2–29
Application - 2
59I Peak Overvoltage
Most overvoltage relays operate based on the RMS
value of voltage. There is, however, a system
phenomenon known as ferroresonance which may
occur on a lightly loaded, islanded system. As the
name implies, a system experiencing
ferroresonance is in resonance, but the inductance
is highly nonlinear, being variable as the transformer
core cycles in and out of magnetic saturation. At
this time, the voltage waveform will be expected to
be very rich in harmonics, to the extent that it is
possible that the peak voltage of the nonsinusoidal
wave will be dangerously high, even though the
RMS value of the same voltage remains in an
acceptable range.
Because it is necessary to describe voltage for this
purpose in terms of the peak value of voltage (not
RMS), it is convenient to define the parameter
setpoints in per unit of the peak of the nominal
sinusoidal waveform. The per unit value is based
on the nominal voltage setting. As an example, for
a nominal voltage of 120 V, the one per unit
instantaneous peak voltage is 120 x S2 = 170 V.
Save
Cancel
@ : WARNING, Function DISABLED until output selected!
(59I) - PEAK OVERVOLTAGE
Magnitude:
Delay:
1.05 p.u.
1 Cycle
1.50 p.u.
8160 Cycles
#1
OUTPUT
8
7
6
5
4
3
2
1
FL
6
5
4
3
2
1
Blocking Input
@
Figure 2-19
M-3822 IPScom
®
for Windows™ Peak Overvoltage (59I) Setpoint Ranges
Path
: Relay Menu/Setup/Setpoints/(59I) Peak Overvoltage
COMMAND BUTTONS
Save
Saves all information to the relay.
Cancel
Returns the user to the previous window; any changes to the displayed information are lost.
If this function is enabled, the following settings are applicable:
59I PICKUP
________ PU
59I DELAY
________ Cycles
Typical pickup setting is between 1.3 to 1.5 PU.
A time delay of 10 cycles provides fast protection and pre-
vents misoperation during system disturbances.
Summary of Contents for M-3520
Page 1: ...Instruction Book M 3520 Intertie Protection Relay ...
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