Rectangular copper wire

Hello all. In Medium voltage motors is commonly used rectangular copper wires insulated with a film of PETTP and Mica.

Can you explain what is the use of the 2 insulators? I always thought that the mica was the insulation that gives to the film the high dielectric strength and corona effect, and that the PETP was the carrier with good, but less dielectric strength than mica.

But one manufacture of this rectangular copper wire told me that the PETP was the responsible for the high dielectric strength. Which one is the correct answer?

Another question is, what is the best insulation method for Medium Voltage motors? 3 layers of mica petp film overlapped by 33%? 1 butt lapped by 66%?

Many thanks.

The main consideration in selecting an insualted wire is what is the end use, the required thermal rating, and the environment. Rectangular wires can be coated with the same enamel or varnishe insluations that round conductors are generally coated with. Whlle some large round wire may also be wrapped wiht vairous fibers, tape, or paper (coated and non-coated) products, you see this more often with rectangular wires which are used in larger motors and transformers.

When you do a 33% overlap you would have the effect of 3 layers. I don;t think you could have a single butt lap and 66% at the same time with a single tape because a butt lap by name means that it is "edge to edge."

to make it easy I took the following from the Sam Dong Web site and I am sure that other insulated wire manufacturers and insulation suppliers have similar information.



Sam Dong Special insulation materials, such as Glass yarn, Polyester-Glass yarn and Kapton, are lapped on bare conductors/tube or enameled wire for both rectangular and round wire and then, impregnated with epoxy.

With the partially cured epoxy - insulating material after winding, the wires are adhered to each other during processing in the baking oven to provide a very strong finished product. This special insulated rectangular wires are used for generators and special motors which require superior heat and vibration resistance.

Single or Double Glass Yarn Insulated Rectangular Wire

Non-Alkali glass yarn (E class) has superior physical characteristics and heat resistance and is used for nuclear power generators and traction motors.

Polyester-Glass Yarn Insulated Rectangular Wire

Polyester-glass yarn has excellent physical characteristics, superior heat resistance and especially superior flexibility thus it is predominantly used for stator coil of turbine generator.

Mica Tape Insulated Rectangular Copper Wire

Mica-Polyester compounds generally comprise Mica paper on which a polyester film coat (PETP) is spread using an epoxy resin. Mica paper is a type of paper composed only of small strips of Mica with no admixture or bonding material (100% Mica).

Sam Dong supplies a comprehensive range of mica covered rectangular copper wires that are extensively used in the electrical and electronic industry. Our range is available in various standard as well as customized specifications at industry leading places.

Mica or PET + Mica Covered Rectangular Copper Wire is suitable for class ‘F’ (155°) insulation and it is applicable for manufacturing fields as below.

Application of Mica Covered Rectangular Conductors
•High & Low Voltage Motors
•Generator windings
•Dry Type Transformers

Enamel - Glass Yarn Insulated Rectangular Wire

Enamel-glass yarn insulated rectangular wire is enameled, covered by glass yarn then, impregnated with epoxy. Such a wire is mostly used for generators as well as industral motors, designed for high thermal and mechanical loads at high operation voltages.

Kapton Insulated Rectangular Wire

Kapton (Polyimide film) insulated rectangular wire is designed for use in applications involving high operating thermal & voltage and such wire is used in aerospace and automotive applications, relays and traction motors, etc.

The Rectangular wires in motors are used to reduce the overall machine size and to limit the centrifugal forces. The size of slot in motor depends on the Electric and magnetic loading of machine and directly affects the performance of machine. Rectangular wires are easy to install and take less space in comparison to circular conductors. Due to less space between them there will be controlled vibrations which can damage the mica layers.
The use of PETP tape serves two purposes. One it is a dielectric and seconds it has good mechanical properties. Definitely the mica has higher dielectric strength and high operating temperature in range of 850deg.C. On the same time it is brittle and loose in nature. The motors are always subject to high vibrations and air noises which can easily damage the fragile mica layers which always bond over glass tapes. The twisting and turning aging can damage the fragile mica. The PETP tapes keep the mica at place and not let it fall during machine operation which can cause premature dielectric failures.

Regarding the following "The Rectangular wires in motors are used to reduce the overall machine size and to limit the centrifugal forces. The size of slot in motor depends on the Electric and magnetic loading of machine and directly affects the performance of machine. Rectangular wires are easy to install and take less space in comparison to circular conductors." this might be true in some motors but since some motors are very tiny, they do not use rectangular wire. In most cases, rectangular wire is only used in ver large hoursepower motors and probably because the larger conductor can carry more voltage and heavier load. Some rectangular wire is hollow so coolants can pass through the coils. Rectangular wires cannot be wound in some of the same configurations as round wire simpley because is it generally much larger in cross sectional area and a square or rectangular item does not bend or twist as easy as a round wire. While a large round wire may be as large as 4-6 mm it is not unusual for rectangular wire to be 20 mm wide by 5-6 mm thick. I am not sure how rectangular wire will allow you to reduce the centrifugal force .