4.51
Date Code 20081022 Instruction Manual SEL-787 Relay
Protection and Logic Functions
Voltage-Based Protection
Voltage-Based Protection
The following information applies to relay models with voltage inputs.
Undervoltage
Function
Overvoltage Function
When you connect the SEL-787 voltage inputs to phase-to-phase connected
VTs (single-phase or three-phase), as in Figure 2.16 or Figure 2.17, the relay
provides two levels of phase-to-phase overvoltage and undervoltage elements.
When you connect the SEL-787 voltage inputs to phase-to-neutral connected
VTs (single-phase or three-phase), as in Figure 2.16 or Figure 2.17, the relay
provides two levels of phase-to-neutral overvoltage and undervoltage
elements. The SEL-787 also includes two levels of negative-sequence
overvoltage elements. Use these elements for alarm or trip when three-phase
voltage inputs (wye or delta) are connected to the relay.
Each of the elements has an associated time delay. You can use these elements
as you choose for tripping and warning. Figure 4.29 and Figure 4.30 show the
logic diagram for the undervoltage and overvoltage elements, respectively. To
disable any of these elements, set the level settings equal to OFF.
Table 4.18 Undervoltage Settings
Setting Prompt Setting Range
Setting Name :=
Fa cto r y Defau lt
PHASE UV LEVEL OFF, 12.5–300.0 V 27P1P := OFF
PHASE UV DELAY 0.0–120.0 sec 27P1D := 0.5
PHASE UV LEVEL OFF, 12.5–300.0 V 27P2P := OFF
PHASE UV DELAY 0.0–120.0 sec 27P2D := 5.0
Table 4.19 Overvoltage Settings
Setting Prompt Setting Range
Setting Name :=
Fa cto r y Defau lt
PHASE OV LEVEL OFF, 12.5–300.0 V 59P1P := OFF
PHASE OV DELAY 0.0–120.0 sec 59P1D := 0.5
PHASE OV LEVEL OFF, 12.5–300.0 V 59P2P := OFF
PHASE OV DELAY 0.0–120.0 sec 59P2D := 5.0
NSEQ OV LEVEL OFF, 12.5–300.0 V 59Q1P := OFF
NSEQ OV DELAY 0.0–120.0 sec 59Q1D := 0.5
NSEQ OV LEVEL OFF, 12.5–300.0 V 59Q2P := OFF
NSEQ OV DELAY 0.0–120.0 sec 59Q2D := 5.0
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