Table of Contents
Advertisement
UPLC™ Application Manual
(+)
TB6–1
Channel 1 DTT
Loss of Channel 1
TB6–2
TB4–1
Loss of Channel 2
*
Channel 2 DTT
TB4–6
* Output is normally energized,
LOR
therefore contact would be open
(–)
Figure 3–15.
Dual Channel Direct Transfer Trip with Throwover
to Single Channel.
A dual channel system is recommended for direct
trip applications. Two FSK channels should be
used in series, so that both must trip before the
breaker is tripped. Many tests have indicated that
dual channels improve the security of the direct
trip system by several orders of magnitude. Use of
a dual channel system has very little effect on
dependability, even if both channels are on the
same transmission medium.
If you want to increase the dependability, you can
modify the dual channel transfer trip scheme to
allow a single channel trip when there is failure of
the other channel. A typical Dual Channel
Throwover to Single Channel Scheme is illustrat-
ed in Figures 3–15 & 3–16.
3.3
Special Considerations
The UPLC™ frequency-shift equipment can oper-
ate in either the two- or three-frequency mode.
The three basic frequencies are as follows (see
Figure 3–17):
f C Center frequency
f H High-frequency, is a frequency shift (∆f)
above f C
Page 3–16
(+)
TB4–1
TB6–3
*
Channel 1 DTT
TB4–6
TB6–4
TB6–3
TB6–1
Channel 2 DTT
TB6–4
TB6–2
(–)
Dual Channel Direct Transfer Trip with Throwover
f L Low-frequency, is a frequency shift (∆f)
below f C
The value of ∆f depends on the bandwidth of the
UPLC™ set. For a bandwidth of 1200 Hz, ∆f is
500 Hz. A bandwidth of 300 Hz yields a ∆f of
100 Hz, while the 600 Hz bandwidth ∆f can be
either 250 or 100 Hz. The center channel frequen-
cy (f C ) can vary from 30 to 535 kHz (in 0.1 kHz
steps).
In the two-frequency systems, only f H and f L are
used. The two frequencies function differently and
take on different labels when operating with the
different types of protective relay systems.
3.3.1
Directional Comparison
Unblocking (2-Frequency)
The higher frequency (f H ), or "Guard" frequency,
is transmitted continually as a blocking-type sig-
nal during normal conditions, to indicate that the
channel is operative and to prevent remote relay
tripping when external faults occur.
For a fault sensed by the local overreaching pilot
relay, the transmitter is frequency-shifted to a low
frequency (f L ), called "Unblock" frequency. The
TB6–1
Channel 1 DTT
Loss of Channel 1
TB6–2
TB4–1
Loss of Channel 2
*
Channel 2 DTT
TB4–6
* Output is normally energized,
LOR
therefore contact would be open
Figure 3–16.
to Single Channel.
TB4–1
*
TB4–6
TB6–1
TB6–2
Advertisement
Table of Contents
Troubleshooting
