Example Hybrid Applications and Recommended Configurations
When applying hybrids, the number of transmitters and receivers, as well as the application of each (DCB/On-Off or transfer trip/FSK), will determine what hybrid configuration will work best for each system. There are several different ways to connect hybrids but generally there are best practices that should be observed. The examples shown below illustrate typical hybrid configurations and show how hybrids work together. The exact performance characteristics of individual hybrids are discussed later in this manual.
- RFL Power Line Carrier Hybrid Pro™ System
- About Hybrids
- Example Applications and Recommended Configurations
- Hybrid Types
One Transmitter, One Receiver (FSK)
Here, a skewed hybrid is used to combine a single transmitter / single receiver onto one coax cable for connection to a single tuner. This is a typical single-function, single-phase-to-ground coupled FSK system.
Two Transmitters, Two Receivers (FSK)
Here, there are two transmitters, so a balanced hybrid (used to combine transmitters) is added. The output of the balanced hybrid is fed into the TX port on the skewed hybrid. Instead of coupling just one transmitter, a skewed hybrid can pass multiple transmit signals, so long as they are combined with balanced hybrids first.
Note that in this configuration there are also two receivers, but they do not need to be combined with a hybrid, as is the case for the transmitters. Because receivers are highly selective and are high-impedance devices, they can be directly paralleled and will not load or otherwise interfere with each other.
This example could represent several different applications. TX1/RX1 might be DTT and TX2/RX2 might be DCUB or POTT; or, TX1/RX1 and TX2/RX2 might represent a dual-DTT scheme.
Three Transmitters, Three Receivers (FSK)
This system illustrates how the output of one balanced hybrid can be an input to another balanced hybrid, to accomplish the coupling of more than two transmitters in a PLC system. Again, the output of the last balanced hybrid is fed into the TX port on the skewed hybrid.
This example may represent a dual-DTT/DCUB system. Here, it is best to make TX1/RX1 and TX2/RX2 the DTT channels, so that both will have equal losses, and to make TX3 the DCUB channel so that DCUB, as the primary protection scheme, has the least loss through the hybrids.
Two Transmitters, Two Receivers (FSK and On-Off/DCB)
This example is similar to the previous two-transmitter/two-receiver FSK example - one balanced hybrid, one skewed hybrid, and two individual relaying channels. The main difference here is that TX2/RX2 is a 2-wire DCB channel (the transmit and receive are directly tied together) so there is only one coax connection to/from the unit. In these cases, the DCB channel TX/RX signals are treated as a transmitter. Like a transmitter, they are connected to the input of a balanced hybrid.
Two Transmitters, Two Receivers, Phase-to-Phase Coupled (low loss method)
This example shows two transmitters and two receivers in a phase-to-phase coupling application. Here, once the signals have been combined onto a single coax connection the signals are “split”. Then, two coax cables are run from the splitter out to the switchyard, adding redundancy and dependability. There are variations of the connection scheme – some line tuners can be equipped with a splitter circuit – but the scheme depicted in this example will provide the best reliability for this phase-to-phase application. This is because there will be two coax cables going out to the tuner, and ideally these will be run in separate cable trays.
It should be noted that the signals which are “split” between phases at one end of the circuit are re-combined at the terminating end of the circuit. Therefore, the splitter does not add any additional loss to the PLC channel.
It should also be noted that the splitter can be applied with different transmitter/receiver and hybrid combinations, not just the one shown.
Two Transmitters, Two Receivers, Phase-to-Phase Coupled (high reliability method)
This example shows another variation of a phase-to-phase coupling application. This type of hybrid scheme is used when two independent relaying channels are being applied. The difference between this circuit and the one is that there are independent coax cables entering and leaving the phase-to-phase coupling hybrid. No single point of failure, other than the splitter/combiner itself, is present (hybrids very rarely fail – they are ruggedized, passive devices).
This circuit introduces significant loss into the channel as compared to the previous example, but it allows the designer to keep the PLC channels and connections functionally and logically separated while providing good isolation between the channels.
TX1/RX1 and TX2/RX2 might be part of redundant protection schemes. It should be noted that the splitter/combiner can be applied with different transmitter/receiver and hybrid combinations, not just the one shown.
Two Independent Relay Channels, Three-Phase (Mode 1) Coupled
This example shows a “mode 1 combiner” circuit, used in three-phase / mode 1 coupling applications. This hybrid scheme is typically used only on the most critical lines and at transmission levels of 500 kV and above. It is the most reliable method since the loss of any one phase should not cause the channel to fail. The losses through this circuit are less than in the splitter/combiner phase-to-phase application of the previous example. However, the application requires a third set of coupling equipment – tuner, CCVT, and trap – so it is also the most expensive.