dcsimg
Electrical Properties

Electrical Properties

As with all plastics, Desmopan® has a relatively low electrical conductivity. It can therefore be used as an insulating material in applications such as cable sheathing or cable connectors. By virtue of Desmopan®’s outstanding mechanical properties, all-TPU cables have even been produced as special constructions in isolated cases. The electrical properties, and particularly the electrical resistance and dielectric properties of Desmopan® thus have a relatively high importance.

Electrical measurements on Desmopan® are conducted solely on annealed specimens (specified annealing conditions must be observed for the individual Desmopan® grades). It must be borne in mind that the resistances and dielectric parameters are a function of the moisture content and the temperature of the specimens as well as of the measuring frequency. All the specimens must therefore be acclimatized prior to the measurement in accordance with the applicable standard (standard climate).

The electrical data required for Desmopan® are established in the Thermoplastics Testing Center (TTC), which can conduct the electrical tests set out below and is also available to external customers.

Electrical testing standards
Dielectric characteristics
DIN IEC 60250
DIN 53483
Electrostatic charging
DIN 53486
Electrical resistance (e.g. surface resistivity, volume resistivity)
DIN IEC 60093
VDE 0303 Part 30
DIN 53482
Dielectric strength
DIN IEC 60243-1
CTI/tracking
DIN IEC 60112
Arc resistance
ASTM D495
Electrolytic corrosion
IEC 60426
High voltage tracking resistance
DIN IEC 60587

Electrical resistances

The surface resistivity and the volume resistivity are the two key characteristic values that are typically measured for TPU to this end. Both values are measured to IEC 60093. The measurement setup is shown in the Thermoplastics Testing Center (TTC), together with a view of the specimen.

The surface resistivities that are measured for Desmopan® are between 1013 and 1015 Ω. The volume resistivity that is measured, by contrast, is between 1011 and 1015 Ω x cm. With both resistivities, the measured value similarly falls with the hardness. For grades with a hardness of approximately 70 Shore D, a value of 1015 is measured, falling to the lower value at the more flexible end of the product range for grades with a hardness of approximately 70 Shore A.

Dielectric properties

For TPU, it is the dielectric constant and the loss factor that are important.

The dielectric constant is an unnamed ratio which specifies the factor by which the capacity of a given capacitor increases if an insulating material is placed between the capacitor plates instead of a vacuum. It thus constitutes a measure of the capacity of insulating materials to separate electric charges from each other.

The dielectric loss factor, in turn, is a measure of the energy absorbed in the alternating field of the insulator. Both values are temperature and frequency-dependent and are determined on the basis of IEC 60250 in the test setup shown in the Thermoplastics Testing Center (TTC).

The dielectric constant values measured for Desmopan® are between 8.0 and 4.0. These fall from higher hardnesses towards lower hardnesses, in the same way as the resistance values. Polyether grades generally have slightly higher dielectric constants than polyester grades. One grade displays a slight fall in the value as the frequency increases.

The dielectric loss values measured for Desmopan® are between 0.10 and 0.03. The values are inversely proportional to the hardness, i.e. they increase from the hard grades towards the more flexible grades.

No notable differences are evident between polyether grades and polyester grades. The value increases with the frequency.

Tracking

Electrically conductive paths can form on the surface of solid insulating materials as a result of electrolytic impurities. These are the “tracks” that develop when a voltage is applied.

This tracking is measured in the form of the Comparative Tracking Index (CTI), shown in the Thermopastics Testing Center (TTC). All the Desmopan® grades measured to date have a CTI of 600.

Test piece:
≥  20 mm x ≥ 20 mm x ≥ 3mm
Test voltage:
between 100 V and 600 V (50 Hz) in 25-V steps
Test solution A (CTI A)
395 Wcm
Test solution B (CTI B)
198 Wcm
Drop interval:
30 s
Drop volume:
20 mm³
Failure criteria:
Current on breaking ≥ 0.5 A > 2s Material burns

Dielectric strength

This is the electric field strength at which breakdown occurs in the insulating material; it thus constitutes a measure of the insulating capacity of electrical insulators.

The test is conducted to IEC 60243 – 1 and is set out in a schematic diagram in the Thermopastics Testing Center (TTC).

The dielectric strengths of polyester Desmopan® grades increase from 22 to 32 kV/mm with an increasing hardness. The dielectric strength of polyether Desmopan® grades is higher. This is 35 kV/mm for lower hardnesses, rising to 38 kV/mm for higher hardnesses.

LOCATIONS & CONTACTS
Login
Register for more information
Forgot your password?