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FAQ

Use our FAQ section to answer questions about our products and their use

FAQ

1. Is there any product spray or resin that can be applied into and upon porcelain insulators that have chipped to preserve the insulator’s properties?

If there is a crack or fissure in the porcelain, you must change the unit, since the dielectric has been drilled. If there is an overflow or a chipping in one of the sheds or in the bushing base, you can use the following to fully restore the shed or bushing:

100 parts of ARALDIT GY 6010
22 parts hardener HY 95

Note 1. This chemical product is corrosive and can cause severe irritation to the skin and eyes. It must be handled with caution. After handling the product wash your hands thoroughly.

Note 2. To give viscosity to the mix and make it mushy to facilitate application, you can add alumina or powdered silica sand with an ASTM 270 sieve.

Note 3. It is very important to clarify that the restoration work in any insulator assembly is short-term, while replacement units are acquired and installed to ensure longevity.

2. Is it appropriate to use pin type insulators for circuits with a voltage equal to 34.5kV and located 14.760ft above sea level?

At 4.500 MASL the flashover voltage values and the basic insulation level (BIL) decrease due to the reduction of atmospheric pressure which makes air ionization conditions more favorable.

In this case pin type insulators can be used without any problem; however it should be noted that the electrical characteristics described in the catalog are no longer valid because these are calculated for heights between 0 (zero) and 1.000 MASL (3.280 ft).

A correction factor must be applied to find the true basic level of insulation and dry flashover voltage at the calculated altitude (see ANSI C29-1 standard).

In high-elevation areas, if a high keraunic conduct creates holes in the pin type insulators due to atmospheric discharge, it is recommended pin type insulators be replaced with line post insulators, since these are electrically impenetrable and will improve radically the reliability of the circuit.

3. What is the approximate BIL of a chain of 4 insulators; and is it the same as the BIL of an individual unit increased fourfold?

You cannot multiply by 4 the BIL of an individual unit to obtain the equivalent BIL of a chain of 4 units. The electric field distribution on the chain is not linear and the tables developed for this purpose should be consulted.

4. What are the differences between the GAMMA bushings references 5209 and 5275?

The 5209 is a bushing type 15-18kV. It is equal to 5275 but features an RF enamel that has been applied internally and in the base seat.

5. An insulator in a substation suffered a lightning strike that broke one of the sheds. To repair it, we used NORDBAK BRUSHABLE WHITE CERAMIC manufactured by LOCTITE. Is this procedure sufficient to repair the shed?

The type of material used to glue the pieces together may be any kind of resin, epoxy putty or Araldite (which support UV radiation), since their main purposes are the following: not to leave sharp edges that generate electrical noise; to standardize the creepage distance that was altered after losing a piece of bel); to standardize the surface aesthetically and not leave gaps that accumulate pollution. What is most important is to ensure that the surface fractures in the sheds did not generate deep cracks in the insulator body, which, in the case of a switch, can lead to an explosion or flashover for loss of insulation or leakage of the insulating element (be it gas or oil). If it is proven that the piece has not suffered internal damages that may have compromised its integrity (including a fortiori a switch under high temperatures and pressures), there is no problem in having pasted up the pieces of sheds with some glue or epoxy putty. We suggest conducting a very strict control of the bushing to verify the absence of any leaks and to avoid accumulating contamination (deposits of dirt or fungus growth). In addition, it is important to carry out a thermography test to observe the repair to the affected area, with the aim to prevent and avoid future failures.

6. What characteristics are different in the insulation of HVDC systems?

The only difference with these insulators is the creepage distance, which should be very high (values close to 50mm/KV), since contamination in the presence of an unidirectional and constant electric field “sticks” to the surface insulator, increasing the negative effect. To prevent corrosion of the ironworks (which is accelerated due to the unidirectional electric field) a properly galvanized exterior is required.

7. Questions about radio-influence: Is there a standard value of RIV for different voltage levels? Why is it important for an insulator design to meet the value specified in the standard? What impact is there in the insulator operation when a value of RIV is below under the provisions of the standard?

As a general rule each insulator design has a value of influence radio. Look at the different ANSI models in our catalogs. It prevents the insulator generate noise at high frequencies that can affect telecommunications. If the value is lower, it means it will generate less noise and therefore will interfere less in telecommunications.

8. How should one dispose of porcelain insulators?

Insulators removed from distribution or transmission lines can be discarded in landfills. Or they can be ground or milled for use as filler in refractory material, mortar or as construction fill, given the high stability characteristics in the porcelain. Note: In the case of insulators containing metal parts, the ironwork should be separated. The porcelain can then be used for the purposes above and the ironworks can be used as scrap in smelting processes.

9. Can the test of steep wave front in air for insulators – as stipulated in the IEC 61211 standard Insulators of ceramic material or glass for overhead lines with a nominal voltage greater than 1000 V, Impulse puncture testing in air – result in a variation?

The IEC 61211 standard for the test of drilling for air-pulses in insulators states that a pre-calculated impulse voltage and monotonic pulse wave cut by the insulator flashover should be applied. The wave front must be adjusted to obtain the specified peak value. Besides the peak value, there is no requirement for the shape of the wave front. As indicated above, the waveform to be applied is not specifically defined, though the idea is to apply a test approach comparable to what it was given in previous requirements of 2500 kV/us, found in other specifications. It is for this reason that the laboratory should make the necessary adjustments so that the wave applied is as comparable as possible to that required.

10. What happens if longer or shorter spigots are used than those recommended for mounting pin type insulators?

When the spigot is shorter, a flashover may occur at a lower voltage than defined in the specifications. If the height of the spigot is greater than the distance arc, the flashover occurs at the voltage defined in the specification of the insulator, regardless of whether the height of the spigot is further increased.

11. Explain why VFIC in insulators for 35 kV is 170 kV and for 45 kV is 200 kV, do not include voltage of 300 kV in the norm?

As established in the norm, most of the voltages induced by lightning strikes near the line are below the value of 300 kV. This is a reference value, as the discharges may have varying magnitudes depending on a number of factors. That is why the technical standards for distribution levels have established insulation values for the different voltage levels , namely: Nominal Max Tension of Basic Insulation Level System of 15.5 kV, 110 kV, 25.8 kV, 150 kV, 38 kV, 200 kV, 250 kV, 48.3, 72.5 250 kV. These insulation values are sufficient to ensure good performance of the equipment against possible discharges that may occur. However the possibility exists that discharges could occur at or above 300 kV, although there are very few possibilities according to the established levels. Surge arresters (lightning rod) also help to protect equipment by limiting the residual voltage to which they are subjected.