Mica tapes and mica paper
The only insulation that survives partial discharge for thirty years
RHOMICA conductor and main-wall tapes for stator bars and coils up to 220 kV, built for your VPI or resin-rich process rather than sold as one fixed construction.
- Thermal class 155 / 180 / 200
- VPI and resin-rich
- 15 – 40 mm widths
- To IEC 60371
Which mica tape does your process need?
The process decides the tape, not the other way round. Tell us whether you impregnate after taping or press a resin-rich build, and the choice narrows to one or two constructions.
| RHOTEK grade | Process | Construction | Specify it when |
|---|---|---|---|
| RHOMICA.flex | VPI and resin-rich | Mica paper on glass fabric | General stator bars and coils, taping around tight radii |
| RHOMICA.therm | Resin-rich | Mica paper, glass fabric and PET film | Coils pressed to final dimension before cure |
| RHOMICA.por | VPI | High-porosity mica paper on glass | Thick main walls that must take up resin completely |
| RHOMICA.cond | VPI and resin-rich | Fine mica paper, polyimide backed | Turn and conductor insulation inside the slot |
| RHOMICA.cp | All processes | Semi-conductive tape, graded resistance | Corona protection and end-winding stress grading |
Why mica, and why nothing else will do
Every organic insulation erodes under partial discharge. Mica does not, because it is a mineral. That single property is why it has held the main wall of high-voltage machines for a century, and why no polymer has displaced it.
- Mineral platelets resist the electrical erosion that destroys organic film
- Thermal class 155, 180 or 200 depending on carrier and resin system
- Carrier and resin matched to your taping tension and impregnation process
- Conductor and main-wall tapes specified together as one insulation system
Where mica tape is specified
Mica goes wherever the voltage is high enough that partial discharge, not heat alone, decides how long the winding lasts.
Turbo and hydro generators
Main-wall and conductor insulation for stator bars up to 220 kV, where a rewind costs more than the machine earns in a year.
High-voltage motors
Form-wound coils from 3.3 kV upward, in both VPI and resin-rich manufacture.
Traction motors
Class H builds for rail and heavy haul, where vibration and thermal cycling run together.
Wind turbine generators
Insulation systems qualified for 25 years of offshore service with no planned rewind.
Dry-type transformers
Barrier and layer insulation where a higher thermal class allows a smaller core.
Fire-survival cable
Mica tape barriers that keep a circuit alive while the cable around it burns.
Typical technical properties
Representative values for a 0.14 mm VPI main-wall tape, tested to IEC 60371-2. Full datasheets are issued with every quotation.
| Property | Test basis | Typical value |
|---|---|---|
| Tape width | Mechanical | 15 – 40 mm standard |
| Thickness | IEC 60371-2 | 0.08 – 0.20 mm |
| Mica content | IEC 60371-2 | 40 – 50 % by weight |
| Resin content, VPI | IEC 60371-2 | 5 – 9 % |
| Resin content, resin-rich | IEC 60371-2 | 32 – 38 % |
| Volatile content | IEC 60371-2 | < 1 % |
| Tensile strength | IEC 60371-2 | ≥ 50 N / 10 mm |
| Breakdown voltage | IEC 60243 | ≥ 2.5 kV per layer |
| Thermal class | IEC 60085 | 155 (F), 180 (H), 200 (N) |
| Carrier | Construction | Glass fabric, PET film or polyimide film |
A typical 11 kV stator coil
Conductor and main-wall tapes are quoted as a pair, because thermal expansion, resin chemistry and taping tension have to agree across the whole build.
| Position in the coil | Grade | Why that one |
|---|---|---|
| Conductor insulation | R1077-09 | Calcined mica paper on glass fabric, standard turn insulation |
| Conductor, tight radii | R1015-09 | Uncalcined paper, higher flexibility around the nose |
| Conductor, Class H | R1090-10 | Polyimide backed, for 180 °C continuous service |
| Main wall, VPI | R2099 | Standard main-wall tape for vacuum pressure impregnation |
| Main wall, thick build | R2035 | High porosity, so resin reaches the full wall thickness |
| Main wall, resin-rich | R3009-14 | B-stage epoxy, pressed and cured to final dimension |
Supplied the way your taping head runs
Tape that will not feed is worthless however good the mica is. Slitting and winding happen in-house, so width tolerance, roll tension and splice count stay ours to control.
Slit tape rolls
From 15 mm width, wound to your core size and traverse length.
Wide rolls
For hand taping and repair work where machine feed is not used.
Mica paper
Uncoated calcined and uncalcined paper for your own converting.
Rigid mica sheet
Pressed muscovite and phlogopite board for heaters and barriers.
Corona protection
Semi-conductive and stress-grading tapes matched to the main wall.
Splice-free winding
Long-length rolls specified when a splice would stop the taping head.
Why buyers move their mica tape to RHOTEK
The process comes first
Tell us VPI or resin-rich, your taping tension and cure schedule. The construction is set to that, not pulled from a fixed catalogue.
Conductor and main wall together
Both tapes quoted as one system, so the chemistry and expansion behaviour agree across the coil.
Samples before qualification
Trial rolls for your own taping trials, so the first production bar is not the first test.
Documentation that passes audit
Certificates of conformity, batch traceability and test data with every delivery.
From enquiry to first delivery
Tell us the machine
Voltage class, thermal class, VPI or resin-rich, and the tape widths your heads accept.
Get a system and a sample
We propose conductor and main-wall tapes as a pair, with datasheets and trial rolls.
Qualify and release
You run taping and impregnation trials, we adjust the build, then agree tolerances and call-off.
Mica tape questions
Why is mica still used when modern polymers exist?
Because mica is a mineral and does not erode under partial discharge. Every organic insulation degrades when partial discharge is present, and above roughly 6 kV it always is. No polymer film has displaced mica in the main wall of a high-voltage machine for that reason.
What is the difference between VPI and resin-rich mica tape?
A VPI tape carries very little resin, typically 5 to 9 per cent, because the winding is impregnated after taping. A resin-rich tape carries 32 to 38 per cent B-stage resin and is pressed and cured to final dimension. The two are not interchangeable: a VPI tape in a resin-rich process gives a dry, porous wall.
What is the difference between calcined and uncalcined mica paper?
Calcined paper has been heat treated to drive off bound water, which raises the thermal class and the discharge resistance. Uncalcined paper is more flexible and conforms better around tight radii, so it often appears in conductor insulation while calcined paper carries the main wall.
Which thermal class do I need?
Class 155 (F) covers most industrial motors, Class 180 (H) is normal for traction and modern generators, and Class 200 (N) is specified where the hot-spot margin is tight. The class comes from the carrier and resin system, not from the mica.
Do you supply corona protection and stress grading tapes?
Yes. Semi-conductive slot corona protection and graded end-winding stress control tapes are supplied matched to the main-wall build, because the two have to be compatible chemically and dimensionally.
What tape widths and roll lengths are available?
15 to 40 mm is standard, slit to your tolerance and wound to your core size and traverse length. Where a splice would stop the taping head we specify long-length splice-free rolls.
Can you match an existing tape we already use?
Usually. Send the incumbent designation, a datasheet if you have one, and ideally a sample roll. We match construction, resin content and thermal class, then send trial material for your own qualification.
What is the minimum order and lead time?
MOQ depends on width and construction, and trial quantities for qualification are available in small volumes. Send your requirement through the form and we will confirm MOQ, lead time and price for your build.
Get a mica tape quote
Send the machine rating, thermal class and whether you run VPI or resin-rich. Our materials engineers reply with a conductor and main-wall proposal, datasheets and a price, normally within one working day.
- Phone
- +91 20 6000 0000
- [email protected]
- Head office
-
Lodha Signet 1, Premier Colony Road
Sector Kalyan, Mangaon, Navi Mumbai
Thane, Maharashtra 421204
India