Download final1-template-publishable-summary-pdman

PDMAN
Partial Discharge Management In Compact Insulation
Systems
State of the art – Background
Electrical systems used in aircraft have previously
been used at reasonably low voltages which have
not been associated with a significant risk of
electrical discharge. A move towards More Electric
Aircraft (MEA) has increased the load requirements
and quantity of power electronics on-board
modern aircraft. These additional power
requirements have led to an increase in system
voltage, placing the components at increased risk
of electrical discharges occurring. Through this
push to increase performance, the requirements to
ensure they operate safely and reliably remain the
same. This project focused on the means to
eliminate, control and evaluate partial discharge in
power electronic components.
The use of any high voltage system on an aircraft
introduces a risk of damage from electrical
discharge. Partial discharges are small discharges
that do not completely bridge a gap between two
electrodes and can occur in a range of locations,
such as within voids in machine and actuator
winding encapsulation systems, around sharp
edged electrodes and on the surfaces of insulating
material across which an electric field is present.
Partial discharge is difficult to detect, yet the
presence of partial discharge can reduce the
service life of a system by degrading insulation.
Repetitive discharge events can cause irreversible
mechanical and chemical deterioration of the
insulating material. Damage can be caused by the
energy dissipated by high energy electrons or ions,
ultraviolet light from the discharges and ozone
attacking the insulation. The chemical
transformation of the dielectric can also tend to
increase the electrical conductivity of any
surrounding dielectric material and can increase
the electrical stress in the remaining unaffected
insulation, leading to an acceleration of the
breakdown process.
The ideal insulation system design would see
partial discharge eliminated and to some extent
the above issues can be managed through careful
design of converter and selection of insulation
materials. However, the low air density of a low
pressure / high temperature environment
experienced by many machine insulation systems
is still likely to make elimination of partial
discharge an option that can only be achieved
through significant compromise in power density.
The alternative to eliminating partial discharge is
the evaluation of the insulation system to ensure it
remains resilient to partial discharge over the
duration of its life, i.e. partial discharge can exist
without compromising operational performance.
The manner in which to evaluate the ability of an
aerospace insulation system to fulfil this role is,
however, not clearly defined by standards which
are designed to cover machines operating in a
standard industrial environment.
Objectives
This project aimed to progress the state of the art
in aerospace power electrical component design by
delivering the following outputs / innovations:
•
Providing clear design guidelines for the
selection of insulation systems for use in wound
components and connecting components for a
range of environmental conditions along with
illustrative guidance on how the choice influences
the power density of the component
•
Demonstrating the key mechanisms
associated with the ageing of wound components
and connecting components to support best
practice in the selection of insulation systems and
the development of appropriate test
methodologies for use during equipment
qualification
•
Delivering recommendations for test
procedures required to support equipment
qualification and assessment during series
production. These recommendations, where
appropriate, will be based on existing IEC guidance
in this area but will be modified to reflect the
challenges associated with deployment in an
aerospace system.
Description of work
WP1 began with the definition of a reference
system. This system included a wound component
representative of a typical electric motor or
generator used in commercial aircraft along with
suitable connecting components. In addition to the
components it was also important to define a
range of operating conditions; such as pressure,
temperature, humidity and electrical loads. These
were all defined to be representative of a real
flight cycle. In parallel to defining the system to be
investigated, a series of models were developed to
simulate the partial discharge behaviour under a
range of operating conditions. These models
became the basis for the first draft of the design
tool.
WP2 saw the requisition of a number of test
samples that were representative of the reference
system. These samples ranged from twisted pairs,
motorettes and fully assembled stators. In addition
to the large quantity of reference samples a
number of alternative design motorettes were
ordered to compare the relative performance of
different materials. WP2 mostly comprised
experimentation, with all the samples being
benchmarked for Partial Discharge Inception
Voltage (PDIV) and several investigations into the
effects of environment and voltage waveform on
the PDIV. It was quickly discovered that there were
issues with impulse testing according to IEC61934
when the sample was at low pressure. The
database of results accrued during WP2 was also
used to optimise and validate the suite of design
tools.
WP3 was predominantly focused on the effects of
several ageing mechanisms on the insulation
performance of the components. The ageing
mechanisms identified as key for investigation
were:
Thermal Ageing: Thermal degradation of
polymeric insulation can occur because of many
different processes. The objective was to
determine at which temperature there would be a
significant decrease in the dielectric performance
of the insulation system as a whole.
Thermal Cycling: Aside from the risk of
elevated temperatures causing thermal
degradation, there is also a risk of mechanical
stress on the insulation due to differential thermal
expansion. This is especially true for secondary
flight control systems that may be sat at ambient
temperatures (as low as -55°C) before being
energised.
Vibration: Degradation could occur
through friction or fatigue.
Electrical Ageing: Predominantly caused
by operating at voltages above PDIV where the
cumulative effect of discharges can result in the
erosion of the insulation.
A number of samples were aged using the above
mechanisms to determine at which point they
would become an issue from a partial discharge
perspective. After each ageing phase the samples
were tested for PDIV, subjected to a high humidity
environment, an overvoltage applied and their
insulation resistance checked.
Results
The knowledge gained from the project has
resulted in a series of design guidelines to help
better inform the design of insulation systems for
aerospace components. Specifically, the findings
were used to develop a bespoke version of the
qualification procedure in IEC 60034-18-41. This
procedure is more relevant to the types of wound
component used in aerospace environments.
Another major output of the project is the design
tool which will enable different insulation designs
to be compared at the early design stage.
It is expected that, pending SAE approval, the
knowledge gained from the project will be
disseminated in an SAE Aerospace Recommended
Practice. This information should benefit the wider
aerospace community and help to advance the
state of the art.
a) Timeline & main milestones
1 - Kick-off meeting (M1)
2 - Development of reference system (M2)
3 - Agreement of sample types / materials to be
tested in WP2/3 (M4)
4 - Receipt of test information from WP2 to
improve design tool accuracy (M9)
5 - Agreement on manufacturing process
techniques to be investigated in WP2 (M8)
6 - Development of ageing test rigs (M6)
7 - 12 month review (M12)
8 - Project closeout (M30)
b) Environmental benefits
By improving the design of insulation systems the
overall power density of machines can be
improved. This will have an effect on the efficiency
and mass of the components and ultimately have a
positive impact on the fuel efficiency.
c) Maturity of works performed
The main outputs of the project will provide many
benefits for the topic manager by aiding their
design and qualification procedures. This will
enable the next generation of electrical systems to
be developed faster and cheaper as well as
ensuring they remain safe. Increased power
density should bring performance benefits such as
a reduction in fuel consumption and a reduction in
CO2 emissions.
Project Summary
Acronym: PDMAN
Name of proposal: Partial Discharge Management In Compact Insulation Systems
Technical domain: SGO
Involved ITD
Grant Agreement: 338528
Instrument: Clean Sky JU
Total Cost: EUR 482359.2
Clean Sky contribution: EUR 361769.4
Call: SP1-JTI-CS-2012-03
Starting date: 01/10/2013
Ending date: 31/03/2016
Duration: 30
Coordinator contact details: Ian Cotton. [email protected], +44 0161 306 8735
Project Officer:
Antonio Vecchio
[email protected]
Participating members