
4.49
Date Code 20170814
Instruction Manual
SEL-700G Relay
Protection and Logic Functions
Group Settings (SET Command)
The Z2CO setting defines the element offset for the three-phase faults. You
can apply an offset, typically equal to the generator impedance, to provide
generator phase backup protection.
The Z2CD setting defines the Zone 2 element definite-time delay.
Set 50PP2 to its minimum value, unless a special condition requires a higher value.
Set Z2ANG equal to the angle of the transformer plus system impedance
defined by the Zone 2 reach setting. The relay places the distance element
maximum reach along a line at the angle defined by the Z2ANG setting.
The phase distance elements are enabled when the result of 21CTC equals
logical 1. The elements are blocked when the 21CTC SEL
OGIC
control
equation result equals logical 0. Typically, the 21CTC SEL
OGIC
control
equation should be set so that the elements are enabled when the generator
main circuit breaker is closed (NOT 3POX). You can add other supervisory
conditions if necessary for your application.
Settings Calculation.
Collect the following information before setting the
compensator distance.
➤
Zone 1 and Zone 2 reach apparent impedance magnitude and
angle
➤
Generator step-up transformer connection (only necessary if
Zone 1 or Zone 2 mho element is used and set to reach through
the transformer)
➤
Zone 1 and Zone 2 coordination time delay
➤
Generator rated minimum power factor and maximum
emergency loading
Recommendations.
The compensator distance elements provide backup
phase fault protection for the system, step-up transformer, and generator. Zone
2 is typically set to reach far out onto the system. Usually, a fault study is
necessary to determine the magnitude and angle of the apparent impedance
seen by the generator relay during a system fault. Set the reach (ZnC) equal to
the apparent positive-sequence impedance calculated by fault study for a
three-phase fault at the targeted reach limit point on the system. All distance
element reaches and offsets are set in secondary ohms.
After determining the minimum reach setting necessary to obtain the
sensitivity you want with all system breakers closed, you can determine the
element sensitivity when one or more local bus circuit breakers are open. This
operating contingency review shows with which relays the Zone 2 element
time delay must coordinate. Zone 1 is usually set shorter than Zone 2, with a
corresponding shorter time delay.
The distance element offset necessary for each zone depends on the location
of the relay current transformers. If current transformers are connected near
the generator neutral, as in Figure 2.17 or Figure 2.19, and the element is used
to protect for a zero-voltage three-phase fault external to the generator
differential zone, set the distance element offsets equal to 10 percent of the
generator X'd. If current transformers are located at the terminals of the
generator, as in Figure 2.18, set the distance element offsets equal to the
generator X'd. Offsets for Zone 1 and Zone 2 should be set equal, unless some
special performance characteristic is necessary.
The Relay Word bits 21C1T and 21C2T are configured to shut down the
generator in the factory-default logic. See Trip/Close Logic Settings for
NOTE:
Loss-of-potential (LOPX)
supervision is built into the element
logic, so it does not need to be added
to the 21CTC SEL
OGIC
control
equation setting.
Содержание SEL-700G Series
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