I was wondering if someone could please explain the principles of high voltage power and transformers. I understand about electricity but have never really understood much beyond the consumers side. ino a transformer in simple terms is two windings one with more than the other depending if you want a step up or step down transformer, and has sheets of laminated steel which through emf are energised and produce the current on the secondary winding but firstly do power stations supply a neutral to step down transformers or is it simply a line supply? When the neutral from the consumers is sent back to the transformers central point that's connected to ground is this connected to a neutral or does this complete the circuit by being connected to the phase points? any help would be appreciated I'm sure this sounds very stupid to most.
Hi Spen In general, transmitting at high voltage means low current so the cables can be much smaller diameter. The neutral only comes into play at the consumers end. Have a look at this link and see if it helps. http://electrical-engineering-portal.com/general-principles-of-electricity-supply-systems Kind regards
Siemens have some very good guides on electrical supply systems,the one below is 372 pages, covers everthing, from low, medium & high supply, switchgear,transformers,protective devices,etc, for some it's heavy reading,& some will find it hard going, but it is very informative, & a favourite of mine. https://w3.siemens.com/powerdistrib...c_power_distribution_technical_principles.pdf
High voltage is used is to overcome transmission losses. Higher voltage, lover current, lower losses. Smaller CSA cables, longer runs. The power station will output in star, having its centre point earthed down to ground, transmitting just the three phases. This will enter a transformer where it is stepped up for transmission on the national grid at 132,000 and 400,000 volt. The input of the transformer will be delta, so no neutral (remember, just three phases transmitted). The output from the transformer will be star, centre point earthed. This is the same throughout the whole distribution, 25,000 > 400,000/250,000/132,000 > 66,000 > 33,000 > 11,000 > 400. The input is always delta, the output star. It has to be a star output to provide the reference to earth. If a line falls, or there's a fault to earth, a return path is in place to operate protection.
thanks for all that very helpful. its not something ive ever had to learn but its something that's interested me but struggled to find the correct links. seem to find a lot to do with usa transmission which is similar but nothing on the uk.
thanks bazza made a great read. it didn't explain what a 11kv ring main unit was for tho is this a common item?
Most substations will have an RMU. It is basically three, three position switches joined together. One switch will isolate just the transformer, one will isolate just one input, the other switch the other input. 11kv distribution is usually run as a ring for redundancy. You can therefore open a switch in two individual RMUs and completely isolate the link between them, while keeping everyone on supply. You can then work on the cable, add new RMUs etc. Each of the three switches have three positions. OPEN, CLOSED, EARTHED. You switch from CLOSED to OPEN on both ends of a cable run, then switch from OPEN to EARTHED on at least one end. This earths all three phases down, making it safer to work on the cable. Getting the sequence wrong results in a huge bang. RMUs can have metering modules added to meter the 11kv connection to the substation, and also have motored switching included to allow remote operation by switches or earth leakage detection etc. There can also be shunt trips which are spring loaded, and a quick pulse of 110v or 24v will cause them to open the output to the substation, commonly used where the DNO supplies a building at 11kv. It provides an emergency stop facility in the private switch room to open the locked DNO RMU in an emergency. The DNO would then have to attend to reset.
aghh yeah ino the ones oddly enough have been working on the ex MOD site in Bradford installing cctv managed to get into the old switch rooms which have all the old switch gear still in and two of these rmds both have been isolated and earthed for maintenance. cant remember what is said but it was something earthed. they both had relays on them and meters. next door where the old oil filled switch gear still in use bloody huge things with solenoid valves to open them and huge earthing pins for isolaton. then next door was a room filled with earth leakage relays and meters. the site has three 11kv supplys as it needed to synchronise atleast two together in order to start the mac 5 wind tunnel. didn't really appreciate it all until now its half the reason why I became interested in understanding it a little more.
Military sites usually have at least two sources of HV, and even then, they treat the grid as their "backup". In times of war or high alert, they will usually utilise their own gensets, the grid acting as their backup.
it has a back up supply from Bedford then its own supply from the station about a 25km run. They used to supply the airfield from there aswell. They still have 7 lv transformer's dotted around the site feeding the large warehouses that used to have separate smaller wind tunnels in and other bits they had dotted around the site. They have one to just to supply the bodyflight tunnel
I wound high voltage transformer windings for 40 years, didn't have a clue about the technicle side. Some of the windings had 10 tons of copper in them.
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