3-44 Breaker Logic Date Code 20010731
SEL-352-1, -2 Instruction Manual
Figure 3.26 shows the default loss-of-dielectric logic used in the SEL-352 Relay. Assign LOD1
and LOD2 to inputs connected to pressure switches used to measure the dielectric gas pressure of
the circuit breakers. Assign LODCT to inputs connected to a switch monitoring the dielectric
pressure of the CTs.
Figure 3.26: Loss-of-Dielectric Detection Logic
Setting Description
Dielectric Pressure Level Indicators (LOD1, LOD2, LODCT)
Use SET G <ENTER> to access and set the dielectric pressure level indicators. Use any
optoisolated input to control these Relay Word bits. For example, if IN101 is used to indicate
the first level of pressure, set LOD1 = IN101. Repeat this for each input. The input settings are
actually SEL
OGIC control equations. Use any combination of Relay Word bits according to the
SEL
OGIC control equation criteria in Section 4: Relay Logic.
Two inputs are used to monitor two separate breaker gas pressure thresholds. A pressure device
that monitors the breaker should apply control voltage to the SEL-352 Relay input when the
pressure drops below the preset value. The high threshold asserts LOD2, and the low threshold
asserts LOD1.
As pressure drops below the high threshold (LOD2), the L2pu timer starts timing. If the L2pu
timer expires before the low threshold (LOD1) is reached, a pending failure is declared
(LODPF). If the transition from the high to the low threshold is faster than the L2pu time (less
60 cycles), a breaker failure is declared (LODBF).
The LODCT input is used to monitor current transformer gas pressure. A pressure monitoring
device should apply control voltage to the LODCT input when the pressure drops below the
preset value. After 60 cycles of this low pressure condition, a pending failure is declared
(LODPF).
Loss-of-Dielectric Logic Enable (DELOG)
Range: OFF, ON, CUSTOM
Use SET <ENTER> to access the DELOG setting. Enable, modify, or disable loss-of-dielectric
logic.
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