Electric insulator glass

Electric insulator glass can be designed in different types, such as suspension insulator, line posts, station posts and pin insulator for electrical systems.

Electric insulator glass is normally designed in suspension insulator, more and more glass suspension insulator used Europe and America.

The structure of Electric insulator glass

Electric insulator glass is made from toughened glass, suspension insulator is used in suspension insulator string on different voltages.

Electric insulator glass is usually used similarly as porcelain insulators on electrical systems for supporting and insulating.

What are the advantages of polymer pin type insulator?

As new high-voltage products, Polymer pin type insulator with many electrical performance advantages. Polymer pin type insulator can be called composite pin insulator, compared with the traditional porcelain pin insulators, weight polymer pin type insulator lighter, and transportation or installation process easier than porcelain pin insulator.

advantages of polymer pin type insulator

advantages of polymer pin type insulator

In addition, the surface of the shed polymer pin type insulator has a number, and the distance between the two shed relatively large. This design in the face of rain or dusty environment, allowing dust and water droplets falling more convenient, reduce the possibility of flashover occurred.

Polymer pin type insulator material used is silicone rubber, this material has a strong anti-UV properties. In some sunny areas with high UV index Africa, good UV resistance can ensure the safe operation of transmission and distribution lines.

Polymer insulator made of silicone rubber material can withstand strong impact, when faced with shootings and other emergency situations safer. Especially in a cold environment, the impact resistance polymer pin type insulator is an important factor in avoiding damage.

How long is insulator service life?

When customers select insulators, the aging of insulator and service life of insulator must be thought of, and this is also the insulator manufacturer focusing on.

Insulator service life:

Insulator products under the condition of the usage standard, and to maintain its performance is not lower than the factory standard, the minimum term is insulator service life. Glass insulator service life depends on the metal accessories, the service life of porcelain insulator and composite insulator depends on insulation parts. Glass insulator service life is longer than the porcelain insulators and composite insulators. The service life of composite insulator depends mainly on composite material aging.

composite insulator deadend type-Orient Power

composite insulator deadend type

We can study the definition of the ageing of insulators and the internal and external factors involved and reviews the general phenomena and the causes of it.

In order to reduce the expansion stress resulting from cement's expansion and prolong the life-span of porcelain insulator, a thin asphalt buffer layer is coated between the porcelain and the cement. The Statistics analysis of the composite insulators in service shows that the composite insulators have better electrical performance, anti-aging and good stabilization year by year.

Insulator inspecting technique and life management technique is the study issue of electric power industry at present. It is proved experimentally that aging of composite insulator is very slow, and can not threaten the service safety of overhead lines.

What is the dry arcing distance of insulator?

Dry arcing distance is linear discharge distance, namely, the shortest distance along the surface of the insulator sheds or the sum of the shortest distance.

Arcing distance (also called flashover distance): the shortest distance in the air external to the insulator between the metallic parts which normally have the operating voltage between them. Refer to IEC61109.

composite insulator dead end type-Orient Power

composite insulator dead end type

Insulator is generally end up and down had screw teeth insert, then there is the umbrella group, dry arc distance is along the teeth to the umbrella group of top has been connected to another screw tooth distance.

The dry arcing distance of an insulator is fixed value, even to the insulators having the same voltage. The dry arcing distance of an insulator depends on the system voltage, Operational environment and so on. For example, we suppose that in those areas where the thunder happens frequently the dry-arc distance should be added up to 1050mm from original 1000mm in 110kV line.

The dry arcing distance of insulators is very important. When customers come from all over the world order insulators from insulator supplier, they should provide drawings or requirement details, including the dry arcing distance of insulator, and then insulator supplier will design and manufacture the insulator product for them.

What is the creepage distance to the ground or specific creepage distance?

What is the creepage distance to the ground?

The creepage distance to the ground means the creepage distance of an insulator plus the height between an insulator and ground. (This is called overhead height.)

Some insulators should use the shelf when installed, some insulators use overhead steel pipe frame, such as aerial lightning arrester installed in power plant to use the steel pipe and then installed the insulation base. So the sum of the insulator creepage distance plus overhead height is creepage distance of the insulator to the ground.

composite insulator station post type-Orient Power

composite insulator station post type

What is the specific creepage distance of an insulator?

The specific creepage distance of an insulator refers to the ratio of the creepage distance of an insulator and the insulator’s highest running voltage; the ratio of the creepage distance (cm) and working voltage (KV) is called specific creepage distance.

For example: 3.1 cm/KV said above the ratio is 3.1.

Specific creepage distance is used to describe anti-pollution level. 3.1cm/kV is grade 4 anti-pollution. Insulators product if used on 10kv, the creepage distance is greater than 310 cm. 10kv is running voltage, and the voltage is typically calculated on the highest voltage (i.e., 12kv), so to meet 4 anti-pollution, namely the creepage distance can need up to 372 cm.

Specific creepage distance under the condition of 3.1cm/kV is IV filth level, and 2.5cm/kV is III filth level.

What is the creepage distance and protected creepage distance of insulator?

Creepage distance and protected creepage distance are main parameters for electrical insulator, especially creepage distance of insulator.

What is the creepage distance of insulator?

Creepage distance of insulator, also called the leakage distance, is the shortest distance between two conductive parts measured along the insulator surface. You can say that it is the creep path length of electric conducting department from the top of the insulator to the bottom of the metal department along the insulator surface, or the shortest distance of outer surface of the insulator insulation end to the other end.

The total creepage distance of an insulator shall be not less creepage distance requested by the pollution level for the site.

What is the protected creepage distance of an insulator?

Protected creepage distance of an insulator means part of the creepage distance on the illuminated side of the insulator which would lie in shadow if light were projected on to the insulator at 90°(or 45°in special cases) to the longitudinal axis of the insulator.

The creepage distance and protected creepage distance of insulator is common technical terms; we should know this knowledge before designing, manufacturing insulators.

Polymer insulator material

Mail insulating material for polymer insulator

In the past many years, a large variety of polymeric insulating materials have been developed, but only some have shown success in outdoor insulation. Now days, there are basically three classes that are in significant used:

1. Epoxy resins

2. Ethylene propylene rubbers

3. Silicone rubbers

Epoxy resins for polymer insulator

The epoxy resins have shown successful long term performance in clean environments, but under contaminated conditions their performance has been far from satisfactory. Therefore, epoxy resins use has been restricted to specific conditions. They are suitable for distribution class insulators up to about 69kV.

Ethylene propylene rubbers for polymer insulator

Three types of ethylene rubbers are in use for outdoor polymer insulator:

1: ethylene propylene monomer (EPM)

2: ethylene propylene diene monomer (EPDM)

3: co-polymer of ethylene propylene and silicone (ALLOY)

They are suitable for insulators up to 765kV. Their long term performance has been successful in clean environments.

Silicone rubber for polymer insulator

Silicone rubber has proven to be the most reliable polymer material for outdoor electrical insulation. It has three common types:

1. room temperature vulcanized(RTV)

2. high temperature vulcanized(HTV)

3. liquid silicone rubber(LSR)

Silicone rubber is able to maintain their hydrophobicity for longer periods of time. This is very important as it has the ability to suppress leakage current activity therefore preventing flashover and power system outages. Todays ,the trend is toward using silicone rubber for the housing of all types of overhead line polymer insulators.

Test for composite insulator

Test for composite insulator, there is the following test from the born of insulator to end user to use it in transmission line or distribution line:

1. Design tests

2. Type tests

3. Sampling tests

4. Routine tests

All the above composite insulator tests should be done in accordance with the requirement of IEC 1109, IEC 383, ISO 1460 and also the requirements of customers.

For design and type test for composite insulator

Design and type test should be done by the relevant Independent/International or National Testing/Standards Authority of the country of laboratory or manufacture (or ISO/IEC 17025 accredited laboratory). And the manufacturers will get a composite insulator certificate from laboratory or manufacture.

Test items of composite insulator for design and type test:

1. Tests on interfaces and connections of metal fittings

2. Assembled core load-time test

3. Test of housing: tracking and erosion test

4. Tests for the core material

5. Flammability test

6. Dry lightning impulse withstand voltage test

7. Wet power frequency test

8. Mechanical load-time test and test of the tightness of the interface between end fittings and insulator housing

Routine and sample test for composite insulator

These two tests for composite insulators can be done at the factory before shipment and should be done according to IEC 1109 and applicable latest IEC standards.

It concludes:

1. Verification of dimensions;

2. Verification of the locking system;

3. Verification of tightness of the interface between end fittings and insulator housing;

4. Verification of the specified mechanical load;

5. Galvanizing test (by Gravimetric method

Composite insulator materials

Composite insulator materials include the core material, metal end fittings materials and housing materials. Each material is to provide different performance and properties.

1. Core: The internal core of a non-ceramic composite insulator consists of a fiberglass reinforced plastic (FRP) rod. It is the primary mechanical load-bearing component of the insulator. The strength of the rod depends on the types of materials used, the diameter, and the percentage composition of glass fiber and impregnating resin. Generally, almost all manufacturers use E-glass (electrical) fibers and epoxy resin. ECR-glass (electrical chemical resistant) fiber is generally no longer used in the manufacturing process, but acid-resistant fiber is becoming available upon request. Acid resistant fiber may protect against brittle fracture caused by stress corrosion of the rod when the rod is exposed to moisture and corona discharge. Polyester and vinylester resins have been used but are uncommon.

During fabrication, the individual glass fibers are equally tensioned to axially align each fiber parallel to the rod axis. The fibers are placed in a resin matrix such that each glass fiber is impregnated with the resin. The combination is then cured at a high temperature, allowing the individual fibers to bond to the resin matrix. This manufacturing technology is known as pultrusion. Generally, 60 to 70 percent of the FRP rod volume contains glass fibers.

2. Metal End Fittings: The strength of a composite insulator not only depends on rod materials and rod diameter, but also on the metal end fittings material type and the bonding procedures used to attach the metal end fittings to the FRP rod. Metal end fittings should be made from a good commercial grade of iron or steel and should be galvanized in accordance with ASTM A153, “Standard Specification for Zinc Coating (Hot-Dip) on Iron and Steel Hardware”. Metal end fittings may also be manufactured from a good grade of stainless steel. Aluminum is not recommended.

Metal end fittings should be designed to effectively transmit the mechanical loads to the insulator core (FRP rod). The attachment of the metal end fittings to the FRP rod is important and should be performed with a symmetrically controlled crimping method that compresses the metal radially onto the rod without damage to the rod fibers or resin matrix. Excessive compression may crush the rod and cause de-bonding between the rod and the end fittings, which may reduce the mechanical strength of the insulator. Insufficient compression may cause slippage between the rod and the end fittings. It is critical that the manufacturer provide the utility with documentation that details quality control procedures and crimping machine control mechanisms that prevent FRP rod damage and metal end fittings slippage.

Metal end fittings should be properly sealed to prevent moisture contact with the FRP rod. This seal should never be broken during testing or otherwise.

ANSI C29.11, “Composite Suspension Insulators for Overhead Transmission Lines - Tests” defines the following testing procedures for composite suspension insulators to confirm the integrity of the metal end fittings interface:
*Prototype Tests:

Power Frequency Voltage Test

Sudden Load Release Test

Thermal Mechanical Test

Water Penetration Test

Steep Front Impulse Test

*Sample Test:

Mechanical Load Test

Galvanizing Test

*Routine Tests: Tension – Proof Test

The tensile strength of metal end fittings attached to the FRP rod should equal or exceed the specified mechanical load (SML) rating defined for the composite suspension insulator. Similar testing procedures to confirm the integrity of the metal end fittings interface for composite line post insulators are specified in ANSI C29.17, “Insulators - Composite - Line Post Type”.

3. Housing: The housing is composed of a sheath and weathersheds, both are made of a polymeric compound. The sheath covers the fiberglass core to protect it from the external environment while the weathersheds provide the required leakage distance and electrical insulation strength.

It is important when considering housing materials to determine which type of material is best suited for the insulator application. Housing materials are generally made from EPR or SR. An alloy material of EPDM and silicone additive is also available. The weathersheds and sheath may be bonded together during the vulcanization process or molded into one piece by injection molding. The sheath is generally bonded to the rod, but a void-free silicone grease interface is also available. The housing may be either bonded to the metal end fittings or sealed to prevent moisture ingress to the FRP rod.

Experience has shown that the performance of different formulations varies for a given environment. Therefore, the utility should obtain written verification from the manufacturer that the insulator housing material considered will provide satisfactory performance in the particular environment to which the insulator is to be subjected by the purchaser. SR housing materials have exhibited the best short-term flashover performance and are generally recommended in areas with heavy contamination.

As one of composite insulator manufacturers in China, our Composite insulator materials include housing –silicone rubber, core-FRP and end fittings-galvanized steel.

Guide for selection of insulator creepage distances to suit polluted conditions

Pollution level	Minimum nominal specific creepage distance(a) (mm/kV)(b)
I–Light	16
II–Medium	20
III–Heavy	25
IV–Very heavy	31

Notes:

1. For actual creepage distances the specified manufacturing tolerances are applicable (IEC 60273, 60305, 60433 and 60720).
2. rms value corresponding to the highest voltage for equipment (phase to phase).
3. In very light polluted areas creepage distances less than 16 mm/kV can be used depending upon service experience. 12 mm/kV seems to be a lower limit.
4. In cases of exceptional pollution a specific nominal creepage distance of 31 mm/kV may not be adequate. Depending upon service experience and/ or laboratory test results a higher value of specific creepage distance can be used.

electrolyte with moisture from rain or condensation. When the grease becomes saturated with dirt it must be removed and a new coat applied.

Greasing is not recommended for use with anti-fog insulator shed profiles.

The grease tends to get trapped in the grooves on the underside of the shed and bridged by conductive dirt forming on the grease surface thereby reducing the overall insulator creepage distance.

Calculation of specific creepage path

Typical creepage values for either cap and pin insulator strings or post insulators at 132 kV under very heavy pollution, classification IV, would be determined as follows:

Nominal voltage                                           132 kV rms

Rated voltage                                              145 kV rms

Maximum rated voltage phase to phase

Creepage (from Table)                                 31mm/kV

Test creepage distance                                145kV * 31mm/kV = 4495mm

From manufacturer’s details:

Typical substation insulator                          80 kN minimum failing load

Creepage                                                   330mm

Spacing distance                                        127mm

Number of insulators required to provide 4495 mm creepage using cap and pin porcelain string insulators =4495/330 = 13.6. Therefore the minimum total number of insulators per string would be 14. In this case failure of one unit would reduce the creepage distance to 4165 mm, equivalent to an effective value of 28.7 mm/kV @ 145kV-rated voltage. However, at the nominal system voltage of 132 kV the design value is maintained at 31.5mm/kV. Minimum length of suspension insulator string =14 * 127 = 1778mm. Alternatively, 15 insulators per string could be specified in order to maintain the recommended creepage distance at 145kV-rated voltage under a one insulator shed failure condition. This allows full overhead line operation between normal line maintenance outages at the expense of increased overall string length of 1905mm.