The power system
cannot be measured from available signals. This may happen if the signals are not present or are heavily distorted. Before
reverting to the nominal frequency, the frequency tracking algorithm holds the last valid frequency measurement for a safe
period of time while waiting for the signals to reappear or for the distortions to decay.
The phase sequence of the power system is required to properly calculate sequence components and power parameters.
setting matches the power system phase sequence. Note that this setting informs the relay of the
actual system phase sequence, either ABC or ACB. CT and VT inputs on the relay, labeled as A, B, and C, must be con-
nected to system phases A, B, and C for correct operation.
FREQUENCY AND PHASE REFERENCE
phase angle reference. The AC signal used is prioritized based on the AC inputs that are configured for the signal source:
phase voltages takes precedence, followed by auxiliary voltage, then phase currents, and finally ground current.
For three phase selection, phase A is used for angle referencing (
phase signals is used for frequency metering and tracking (
ing fault, open pole, and VT and CT fail conditions.
The phase reference and frequency tracking AC signals are selected based upon the Source configuration, regardless of
whether or not a particular signal is actually applied to the relay.
Phase angle of the reference signal will always display zero degrees and all other phase angles will be relative to this sig-
nal. If the pre-selected reference signal is not measurable at a given time, the phase angles are not referenced.
The phase angle referencing is done via a phase locked loop, which can synchronize independent UR-series relays if they
have the same AC signal reference. These results in very precise correlation of time tagging in the event recorder between
different UR-series relays provided the relays have an IRIG-B connection.
cial variable-frequency applications.
The frequency tracking feature will function only when the L60 is in the "Programmed" mode. If the L60 is "Not Pro-
grammed", then metering values will be available but may exhibit significant errors.
When voltage is supplied to the relay through a VT, it is advisable to assign a source configured with a
phase VT voltage (source 3 or 4) to track system frequency from voltage. Source 1 should be assigned to
track frequency from current.
FREQUENCY AND PHASE
REFERENCE: SRC 1
value is used as a default to set the digital sampling rate if the system frequency
setting determines which signal source is used (and hence which AC signal) for
should only be set to "Disabled" in very unusual circumstances; consult the factory for spe-
L60 Line Phase Comparison System
Range: 25 to 60 Hz in steps of 1
Range: ABC, ACB
Range: SRC 1, SRC 2, SRC 3, SRC 4
Range: Disabled, Enabled
), while Clarke transformation of the
5.3 SYSTEM SETUP
5.3.2 POWER SYSTEM
) 3 ⁄
) for better performance dur-