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Insulation material for coil electrical isolation

Insulation material for coil electrical isolation

As mentioned in the induction furnace coil section, insulation material provided by our company is from a wide spectrum of composite compounds and grades. Here the properties and application is discussed more in detail.

Coil supports

Also called traverse or ruler, fixing the distance between coil turns and coil diameter during time is of composite insulation material which is a compound of fiberglass and resin epoxy having various properties according to the grades of the used fiberglass and resin like high electrical resistance to guarantee coil turns isolation, tensile and flexural strength to bear forces and tensions caused by electromagnetic fields and extremely low moist absorbing to maintain the properties.

 

 

Maximum

Water

Absorption

Content

 

Flammability

Class

Operation

Temperature

Flexural

Strength

CW/LW

Tensile

Strength

CW/LW

Electrical

Strength

 

Breakdown

Voltage

A/D-48.5

 Resin

(Matrix)

 

Reinforcement grade

NEMA3

type

composite

% UL94 Mpas Mpas KV/mm KV
0.25 H-B 140/130 345/415 245/275 27.5/17.7 45/40 Normal

epoxy

Woven Glass Fibers G-10 fiberglass
180/170 High temperature epoxy G-11
V-1 140/130 Fireproof epoxy FR-4
180/170 High temperature epoxy &

Fireproof

FR-5
0.60 V-0 140/120 125/125 55/55 11.8 40/15 polyester Glass Mat GPO-3
2.20 H-B 125/115 96.5/115 62/48.5 19.6/11.8 23/2.5 Phenolic Linen fibers CE/LE fiber

bony

Support drilling is done precisely using computer design plans by CNC machine.

 

All the mentioned supports of different grades can be provided in both raw and cut and drilled shape, by Araz Trans Co.

Special epoxy-based varnish

This liquid insulator is based on epoxy produced by Elantas, Italy and with easy usage (spraying) and desirable properties is very common among manufacturers. This single-material liquid is sprayed by air pressure pistol easily dried at environment temperature (air-dried) or outdoor space in half an hour at most ready to operate. This insulation liquid is used quite easily against to compound insulation liquids including base and hardener. The only point to consider is mixing with proper solvent up to maximum 3%.

Below table summarizes properties of the mentioned epoxy-based insulation liquid:

 

amount  the unit measurement

standard

 

quantity
960-1000 gr/lit DIN 51757 Density ( at 23°C)
≤ 5 mg IEC 62 at 23°C  

Water absorption

content

≤ 10 at 23°C , 30 min
≥ 140 KV/mm IEC 60464-2 after water

immersion

Electrical Strength
≥ 100 at temperature

above 23°C

15-20 min min & h – – – touch-dry Drying time at 23°C
2 h non Slip

mood

24 h fully dried
3-5 min min & h – – – touch-dry Drying time

at 80°C

15 min non Slip

mood

2 h fully dried

Electrostatic insulation powder

As mentioned in the coil section, electrostatic insulating powder used by Araz Trans Co. is introduced by Inductoterm company commercially called Inductoflex2M. The most outstanding characteristics of this epoxy-based insulation is durability against cracks and peeling duo to tension on the coil turns. High heat resistance, good electrical insulation and even adhesiveness to the surface while dispersed are other properties of the material. It can solely help insulate the coil and under standard conditions no liquid or tape insulations are demanded. The only problem to apply this insulation is the lack of equipments to do the process which are the special tool to disperse and the coil-sized stabilizing furnace.

Below table presents various characteristics of the Inductoflex2M :

the amount of the unit measurement

standard

quantity
Dark blue – – – – – – Color
0.25-0.30 mm – – – Layer thickness
1.25-1.30 gr/cm3 ISO 8130-2 Density

( at 23°C)

≥ 30 KV/mm IEC 60243-1 Electrical

Strength

200-220 °C – – – Preheating

temperature

object

200 °C

3-8 min

°C , min – – – Post curing

time &

temperature

Insulating tapes for coil isolation

Araz Trans uses various kinds of insulation tapes for coils relative to costumer demands and operation conditions. Below a  brief discription is presented:

Fiberglass Tape

This tape, also publicly called “silk tape”, is one of the most common types of insulating tapes for coils. Fiberglass tapes are composed of resin-less glass fiber strings. Not applying resin makes it more heat-withstanding up to 400-500 C degree.

The suggested wrapping overlap for silicon rubber tape is 50% (two-ply).

Silicon Rubber Tape

This rubber-based tape, among all othe coil insulation tapes, is the least moist-absorbant. On the contrary, low isolation capability and heat resistance are the weak points for this tape.

The suggested wrapping overlap for silicon rubber tape is 50% (two-ply).

Nomex Tape

Nomex is among meta-aramyd fibers with vast application for sensitive aims in sophisticated industry application. Against other usages in power industry (compounded with other insulating materials), for coil isolation according to urgent need to have flexibilty, it used solely which offers high electric isolation and low moist-absorbance but higher expenses.

The suggested wrapping overlap for silicon Nomex tape is 50% (two-ply).

Mica Tape

Based on Maskovit or Phlogopite, mostly mixed with this fiberglass or Teflon layers. Having highest resistance against heat amongst other tapes for coil isolation, this type has low insulating characteristic and higher moist absorbance and hence decaying probability.

The suggested wrapping overlap for Mica tape is 50% (two-ply).

Kapton Tape

Kapton tape, in comparison to other tape types, offer more reliability. High electrical isolation, almost no moist absorbance and relatively high heat resistance are the advantages of this tape. On the other hand, high isnulation expense is the most remarkable weakpoint for Kapton tape. Kapton tape is composed of thin poly-amid films with rough thickness of 25 to 50 micron.

The suggested wrapping overlap for 50 micron tape is 50% (two-ply) and for 25 micron is tape 75% (four-ply).

Below graph compares different insulation tapes from electric isolation level at operation temperature and the maximum tempered heat aspects:

Spacer (Segment)

For isolation aims, using insulating material in all electrified parts of the induction furnace is of high importance and inevitable. The slightest isolation issue in the electrical parts will lead in fault and melting interruption. One important isolation aspect is applying spacer or segment between coil turns. Aside from isolating turns, spacers help solidify the refractory. Spacers are made of Mika or fiberglass and are shaped in crescent or cubic form which are used in continuous and sectional way, respectively.

  • Mika spacers are more heat-resistant in comparison to fiberglass ones and henceforth more expensive to use.
  • Crescent spacers are more solid than the cubic ones.
  • Continuous crescent spacers are machined and placed on top of each other in beehive form with definite overlap (0-50%). The more the overlap is, the solidity and reliability is higher but in return, moist will run out of refractory more slowly while sintering.