3-88
Line Current Differential, Distance, Out-of-Step, Overcurrent,
Date Code 20011112
Voltage, Synchronism Check, and Frequency Elements
SEL-311L Instruction Manual
Underfrequency Element
For example, make settings:
NFREQ = 60 Hz
(nominal system frequency is 60 Hz)
E81
≥
2
(enable frequency element 2)
81D2P = 59.65 Hz
(frequency element 2 pickup)
With these settings:
81D2P < NFREQ
the underfrequency part of frequency element 2 logic is enabled. 81D2 and 81D2T operate as
underfrequency elements. 81D2 is used in testing only.
Frequency Element Operation
Refer to Figure 3.57.
Overfrequency Element Operation
With the previous overfrequency element example settings, if system frequency is less than or
equal to 61.25 Hz (81D1P = 61.25 Hz), frequency element 1 outputs:
81D1 =
logical
0
(instantaneous
element)
81D1T = logical 0
(time delayed element)
If system frequency is greater than 61.25 Hz (81D1P = 61.25 Hz), frequency element 1 outputs:
81D1 =
logical
1
(instantaneous
element)
81D1T = logical 1
(time delayed element)
Relay Word bit 81D1T asserts to logical 1 only after time delay 81D1D.
Underfrequency Element Operation
With the previous underfrequency element example settings, if system frequency is less than or
equal to 59.65 Hz (81D2P = 59.65 Hz), frequency element 2 outputs:
81D2 =
logical
1
(instantaneous
element)
81D2T = logical 1
(time delayed element)
Relay Word bit 81D2T asserts to logical 1 only after time delay 81D2D.
If system frequency is greater than 59.65 Hz (81D2P = 59.65 Hz), frequency element 2 outputs:
81D2 =
logical
0
(instantaneous
element)
81D2T = logical 0
(time delayed element)
Summary of Contents for SEL-311L
Page 6: ......
Page 8: ......
Page 26: ......
Page 54: ......
Page 144: ......
Page 216: ......
Page 252: ......
Page 302: ......
Page 338: ......
Page 480: ......
Page 484: ......
Page 486: ......
Page 502: ......
Page 532: ...12 28 Standard Event Reports and SER Date Code 20010625 SEL 311L Instruction Manual 4 ...
Page 552: ......
Page 554: ......
Page 574: ......
Page 576: ......
Page 596: ......
Page 602: ......
Page 628: ......
Page 656: ......
Page 662: ......
Page 664: ......
Page 688: ......
Page 700: ......
Page 716: ......
Page 722: ......
Page 734: ......