Introduction To Ac Sources - GE L60 Instruction Manual

5 SETTINGS
• TARGET setting: This setting is used to define the operation of an element target message. When set to Disabled, no
target message or illumination of a faceplate LED indicator is issued upon operation of the element. When set to Self-
Reset, the target message and LED indication follow the Operate state of the element, and self-resets once the oper-
ate element condition clears. When set to Latched, the target message and LED indication will remain visible after the
element output returns to logic 0 - until a RESET command is received by the relay.
• EVENTS setting: This setting is used to control whether the Pickup, Dropout or Operate states are recorded by the
event recorder. When set to Disabled, element pickup, dropout or operate are not recorded as events. When set to
Enabled, events are created for:
(Element) PKP (pickup)
(Element) DPO (dropout)
(Element) OP (operate)
The DPO event is created when the measure and decide comparator output transits from the pickup state (logic 1) to
the dropout state (logic 0). This could happen when the element is in the operate state if the reset delay time is not '0'.
a) BACKGROUND
The L60 can be ordered with one or two CT/VT modules. With one module, the L60 will support complete phase compari-
son functionality as well as backup current functions. Only one three-phase CT input is available for line currents with one
CT/VT module. If two breakers are involved in an application, the current must be summed externally. With two CT/VT
modules, the L60 allows the connection of two breaker CTs directly to the relay, processing the currents individually for
some functions and summing them for other functions by employing the 'sources' mechanism.
Two CT/VT modules are generally required on systems with breaker-and-a-half or ring bus configurations. In these applica-
tions, each of the two three-phase sets of individual phase currents (one associated with each breaker) can be used as an
input to a breaker failure element. The sum of both breaker phase currents and 3I_0 residual currents may be required for
the circuit relaying and metering functions. Two separate synchrocheck elements can be programmed to check synchroni-
zation between two different buses VT and the line VT. These requirements can be satisfied with a single L60, equipped
with sufficient CT and VT input channels, by selecting proper parameter to measure. A mechanism is provided to specify
the AC parameter (or group of parameters) used as the input to protection/control comparators and some metering ele-
ments. Selection of the measured parameter(s) is partially performed by the design of a measuring element or protection/
control comparator by identifying the measured parameter type (fundamental frequency phasor, harmonic phasor, symmet-
rical component, total waveform RMS magnitude, phase-phase or phase-ground voltage, etc.). The user completes the
process by selecting the instrument transformer input channels to use and some parameters calculated from these chan-
nels. The input parameters available include the summation of currents from multiple input channels. For the summed cur-
rents of phase, 3I_0, and ground current, current from CTs with different ratios are adjusted to a single ratio before
summation. A mechanism called a "Source" configures the routing of CT and VT input channels to measurement sub-sys-
tems.
Sources, in the context of L60 series relays, refer to the logical grouping of current and voltage signals such that one
source contains all the signals required to measure the load or fault in a particular power apparatus. A given source may
contain all or some of the following signals: three-phase currents, single-phase ground current, three-phase voltages and
an auxiliary voltages from a single-phase VT for checking for synchronism.
To illustrate the concept of sources, as applied to current inputs only, consider the breaker-and-a-half scheme below. Some
protection elements, like breaker failure, require individual CT current as an input. Other elements, like distance, require the
sum of both current as an input. The phase comparison function requires the CT currents to be processed individually to
cope with a possible CT saturation of one CT during an external fault on the upper bus. The current into protected line is the
phasor sum (or difference) of the currents in CT1 and CT2, depending on the current distribution on the upper bus.
GE Multilin L60 Line Phase Comparison Relay
5.1 OVERVIEW

5.1.3 INTRODUCTION TO AC SOURCES

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