Document KGdb5dEd0qvBw8vQMQ4pBYpdN

>u- * 0S**)V"* STLCOPCB4059850 TRANSMISSION/DISTRIBUTION/ COVER STORY `V : - - -f...... '' . 0k: i. ; jM Ml' . .4* m . ... V HiL-m- . . .J m i'.r*f. - 4 ; ......... JZSZZSSSE.'ZfVJ ....irrsiat::-' : t ***->"-ix' - *9 *^*T " . --* ' * *: . ' ' 'T ~v : ;'&?' " 4 \ " . "t-. A-"**'*' 4 r Ii 41. i .. * '' /Z ,--.`1;. ' -kat ;A\ . . ., f j rr* ` m r " -Tr 'f i -ii' A /\ / > tr H ir illl (I :r': I " `rlL.j', -* . :f . ,M -Vj .. i ' ; ; 1,1 `V`.v i?. ;V> ' rm' fi!lnir'i*t r'irr'ir'fi j* Location of thermocouples in and on pipe should provide data that will advance knowledge of thermal behavior of this cable ri. tr* '. S Pipe cable acts as operating laboratory The need to install a short run of pipe-type cable into a substation gave Philadelphia Electric Co a chance to provide instrumentation to accumulate thermal data A built in monitoring system for aver-. age conductor temperature, extensive thermocouple coverage, a refined oilcirculation system, and a premolded splice ill make Philadelphia Electric Co's new 220-kv pipe-type cable an op erating 'aboratory. The cable is part of a circuit that car ries an average of 350 Mva from Gray's Ferry Substation in Philadelphia to the Schuykill Substation in the south western section of that city. The circuit is primarily overhead, but obstacles in the immediate vicinity of the Gray's Ferry Substation, including a high rail road embankment, made it necessary to terminate the overhead line about 1,000 ft from the substation and run the rest of the way in pipe-type cable. The cable traverses a variety of ther mal environments in the short run into the substation. These include a steammain crossing, a macadam parking area, the aforementioned railroad embank ment, and the unpaved yard of the sub station itself. George Freas, senior engi neer in the T&D Section of PE's Engineering & Research Dept, ex plained that this, in part, resulted in the decision to employ extensive thermo couple coverage to detect hot spots, and to equip the cable with an oil-circula tion system. According to Freas, equipping the cable with heat-detection and -control devices is also part of a test program to accumulate data on heat flow in HPOF cables. Study of these data hopefully will provide the industry with informa tion not now available on heat dis sipation, transient loading effects, and other thermal phenomena. Freas also hopes that better data may lead to sub stantial improvement in dollar-per-ampere costs, brought about by the better design that may be possible with fuller understanding of the thermal perform ance of this type of cable. The thermocouple coverage is de signed primarily to detect hot spots. Eight thermocouples are either attached directly to the shielding tapes of the conductors, or positioned in the oil stream. Specifically, a thermocouple is attached to the shielding tapes in each of the terminal trifurcators, to the shield of the cable directly beneath the rail road embankment, to the shield of a special precast, molded, quartz-epoxy joint at an intermediate location, in the oil stream of the terminal trifurcators and at the precast joint, and on the pipe itself at the center and both ends of a sleeve through which it runs underneath the emba ikment In addi ion to this complete thermo couple coverage, the cable has another feature designed to obtain thermal in telligence. Edward Eich, chief engineer for H-V cables at Anaconda, which sup plied the cable, explained the method whereby average conductor tempera ture under actual operating conditions is constantly monitored: A No. 26 AWG nylon-insulated nickel wire is positioned in the interstice at the center of the segments of the 2,500 MCM conductor. This wire runs the entire length of the cable, passing through the joints, and terminates at a transmitter located within the pothead corona-shield. This device comprises a resistance bridge which measures the resistance of the sensing wire, and an FM transmitter. The bridge output modulates the signal broadcast by the transmitter to a remote receiver. The signal is demodulated at the receiving station and displayed on a meter as av erage conuuctor temperature. A signal of 0 to 5 v covers a temperature range of 20C to 120C. The particular receiver in use at Gray's Ferry broadcasts at 95.0 Mhz, and can bo picked up on any FM re ceiver near the potheads. An accuracy of _!6 deg C is attained, and the signal can be received reliably even through severe corona or other RJ. Carrying the sensing wire through the splices required special splicing techniques. One segment of each of the two conductors to be spliced was care fully cut back to expose the wire. The wire was then spliced and insulated and tucked back into the center interstice of the segments. A smooth piece of plastic, shaped to match the segment of the conductor that was cut away, was then inserted into the gap in the conductor. This plastic-filled gap was positioned to be within the connector barrel, so that ampacity was not lost. A possible bonus feature of the tem perature-sensing system is that, in case of fault, and assuming that the sensing wire welds to or contacts the phase con ductor, a precise bridge location of the . > yj O Reprinted from August 15,1970 issue of Electrical World <S> Copyright 1970, McGraw-Hill, Inc, All rights rcstrvod STLCOPCB4059851 Cobra-like feeding tubes take conductors smoothly from reels down through riser conduits to direct-buried trifurcators Center-phase pothead is topped by transmitter, contained in fiber glass housing visible just above splicing platform fault can be made by comparing the re sistance of the sensing wire on the faulted conductor to that of an un damaged one. Forced oil circulation has also been applied to this line, and is included in the overall temperature-study program. A 4-in. pipe runs parallel to the cable pipe for its entire length, and is con nected into each of the terminal trifurcators. forming a closed circulation system. The oil is pumped through this loop by a 100-gpm single-stage cen trifugal pump installed in the 4-in. re turn pipe, and operating at 10) psi. The pump is coupled to a 25-hp, 230-v, 3phasc motor. Flow is automatically con trolled to produce any flow from. 5 to 100 gpm, and can be reversed. The flow is measured and controlled by a turbine meter and a motorized ball valve. Pumping and metering equipment, the chart recorders for the thermo couple outputs, the average-conductortemperaturc receiver, and the pumpingplant equipment arc all contained in a 5 x 7-fi housing at the subsiation. The conductors themselves are in stalled in a lO^i-in.-diameter pipe. This . size was selected because the cable crosses under the railroad embankment adjacent to the substation at a depth of 35 fL This severe change in elevation, in addition to a change in direction as the circuit approaches the embankment, created a high jam ratio in the pipe bends. The larger diameter was chosen to mitigate this. The pipe sleeve through which the cable pipe crosses under the embank ment was pumped full of a sluny of clay and water to prevent the presence of air pockets in proximity to the pipe. Two 2-in. plastic pipes dre also installed in this sleeve, spaced 90 deg apart and attached to the pipe proper. Water will be circulated through these in a later phase of the temperature study to deter mine the effect of such water-cooling. Low'-profile terminal structures at ei ther end of the pipe required a different arrangement from the usual above ground trifurcations. The trifurcations were buried directly in the ground about 50 ft from each terminal struc ture. The three individual riser pipes ex tend from this point to the structure, where they sweep up to the potheads through 6-ft-radius bends. The riser pipes are made of type 304 stainless steel for corrosion protection, and are 5 9/16 in. in diameter. The potheads themselves are G&W with sky-blue porcelains and 4-in. safety heads with rupture discs. Separate from the basic aim of devel oping heat-dissipation data, but also de velopmental in nature, is :hc use of the precast, molded, quartz-epoxy splice. This splice, called Volialit, was devel oped by Pirelli, and is marketed in the United States by Anaconda. Several joints of this type were installed by Con Edison on a 138-kv cable, but Freas and Eich knew of no instance in this country where they had been applied at 220 kv. The splice consists of a sleeve of quartz-epoxy with a cast-in shield. This shield, in the assembled splice, is in contact with the special connector, and serves to distribute and control the stress. The ends of the conductor are prepared simply by cutting back the factory insulation just far enough to in stall the connector. The insulation is cut off square, and no stepping or penciling is required. After the connector is com pressed on, the sleeve is slid into place, whereupon the shield and connector lock into contact. Tape is hand-applied in a taper from the shoulder of the sleeve to a point 15 in. out on the cable. The sleeve itself is 30 in. long and 8.5 in. in diameter, and the individual finished conductor splice is only 5 ft long. This compares to the 13 ft required by hand-taping at this voltage with this size of conductor. Freas estimates that about $t00 was saved on this one joint as compared to hand-taping costs. This saving was real ized even though material costs for the Voltalit were S 1,400 more than the cost of taping materials would have been. He feels, however, that a very important additional advantage accrues from the uniformity obtained from splice to splice, and the obviation of the h gh de gree of skill required by hand-applied taping. > The cable piping is isolated from ground by polarization cells at each ter minal. By thus isolating the system, ade quate protection can be afforded the entire length of pipe by a 12-lb anode at each terminal. Size of transmitter that broadcasts signal of conductor temperature is shown here DSW 201785 STLCOPCB4059852