Aerospace & Defense Technology - October 2022 - 14

eVTOL Technology
With relatively low-energy corona
effects, connectors that use conductors
with large radii and designs that avoid
sharp points and edges help minimize
air ionization.
To protect against air ionization
breaking down dielectric between pins,
each pair of conductor pins must maintain
an adequate clearance distance as
measured through air. These values will
change as altitude and temperatures
change. Electric discharges can also
occur on or close to the insulation surface.
A localized, partially conductive
path on the insulation surface is termed
" arc tracking. "
To minimize electric discharges
along the insulation's exterior, each
pair of conductive parts (including the
binding surface of equipment) must
maintain adequate creepage distance
as measured on the insulation surface.
Creepage distance is typically equal to
or larger than clearance distance. Minimum
creepage distance can be determined
by the insulation's Comparative
Tracking Index (CTI).
(3) Avoiding arc tracking damage -
Designers need to minimize breaches
in insulation to avoid electrical arcing
between wires.
Current on the outer surface of polymeric
insulators has the ability to create
carbon tracks that damage insulation.
Carbon tracks can cause the insulator
to lose its dielectric properties and
become an electric transmitter instead.
Electrical arcing can then occur across
the conductive path, resulting in power
loss with a high probability of ignition.
As noted above, maintaining proper
creepage distance and using insulation
materials that maintain their dielectric
properties in HV conditions are critical.
(4) Handling high network operating
voltages (>3kV DC) - Designers need
to select relays and contactor components
that can withstand extreme electrical
stress.
Higher network operating voltages
impose significant demands on
relays and contactors used for propulsion
motor power switching, battery
charging management, comfort heating
for passengers, and other auxiliary
functions. HV relays and contactors
are available to meet demanding peak
14
Plug
Reception
(6-Position Shown)
Housing
Threaded
Coupling
Ring
Wire
Contact
Cavities
(6-Position Shown)
Wire
Hex
Nut
Figure 1. HV connectors protect adjacent pins from arcing by using a male insulation ring that surrounds
the female part prior to electrical contact. (Courtesy TE Connectivity)
load capacity, operating temperature,
coil efficiency, short-circuit protection,
breaking capacity, and other critical
requirements, such as robust shock and
vibration performance.
(5) Dealing with skin effect - Designers
need to minimize opposing eddy currents
to reduce the effective resistance of
conductors at higher frequencies.
When determining proper shielding
and filtering for electromagnetic
compatibility (EMC), designers must
account for skin effects - the tendency
of AC to flow close to the surface of
a conductor. Skin effect is the result of
eddy currents induced by the changing
magnetic fields of alternating current
and, therefore, is a factor in nearly every
AC design. Printed circuit board (PCB)
traces and other aspects of AC power
circuits can be designed to negate skin
effect, but expert planning is required.
(6) Managing size and weight constraints
- Designers need to select smaller
components to trim aircraft loads.
Components employed in high-power
electrical energy storage and management
in industrial applications tend
to be hefty. Fortunately for aircraft,
high-efficiency relays and contactors
are available that can handle higher
voltage and amperage within a compact
footprint. For example, well-known
KILOVAC high voltage relays and contactors
from TE Connectivity (TE) offer
voltage ratings up to 70kV DC and current
ratings up to 1,000 Amps (A) while
providing a useful size-to-power ratio.
Compact cables, terminations, and
mobilityengineeringtech.com
connectors are also available to meet
demanding size, weight, and power
(SWaP) requirements.
Thermal Challenges
(7) Managing thermal issues -
Designers need to dissipate heat in
composite structures to create a stable
electrical/electronic environment.
Dissipating heat in composite structures
is difficult. Pick-up voltage (VPI)
and coil resistance (RC) change as
the temperature of wires and relays
change. To ensure electrical stability,
the designer must determine the
steady-state characteristics for the
temperature and voltage combination
of a DC relay's operating conditions.
The same is true for AC applications,
although their VPI varies less with
temperature than DC relays. This
evaluation ensures proper product
selection.
(8) Battery charge cycles - Designers
need to enable higher energy transfer
rates by optimizing heat distribution
and balance.
High Power Charging (HPC) for
direct current (DC) presents a challenging
electric load profile in eVTOL
and UAM applications. Individual
components are subjected to temperature
extremes at resistance points along
the HV path. For HPC system safety, a
simulation can apply dynamic load
profiles along the complete HV path
to identify potential thermal bottlenecks.
Every microohm (µΩ) of resistance
counts. Areas to reduce resistance
Aerospace & Defense Technology, October 2022

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Aerospace & Defense Technology - October 2022

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