator must be redistributed
to other synchronous generators on the system. Secondly, a synchronous generator is not designed to operate
as an induction generator. Excessive heating results in the damper (amortissuer) windings, slot wedges, and
in the surface iron of the rotor due to the slip frequency current flow when a synchronous generator is operated
as an induction generator.
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