Control Cables for Upstream Substation Signals & Tripping

[SK07]

I have been regularly using multiple core 2.5 sq.mm XLPE/LC/PVC/SWA/PVC Control cable for signals & tripping between Upstream and downstream Substation with distance upto 5-6 Kms.
The signals are as,
1. Solkar Pilot Wire for Differential Protection Relay - ANSI NO. 87
2. Inter Trip Send - ANSI NO. 94
3. Inter Trip Receive - ANSI No. 85
4. Upstream Earth Switch Inter lock
5. Upstream Circuit Breaker ON Status
6. Downstream Circuit Breaker OFF Status

However, in one of my recent Projects the distance between Upstream and Downstream Substation is close to 11 Kms.

My question is - Can I still use the same Control Cable ''multiple core 2.5 sq.mm XLPE/LC/PVC/SWA/PVC''.

 

[davidbeach]

I'd be looking at some means of sending all of that over fiber optic cable. My preference is that any protection or control circuit that leaves the ground grid do so on fiber.

 

[SK07]

davidbeach (Electrical) - Thanks for your response.
I will come back to your suggested alternative / preference.

As of now, my concern here is,

Can I use ''multiple core 2.5 sq.mm XLPE/LC/PVC/SWA/PVC'' for a length of close to 11kms for signals / tripping as mentioned above.

Is it workable?
Does it have any disadvantages?

 

[dpc]

If the control voltage is dc, it is a simple voltage drop calculation. If the control voltage is ac, it won't work.

 

[ScottyUK]

If the cable is carrying DC then you need to be aware of the transient effect of inter-core and core-ground capacitances dumping charge into unexpected places* in the circuit. With a multicore it can become complex to model all the interactions although not impossible if you use LTspice or something similar. A large capacitor dumping charge can easily operate an opto-isolator input, and in bad cases can operate a sensitive mechanical relay. Some manufacturers offer high burden intertripping relays for this type of application, but you can run into volt-drop problems getting them to pull in.

You can use voice-frequency over a private telco circuit for signalling, but it's generally not fast enough for protection.

* 'unexpected places': refer to Murphy's Law, and note that Murphy was an optimist!

 

[karls2]

optic fiber for these kind of informations / protections, it's the best way to avoid most of the problems when you have long distance.

 

[slavag]

For some kind of signalization, or not critical interlocks, possible, as dpc said above: calculate voltage drop.

trips, no and no, see ScottyUK post.

Today, rule of thumbs, if it's longer then 500m, use fiber optic.
BTW, SEL2506 a best solution ( IMHO ).

 

[SK07]

I got the message that Fibre Optic is prefered and I will work on that for future projects.

But for present with multiple core 2.5 sq.mm XLPE/LC/PVC/SWA/PVC,
ss far as voltage drop is concerned, potential free contacts are used.
The voltage required is provided locally at host substation using 110V DC System.

Do you still see any issues? - for both signals and tripping.

 

[davidbeach]

Voltage drop isn't your only problem. If you have energized conductors near an open, unenergized conductor, you could be seeing capacitive coupling into that conductor; perhaps to the point of asserting a false indication. Back in the true "pilot wire" days it was one pair of conductors running a current loop. That loop could carry only one signal but it was fairly immune to noise and other effects. Now you want to put a bunch of conductors together and have high impedance inputs looking at voltage levels over relatively long distances.

Let us know of your misoperations.

 

[itsmoked]

I would bet against it ever working over 6km.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[SK07]

Now the conclusion is to use Fibre Optic Cable. Agreed.

To use FO Cable do i need to replace the existing planned multiple core 2.5 sq.mm XLPE/LC/PVC/SWA/PVC WITH FO Cable ONLY or some additional components are required within MV Switchgear Panel or outside it.

Thanks

 

[slavag]

You need add two Remote IO devices.

please see SEL2506 ( I'm not salesman of SEL ).
I was used it in two projects, grate, simple and cheap. 8 inputs, 8 outputs, direct 110V DC connection.

Of course two patch panels for fiber optic, please use 100% redundancy for FO.

 

[slavag]

important point for trips: transmission time of signal must be speedy, SEL2506 is give few ms.

 

[SK07]

can the patch panels be housed within MV Switchgear or need a separate enclosure/ panel.

 

[itsmoked]

slavag; You say 100 redundancy. Specifically what needs to be redundant? Everything? The SEL2506 and even the fibers?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[slavag]

Patch panels on the DIN rail, in the MV panel only, not needed additional enclosure.
something like to:

http://www.industrialnetworking.com/Manufacturers/DINSpace-SNAP-DIN-Rail-Fiber-Patch-Panels

you can use SEL2505, possible installation in LV compartment of MV cubicle

Keith.
I meant only fiber optic wires, that means 4 wires minimum.

 

[SK07]

Just to recap:

the signals between Upstream and downstream Substation at a distance of 11 kms are as,
1. Solkar Pilot Wire for Differential Protection Relay - ANSI NO. 87
2. Inter Trip Send - ANSI NO. 94
3. Inter Trip Receive - ANSI No. 85
4. Upstream Earth Switch Inter lock
5. Upstream Circuit Breaker ON Status
6. Downstream Circuit Breaker OFF Status

As I understand from above post Fibre Optic cable is the right solution. However, due to some project concerns, we have discussed with the Contractor and are being offered a alternative solution to go for SCREENED XLPE/PVC/SWA/PVC control cable of 20 C (10 pair)

Kindly confirm if it is a workable solution.

 

[davidbeach]

I'm sure it is physically possible to install the cable. Beyond that, what does "workable" mean? I certainly wouldn't bet my career on it.

 

[jghrist]

I think at a minimum, a separate shielded cable should be used for the pilot wire. What kind of differential relay is being used? What does the manufacturer recommend for pilot wire? What kind of protection are you providing for ground potential rise?

 

[Marmite]

You can't run Solkor R or Rf pilot wire protection over a fibre, so if you change to fibre you will need to adopt a different differential relay. The relay manual has information on the recommended electrical characteristics of the pilot. Solkor N is the equivalent Reyrolle/Siemens relay for fibre but there are many others.

You can do intertrip send/receive over a pilot using something like an Areva GCM05 intertrip send/receive relay.

I wouldn't recommend doing any interlocking over a pilot. If you do, then you should at least build in safeguards against stuck contacts or open circuits for example by making it two bit, using changeover switches. eg 1-0 and 0-1 are valid, 0-0 or 1-1 indeterminate (lock out)

Regards
Marmite

http://files.engineering.com/getfil...-1e1eab937a62&file=GCM05_Inter-trip_Relay.pdf