BECKWITH ELECTRIC Syncrocloser M-3410A, Instruction Book

Page: 85 / 225

M-3410A Instruction Book
3–14
(27) Undervoltage
X
#1
Save
Cancel
#2
Pickup:
Delay:
Pickup:
Delay:
Outputs
Outputs
Blocking Inputs
Blocking Inputs
4.0%
1 Cycle
4.0%
1 Cycle
100.0%
8160 Cycles
100.0%
8160 Cycles
2
2
2
2 1
1
1
1
FL
FL
Figure 3-18 M-3810A IPScom
®
for Windows™ (27) Phase Undervoltage Setup Dialog Screen
Path : Relay/Setup/Setpoints/27 Undervoltage
COMMAND BUTTONS
Save Saves all entered information to the control.
Cancel Returns you to the previous window; any changes to displayed information are lost.
■
NOTE : Pickup ranges (4% to 100%) are of Nominal Voltage.
27 Phase Undervoltage, 3-Phase
Generator Protection
: The Undervoltage function
(27) may be used to detect any condition causing
long- or short-term undervoltage. This is a true
three-phase function in that each phase has an
independent timing element.
Magnitude measurement depends on the 59/27
Magnitude Select setting. (See Section 3.1, Relay
Configuration, Relay Setup.) When the RMS option
is selected, the magnitude calculation is accurate
over a wide frequency range (10 to 80 Hz) and an
additional time delay of 20 cycles (beyond the set
delay) may occur. If DFT is selected, the magnitude
calculation is accurate near 50 or 60 Hz, and the
timer accuracy is
&
2 cycles. RMS selection is
recommended for generator protection applications,
as RMS calculations are accurate over a wide
frequency range.
Intertie Protection : Voltage is commonly suggested
as an efficient means to protect against islanding.
Notably, unless the Dispersed Generation (DG)
includes very high-speed generator excitation
response, the island case where load is greater
than generation will result in a rapid drop of voltage.
Except for those systems prone to ferroresonance,
the voltage waveform will remain essentially
sinusoidal, making the use of DFT (RMS value of
fundamental frequency component) for the
measurement. This function is typically set at 90%
to 95% of nominal voltage (in accordance with the
lower limit allowed for supply to customers), with a
1 second time delay to prevent incorrect operation
from a voltage dip caused by an external fault. The
59/27 magnitude select setting of DFT is
recommended for intertie protection applications.