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What equipment and elements would you need to tap a 69 kV line? 1

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Dvhez

Dvhez

Electrical
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Is it enough with a disconnecting switch and a circuit breaker?. The idea is to tap this 69 kV line and extend it over 2 km to arrive at a projected substation with 2x30 MVA transformers (n+1 redundancy criteria) to downstep the voltage level to 23 kV.
Thanks for your time. If you have a book of reference please recommend it to me!
 
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If you are in North America a circuit switcher may do. I'd recommended LA's on the incoming 69kv.
 
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A circuit breaker or circuit switcher would not be absolutely necessary, depending on the situation, but highly advisable. If you put in a breaker, you'll have to include suitable relaying, CTs, and perhaps PTs, if only for local power. And of course, you need to the land to install, grounding, fencing, permits, etc. Also need to consider impacts on existing relaying at the terminals of the line.
 
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Many of the customers find it easier to locate the Disconnector, CB, CT/VT/LA etc. at the primary of transformers and nothing at the OHL tap-off.
There is advantage if a CB etc. can be located at the tap-off, but practical issues dominate.
More importantly, protection issues are also to be factored while making the decision, as the tap-off is going to have a bearing on the reliability of the existing two terminal OHL.
Considering it is only 2-km to the new substation that will have 2x30MVA transformers, it would be more appropriate to go in for Loop-in Loop-out of the existing line at the new Substation. This would enhance the power source reliability at the new substation. You are already planning redundancy in transformers and this will provide redundancy in the Lines as well.
Bonus is that there will not be deterioration in the reliability of the existing OHL which would other wise happen with tap-off.
 
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You don't need the breaker. It's nice to have a high side breaker on transformers, but not really that common. A high-side disconnect switch or circuit switcher is probably your best bet.

Communications with the utility may be required for transfer tripping, or if you have low side generation.
 
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I would say the minimum at the tap point would be a three way switch that could allow isolation of a bad line section and continued operation. I like RRaghunath's solution better.
 
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Minimum would be a three-way switch on a pole, if you are willing to accept that a fault on the tap will be cleared by the main line's protective device(s). You also have to be willing to accept that the line will be radial from there to the substation.
If budget allows, I like RRaghunath's suggestion that you consider looping the line into and out of the substation for reliability and operational flexibility.
For transformer protection at the station, I prefer circuit breakers to circuit switchers. There isn't much cost difference between the two options and circuit breakers provide a larger zone of protection because they typically contain their own CTs.
Circuit Switchers usually rely on CTs within the transformer for fault detection. If a primary bushing or arrester fails (or if a large animal should happen to cause a fault at said bushing or arrester), a circuit switcher looking at transformer CTs won't see the fault current.
 
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Consider the required maintenance intervals of device at the tap. Circuit breakers/switchers eventually require maintenance, which would mean both transformers out of service.

At 115 kV we generally use dead tank breakers rather than circuit switchers unless a spacing issue required a candlestick type configuration. There is very little purchase price difference between a dead tank breaker and a live tank breaker (i.e. circuit switcher). I don't know if the same applies at 69 kV. If you put an interrupting device at the tap point, a dead tank breaker would include CTs.

Consider making the disconnector switch at the tap a motor operated switch so that tap can be quickly isolated if a fault occurs on the tap.
 
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Dvhez, Wouldn't you like to say some thing!
Two way interaction is always more interesting, isn't it!
 
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Due to the wide variation of requirement, we suggest getting a qualified Power Engineer familiar with the local engineering practice to develop a preliminary design and major equipment specs.
Usually, local power utilities is a good source that might help with typical design and specs for different applications including owner substation that will help to determine the usual equipment to be connected to the utility power network.
A generic partial list is suggested as follow:
* Protective device: Fuses, circuit switcher, circuit breaker (live or dead tank)
* Disconnect Switch: Vertical break, double break, center break, etc.
* Instrument transformers: PT or CCVT & CT (not required for fuses, free standing CT for live tank or bushing CT for dead tank Bkrs.)
* Transformer & Reactors: Power Transformer (with or without tap changer), distribution trasformer for auxiliary station power, regulating transformer (if NLTC) is provided in the main power transformer.
* Shunt Capacitor bank for voltage regulations.
* Protection and control: Relay and control panels (not required for fuse), revenue meters.
* Surge Arresters: (transformer usually furnished with arrester)
* AC & DC Aux. Power Subsystems: LV protective devices (MCCB and/or fuses), panelboards, transfer switches, batteries, battery chargers.
* Communication System: SCADA, power line carrier, telephone lines, etc
* Ancillary System: Lighting, security alarm, fence & gates, surveilance equipment (NERC CIP requirement, grounding (earthing), etc.
* Miscellaneous: Steel Support Structures, raceways (trenches, conduit, direct buried, etc.) fire wall and oil contaitment for transformers & reactors, HVAC for control house, fire suppression, drainage system, access road, etc.
 
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