H TENS ON ION LINES
STRINGING AND CO2
able places such as road crossings, near villages and other inhabited places. These anti climbing devices prevent persons e live power conductors or their vicinity. The anti climbing devices
.4 MMISSIONING OF E.H.T LINES :-
4.1 2.4.1.1
The di ensions indicated in the figu d ions and arrangement.
ANTI-CLIMBING DEVICES :- These devices are provided to towers at a height of about 3.00 Mtrs. from ground at vulner
from reaching th
are made of M.S angle and barbed steel wire. The arrangement of anti climbing devices are fixed to the tower legs is shown in the Figure – 2.10.
2.3.4.3 DANGER PLATES :- 16 guage M.C sheet of size 200 x 325 Mtr. is used as Danger Plate. The word ‘DANGER’ in English and Local Language shall be inscribed on the Plate. Danger sign depicting of a skull above two bones is painted on the Danger Plate. The voltage at which the E.H.T line is charged is also indicated on the plate. Provision is made in the danger plate to fix it on the tower leg with 16mm bolts.
2.3.4.4 NUMBER PLATES :- Each tower in any transmission line is allotted a number in a serial order commencing from one terminal tower and ending with the terminal tower on the other end. The number plate is made of 16 guage sheet of 100 x 150 Mtr. Size. The number is enameled in Red on white enameled background. The number plate is fixed to the tower body at about 4 Mtrs ground level.
2.3.4.5 PHASE PLATES :- Each angle tower is provided with a set of three circular discs of 0.100 mtr. dia each enameled in Red, Yellow and Blue. These phase plates are fixed to the towers at a height of about 4 mtr., above ground.
STRINGING AND CO 2
2. Design Aspects of Tensioning of Power Conductors and Ground Wire (S)
The following shall be the basis for evaluating stringing data in respect of power conductor.
(a) The minimum factor of safety for conductor at minimum temperature of 10oc and under full wind pressure shall be 2.00
ate tensile strength of the conductor
(c tipulation, the value of stress in Kgs per
Sq.mm ‘f’ in the power conductor at 32oc and still air is decided while
.4.1.2
ave to be calculated. The tensions in the conductors and groundwire (s) have to be evaluated 2/3 full wind pressure at minimum temperature of 10 c for arriving at the transverse and longitudinal forces acting on the tower.
d to evaluate value of stress ‘f2’ in the power conductor at temperature. T2 and wind
quation.
are loading factors.
(b) The conductor at every day temperature of 32oc and under still air shall not be tensioned to more than the values indicated below in percentages of ultim
Initial unloaded tension - 35% of Ultimate Tensile Strength of conductor Final unloaded tension - 25% of UTS of conductor
) Taking into consideration the above s
designing the towers. Hence the value of ‘f’ is fixed based on which the design aspects of power conductors have to be evaluated.
2 As already stated in the foregoing paras, the values of sag of power conductor at maximum temperature of 75 oc and still air and at minimum temperature of 10oc and still air have to be calculated for different span lengths to prepare sag-template.
The values of sag are obtained only when values of conductor tension are known.
Also, the atmospheric temperature may vary at different times of stringing (or tensioning) the conductor. In other words, the values of tension of power conductor at still air and at different temperatures ranging from 10oc to 60 oc h
for full wind pressure at 32 oc and
o
The following procedure shall be adopted for arriving at the tension in conductor or ground wire at a given temperature and wind pressure and for a given span length (equivalent span).
Let the stress in power conductor at every day temperature of 32oc and still air be
‘f’ kg per sq.mm for normal span ‘l’ mtrs. These values of ‘f’ and ‘l’ are decided for design of towers and shall form basic design criteria. It is now require pressure P2 for a span length of ‘l2’. The relationship between the values of ‘f’ and
‘f2’ in terms of other quantities is given by the following e
f2 – (f- Ext – I2 K21 q2 E) = I2 K2 Q22 E
l2 Span for which stress ‘f2’ is to be calculated Unit weight of conductor = W/A Kg/Mtr/Sq.mm
ain, ‘W’ is weight of conductor/ground wire per metre length and ‘A’ is area of cross section in square millimeters. q and q2
ere P The val Thus q2
H and P2 are wind pressures.
ue of ‘p’ is considered to be equal to zero as the stress ‘f’ pertains to still-air condition.
= 0 + W2 = 1 or q = 1 W2
But q √ P2 = 2 + W2
2.4.1.3
in Figure
The Sa nsi n Vs. Tension for
different atmos Vs. te erent span lengths.
It may noted va es of t given span may be
taken fr s also to be
noted that t y the
-ln3 I1 + I2 + I3 + ---- ln
HOW TO READ THE CHART :- It is required to know the quantum of tensioning to be made to the conductors/groundwire at angle towers on either side. The equivalent ed at the site temperature is known. Choose the value of
e of tension at the two angle W2
As all the other values are known in the above equation, the values of f2 can be calculated for different span lengths at any given temperature or at different atmospheric temperatures for any given span at still air as well as at full wind.
STRINGING CHARTS : Also known as Sag-Tension Charts, these charts are required for deciding the value of tension to be applied to power conductor/ground wire at two consecutive angle points. A typical stringing chart is shown
2.11.
g-Te on chart consists of two sets of graphs (viz) (i) Spa pheric temperatures and (ii) Sag nsion for diff be in this connection that the lu ensions for a
om the tension statements pertaining to different temperatures. It i he value of span length in the span vs. tension curves is actuall equivalent span ‘I’ which is given by the following formula.
Ruling span l = √ I3 + I32 + I33 +
Where I1, I2, I3, etc., are the individual spans between two consecutive tension points or in other words between two angle locations. The Sag Vs. Tension curves in the chart correspond to different values of individual spans.
span shall be arriv
temperature indicated in the Chart nearest to the site temperature. Choose the Span Vs. Tension Curve corresponding to that nearest temperature. Read the value of tension in Kgs corresponding to the equivalent span. Note this point at ‘S’ the conductors/steel wire is to be tensioned to this valu
e two angle towers, there are individual spans. It is now required
e value of sag in respect of other individual spans between
.4.4
.4.4.1 SUSPENSION HARDWARE
Single Suspension hardware assembled with required number of Ball and Socket type
ith two stacks of insulators are used for the tangent towers on either side of river crossing spans, road crossing span etc.
The com le suspension hardware are indicated below.
1.
2. case of double suspension hardware
3. Two yoke plates – one connecting two ball clevises to the two stacks of insulators and lators of the two insulators stacks. The bottom yoke is also connected to the
4. In case of single suspension hardware the bottom most insulator is connected to the
5. One set of line side arcing horns 6.
7. e, two suspension
clamps are provided to support twin conductors 8.
towers. In between th
to know how much sag should be allowed in each individual span. Choose the tension vs. sag curve corresponding to the value of span length nearest to the individual span for which sag is to be computed. Draw a horizontal line from the above point S to cut the above chosen tension vs. sag curve. From the point at which the curve is cut, draw a vertical line and read th
the two angle towers.
2 LINE MATERIALS FOR STRINGING POWER CONDUCTORS 2
There are three types of Suspension hardware in the normal use viz., (i) Single Suspension hardware with fixed type arcing horn (ii) Single Suspension hardware with adjustable arcing horn on tower side (iii) Double Suspension Hardware
insulators are used to support the power conductors from the crossarms of tangent towers. The single suspension hardware provided with adjustable arcing horns on tower side are used on approach tangent towers near the substations. The double suspension hardware assembled w
ponents of sing
Ball hook with provision to fix adjustable or fixed arcing horn Socket clevis to fix ball hook to yoke plate in
another connected to two socket clevises which are in turn connected to the bottom most insu
suspension clamp through clevis-clevis or clevis link. Provision is made in the bottom yoke to fix line side arcing horns. All these components are required for double suspension hardware set.
suspension clamp through socket clevis which has provision to fix line side arcing horns.
One set of tower side arcing horns is provided in case of 132 KV, 220 KV and 400 KV hardware
One suspension clamp. In case of 400 KV suspension hardwar
Corona Control Rings are to be fixed to the yoke plate which in turn connects the suspension clamps through clevis eyes in case of 400 KV single suspension hardware.
A typical 400 KV single suspension hardware set is shown in Figure 2.12.
2.4.4.2
tion an d400 KV hardware suitable for insulators of 20 mm., ball
c c 600
c e, the maximum value of Radio Influence
.4.4.3 TENSION HARDWARE
There are three types of tension hardware sets normally used (viz) (i) Single tension hardware (ii) Single Tension hardware with adjustable arcing horns and (iii) Double tension hardware. The tension hardware sets are used at angle locations.
Two sets of hardware are required to clamp the conductor(s) for each phase connected in turn by a jumper. Thus, per each angle location of a single circuit line, six sets of tension hardware are required per each angle location for a single circuit line and twelve sets for a double circuit.
TECHNICAL REQUIREMENTS OF EHT SUSPENSION HARDWARE
The 132 KV and 220 KV suspension hardware shall be suitable for insulators of 16 mm ball designa
designation
The breaking/failing load of suspension hardware shall be 7000 kgs.
The slip strength of the suspension clamp shall be 25% of the ultimate tensile strength of onductor
In ase of 400 KV suspension hardware, the magnetic power loss corresponding to Amps per sub-conductor shall be not more than 7 watts.
ase of 400 KV suspension hardwar In
voltage for the complete string (i.e.,) including grading/corona rings, arcing horns, clamps etc. at 266 KV R.M.S shall be 500 Micro volts.
In case of 400 KV lines, the corona extinction voltage for the complete string is 320 KV (RMS).
2
Normally, single tension hardware sets with fixed arcing horns on tower side are used for angle locations of 132 KV and 220 KV lines. The single tension hardware sets with adjustable arcing horns are used on angle towers of the approach locations of the connected E.H.T substations. The actual spacing between the spheres of the tower side and line side arcing horns is adjusted as per the insulation co-ordination decided for the connected substation near the approach towers. Double tension hardware sets are used for angle towers on either side of river crossing spans and railway crossing spans in case of 132 KV and 220 KV lines and for all angle towers of 400 KV lines. The double tension hardware sets have provision for assembling two stacks of insulators.
The single tension hardware has in general the following components . i) ‘D’ shackle.
ii) Ball link with provision to fix arcing horn.
iii) Socket clevis with provision to fix arcing horn.
iv) Tower side arcing horn (fixed or adjustable).
v) Line side arcing horn.
vi) Compression type deadened cone.
The double tension hardware has in general the following components.
i) Ancho ii) Link.
iii) Anchor shackle connecting link and yoke plate.
iv) Yoke plate on tower side.
v) Tower side arcing horn connected to the yoke in between the two stacks of insulators.
vi) Two ball clevises connecting two insulator stacks to the tower side yoke.
vii) Two socket clevises connecting th most discs of the two insulator stacks to the line side yoke plate.
viii) Line side yoke plate with provision to fix line side arcing horn.
ix) Line side arcing horn fixed to the line side yoke plate in case of 132 KV and 220 KV lines or Corona control ring in case of 400 KV lines.
x) Clevis-Clevis to connect line side yoke plate to the compression type deadend tension clamp for 132 KV and 220 KV lines. Two clevis eyes in case of 400 KV lines.
xi) Two sag adjusting plates connecting clevis eyes to the anchor shackles on line side for 400 KV double tension hardware.
xii) Two anchor shackles connecting sag adjusting plates to the compression type deadend clamps, in case of 400 KV double tension hardware.
xiii) One compression type deadend tension clamp for 132 KV and 220 KV double tension hardware and two numbers for 400 KV double tension hardware.
r shackle connected to the tower crossarm.
e bottom
ension hardware is shown in Figure- 2.13
2.4.1.1 TECHNICAL REQUIREMENTS OF E.H.T. TENSION HARDWARE:
i. The tension hardware shall be suitable for use with Ball insulators with designation/shank pin dia of 20 mm.
ii. The minimum failing load of the hardware set shall be 95% of the breaking load of nductor
iii. The compression type deadened cone shall be compressible with 100 ton hydraulic compressors to obtain requisite results after compression with reference to dimensions and bondage.
iv. In case of 400 KV lines, the R.I.V. for complete string (i.e.,) including grading/corona rings, arcing horns, clamps etc. at 256 KV (rms) shall not be more than 500 Micro volts
v. The corona extinction voltage for complete string shall be 300 KV 2.4.4.5 INSULATORS:
Ball and socket type disc insulators are assembled to the 132 KV, 220 KV and 400 KV suspension and tension hardware, certain important design aspects and other details are indicated below :
Sl.
No.
Description 132 KV lines 220 KV lines 400 KV lines A typical 400 KV Double T
and socket type disc
co
1. Type of insulators Ball and socket type disc insulator
Ball and socket type disc insulator
Ball and socket type disc insulator 2. Dimensions of insulators of
suspensions string
255mm x 145mm 280mm x 145mm 280mm x 145mm 3. Dim nsions of insulators fo
ten n
5. Number of insulator disc per double suspension string
13
2 x 9 nos. 2 x nos. 2 x 23 nos.
6. Number of insulator discs per single tension string
10 nos. 14 nos. 24 nos.
7. Number of insulator discs per each double tension string
2 x 10 nos. 2 x 14 nos. 2 x 24 nos.
8. El o or 9. Electro Mechanical strength for
suspension string insulator
00
11,500 Kgs. 11,5 Kgs. 16,500 Kgs.
10. Total creapage distance of each disc insulator for suspension strings
280 mm 280 mm 315 mm
11. Total creapage distance of each disc insulator for tension string
280 mm 280 mm 330 mm
12. Minimum impulse dry withstand voltage (wave of 1 x 50 Micro second) for each disc insulator (I.E.C standard)
110 KV 110 KV 120 KV
13. One minute power frequency withstand voltage for each disc insulator 14. Power frequency puncture voltage
per each disc insulator
110 KV 15. Size and designation of bal pin
shank for suspension string discs
16 mm 16 mm 20 mm
16. Size and designation of bal pin shank for tension string discs
20 mm 20 mm 20 mm
17. Maximum Radio Influence Voltage at 10 KV (RMS) for each 18. Corona extinction voltage for
complete (RMS) string both suspension and tension strings
- - (RMS)
320 KV
19. Maximum RIV for complete
str b d
tension
- - 500 Micro volts
ing oth volts suspension an strings
A typical string insulator disc is shown in figure-2.14 with part-wise descriptions
2.4.4.6 GROUNDWIRE CLAMPS AND ACCESSORIES
Normally for 132 KV and 220 KV lines, only one Groundwire is used, while for 400 KV lines two Groundwires are required. One groundwire suspension clamp is required for each groundwire for every tangent tower. Each suspension clamp is provided with tinned copper earth bond which is in turn connected to the tower body. Two ground wire tension clamps are required per groundwire per each angle tower. Each of these tension clamps is provided with tinned copper earth bond, which is to be connected to the tower body. Groundwire midspan joints are used for jointing two pieces of groundwire. After fixing the two end portions of the groundwires to be jointed, the midspan compressor with suitable die set.
2.4.4.7 POWER CONDUCTOR ACCESSORIES
i) PRE-FORMED ARMOUR RODS :- The preformed armour rod re used at the
t e he r
condu hich is to be clipped in a su
Each set of preformed armour rods ge f 11 n
lines (PANTHER ACSR), 12 Rods for A ACSR) and 12 rods for 400 KV lines (MOOSE ACSR). ur rods are of helical shape and made of aluminium alloy w m tensile strength of 3500 Kg/ sq.cm. The armour rods can be fix uctor by hand. For 132 KV and 220 KV lines, either ball ended or parr re accepted. For 400 KV lines, parrot ball ended rods are speci ip strength of suspension clamp over the conductor wound with armour rods shall be not less than 25% of the ultimate tensile strength of the conductor. For 400 KV lines, the RIV, at 266 KV (rms) phase to ground shall not be more than 500 Micro volts.
ii) MIDSPAN COMPRESSION JOINTS :- The compression type joints are required for jointing two ends of two pieces of ACSR conductors. The compression joint consists of (a) outer sleeve made of Aluminium (extruded tube) and (b) inner sleeve made of Mild steel hot dip galvanized. After inserting the steel core portions of the conductors to be jointed into the steel sleeve, the same is compressed by means of 100 tonne hydraulic compressor fitted with suitable die set. The steel sleeve duly compressed with steel core portions of two conductors is fixed in the outer Aluminium sleeve alongwith the aluminium strands of both the conductors. Then the aluminium sleeve is compressed together with steel sleeve and aluminium strands by means of 100 tone Hydraulic Compressor fitted with suitable die set. Both the steel sleeve and the aluminium sleeves are compressed from round to hexagonal shape. The failing load of the compression joint shall be not less than 95 per cent of the breaking load of conductor. For 400 KV lines, the radio interference voltage at 260 KV rms, phase to ground shall shall not be more than 500 Micro volts
i) REPAIR SLEEVES:- The repair sleeve is of tubular shop with a sliding (removable) part known as a ‘Keeper’. If a few strands (not more than three) of the conductor are found to be cut or damaged, the repair sleeve is to be fixed to the conductor over the damaged portion and compressed by means of 100 ton hydraulic compressor fitted with suitable die set. The repair sleeves are made out of aluminium extruded sections.
s a ang nt locations. The armour rods
ctor w
are wound over t
spension clamp of the suspension hardware.
nerally consists o 220 Kv lines (ZEBR
The preformed armo hich has a minimu
ed over cond ot bill ended rods a fied. The sl
portion of powe os. rods for 132 KV
ii
The compressor die used for repair sleeve is the same as that used for midspan he repair sleeves als are compressed from round to hexagonal shape. The minimum failing load of re pair sleeves used in 400 KV lines shall have
micro volts at 266 KV (rms), phase to ground
ded and behave eccentric to the wind force and (iii) Aeolian vibration; the vibrations with frequencies from 3 to 12 HZ occur in the conductor and lead to fatigue failure at the root. As the aeolian vibrations are known to be most detrimental, the
ded and behave eccentric to the wind force and (iii) Aeolian vibration; the vibrations with frequencies from 3 to 12 HZ occur in the conductor and lead to fatigue failure at the root. As the aeolian vibrations are known to be most detrimental, the