Schweitzer Engineering Laboratories SEL-387E - Definite-Time Characteristic; Frequency Element; Application Description; Operating Characteristic

Date Code 20080110 Protection Functions 3-59
SEL-387E Instruction Manual
Definite-Time Characteristic
None of the elements is equipped with a definite-time delay. If you want a definite-time
characteristic, use a SEL
OGIC control equation variable and corresponding built-in time-delay
pickup and dropout timers.
F REQUENCY E LEMENT
Application Description
The SEL-387E Relay provides six levels of over-/underfrequency elements. Each element can
operate as an overfrequency or as an underfrequency element, depending on its pickup setting. If
the element pickup setting is less than the nominal system frequency setting, NFREQ, the
element operates as an underfrequency element, picking up if measured frequency is less than the
set point. If the pickup setting is greater than NFREQ, the element operates as an overfrequency
element, picking up if measured frequency is greater than the set point.
Operating Characteristic
The SEL-387E Relay determines system frequency using the A-phase voltage.
Note : All frequency elements are disabled if any phase voltage is less than a settable voltage,
27B81P. Use the relay frequency elements for simple abnormal frequency protection.
Six frequency elements are available. The desired number of frequency elements are enabled
with the E81 enable setting:
E81 = N (none), 1 through 6
as shown in
Figure 3.36. Frequency is determined from the voltage connected to voltage
terminals VA-N.
_
+
_
+
_
+
Setting/
Voltages
27B81P
V
A
V
B
V
C
Three-phase voltage
connected TPVI=Y
VA low
VA, VB, or
VC low
0
5
CYC
Relay
Word
Bit
27B81
To Frequenc
y
Element Logic
DWG: M387E050
Figure 3.36: Undervoltage Block for Frequency Elements