3-Freq. Systems; Directional Comparison Unblocking (2-Frequency) - Ametek UPLC-II System Manual

3.7.1 3-Freq. Systems

The UPLC-II™ also provides for three-frequency
system applications (Fig. 3–21), e.g., Directional
Comparison Unblocking with Direct Transfer
Trip, or Permissive Overreaching Transfer Trip
with Direct Transfer Trip. All three frequencies
are closely-controlled discrete frequencies within
the equivalent spacing of a single wideband or
extra wideband channel. In applying a three-fre-
quency system, the Direct Transfer Trip keying
inputs shifts the channel low (i.e., –250 Hz for 600
Hz bandwidth) and the unblock key shifts the
channel high (i.e., +250 Hz for 600 Hz band-
width).
See figure 3-27, near the end of this chapter, for a
sample schematic.
3.7.2 4-Freq. Systems
The UPLC-II™ can be purchased with the option
of setting it for a four-frequency system (Fig. 3–
22). The purpose is to use one PLC channel to per-
form two independant trips. It is similar to the
three-frequency system but is able to key two
relaying inputs simultaneously, where as with the
three-frequency system, if both inputs are keyed
simultaneously, only the DTT frequency is output.
Four frequencies are utilized within either a
600Hz bandwidth or a 1200Hz bandwidth system.
For frequencies, refer to the specifications in chap.
2.
Bandwidth/Shift can be 600Hz, +/-
250Hz or 1,200Hz +/- 500Hz. The
receiver is able to discriminate between
these four frequencies and provide the
necessary input to the logic portion.
The logic is two sets of the full unblock
logic. This allows you to select either
command function, DTT or Unblock.
Should both inputs be keyed simultane-
ously, the frequency that is sent will
engage both Trip A and Trip B outputs.
The trip test feature is not available in the
four-frequency system.
January 2016
3.7.3 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
transmitted power is normally 1 W, boosted to
10 W for the "Unblock" operation.
The Directional Comparison Unblocking system
will generally use the wide band, wide shift (600
Hz BW, ±250 Hz Shift) UPLC-II™ setting. Also,
the most common power output level used will be
the 1 watt block and 10 watt trip. The type of car-
rier applied with this scheme may be varied from
the normal for special circumstances, e.g., when
matching the new UPLC-II™ equipment at one
end of the line with the older TCF, TCF-10, TCF-
10A or TCF-10B equipment at the other end. In
this case, you must apply the wide band, narrow
shift carrier (600 Hz BW, ±100 Hz Shift) to match
the older carrier characteristics.
Trip
Trip
A & B B
F2 f
F1
Figure 3–22. UPLC-II™ 4-Frequency System
Chapter 3. applications
Trip
A
Guard
Freq.
F3 F4
C
Page 3–29
3