Line Traps + Capacitor Coupling Voltage Transformer

[mikelangel78]

Hello,

I'm very interested in PLC systems. I have a Line Trap and a Capacitive Coupling Voltage Transformer installed in a 220kV substation.

I would like to apply the formulas and get the values that leave me to understand how these system works. Where could I find a good guide to sizing and apply calculations? I want to understand how to sizing the Line Trap coil to block the High Frequencys from the PLC systems and I want to understand how does the Capacitive Coupling Voltage Transformer allows that high frequencys to flow to the substations. But I want to see these teory with maths and calculations. Its's possible?

Thanks in advanced

 

[davidbeach]

Something like the old Westinghouse T&D Book might help.

Consider how the impedance of the capacitor in the CCVT differs at carrier frequency compared to the power system frequency. The trap is an inductor in parallel (sort of) with the CCVT, what type of circuit does that make? How does the trap's impedance at carrier frequency compare with it's impedance at the power system frequency?

 

[mikelangel78]

Thank you davidbeach.

I think the Line Trap should be a LC low-pass filter to allows the power frequency to enter in the substation, and the CCVT must have a band-pass filter or a high-pass filter, in that case i'm not sure, because the PLC frequencys, I think I've read this somewhere, came in a range, and not with a single value...

 

[oldfieldguy]

IIRC, the line trap or wave trap is a parallel resonant circuit which is tuned to BLOCK the carrier frequency. We placed one at each end of a high voltage line where we used carrier channel equipment for protection, the idea being that the wavetraps made sure that the carrier signal stayed only on the line were we needed it. The CCVT was used as the injection point for the carrier signal. I seem to remember some carrier frequencies in the 100 kHz range.

At the tuned frequency, the wavetrap is an almost infinite impedance, while at 60 Hz, it is nothing but a small induction coil, the capacitive leg of the LC circuit being an impossibly high impedance at 60 Hz.

The carrier itself was keyed or unkeyed by protective relaying. The presence or absence of the carrier at the far end of the protected line determined the actions of the relaying at that terminal.

old field guy

 

[melspuds]

I just googled powerline communication and what a surprise HV & MV transmission lines are now using up to 200Mbps broadband.
LV lines up to 3Mbps going through transformers to our smart electric meters. Things have really changed, a few years ago (5 to 10 year). Voice betwwen one sub to another substation was bad, with only one voice at a time, one direction only.
oldfieldguy, I believe your post is very true.
Mike, I wish you luck.
ps: don't google plc
Dave

 

[scottf]

The 3 main components, outside of the transceivers themselves, are the line trap, coupling capacitor (normally part of the CCVT), and line tuner.

I've attached a couple of things (combined file) I had at my fingertips that might help:
- A line trap presentation I wrote some years ago
- A good summary of the overall system from the former Pulsar

GE has published some good system summaries as well but I don't have an electronic copy at hand.

On your above post...a line trap essentially can come as a resonant filter (single-frequency or two-frequency) or a band-pass filter (wide band or high pass). Same goes for the line tuner essentially.

The coupling capacitor does not have any filtering function. It's function is to couple the carrier frequency range (50-500kHz typically) from the HV line to the line tuner. The insertion loss of the coupling capacitor is mainly a function of its capacitance. From a PLC perspective, higher capacitance is better, meaning it either results in lower insertion losses or higher bandwidth, depending on how you want to present it and the type tuning being done.

 

[mikelangel78]

Thank you very much all of you. A special thanks to scottf. Great file!!