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Substation Insulator Strings
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(Mechanical)
(OP)
8 Feb 19 21:56Hello!My name is Luis. I've not any electrical background. I work in an engineering company (in the drawing area). Not long ago I saw some drawings of a Substation and I was curious to realize the following components:I someone could explain my questions I'll be very happy.Luis
Replies continue below
(Electrical)
8 Feb 19 22:06I suspect it would be a spark gap that hopes to provide a path to earth-ground during over voltage events like a lightning strike. That distance between the two bends would be a pretty accurate voltage regulator in that it would arc at a pretty specific over-voltage. The insulator itself is a fairly lousy 'regulator' as its stand off voltage will vary greatly based on age, dirt, and moisture.Cool drawing, thanks.Keith Cresskcress - http://www.flaminsystems.com
(Mechanical)
(OP)
8 Feb 19 22:17Hi Keith! Thanks for the answer and the kindness. But I still have not noticed something ... in this drawing ... in normal operation, without over-voltages, on the substation side the voltage is 400kV?I'm sorry if the question is stupid, but I do not understand anything about this area.Thank you,Luis
(Electrical)
8 Feb 19 22:31That end of the string is at zero volts.
Bill
--------------------
"Why not the best?"
Jimmy Carter
(Mechanical)
(OP)
8 Feb 19 22:40Hi Waross! Thank you but I did not understand very well ... I'm sorry ... I must be very stupid :(The point A is at 400kVThe point B is at 0 voltsIt's that?
(Electrical)
8 Feb 19 22:53Point A is 230kv, point B zero volts.
(Mechanical)
(OP)
8 Feb 19 22:56Hi Mbrooke!Thank you for the answer...but why point A is 230kV and not 400kV?
(Electrical)
8 Feb 19 22:56You just complicated things a bit for mr luiscunhaIt is true, of course. But I think that we need to add that L-GND on a 400 V system is 230 kV.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
(Electrical)
8 Feb 19 22:58kV..
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
(Mechanical)
(OP)
8 Feb 19 23:02Hi Mr. Gunnar. For a layman like me and in order to realize that... at point A will have 400kV and at point B will have 0V. It is that? Thank you in advanced. My best regards.
(Electrical)
8 Feb 19 23:10No, it is 230 kV, actually. Just as Mbrooke said.You need to understand that the 400 kV are measured between the phases (lines) in a three-phase system while the voltage across the insulator string is 400 kV divided into square root of three. That results in 230 kV across the string. Same as in a houshold system - only at a different level. Usually 400 V and 230 V.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
(Electrical)
8 Feb 19 23:27230kv line to ground, in most 3 phase systems voltage is higher between phases then it is to everything grounded.
[Post Deleted](Mechanical)
(OP)
8 Feb 19 23:46Please. Do not get into a discussion because of my questions and doubts. My intention is try to understand and thank you both. I think this is a fascinating area. From what I realized it is wrong to say that in a three-phase system a conductor has 400kV, because that is the measure between conductors. If you "look" at only one phase, the reference point will be the ground.
(Electrical)
8 Feb 19 23:55In terms of insulators the reference point is usually ground- you are only holding back the voltage from one phase to ground. This is the phase to phase value divided by 1.73.
So on a 500kv line, the phase to ground voltage is 288kv.
1.73 comes from the square root of 3. Just how the math works out.
(Mechanical)
(OP)
9 Feb 19 00:05Thank you Mbrooke! I think in getting there ;) thank you for your time and patience.
(Electrical)
9 Feb 19 00:10It depends:If by 400 kV you mean 400 kV to ground then the voltage is 400 kV.If by 400 kV you mean a 400 kV system, then the voltage to ground is 230 kV.And,If the transmission system is DC then the voltage to ground for a 400 kV system will be 200 kV.I can look over either shoulder and see, about a mile away, a 500 kV DC transmission line.The end of the insulator attached to the tower should always be at zero Volts. If it is more than zero Volts then something has gone very seriously wrong.
Bill
--------------------
"Why not the best?"
Jimmy Carter
(Electrical)
9 Feb 19 00:13@luiscunha- ask what you need- don't hold back. I'm willing to answer any and all questions you may have. It is a pleasure :)
If you are looking for more details, kindly visit arcing horn in transmission line.
(Electrical)
9 Feb 19 01:20Bill, why would a 400kV DC system result in 200kV to earth?Keith Cresskcress - http://www.flaminsystems.com
(Electrical)
9 Feb 19 02:43Keith, I'm guessing Bill was referring to a bipolar HVDC system since that is the type most in use today, and if so, he's correct.xnuke"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand,Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
(Electrical)
9 Feb 19 03:43Hi X; Hmmm. Bipolar. So +200kV and -200kV on parallel conductors and they call that 400kV?
Keith Cress
kcress - http://www.flaminsystems.com
(Electrical)
9 Feb 19 05:16Sort of like calling two 120 Volt circuits with a common neutral 240 Volts.They do carry a neutral with that line. The neutral is a lighter gauge and the insulators strings are much shorter than on the hot lines..
Bill
--------------------
"Why not the best?"
Jimmy Carter
(Mechanical)
(OP)
9 Feb 19 16:34Hello! Absurdly, if a person could climb up the metal structure and sit in Point B, no harm would happen to him?
(Military)
9 Feb 19 18:59In theory, no harm at all - but you'd be sitting in an area with quite high fields, and making sure that the distance between all your extremities and all the live conductors is comfortably greater than the length of that spark gap is not so easy.
In practice, you'd wear a safety tether to stop you breaking your neck when you slipped and fell - then spend the whole time worrying about what happened if the dangling tether got too close to the 400kV line hanging underneath the insulator string (or if it was you dangling close to that line).
A.
(Electrical)
10 Feb 19 01:23Not absurd at all, have a look at this:Sorry for all the vids, but just to give various perspectives.
(Mechanical)
(OP)
10 Feb 19 19:59Hello!
@zeusfaber thank you very much for the explanation was quite enlightening!
Mbrooke, Thank you once again for your patience and willingness to help me understand this issue. This forum is certainly very useful especially as people like you who, however banal, who may seem the questions, seek to help and impart knowledge.
2
cuky(Electrical)
10 Feb 19 23:15Below are some background associated with arcing horn applications for OH Transmission LinesARCING HORN OR PROTECTIVE SPARK GAP:a) Is a protective element against overvoltage for insulator in OH transmission line & equipment bushings.b) The arcing horn is set with the least path impedance than the insulators such as in the event of flashover overvoltage an arc strike between the air gap on the metallic elements instead of across the insulators.c) Somehow, arcing horn and corona rings installed at the end of the insulator assembly help to reduce the number of the disk insulators while maintaining the desirable electrical strength (BIL & BSL).d) In North America, many OH Lines use corona ring and less common to spec. out arcing horns. In Europe, it is a common practice for overhead T. Lines specify arcing horns in OH T. Line and equipment such as power transformer.e) One of the benefits of using arcing horn is the cost and the capability to operate with high discharge energy of lightning strike or back-flashover overvoltage.f) Some of the downsides of use of arching horns are the wide operation performance due to the weather-related dependance including air moisture, temperature, contamination among other factors that influence the system reliability.g) In the last couple of decades, T. Lines metal oxide surge arresters are used as an option with less weather dependance performance than the arcing horn.Below is an excerpt showing a sample of the field stress distribution between the air gaps of the arcing horn and across the insulator.I hope this help to visualize the operation performance of the arcing horn.
(Electrical)
11 Feb 19 04:19Major disadvantage of arcing horns is that after the surge discharge, there will be a power frequency power flow through ionized air that will cause power interruption. With arcing horns arc flash over voltages are quite high with steep fronted surges ie very little protection.In the days of old type surge arresters(silicon carbide blocks with series air gaps) arcing horns used to be provided with bushings due to erratic protection levels of arresters + to provide uniform protection margins over the entire surge rage. With modern metal oxide arresters, arcing horns are superfluous and rarely used with transformer bushings.
(Mechanical)
(OP)
12 Feb 19 16:56Very interesting! In this case, if I understood correctly, the distance between the arching horns should be such that in normal operating conditions, there is no arc between points A (230kV) and B (0V) and in the event of an overvoltage/surge discharge, that same distance, offers the least resistance path, that conduct the discharge by the arching horns and not the by insulator string.
(Electrical)
12 Feb 19 18:02I believe you are correct, luis; note however that the behaviour of arc gaps can be graphed similarly to a b-H curve for magnetic hysteresis, in other words once the air between the horns is sufficiently ionized and the air gap breaks down, the established arc will continue to conduct what is essentially fault current to ground, and it is this current that is detected by the circuit protective schemes, subsequently tripping the circuit breakers or other protective devices and taking the circuit off potential. Re-energization of the circuit in a short interval is normally performed by automatic reclosing features, nevertheless there will be a definite, even if very brief, interruption of the power supply.In contrast to this, modern metal oxide varistors, as prc has noted, have a very linear [even if the line is curved] characteristic of conductance/applied voltage, meaning that as the overvoltage subsides and the voltage applied across the varistor returns to its normal range, the varistor's conductance will again fall to next to nothing / its resistance will again rise to a very high value, the upshot being that the line voltage is not collapsed below its normal values as with horn gaps.
CR
"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]
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Standard Arcing Horn
High-speed, snap-out arcing horns are standard equipment on all transmission switching applications. Fabricated from beryllium tube, the rod is tapered to achieve high tip speed during the first cycle after separation. A black neoprene snubber attached to two stainless steel support rods is provided to prevent recoil into the open gap during operation. A copper hook acts as a catcher for the arcing horn during opening, allowing a suitable open gap to be developed before the horn releases with great speed.
Standard arcing horns are suitable for interruption of limited amounts of line charging and transformer magnetizing currents. In performance, this horn is comparable to horns offered by other manufacturers.
Line Drop Rating Voltage (kV) Current (A) Approx. Line length (miles) 69 & Below 15 62 115 6-8 17 138 3-4 7 161 2 4
High Velocity Whip
For interruption of substantially greater amounts of line charging current, SEECO has developed the High Velocity Whip (HVW), a spring loaded, stored energy arcing horn, which achieves a very large air gap within the first cycle after separation. The whip also employs a Delrin® tip, which assists in the dissipation of ionized gases. Tested at NEETRAC, the HVW outperformed all other arcing horns in head to head competition.
The HVW is available for use with all SEECO side, center, center Vee and double end break switch configurations, at voltage ratings of 46-230 kV.
Line Drop Rating Voltage (kV) Current (A) Approx. Line length (miles) 69 & Below 33 133 115 15 56 138 10 35 161 6 20
Single Bottle Interrupter
SEECO manufactures a single bottle interrupter for those applications where the recovery voltage does not exceed 30 kV peak and the maximum interrupting current is amps or less. Less expensive than multi bottle interrupters, single bottle devices offer substantial cost savings but with reduced functionality and more limited switching applications. An off-setting disadvantage can be the occasional confusion experienced by field personnel who often struggle with understanding the limitations of the single bottle device relative to the broader functionality of the multi bottle interrupter. Single bottle interrupters can be installed initially with the switch or added later as a field retrofit or upgrade.
Common switching applications for single bottle interrupters include:
This interrupter can be used with both SEECO and non-SEECO group operated switches, including side-break, center-break, center Vee and vertical-break configurations. Please refer to product catalog section PC-007-02 and this webpage for additional information.
For two and three-way phase-over-phase switching applications, SEECO offers a single bottle interrupter that is shared by all ways of the switch. Like the multi bottle interrupter below, the cost of the interrupter unit is spread across each way of the switch, making the cost 'per way' progressively less expensive; all ways of the switch participate in the full functionality of the device. Please refer to product catalog section PC-007-01 and this webpage for additional information.
Multi Bottle Vacuum Interrupter
For maximum sectionalizing flexibility, SEECO manufactures multi-bottle vacuum interrupters that provide a broader range of interrupting capability, including load dropping, line dropping and loop splitting. Multi-bottle interrupters simplify switching 'rules' and reduce the confusion frequently experienced by operating personnel over the capability (device rating) and appropriate use of more limited devices. Multi bottle interrupters can be installed initially with the switch or added later as a field retrofit or upgrade.
In transmission sectionalizing applications, the use of (multi bottle) interrupter switches helps extend the operating life of more expensive circuit breakers by reducing unnecessary operations and wear, allowing breakers to be reserved for their intended duty of fault interruption. On a cost per operation basis, interrupter switches are substantially more economical and better suited for general line sectionalizing purposes.
When used in conjunction with two and three-way switches, the benefits of multi-bottle interrupter devices are significant. One interrupter unit (column) is used per phase and is mounted on the stationary, non-rotating insulator; the interrupter unit is then shared by each way of the switch. The shared interrupter increases the cost savings achieved by utilizing two and three-way switches and magnifies the 'bundling' effect.
Upright (vertical) Mounting
For two and three-way switches of any voltage and one-way switches rated 115 kV and up, the interrupter column is always mounted upright (vertical). For one-way switches rated 46-69 kV, the interrupter column can be mounted either upright or cantilever. For additional information on multi bottle devices mounted upright, please refer to product catalog section PC-007-01 and this webpage.
Cantilever (horizontal) Mounting
For SEECO one-way, phase-over-phase switches rated 46-115 kV, the interrupter column can be mounted cantilever which permits more compact phase spacing, reducing pole height and cost. Cantilever mounting of the interrupter is not available on two and three-way switches, and on one-way switches rated 138 kV and up. For additional information on multi bottle devices mounted cantilever, please refer to product catalog section PC-007-04 and this webpage.
Vertical Break Mounting
SEECO type VM multi bottle interrupters can also be supplied with SEECO vertical break switches as well as those offered by other manufacturers, with voltage ranges of 46-230 kV and current interruption ratings through amps. For additional information on multi bottle devices mounted on vertical break switches, please refer to product catalog section PC-007-03 and this webpage.
Line Drop Rating Voltage (kV) # of Bottles Current (A) Approx. Line length (miles) 46 & Below 2 100 331 69 3 100 220 115 4 40 37 115 5 100 132 138 5 20 40 138 6 100 110 161 6 25 42 230 8 40 Consult Factory
Brand Compatibility
In response to very strong interest from our customers and the general market, SEECO has begun adaptation of our existing single and multi bottle interrupter products for use with other brands of group operated switches. It is our intent to eventually offer vacuum interrupter devices for all major brands and switch configurations. SEECO is currently working closely with Pascor Atlantic, USCO and Royal Switchgear. Interrupter kits will also be developed for Southern States, S&C, Pascor, Turner and others as they are requested by customers.
For general questions about SEECO interrupters and compatibility with other brands and configurations of group operated switches, please contact the factory or your local SEECO representative.
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