Schweitzer Engineering Laboratories SEL-787 - Page 136

4.58
SEL-787 Relay Instruction Manual Date Code 20081022
Protection and Logic Functions
Voltage-Based Protection
Figure 4.36 Volts/Hertz Inverse-Time Characteristic, 24IC = 2
Power Elements
You can enable up to two independent three-phase power elements in the
SEL-787 relay. Each enabled element can be set to detect real power or
reactive power. When voltage inputs to the relay are from delta connected PTs
or when single voltage input is used, the relay cannot account for unbalance in
the voltages in calculating the power. Take this into consideration in applying
the power elements.
With
SELOGIC control equations, the power elements provide a wide variety of
protection and control applications. Typical applications are:
➤ Overpower and/or underpower protection/control
➤ Reverse power protection/control
➤ VAR control for capacitor banks
24ITD = 5.0
24ITD = 7.5
24ITD = 1.0
24ITD = 0.1
100 120 140 160 180 200
0.01
0.1
1
10
100
1000
10000
24C2T Operating Time
(seconds)
Volts/Hertz (%)
(24IP = 100%)
24ITD = 10.0
24ITD = 0.5
t
p
24 ITD
3V
sec
PTR••
freq
-----------------------------------------
FNOM
VNOM 10
3
⋅
--------------------------------
•
24 IP
100%
--------------
--------------------------------------------------------------------------------
⎝⎠
⎜⎟
⎜⎟
⎜⎟
⎜⎟
⎛⎞
1–
⎝⎠
⎜⎟
⎜⎟
⎜⎟
⎜⎟
⎜⎟
⎛⎞
2
------------------------------------------------------------------------------------------------------
ondssec=