GB2306795A

GB2306795A - Apparatus for washing energised insulators

Info

Publication number: GB2306795A
Application number: GB9513821A
Authority: GB
Inventors: Yosuaki Ohata
Original assignee: Individual
Current assignee: Individual
Priority date: 1995-07-06
Filing date: 1995-07-06
Publication date: 1997-05-07
Anticipated expiration: 2015-07-06
Also published as: GB2306795B; GB9513821D0

Abstract

Energised insulators e.g. in a switchyard, are washed using a plurality of convergent nozzles. The convergent nozzles may have an inlet :outlet port ratio in the range 1.5:1 to 5:1 (Figure 1); a smooth convex inner surface between the inlet and outlet (Figures 2 and 3); or a straightening vane in the inlet (Figure 4). A plurality of nozzles in one manifold may be used (Figure 5). The convergent nozzles give high jet speeds leading to increased scattering of water as it strikes the insulators thus the amount of water flowing down the insulators and carrying contaminants is decreased and hence the chance of flashover is decreased.

Description

APPARATUS FOR WASHING AN ENERGIZED INSULATOR This invention relates to apparatus to wash energized insulators in outdoor suitchyards in electrical power stations and substations.

Insulators are used to insulate and support electrical conductors from the ground. When the surfaces of insulators are contaminated by sea salt or other electrolytic contaminants, flashover accidents which can lead to an interruption of power transmission are liable to occur due to a reduction of the voltage resistance of the insulators. To prevent flashover accidents, insulators are washed from time to time with the insulators energized or deenergized.

One type of apparatuses used to wash energized insulators has been fixed-nozzle washing apparatus. Fixed-nozzle washing apparatus comprises water discharge nozzles fixed around each of the insulators.

The nozzles are installed on fixed piping which supplies water to the nozzles providing the required safety distance between the energized parts and the nozzles. The water pressure supplied to the nozzles is 0.49 MPa for insulators of which the rated voltage is not higher than 275 kV, and 2.94 MPa for insulators of which the rated voltage is between 345 kV and 500 kV.

Each of the nozzles used for the fixed-nozzle washing apparatus has plurality of water discharge holes. Each of the water discharge holes consists of a conical part at the inlet side, and a straight tubular part which is connected at the outlet side of the conical part. The taper degree of the conical part is between 1/5 and 1/10. The length of the straight tubular part is three times of the diameter thereof or longer. The ratio(l/m) of the length of the straight tubular part(l) to the length of the conical part(m) is between 3:2 and 2:3.

Fixed-nozzle washing apparatus splashes water from the nozzles over the entire surface of an insulator, at one time, to wash away contaminants.

The voltage resistance of an insulator is lowered by wetting during washing. Therefore, keeping the voltage resistance during washing (hereinafter called washing withstand voltage) as high as possible is required to perform washing without causing flashover.

The washing withstand voltage of horizontally arranged insulators is high, whereas that of vertically arranged insulators is low, because washing water, which becomes conductive by dissolving the washed contaminants, drips along the insulator surface. The washing withstand voltage is significantly reduced when dripping water forms continuous bridges between the sheds of an insulator. The washing withstand voltage is also low when an insulator is washed with high precipitation, because high precipitation increases dripping water and continuous bridges between the sheds are more liable to form.

On the other hand, wind deflects and disperses water jets during their travel. The lower the flow rate of the water jet, the greater the deflection and dispersion. An insulator washing apparatus must sufficiently clean an insulator by reaching the required amount of water under a desired wind velocity to the insulator, inevitablely discharging much water.

Under such contradictory conditions, enhancing the washing withstand voltage by simply reducing the precipitation rate is difficult, therefore the provision of larger spacing between the sheds or other provisions have to be made to the insulator to be washed for keeping the washing withstand voltage high. However, such provisions make the size of an insulator larger.

It has been known that the washing withstand voltage with an applied water pressure at the nozzles (hereinafter called applied pressure) of 2.94 MPa is higher than that with an applied pressure of 0.49 MPa.

According to this fact, the inventor contemplated that the enhancement of the washing withstand voltage by higher applied pressure was due to the higher speed of the water jets when they collide against the insulator (hereinafter called collision speed) which could lead to an increase in scattering water and a decrease in dripping water. However, higher applied pressure calls for a higher pressure rating of the pipings, pumps, or other components of the insulator washing apparatus.

Accordingly, the inventor realized that the collision speed of the water jets could be enhanced, without raising the applied pressure, by enhancing the initial speed of the water jets and reducing the speed loss of the water jets during their travel.

The primary object of the present invention is to provide hot-line insulator washing apparatus which provides high washing withstand voltage on an insulator, without any special provisions to the insulator for hot-line washing, and without raising the applied pressure.

The foregoing object is accomplished in one embodiment by providing an apparatus for washing energized insulators, having a plurality of nozzles fixed at the lateral side of the insulator; each of the nozzles has an interior water passage which comprises an inlet port, an outlet port, and a convergent part connecting the inlet port and the outlet port. The ratio(D/d) of the diameter of the inlet port(D) to the diameter of the outlet port(d)(hereinafter called the diameter ratio) is set to be within the range of 1.5:1 to 5:1 and preferably from 2:1 to 4:1.

The outlet port side portion of the convergent part comprises a convex surface which smoothly continues to the outlet port.

There is a flow straightening vane situated within the inlet port.

By setting the diameter ratio within the range of 1.5:1 to 5:1, the initial speed of the water jet produced from the nozzle can be enhanced, therefore the collision speed of the water jet can be enhanced, at the same time the reach of the water jet can also be enhanced.

By forming the outlet port side of the convergent part with a convex surface which smoothly continues to the outlet port, the initial speed of the water jet produced from the nozzle can be enhanced, therefore the collision speed of the water jet can be enhanced, at the same time the reach of the water jet can be enhanced.

By providing a flow straightening vane in the inlet port, the turbulence which is liable to occur at the inlet port can be eased, therefore a water jet of laminar flow can be produced. With such a water jet of laminar flow, the speed loss of the water jet during its travel can be reduced, therefore the collision speed of the water jet can be enhanced, at the same time the reach of the water jet can be enhanced.

By enhancing the collision speed of the water jet, the amount of water which scattters away from the insulator is increased and the amount of water which drips along the insulator surface is decreased when the water is splashed on the insulator, whereby the washing withstand voltage is enhanced.

By enhancing the reach of the water jet, the required amount of water to reach the insulator under windy conditions is reduced, therefore the precipitation rate to the insulator is reduced. The reduction of the precipitation rate to the insulator reduces the amount of dripping water and contributes to the enhancement of the washing withstand voltage.

The preferred embodiments of the invention will now be described by way of examples with reference to the following drawings in which: Fig.l is a sectional view of the nozzles of an embodiment of the present invention.

Fig.2 is a sectional view of the nozzles of another embodiment of the present invention.

Fig.3 is a sectional view of the nozzles of a further embodiment of the present invention.

Fig.4 is a cut-away view of the nozzle of a further embodiment of the present invention.

Fig.5 is a vertical sectional view of an example of a nozzle manifold.

Ffg.E is a vertical sectional view of a nozzle of prior art.

Fig.7 is a graph showing the relation between the diameter ratio and the nozzle efficiency.

Fig.8 is a graph showing the relation between the water flow rate and the vertical reach of the water jets.

Fig.9 is a plan view of the arrangement of the specimens used for the washing withstand voltage test.

Fig.10 is an elevation view of the arrangement of the specimens used for the washing withstand voltage test.

Fig.11 is a graph showing the relation between the salt deposit density on an insulator and the washing withstand voltage.

With reference now to the drawings and more particularly to Figures 1 to 4 thereof, the typical examples of the nozzles made for the experiments are illustrated.

Fig.1 shows a sectional view of a nozzle 1 of an embodiment of the present invention.

In Fig.1, nozzle 1 has an interior water passage which comprises an inlet port 11 of which the diameter is D and the length is L, an outlet port 12 of which the diameter is d and the length is 1, and a convergent part 13a which has a conical shape and connects inlet port 11 and outlet port 12.

Nozzle 1 has a screw 14 on the outside circumference at the inlet side thereof which enables the nozzle to be connected to a piping.

The ratio of the diameter(D) of inlet port 11 to the diameter(d) of outlet port 12 is set to be within the range of 1.5:1 to 5:1, and preferably from 2:1 to 4:1.

The surface of outlet port 12 is smoothly finished with a reamer, otherwise the pressure loss due to the friction when water passes through outlet port 12 may become significant which leads to a reduction of the initial speed of the water jet.

The length of outlet port 12 is from equal to double of the diameter thereof. When the length of outlet port 12 is longer than double of the diameter thereof, pressure loss due to the friction when water passes through outlet port 12 may become significant. When the length of outlet port 12 is shorter than the diameter thereof, dispersion of the water jet produced from the nozzle may become significant.

The length of inlet port 11 is greater than the diameter thereof. When the length of inlet port 11 is shorter, turbulence generated when water is admitted to inlet port 11 will not be straightened in inlet port 11 and a water jet with turbulence is produced from the nozzle.

A water jet with turbulence is subject to more dispersion and loses its speed during its travel, therefore collision speed of the water jet is reduced.

It is appreciated that the effect of the embodiment in Fig.i is that the loss of water pressure which occurs when water is admitted to inlet port 11 is reduced by easing the flow speed in inlet port 11. By reducing the water pressure loss in inlet port 11, the initial speed of the water jet produced from the nozzle can be enhanced without raising the applied pressure, therefore the collision speed of the water jet can be enhanced, at the same time the reach of the water jet can also be enhanced.

By enhancing the collision speed of the water jet, the amount of water which scatters away from the insulator is increased and the amount of water which drips along the insulator surface is decreased when the water is splashed on the insulator, whereby the washing withstand voltage is enhanced.

By enhancing the reach of the water jet, the required amount of water to reach the insulator under windy condition is reduced, therefore the precipitation rate to the insulator is reduced. The reduction of the precipitation rate to the insulator reduces the amount of dripping water and contributes to the enhancement of the washing withstand voltage.

Fig.2 shows a sectional view of nozzle 1 of another preferred embodiment of the present invention which has one significant difference from the first embodiment previously described.

The difference between the nozzle of Fig.2 and the first embodiment in Fig.l is that there is a convergent part 13b which has convex surface with a radius of R which smoothly continues to outlet port 12, instead of conical convergent part 13a.

It is appreciated that the effect of the second embodiment in Fig.2 is that the loss of water pressure which occurs when water is admitted to outlet port 12 is reduced by easing the diminishing of the stream due to a sudden change in the direction of the water stream. By reducing the water pressure loss in outlet port 12, the initial speed of the water jet produced from the nozzle can be enhanced without raising the applied pressure, therefore the collision speed of the water jet can be enhanced, at the same time the reach of the water jet can also be enhanced.

Fig.3 shows a sectional view of nozzle 1 of a further embodiment of the present invention which has one significant difference from the first embodiment in Fig.1 and the second embodiment in Fig.2.

The difference between the nozzle of Fig.3 and the first embodiment in Fig. 1 or the second embodiment in Fig.2 is that there is a convergent part which comprises a conical surface 13a, and a convex surface 13b with a radius of R which smoothly continues to outlet port 12, instead of conical convergent part 13a in the first embodiment or convex convergent part 13b in the second embodiment.

It is appreciated that same effect of the second embodiment can be achieved by the third embodiment.

Fig.4 shows a cut-away view of the nozzle of a further embodiment af the present invention which has one significant difference from the three embodiments in figures 1 to 3 previously described.

In Fig.4, a flow straightening vane 15 is situated in inlet port 11.

Flow straightening vane 15 preferably has a length greater than the diameter of inlet port 11 and preferably divides inlet port 11 into 4 to 8 sections.

Flow straightening vane 15 can ease the turbulence which is liable to occur at inlet port 11 when water is admitted into inlet port 11 and can produce a water jet of laminar flow. With such a water jet of laminar flow, the speed loss of the water jet during its travel can be reduced due to less interaction with air, therefore the collision speed of the water jet and the washing withstand voltage can be enhanced.

Fig.5 shows a sectional view Or an example of a nozzle mainfold 20.

In Fig.5, nozzle mainfold 20 has a screw 21 which is adapted to be connected to piping, and a plurality of nozzle holding holes 22 at the opposlte side of screw 21 which is adapted to be connected with screw 14 of nozzles 1, providing the desired mutual angles between nozzles 1.

With use of nozzle manifold 20, a plurality of nozzles 1 can be compactly connected to piping and the discharge direction of plural nozzles 1 on nozzle manifold 20 can be easily adjusted at the same time.

In order to investigate the effect of the present invention, various experiments have been carried out using many specimen nozzles. Table 11 and 1-2 show the dimensions of the specimen nozzles (examples from 1 to 30) in accordance with the present invention. The examples from 1 to 8 are in accordance with the first embodiment in Fig.1, the examples from 9 to 22 are in accordance with the second embodiment in Fig.2. the examples from 23 to 30 are in accordance with the third embodiment in Fig.3.

The examples from 31 to 35 are prior nozzles of which the shape is as shown in Fig.6.

Referring to Fig.6 which shows a sectional view of an example of prior nozzles, the nozzle has three water discharge holes of a, b, and c which are radially oriented and arranged in a rou.

Table 1-1

Example d D D/d l m n R L Fig. No.

No. (mm) (mm) (mm) (mm) (mm) (mm) (mm) 1 2.5 9.2 3.68 3 14 No No 42 Fig.1 2 3.0 9.2 3.07 3 14 No No 42 Fig.1 3 3.5 9.2 2.63 4 14 No No 41 Fig.1 4 4.0 11.9 2.98 4 36 No No 24 Fig.1 5 4.5 11.9 2.64 5 35 No No 24 Fig.1 6 5.0 11.9 2.38 5 35 No No 24 fig.1 7 5.5 11.9 2.16 6 34 No No 24 Fig.1 8 6.0 11.9 1.98 6 34 No No 24 Fig.1 9 1.5 6.8 4.53 2 14 No 38 14 Fig.2 10 1.8 6.8 3.78 2 14 No 40 14 Fig.2 11 2.5 6.8 2.72 3 14 No 30.5 14 Fig.2 12 3.0 6.8 2.27 3 14 No 33.5 14 Fig.2 13 3.5 6.8 1.94 3 14 No 36.5 14 Fig.2 14 2.1 9.2 4.38 2 14 No 29 18 Fig.2 15 2.5 9.2 3.68 3 15 No 35.5 18 Fig.2 16 3.0 9.2 3.07 3 15 No 38.5 18 Fig.2 17 3.5 9.2 2.63 4 15 No 41.5 18 Fig.2 18 4.0 9.2 2.3 4 14 No 39 20 Fig.2 19 4.5 9.2 2.04 5 14 No 43 19 Fig.2 20 5.0 9.2 1.84 5 14 No 48 19 Fig.2 21 5.5 9.2 1.67 6 14 No 54 18 Fig.2 22 6.0 9.2 1.53 6 14 No 62 18 Fig.2 23 2.5 9.2 3.68 3 24 14 30.5 18 Fig.3 24 3.0 9.2 3.07 3 24 14 33.5 18 Fig.3 25 3.5 9.2 2.63 4 23 14 36.5 18 Fig.3 26 4.0 11.9 2.98 4 22 14 39 24 Fig.3 27 4.5 11.9 2.64 5 21 14 43 24 Fig.3 28 5.0 11.9 2.38 5 21 14 48 24 Fig.3 29 5.5 11.9 2.16 6 20 14 54 24 Fig.3 Table 1-2

Nozzles transform the pressure head of water into velocity head.

According to Bernoulli's equation, the velocity head of water (V2/2g m) is equivalent to the pressure head (h m), where: V : Velocity of water (m/sec) g : Acceleration of gravity (m/sec2) h : Pressure head of water (m) Nozzle efficiency is defined as the ratio of the total head of water at nozzle's downstream side to that at nozzle's upstream side.

Therefore, nozzle efficiency can be expessed as equation 1 when the velocity head of water at the nozzle's upstream side is negligible:

where C : Nozzle efficiency hl: Pressure head of water at the nozzle's upstream side (m) V2: Velocity at the nozzle's downstream side (m/sec) Obviously from equation 1 the greater the nozzle efficiency, the greater the water jet velocity at outlet port 12 (the initial speed of the water jets), then the greater the collision speed. Measuring the initial speed of the water jets can determine the nozzle efficiency.

Since the flow rate (Q) is the product of the cross-sectional area of the nozzle outlet port (A) and the initial speed of the water jet (V2), measuring the flow rate can determine the initial speed of the water jets. Therefore, substituting Q/A into V2 of equation 1 obtains equation 2:

Accordingly, measuring the flow rate can determine nozzle efficiency.

Nozzle efficiency was measured using the embodiment nozzles which were provided with and without flow straightening vanes 15 in inlet port 11.

Flow straightening vanes 15 had length equal to inlet port 11 and divided inlet port 11 into 4 sectional.

Fig.7 shows the relation between nozzle efficiency and the ratio of the inlet port diameter(D) to the outlet port diameter(d) from the experiment using the nozzles of the examples from 9 to 22 in accordance with Fig.2, and the examples from 23 to 30 in accordance with Fig.3.

According to Fig.7, nozzle efficiency increases significantly when the diameter ratio (Did) exceeds 1.5:1 and reaches 0.90 when the diameter ratio is 2.0:1. When the diameter ratio exceeds 5:1, the nozzle efficiency shows a saturating tendency getting close to 1.0, which is the theoretical upper limit, therefore no remarkable enhancing effect of the nozzle efficiency by an increase in the diameter ratio can be expected.

Flow straightening vanes 15 did not enhance the nozzle efficiency.

The effect of the shape of the convergent part on the enhancement of the nozzle efficiency was also studied.

The nozzle efficiency was compared between the nozzles of the examples from 1 to 8 in accordance with Fig.1 and the nozzles of the examples from 23 to 30 in accordance with Fig.3, and the result was as shown in Table 2.

Table 2

Example d D Did 1 m n R L Nozzle No. (mm) (mm) (mm) (mm) (mm) (mm) (mm) Efficiency 1 2.5 9.2 3.68 3 14 No No 42 0.869 23 2.5 9.2 3.68 3 | 24 14 30.5 18 0.992 2 3.0 9.2 3.07 3 14 No No 42 0.863 24 3.0 9.2 | 3.07 3 24 14 33.5 18 0.980 3 3.5 9.2 Z.63 4 14 No No 41 0.884 25 3.5 9.2 | 2.63 4 23 14 36.5 18 0.931 4 4.0 11.9 2.98 4 36 No No 24 0.869 26 '1.0 11.9 2.98 4 22 14 39 24 0.976 5 4.5 11.9 2.64 5 @ 35 No No @ 24 0.878 27 4.5 11.9 2.64 @ 5 @ 21 14 ! 43 24 0.989 6 5.0 11.9 2.38 @ 5 35 No @ No 24 0.848 28 5.0 11.9 2.38 5 21 14 48 24 0.953 7 5.5 11.9 2.16 6 34 No No 24 0.843 29 5.5 11.9 2.l6 6 20 1 14 54 24 0.949 8 6.0 11.9 1.98 6 34 @ No No 24 4 0.869 30 6.0 11.9 1.98 6 20 14 62 24 0.912 According to Table 2, forming the convergent part with a convex surface which smoothly continues to outlet port 12 can enhance the nozzle efficiency.

Based on the above results, I made an experiment to study the reach of the water jets produced by the nozzles.

The experiment was made using the nozzles of the examples 9, 10, 14, 15, 16, 17, 26, 27, 28, 29, and 30 with and without flow straightening vanes 15 in inlet port 11, and the examples from 31 to 35 (of which the number of water discharge holes was one) without flow straightening vanes 15, under a lateral wind velocity of 7 m/sec, discharging water vertically upwards with applied pressure of 0.98 and 2.94 MPa. Flow straightening vanes 15 had a length equal to the diameter of inlet port 11 and divided inlet port 11 into 4 sections.

The vertical distance from the nozzles where the water jets were laterally deflected by 50cm was defined as the vertical reach of the water jets. This definition was due to the requirement that the water jets should hit an insulator to be washed under a specified wind velocity with sufficient impact to achieve a sufficient cleaning effect, as well as to reduce the amount of dripping water.

Fig.8 shows the experiment results as the relation between the water flow rate on a log scale and the vertical reach of the water jets.

Curve A and B indicate the experiment results using the embodiment nozzles in accordance with Fig.2 and Fig.3 with an applied pressure af 0.98 MPa. Curve A is for the nozzles provided with flow straightening vanes 15 and curve B is for the nozzles without flow straightening vanes 15.

Curve C and D indicate the experiment results using the prior nozzles in accordance with Fig.6 without flow straightening vanes 15. Curve C is for the case of an applied pressure of 2.94 MPa and curve D is for the case of an applied pressure of 0.98 MPa.

According to Fig.8, the vertical reach of the water jets of the embodiment nozzles with an applied pressure of 0.98 MPa(Curve A and B) was longer than that of the prior nozzles with an applied pressure of O.

98 MPa(Curve D); the vertical reach of the water jets of the embodiment nozzles with flow straightening vanes 15 under an applied pressure of O.

98 MPa(Curve A) was longer than that of the prior nozzles with an applied pressure of 2.94MPa(Curve C), when compared on the basis of the same water flow rate. Flow straightening vanes 15 enhanced the vertical reach of the water jets.

Therefore1 it was found that the embodiment nozzles could produce water jets of longer reach with lower flow rate and applied pressure, thus an insulator washing apparatus of less water consumption and lower rated pressure could be realized.

Longer reach nozzles could reduce the water precipitation to an insulator, whereby the washing withstand voltage could be increased.

Based on the above results, the washing withstand voltage test was executed arranging specimens simulating actual insulator washing apparatus.

Fig.9 shows the plan view of the specimens arrangement for the washing withstand voltage test. In Fig.9 three water distributing pipes L, R, and 0 were provided at the lateral side of the insulator 4 at the circumferential positions at the mutual interval of O.666;r radian.

Each water distributing pipe had two pipe ends to install a plural number of nozzles 1 at a lateral distance from insulator 4 of 1.7 m and 2.5 m.

Fig.10 shows the elevation view of the specimens arrangement for the washing withstand voltage test.

In Fig.10, insulator 4 was installed on mount 3; the insulator was rated at 400 kV having an effctive height (height of porcelain part) of 4200 mm, a creepage distance of 12600 mm, a core diameter of 380 mm, an average diameter of 440mm. The insulator had alternating-type sheds of which the larger shed diameter was 510 mm, the smaller shed diameter was 480 mm, and the spacing between the larger sheds of 85 mm. The insulator did not have either drip-cutting sheds nor ribs on the under surface of the sheds.

In Fig.10, riser pipes L and 0 are shown being overlapped at the left side of insulator 4 for the convienience of making the drawing. Riser pipe L has the nozzles from L1 to L4, riser pipe 0 has the nozzles from 01 to 04, riser pipe R has the nozzles from R1 to R4. Each nozzle discharges a solid water jet which is longitudinally distributed on the insulator.

The distance from the energized part (top of the insulator) to nozzles 1 at the top of the riser pipes was 4m which was more than the required safty distance for a rated voltage of 400 kV.

Table 3 shows the outlet port diameter and the water discharge rate at the applied pressure of 0.98 MPa for the nozzles used for the washing withstand voltage test.

Table 3

d Water Discharge Rate at 0.98 MPa Nozzle No.

(mm) (#/min) L 1 4.0 32.7 L 2 3.0 18.4 L 3 2.1 9.0 L 4 1.5 4.6 O 1 4.0 32.7 O 2 3.0 18.4 O 3 1.5 4.6 O 4 1.5 4.6 R 1 3.5 25.1 R 2 2.1 9.0 R 3 1.5 4.6 R 4 1.5 4.6 Nozzles 1 used for the washing withstand voltage test were examples 9 and 14 in accordance with Fig.2 and examples 24, 25, and 26 in accordance with Fig.3 provided with flow straightening vanes 15.in inlet port 11 which had length equal to the diameter of inlet port 11 and divided inlet port 11 into 4 sections. The nozzles were installed on nozzle manifold 20 and then connected to the riser pipes.

The washing withstand voltage test used water with a specific resistivity of 5 k Q -cm, with applied pressure of 0.833, 0.98, 1.274, and 1.67 MPa.

Pollution was applied to the insulator by splashing on pollution liquid containing salt (sodium chloride) and fine soil.

Fig.11 shows the results of the washing withstand voltage test, as the relation between salt deposit density an the insulator on a log scale and washing withstand voltage, plotted with applied pressure as a parameter. Fig.11 also shows the washing withstand voltage characteristics derived from the criterion, which is based on the test results of the prior nozzles with an applied pressure of 2.94 MPa (hereinafter called the criterion value).

The washing withstand voltage is defined as the highest voltage with no flashovers during 4 consecutive washings.

In Fig.11 the washing withstand voltage of the embodiment nozzles, with an applied pressure of 0.98 MPa, was higher than the criterion value by 74% with a salt deposit density of 0.04 mg/sq.cm, 67% with a salt deposit denstity of 0.07 mg/sq.cm, and 36% with a salt deposit density of 0.14 mg/sq.cm. The permissible limit of pollution at the aimed withstand voltage (phase-to-earth) of 267 kV for a rated voltage (phase-to-phase) of 400 kV was more than 0.12 mg/sq.cm, with an applied pressure of 0.98 MPa. The permissible limit of pollution by the criterion value was 0.05 mg/sq.cm.

It was also found that the higher applied pressure gave higher washing withstand voltage; the increase of an applied pressure from 0.98 to 1.67 MPa enhanced the washing withstand voltage by 33% with a salt deposit density of 0.14 mg/sq.cm.

The cleaning effect by washing for one minute was 94X with a salt deposit density before washing was 0.035 mg/sq.cm (therefore the salt deposit density after washing was 0.002 mg/sq.cm), while the cleaning effect was 98.1% with a salt deposit density before washing was 0.29 mg/sq.cm (the salt deposit density after washing was 0.005 mg/sq.cm).

The economical effect of the reduction in applied pressure was estimated on the basis of the following design conditions: Rated voltage: 400 kV Object of washing: 6 bushings 6 coupling capacitors 6 lightning arresters 6 suspension strings 6 tension strings Washable wind velocity: 10 i/sec According to this estimate, reducing the applied pressure fro 2.94 MPa to 0.98 MPa can reduce the cost of the washing apparatus by 40 %.

While a few embodiments of the invention have been illustrated and described in detail, it is particularly understood that invention is not limited thereto or thereby.

Claims

1. Apparatus for washing an energized insulator, having a plurality of nozzles fixed at the lateral side of the insulator; each of said nozzles has an interior water passage which comprises an inlet port, an outlet port, and a convergent part connecting said inlet port and said outlet port; the ratio of the diameter of said inlet port to the diameter of said outlet port being set in the range from 1.5:1 to 5:1.

2. Apparatus as defined in claim 1, wherein said ratio of the diameter of said inlet port to the diameter of said outlet port being set in the range from 2:1 to 4:1.

3. Apparatus as defined in claim 1, wherein the outlet port side portion of said convergent part comprises a convex surface which smoothly continues to said outlet port.

4. Apparatus as defined in claim 2, wherein the outlet port side portion of said convergent part comprises a convex surface which smoothly continues to said outlet port.

5. Apparatus as defined in claim 1, further comprising a flow straightening vane situated within said inlet port.

6. Apparatus as defined in claim 2, further comprising a flow straightening vane situated within said inlet port.

7. Apparatus as defined in claim 3, further comprising a flow straightening vane situated within said inlet port.

8. Apparatus as defined in claim 4, further comprising a flow straightening vane situated within said inlet port.

9. Apparatus for washing an energized insulator, having a plurality of nozzles fixed at the lateral side af the insulator; each of said nozzles has an interior water passage which comprises an inlet port, an outlet port, and a convergent part connecting said inlet port and said outlet port; the outlet port side portion of said convergent part comprising a convex surface which smoothly continues to said outlet port.

10. Apparatus as defined in claim 9, further comprising a flow straightening vane situated within said inlet port.

11. Apparatus for washing an energized insulator, having a plurality of nozzles fixed at the lateral side of the insulator; each of said nozzles has an interior water passage which comprises an inlet port, an outlet port, a convergent part connecting said inlet port and said outlet port, and a flow straightening vane situated within said inlet port.

12. Apparatus as defined in claim 5, wherein said flow straightening vane has a length which is more than the diameter of said inlet port and divides said inlet port into 4 to 8 sections.

13. Apparatus as defined in claim 6, wherein said flow straightening vane has a length which is more than the diameter of said inlet port and divides said inlet port into 4 to 8 sections.

14. Apparatus as defined in claim 7, wherein said flow straightening vane has a length which is more than the diameter of said inlet port and divides said inlet port into 4 to 8 sections.

15. Apparatus as defined in claim 8, wherein said flow straightening vane has a length which is more than the diameter of said inlet port and divides said inlet port into 4 to 8 sections.

16. Apparatus as defined in claim 10, wherein said flow straightening vane has a length which is more than the diameter of said inlet port and divides said inlet port into 4 to 8 sections.

17. Apparatus as defined in claim 11, wherein said flow straightening vane has a length which is more than the diameter of said inlet port and divides said inlet port into 4 to 8 sections.

18. Apparatus as defined in claim 4, further comprising a nozzle manifold which has an entrance hole adapted to be connected to piping, a plurality of exit holes for connecting the inlet ports of said nozzles thereon, and a water passage between said entrance hole and exit holes.

19. Apparatus as defined in claim 8, further comprising a nozzle manifold which has an entrance hole adapted to be connected to piping, a plurality of exit holes for connecting the inlet ports of said nozzles thereon, and a water passage between said entrance hole and exit holes.

20. Apparatus as defined in claim 15, further comprising a nozzle ~manifold which has an entrance hole adapted to be connected to piping, a plurality of exit holes for connecting the inlet ports of said nozzles thereon, and a water passage between said entrance hole and exit holes.

21. Apparatus for washing an energized insulator substantially as described herein with reference to the accompanying drawings.