2-76
Relay Element Settings
Date Code 20060731
SEL-300G Instruction Manual
F
IELD
G
ROUND
P
ROTECTION
Element Description
Functional Description
The SEL-300G works with the SEL-2664 Field Ground Module to provide protection for the
generator field winding.
Connect the SEL-2664 directly to two ends of the generator field winding and the rotor ground
brush. The SEL-2664 calculates the insulation resistance value between the field winding and
ground, and transmits the insulation resistance value to the SEL-300G using a fiber-optic cable
with ST connectors and a transceiver (SEL-2812MR). Consult the
SEL-2664 Instruction
Manual
for detailed instructions on setting up the SEL-2664.
Set the EIA-232 port in the SEL-300G to SEL protocol and 9600 baud rate to start receiving the
insulation resistance value from the SEL-2664. Refer to Figure 1.5 for the connection diagram.
The SEL-300G compares the insulation resistance value to the Field Ground Protection element
(64F) pickup settings (64F1P and 64F2P) to provide indication. Program two different 64F
pickup levels to alarm and/or trip when the insulation resistance value causes the 64F elements
(64F1T or 64F2T) to assert.
If there is no insulation deterioration, there is no leakage path between the field winding to
ground; the insulation resistance value is extremely high. In this situation, however, due to
sensitivity limits, the SEL-2664 calculates a very large insulation resistance value of 20
megohms. As soon as the field winding insulation develops a breakdown to the rotor iron
(assuming the generator rotor iron is connected to ground through a grounding brush), the
SEL-2664 detects a sharp drop in insulation resistance.
The technology used in SEL-2664 does not discriminate between one point of insulation
breakdown and multiple points of insulation breakdown. A single point of insulation breakdown
will not cause any harm to the generator. Multiple points of insulation breakdown could lead to
very serious generator damages because the distribution of magnetic flux in the rotor will be
substantially altered. When a different device (such as a generator vibration detector for
example) is used for the detection of multiple points of insulation breakdown, SEL recommends
using the SEL-2664 to generate an alarm only and to trip with the other device under supervision
of the SEL-2664. When an additional device is not used, it is recommended to alarm and trip
with the SEL-2664.
Содержание SEL-300G
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