4.53
Date Code 20170814
Instruction Manual
SEL-700G Relay
Protection and Logic Functions
Group Settings (SET Command)
Use the 51VCA setting to compensate the voltage-restrained overcurrent
element for the presence of a delta-wye generator step-up transformer
between the generator and system. When the element is not set to reach
through the step-up transformer, set 51VCA := 0. When the element is set to
respond to phase faults on the high side of a delta-wye transformer, and the
system phase-to-neutral voltage phase angle leads the generator phase-to-
neutral voltage phase angle by 30°, set 51VCA := –30°. When the system
phase-to-neutral voltage phase angle lags the generator phase-to-neutral
voltage phase angle by 30°, set 51VCA := 30.
For system backup protection, the SEL-700G provides a choice of voltage-
controlled or voltage-restrained phase inverse time-overcurrent elements or
phase distance elements (discussed earlier in this section). The overcurrent
elements include a settable pickup, curve shape, and time-dial. Ten curve
shapes are available. Curves U1–U5 emulate the popular North American
induction disk relays. Curves C1–C5 emulate popular European analog time-
overcurrent relays. Operating characteristics of the available curves are shown
in Figure 4.62 through Figure 4.71.
When you set 51nRS := Y to enable electromechanical reset emulation, the
relay provides a slow reset that is dependent on the amount of current
measured, similar to an induction disk relay reset. When you select N, the
relay fully resets the time-overcurrent element one cycle after current drops
below the pickup setting, similar to analog and many microprocessor-based
time-overcurrent relays. Select Y or N to match the operating characteristic of
other time-overcurrent protection protecting the system near this generator.
Each of the elements is also equipped with a torque-control setting. When the
equation result is logical 1, the element can operate. When the result is
logical 0, the element cannot operate. Use other protection elements, logic
conditions, or control inputs to supervise these elements if necessary.
Voltage-Controlled and Voltage-Restrained Time-Overcurrent Setting
Calculation
Gather the following information to calculate the voltage-controlled and
voltage-restrained time-overcurrent settings.
➤
Generator nominal voltage, VNOM_X
➤
Generator current for long duration system phase fault, If, A
primary
➤
Generator voltage for system phase fault, Vf, V primary
➤
Generator voltage and current transformer ratios to 1, PTR and
CTR
Choose either the voltage-controlled or voltage-restrained time-overcurrent
element for system phase fault backup protection when overcurrent relays are
used for primary system protection.
Generally, the voltage-controlled element provides adequate backup
protection and consistent performance. Use the voltage-restrained element if
your protection standards or preferences require it.
Voltage-Controlled Time-Overcurrent Settings.
Set the 51CP pickup
setting less than the generator fault duty, which you can calculate by using the
generator steady-state reactance, X
d
(you can use transient reactance X'
d
if the
generator excitation system supports higher fault voltage and current). This
value may safely be below maximum load, because the element is only
enabled during low-voltage fault conditions. Divide the generator fault duty
Summary of Contents for SEL-700G Series
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