Schweitzer Engineering Laboratories SEL-700G Series Instruction Manual Download

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4.141

Date Code 20170814

Instruction Manual

SEL-700G Relay

Protection and Logic Functions

Group Settings (SET Command)

power, set the element pickup lower than this level to account for measuring
errors in the relay, voltage transformers, and current transformers. For
sequential tripping of the generator, you might want low-forward power. The
default settings of the Level 2 power element and associated trip logic is set up
for such an application. The scheme is only permitted to cause a generator
breaker trip after the prime mover trip by the sequential tripping scheme. The
SEL

OGIC

control equations used to implement sequential generator tripping

are shown in Trip/Close Logic Settings later in this section.

The power elements are not supervised by any relay elements other than the
minimum voltage check shown in Figure 4.96. If the protection application
requires overcurrent protection in addition to the power elements, there may
be a race condition, during a fault, between the overcurrent element(s) and the
power element(s) if the power element(s) are still receiving sufficient
operating quantities. Use the power element time delay setting to avoid such
race conditions.

Over- and
Underfrequency
Protection

The SEL-700G Relay uses two different algorithms, phase rate-of-change
(ROC) and zero-crossing (ZC), to measure the frequency of the X and Y sides
and the synchronism-check voltage input (VS). While the relay measures the
frequency of multiple signals, it uses only one signal (V1X, V1Y, I1X, or I1Y)
for frequency tracking. Table 4.39 shows the signals that the ROC method
uses to measure frequency and priority in determining the appropriate signal
for frequency tracking in a specific model of the SEL-700G.

The ZC method uses VAX, VAY, and VS signals to measure the frequencies.
The frequency measured by the ZC method is used when the associated signal
shown in Table 4.39 is too low or when the frequency measured by the ZC
algorithm is outside a window of ± 0.3 Hz from the tracking frequency. The
relay uses the VAX signal to measure the X-side frequency with the ZC
method in all the models except the SEL-700GT and SEL-700GW. The relay
uses the VAY signal to measure the Y-side frequency with the ZC method in
the models SEL-700GT and SEL-700GT+. The relay uses the VS signal to
measure the VS channel frequency with the ZC method in the models
SEL-700G0+, SEL-700G1+, SEL-700GT, and SEL-700GT+.

Each method requires minimum signal level of 10 V or 0.1*(Nominal CT
Rating). The measured frequency is set to nominal frequency setting (FNOM)
if the signal is below the minimum level.

The SEL-700G provides six trip over- or underfrequency elements with
independent level and time-delay settings. When an element level setting is
less than the nominal frequency setting, the element operates as an
underfrequency element. When the level setting is greater than the nominal
frequency setting, the element operates as an overfrequency element.

Schweitzer Engineering Laboratories SEL-700G Series, Instruction Manual

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