Basler BE1-24, Instruction Manual

BE1-24 General Information

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control functions which may be incorporated in the generator voltage regulator.

The sudden removal of load from a generator results in an increase in terminal voltage especially if a
transmission line remains connected as the only load.  The automatic voltage regulator should act to bring
the voltage down to a safe level before equipment damage occurs.  However, in the event of a regulator
failure, the BE1-24 protects equipment from damage.

Load tap changing (LTC) transformers and line voltage regulators may be subjected to excessive volts/hertz
during abnormal system frequency conditions.  This is the inevitable consequence of their constant voltage
control function.  Failure of the LTC controller may result in a runaway condition producing dangerously high
voltages.  The BE1-24 provides close protection for such equipment while allowing a wide range of voltage
control operations.

Figure 1-1 illustrates the advantage of applying the inverse square timing characteristic rather than the two-
step protection scheme.  This provides closer coordination and prevents unnecessary tripping of the
protected equipment.

In this example, two steps of definite time delay overexcitation protection are applied to provide protection
that approximates the transformer damage curve.  One step is set for 110 percent and 60 seconds.  The
second step is set for 118 percent and 6 seconds.  However, by using the inverse square characteristic, the
damage curve can be even more closely approximated.  The resulting protection is more closely coordinated
with adequate margin.  Note that the cross hatched area reveals the overprotected area that results from
use of a two step scheme.

When a transformer and generator are to be protected by a single volts-per-hertz overexcitation relay, the
overexcitation curves for both pieces of equipment must be considered.  Figure 1-2 illustrates a situation
where these two units have different characteristics and yet can both be protected by the BE1-24.  Utilizing
the alarm function (with its definite time delay), and in combination with the inverse square characteristic, the
transformer generator combination may be protected with a single BE1-24 Volts-Per-Hertz Overexcitation
Relay.  If necessary, the instantaneous element can be set to a percentage (105%) of the rated excitation
to provide an early warning alarm.  This alarm can enable the operator controlling the excitation to recover
and prevent tripping.