Basler Electric BE1-11g - Manual (Page 91)

9424200994 Rev N 79
Frequency (81) Protection
Eight frequency (81) elements monitor the frequency of the sensing voltage applied to the BE1-11g. An
element can be configured to protect against underfrequency, overfrequency, or the rate of frequency
change.
The eight, identical frequency protection elements are designated 81-1, 81-2, 81-3, 81-4, 81-5, 81-6, 81-
7, and 81-8. Element logic connections are made on the BESTlogic
™Plus screen in BESTCOMSPlus®
and element operational settings are configured on the Frequency settings screen in BESTCOMSPlus. A
summary of the logic inputs and outputs and operational settings appears at the end of this chapter.
Note
BE1-11g protection systems enabled for IEC-61850 communication
(style Gxxxx5xxxxxxxx) have their frequency protection elements fixed
at four underfrequency elements, two overfrequency elements, and
two frequency rate-of-change elements.
BESTCOMSPlus Navigation Path: Settings Explorer, Protection, Frequency, Frequency (81)
HMI Navigation Path: Settings Explorer, Protection, Settings Group x (where x = 0 to 3), Frequency
Protection 81
Frequency Measurement
For four-wire or single-phase sensing connections, the power system frequency is measured through the
BE1-11g A-phase sensing voltage input. For a three-wire connection, the power system frequency is
measured through the A- and B-phase sensing voltage connections. Power system frequency is also
measured through the BE1-11g auxiliary voltage (Vx) sensing input. Refer to the
Typical Connections
chapter for information on voltage connections.
To measure frequency, the voltage sensed by the BE1-11g must be greater than 10 Vac. The measured
frequency is the average of two cycles of voltage measurement.
Underfrequency and Overfrequency Protection
Underfrequency and overfrequency protection can be useful for detecting load shedding or islanding. For
example, when a source of distributed generation (DG) is suddenly separated or isolated from the electric
utility, the frequency will change quickly from the nominal value (except for the improbable case of a
perfect load-to-generation match). This makes frequency measurement an excellent method for detecting
an island condition.
Any of the eight 81 elements can be configured for underfrequency or overfrequency protection.
Mode
Underfrequency or overfrequency protection is selected through the Mode setting. A setting of Under
selects underfrequency protection and a setting of Over selects overfrequency protection.
Sensing Source
Underfrequency or overfrequency protection can be applied to the voltage sensed at the BE1-11g phase
VT input or auxiliary VT (Vx) input. A Source setting of Phase VT selects the voltage sensed at the phase
VT input and a Source setting of Aux VT selects the voltage sensed at the Vx input.
Security of a load shedding scheme can be enhanced by monitoring two independent VT circuits.
BE1-11g Frequency (81) Protection