ABB SRW, Инструкция, Страница: 2 / 22

I.L. 41-252A
2
for tripping or alarm purpose. These relays will
be sealed in by a reed relay contact if a trip
current is detected.
(5) Reed relay and reset switch — The reed relay
is for monitoring and indication of the actual
trip current flow. The trip current should be
between 0.5 and 30 amperes. Once the trip
current is detected, the reed relay seals in the
trip relays and turns on the trip indicator which
is a magnetic flip-flop disc indicator on the
SRW board. The indicator is reset from the
outside of the case by a push rod located at
the bottom of the cover. With the relay being
energized, the rod touches a push-button
switch and resets the target.
2.2. SRW Module
The SRW module, located at the top of the relay,
contains two LEDs, one magnetic flip-flop indicator,
one thumbwheel switch, one 6PST DIP switch, sev-
eral integrated circuits and associated components.
(1) Indicators
(a) A yellow LED is for the dc power-on condi-
tion.
(b) A red LED indicates that the magnitude of
the reverse power is above the pickup set-
ting.
(c) A magnetic flip target shows that the actual
trip current is detected.
(2) Pickup setting switch — A single pole 10 posi-
tion (SP10T) thumbwheel switch is used. Each
number (or position) represents a reverse
power pickup setting between 1 mA and 40
mA.
(3) Time delay selection — A DIP package con-
taining six SPST switches is used. Each SPST
switch indicates its own delay time. The total
delay time is the summation of the selected
individual times. The timer can be set in steps
of .05 sec. for .2 to 2, .5 sec. for 2 to 21.5 sec
and 1.0 sec for 2 to 63 sec.
(4) All integrated circuits and electronic compo-
nents are used for detecting the power direc-
tion, level, undervoltage condition and trip
logic. If the input voltage is above 30% of rat-
ing and the reverse power level is above the
pickup value persisting longer than the
selected delay time, the logic will energize the
trip relays and close their output contacts.
2.3. Transformer In-rush Module
The In-rush module is located on top of the SRW
module and electrically connected by two bottom
entry connectors to the SRW module. This module
contains five integrated circuits and several discrete
components. A blue link L1 is used to select the
power supply voltage for this module. Positions are
available for 48, 125 or 250 Vdc with the 125 volt set-
ting being the relay shipping setting. The theory upon
which the SRW relay function is based assumes a
sinusoidal waveform which is true for a reverse
power condition. Conditions can occur however,
when the waveform is not a sinusoid, such as an ini-
tial energization of a transformer with little or no load
connected. When a transformer is first energized, a
transient magnetizing or exciting in-rush is not a sine-
wave and may last for several minutes before finally
damping out. The actual time depends on several
factors such as size and location of the transformer,
resistance of the power system from the generator to
the transformer, the saturation density of the trans-
former, residual flux level in the bank and how the
bank is energized. The SRW, due to its high sensitiv-
ity, may false trip after its timer times out under these
types of conditions. The In-rush module will prevent
these types of false trips.
3. THEORY OF OPERATION
The SRW relay is a single phase directional relay
used to protect ac generators from motoring. It
senses the power flow into the generator. If this
power flow persists for a predetermined time, the
generator may be tripped. The relay must sense and
perform the computation of
to
determine a trip, where
I
is a single phase current
(e.g.,
I
a
) and
θ
is the angle by which this current
leads the voltage (e.g., Vac). The maximum sensitiv-
ity angle occurs when the angle
θ
equals 30 degrees.
The sensitivity of the reverse current is 1 milliampere,
and the continuous current capability is 10 amperes.
This relay can be easily modified and adjusted for
any desired maximum sensitivity angle between 0
and 90 degrees.
A block diagram of the SRW relay is shown in
Figure
I
θ
30
°
–
( )
cos
×