3-60
Differential, Restricted Earth Fault,
Date Code 20020129
Overcurrent, Voltage, and Frequency Elements
SEL-387E Instruction Manual
Setting Descriptions
Frequency Element Enable (E81)
Range
: N,
1–6
Set E81 to enable as many as six over-/underfrequency elements. When E81 = N, the relay
disables the frequency elements and hides corresponding settings; you do not need to enter these
hidden settings.
Phase Undervoltage Block (27B81P)
Range
: 20.00–150.00 Vsec
Set the phase voltage value below which all frequency elements will be disabled.
Frequency Element Pickups (81DnP)
Range
: OFF,
40.10–65.00 Hz
Set the value at which you want the frequency element for each of six levels to assert. For a value
of 81DnP less than the nominal system frequency of 60 Hz, the element operates as an
underfrequency element. For a value greater than 60 Hz, the element operates as an
overfrequency element. Note that n can be one of six levels, 1–6.
Frequency Element Time Delays (81DnD)
Range
: 0.04–300.00 seconds
Select a time in seconds that you want frequency elements to wait before asserting. Note that n
can be one of six levels, 1–6.
V
OLTS
/H
ERTZ
E
LEMENT
Application Description
Overexcitation occurs when a transformer magnetic core becomes saturated. When this happens,
stray flux is induced in nonlaminated components, causing overheating. In the SEL-387E Relay a
volts/hertz element detects overexcitation. The SEL-387E Relay provides a sensitive definite-
time volts/hertz element, plus a tripping element with a composite operating time. The relay
calculates the present transformer volts/hertz as a percent of nominal, based on the present and
nominal voltages and frequencies. The settings VNOM and NFREQ define the nominal
transformer voltage and frequency, respectively.
Operating Characteristic
If the torque-control 24TC SEL
OGIC
control equation is true and the present volts/hertz exceed
the 24D1P setting, the relay asserts the 24D1 Relay Word bit and starts the 24P1D timer. If the
condition remains for 24P1D seconds, the relay asserts the 24D1T Relay Word bit. Typically,
you should apply this element as an overexcitation alarm.
