1、ICEA P-47-434 65 m 9007034 0000223 723 = PRESSURIZATION CHARACTERISTICS OF POLYETHYLENE - INSULATED AND -JACKETED TELEPHONE CABLES PUBLICATION P-47-434 JUNE i965 INSULATED POWER CABLE ENGINEERS ASSOCIATON ICEA P-47-434 65 = 7007034 OOOOLL4 65T Copies of this Publication can be obtained by addressing
2、 The Insulated Power Cable Engineers Association 283 Valley Road Montclair, N. J. 07042 Area Code 201 Phone 744-3786 Price $1.50 per copy ICEA P-47-434 65 W 90070LY OOOOL15 57b = PFESSURIZATION CHARACTERISTICS OF POLYETHYLENE one was kept at conditioned room temperature, approximately 23 C, and the
3、other placed in an oven at 50 to 53 C. - i3 - ICEA P-47-434 b5 7007034 OOOOL29 080 = These tests were conducted to show what can be expected to happen to a pressurized cable stored out of doors in the winter, inside a plant or storage area, or out of doors in the summer. The test resuits, charted in
4、 Figure 2-4 show: for -2 to +4 C - 50 percent pressure loss occurred in over i40 days. for approximately 23 C - 50 percent pressure loss occurred in approximately for 50 to 53 C - 50 percent pressure loss occurred in approximately 32 days. 4 days. Calculated values (Kca for dimensions of above sampl
5、e = 0.027) are: Temperature, Degrees C Kg (see Figure 2-2) T.5, Days 1 23 52 4000 to 6000 130 to 200 800 to 1200 i08 to 162 3.5 to 5.4 21 to 32 The above indicates that the measured values are withinthe calculated range. II. with air. in Fig. 2-3. be.used, since this would hold only for a single gas
6、. data with calculated values, the percent pressure drop for air during the initial time, T,S (calculated for nitrogen), can be determined. sure drop for air is 59 percent, resulting in a pressure equal to bl percent of the original (nitrogen pressure drops from 80 percent to 40 percent; oxygen pres
7、sure from 20 percent to approximately 1 percent.) values for T-5, based on cable dimensions and nitrogen with actual measured time for air drop to 41 percent of original pressure as indicated by curves in Figure 2-5 and Figures 2-5 and 2-6 show results on direct burial and aerial cables pressuriaed
8、These tests show a pattern for pressure drop similar to that developed As these cables were pressurized with air, the T.5 concept could not In order to compare measured Figure 2-3 shows the pres- The tabulation below compares calculated 2-60 Cable T. 5 Calculated for N2, DaP Time for Air Pressure Dr
9、op to .hl Percent, Days 100 pair 22 Awg direct burial 25 pair 22 Awg direct Curial 6 pair 19 Awg direct burial 100 pair 22 Awg aerial and duct 25 pair 22 Awg aerial and duct 6 pair i9 Awg aerial and duct 43 to 65 19 to 30 15 to 23 65 to 97 32 to 48 24 to 36 23 18 84 h6 38 Examination of the above ta
10、bulation indicates time for pressure drop to 41 per- cent for direct burial cable to be somewhat less than the average of the calculated range for T.5, but for aerial cables these times are greater than the average of the calculated range for T.5 for 6 pair 19 Awg cable this time exceeds the calcula
11、ted maximum. - 14 - ICEA P-47-434 6.5 m 9007034 OOODL30 BT2 m It is noted that in direct burial type cables the corrugated shield is formed over the inner jacket, resulting in little area of contact between thetwo components. In contrast to this, the outer jackets of either aerial or direct burial c
12、able are extruded over the formed shield, resulting in good conformance and substantial con- tact area. Reeling and handling of the cable does result in some nonelastic shield defor- mation reducing conformance to and area of contact with the jacket. shield and jacket would be expected to reduce the
13、 effective area for gas diffusion through this jacket, and the difference in correlation between calculated and measured pressure drop in the two types of cables is attributed to the difference in shield-to= jacket contact. reels of each cable sise to provide data for within-reel and between-reel co
14、mparisons and to determine the effect of straight or coiled cable configuration on cable pressure- drop rate. Contact between In another independent set of measurements7 samples were taken from at least two For all cables tested, the rate of pressure drop was much greater for the direct This trend a
15、grees with results reported burial cable than for the aerial cable. increased with decreasing cable pair count. y Reference 1. Within one cable construction, this rate Comparative results are listed as follows: Time Required for Air Pressure Drop to 50 Percent of Original Cable Pressure, Days Coiled
16、 Cable Pair Count /AWE Reference 7 Reference 1 Aerial It II 6/19 15, 18 25/22 19, 20, 21, 22 100/22 53 Direct Burial 6/19 942 Il It 25/22 13 H II 100/22 28, 38 28 34 60 1242 17 36 Differences in air diffusion through jackets may be due to test temperatures utilized and to differences in the polyethy
17、lene extruded as the cable jacket, Reference 7 temperature varied from 78-85 F; Reference 1 tests were run at ap- proximately 73 F. An increase in temperature of 9 F will increase rate of diffusion approximately 25 percent. Alm, C.A. and Hillman, R. C.- “Diffusion of Gases Through Polyethylene Cable
18、 Jackets“, Telephone Engineering and Management, Vol. 67 pp. 40-43, 54, May, 1963. 7Medrick, D. S. Report, Anaconda Wire and Cable Company, New York, N.Y. “Gas Diffusion Through Polyethylene Jackets“. Unpublished Project ICEA P-LI7-934 65 9007034 OOODL3L 739 The effect on cable pressure drop of coil
19、ing a cable sample into a single turn is a slower rate of drop. reveals a change of 7-13 percent in the slope for aerial cables and of 6 percent for a single reel of direct burial cables. This change may be due to the polyethylene jacket becoming less permeable under both tensile and compressive ben
20、ding stresses. A comparison between straight and coiled cable samples Variations in pressure drop were observed for cable samples taken within one reel and from different reels. or from different reels, results indicate up to 6 percent difference in slopes. coiled 25 pair of 22 Awg aerial cables, wi
21、thin-reel slopes varied approximately 9 per- cent; different-reel slopes changed up to 12 percent. The variations in slope of other cable sizes from different reels were highest for the 6 pair of i9 Awg aerial cable and lowest for the 6 pair of i9 Awg direct burial cable. For straight 25 pair of 22
22、Awg aerial cables taken within For APPLICATION The practical consequence of gas diffusion through cable jackets is illustrated assume that a quantity of 12 pair of 22 Awg direct burial by the following example: cable is shipped pressurized with nitrogen during the summer, Kc, for this cable is 0.017
23、5. checked after 12 hours standing time, and loaded in a box car. Tenperature of the cable rises to 50 C (122 F) and remains at approximately this level during a 2-week transit period. The following result can be expected: The cable lengths are pressurized to 10 psi at a temperature of 25 C (77 F),
24、After unloading, the cable temperature drops to 20 C (68 F). Kg at 50 C is approximately 200 resulting in a value for T.5 of 200 x 0.017s = 3.5 days. pressure in the cable from 10 psi to approximately 12 psi. Gas diffusion during the 2-week period at 50 C will result in a pressure drop from 12 psi t
25、o 0.75 psi. further pressure drop of 1.5 psi or a pressure of -0,75 psi (gauge) or, in effect, a temporary vacuum. during the transit period is an over-simplification of actual conditions, the exawle does illustrate that under certain conditions gas diffusion can result in complete loss of pressure
26、for cable in shipment. Temperature increase from 25 C to 50 C Will result in increase in The temperature drop after unloading will result in a Although the constant temperature of 50 C assumed to persist SUMMARY Gas diffusion and temperature variations can result in complete loss of pressure in pres
27、surized cable; and therefore even complete loss of pressure is not a positive indication of jacket defects. and measure the rate of pressure drop to check for jacket defects. In such cases it may be necessary to re-pressurize - i6 - 100 I- a! J W PL Figure 2-1 Comparisons of Permeability of Polyethy
28、lene for C02, 02 and N2. ao C O“ io0 20 3oo 40 O 50 6 TEMPERATURE IN OC - 17 - ICEA P-47-434 65 H 9007014 0000133 501 H Figure 2-2 Kg as a Function of Temperature for Nitrogen and Low Density Polyethylene. EMPERATURE FOR NITRO - GEN AND LOW DENSITY POLYETHYLENE. VALUE VARIE ETHYLENE. CURVES SHOW MIN
29、.AND - IO0 O0 IO0 20 30 40 50 6 TEMPERATURE O C - 18 - ICEA P-47-434 b5 707014 0000134 448 Figure 2-3 Pressure Drop in Sealed Cable W 3 cn cn W a A 2 (3 U O lL O a a a - - TIME IN DAYS - 19 - I O0 90 80 70 60 50 W U rn W a o. J z a O IL O 340 a 30 E L oo 20 IO ICEA P-47-434 65 m 7007014 0000135 384
30、m Fig. 2-4 Nitrogren Pressure Test on Samples of Direct Burial Cable. - NITROGEN PRESSURE TEST MADE ON INNER JACKET OF 3 ADJACENT SAMPLES OF 25P 22AWG DIRECT BURIAL CABLE WITH .OiO“ CU SHIELD. (IO LENGTHS) o ROOM TEMP. APPROX 23O C .IN OVEN TEMP 50 TO 53OC -*AREFRIGERATED TEMP. -2C TO 4OC IO 20 30 4
31、0 50 60 TIME IN DAYS O - 20 - 100 90 CL 60 52 50 a O 30 IO Figure 2-5 Air Pressure Test of Samples of Direct Burial Cable. 20 30 40 50 TIME IN DAYS 60 70 DIRECT BURIAL CABLES AIR PRESSURE TEST MADE ON IOSAMPLES INITIAL PRESSURE APPROX. IO P.S.I. MADE AT ROOM TEMPERATURE (APPROX. 23C) ONLY INNER JACK
32、ET PRESSURIZED - 21 - ICEA P-47-434 b5 9007034 0000337 157 m Figure 2-6 Air Pressure Test on Samples of Aerial Duct Cable. TIME IN DAYS AERIAL AND DUCT CABLES AIR PRESSURE TEST MADE ON IO SAMPLES INITIAL PRESSURE APPROX IO P.S.I. MADE AT ROOM TEMP. (APPROX. 23C) - 22 - ICEA P-47-434 65 9007034 0000338 093 Cable under test Neoprene cable cap Typical pressure gauges used during testing Test gauge used to calibrate pressure gauges. Figure 2-7 - 23 -
