Community Research and Development Information Service - CORDIS


HVCPA Report Summary

Project ID: 619012
Funded under: FP7-JTI
Country: Italy

Final Report Summary - HVCPA (High Voltage Connector for PWM Application)

Executive Summary:
Objective of the Research
Topic objective was to demonstrate feasibility of an interconnection system (electrical connectors) suitable to work under specific and unusual electrical parameters when connected to a PWM Generator
A preliminary State of Art Analysis was made followed by fundamental Project documents like DJD, supported by preliminary tests on different materials as product validation
We met expected results and even a bit better than expected in terms of electrical performances. We were also able to compare different materials (PEEK and ceramic) under Partial Discharge Test, togheter with the use of a specific copper alloy able to reach higher temperature compared to what normally used in the connector’s Industry.
Conclusions, suggestions
Our connectors have accomplished requested performances and we could foresee room for improvements, to be of course verified and validated.

Project Context and Objectives:
Over the last years has started the need on commercial aircrafts to replace hydraulic systems with electrical ones. This approach has led to the development of equipment able to carry high powers towards motors, actuators, and other devices. The general trend is to increase the Working voltage to 230 VAC RMS, +/-270 Vdc and 540 PWM. The aim of this project was to design an innovative connectors compliant with 540 volts PWM in an aeronautical environment, keeping in consideration constraints such as dimensions and weight without downgrading mechanical and electrical performances. Therefore that connector has to be able to withstand electrical, environmental and mechanical constraints. The new design is based on the aeronautical standard EN 3645-001 (where applicable).

Electrical constraints:
- Arrangement: 4 crimp contacts
- Current Rating: as per the tables in the attached documents:
Tab A: Permanent Intensity Profile;
Tab B: Usual Intensity Profile).
-Working Voltage: See the attached documents.
-Voltage Proof Test: See the attached documents.
-Partial Discharges Test: See the attached documents.
- Contact resistance: 2 mΩ max.
- Insulating resistance: 5000 MΩ min.
- IP rating (coupled connector): IP 67 according to EN 60529
Environmental conditions:
- working temperature (continuous): (-65 ÷ +200)°C
- max. working temperature for short time (60s min) : 260°C
- max. ambient Temperature: 135°C

Mechanical constraints:
- mechanical life: > 500 mating/unmating cycles
-overall dimensions: smallest size (according to EN3645-001)

Other constrains (from the Reference standard EN3645):
The pair of connectors is characterized:
• By shell to shell bottoming
• By the triple threaded and self-locking coupling system
• By plugs with shielding ring providing protection against radio electrical interference
• By scoop proof shell.
• The connectors are polarized by means of keyways and keys; polarization shall be obtained before the male contacts enter insert of the female contacts and before the coupling ring is engaged.
• The visual check of coupling is obtained by masking of a red color band on receptacle.
• The receptacle housing will be Square flange type.
• The coupling ring is permanently fitted to the plug and allows coupling and uncoupling of the connectors.
• The plug is fitted with a self-locking mechanism and a grounding spring device ensuring electrical continuity between the coupled connector housing.
• An anti-decoupling device shall be provided to maintain complete coupling.
• The connector housings shall be one-piece. They shall contain teeth at the rear over their entire periphery and shall accommodate the rear accessories. The receptacle shall be fitted with a seal for sealing the coupled housings.
• The coupling ring shall be designed so that the male and female contacts engage when it is turned in a clockwise direction and disengage when turned anticlockwise. The coupling threads may have a lubricant a Full locking of the connectors shall occur at about 360°. On completion of tightening of the coupling ring, mechanical contact shall exist between receptacle and plug housings. A red band shall be located on the receptacle so as to be visible when unmated and fully covered when completely mated.
• The receptacle has five keyways which engage with corresponding keys on the plug. The major key is fixed and is wider than the others. Polarization is ensured by the different positions which the minor keys may take. The position of the insert is fixed relative to the major key.
• A blue-colored band indicating that the crimped contacts of the connectors are rear-releasable shall be provided in front of the flange on square flange receptacles. This band shall be positioned so that at least one is visible when the connectors are fitted and when they are mated or unmated.
• The insert for contacts shall be non-removable; it shall be mechanically held in the housing. Sealing shall be provided between the housing and insert
• The mechanical contacts retention system shall be integrated in the hard insert.
• Contact position identification shall be permanent and contrasted on the front face of the insert or the interfacial seal and on the rear face of the grommet
• The mating dimensions of receptacles shall be as per EN 3645-001 § 6-1 “Receptacle mating dimension”.
• The front face of the insert shall be such that sealing is ensured when the connectors are coupled. The interfacial seal of the insert of the male contacts shall be bonded on the hard insert.
• Contacts shall be crimp and removable by rear.
• The grommet shall permit sealing for cable diameters to 3.3 to 5.7 mm and shall not be removable.

Project Results:
Starting from the project constrains the design of this innovative connector has been developed taking in consideration the possibility to improve all the characteristics which could have an impact for future new applications, in terms of current rating, Voltage Proof, working temperature and similar.
The focus point have been the following:
1) define the smallest size of connector as per EN3145-001 able to meet the Voltage Proof Requirement
2) identify an insulator material able to withstand the electrical and thermal requirements
3) define the proper insulator geometry
4) identify a proper shell material and finish able to withstand the thermal requirements
5) identify a proper contact material and finish able to withstand the electrical and thermal requirements
6) identify an grommet material able to withstand the electrical and thermal requirements
7) identify the proper bonding and potting material able to withstand the electrical and thermal requirements

1) In order to define the smallest size of connector the proper clearances in air and creepage distances, able to meet the Voltage Proof Requirement, have been calculated. Several international standards have been considered, like MIL-DTL-38999M, MIL-DTL- 5015, EN50124-1 and EN 60664-1. The results have been that the proper smaller size possible according to EN3145 is the size 23. The assembled connector passed the Voltage Proof Test.
We performed also a destructive test at Sea Level to check the max Voltage admissible for the connector. The flashover discharge occurs at a Voltage value of 6000 Vac RMS (between a contact and the shell).

2) After a technical analysis of the data sheets of several materials, two different type of insulator have been considered and tested: plastic PEEK and Glass Ceramic. The characteristics evaluated have been: BEHAVIOUR AT HIGH TEMPERATURE, RESISTANCE AT PARTIAL DISCHARGES, RESISTANCE AT TRACKING, MECHANICAL CHARACTERISTICS, MACHINABILITY, WEIGHT, and PRODUCTION COST. The best compromise for the Cleansky project constrains is resulted the Plastic Peek. Glass Ceramic has been more appreciated for the High temperature behavior so, for future application in which the thermal aspects will be more significant, it could be taking in consideration.

3) Two different solution have been considered, one piece insulator and two pieces bonded. The main issue has been the Partial Discharges behavior. After the test campaign both the solutions passed the Cleansky requirements, but the two pieces solution seems to be too much subject to the quality of the bonding process. That aspect is due to the difficulty to control the inner quality of the bonding material at the interface between the two pieces, where the presence of air bubble or gaps can be very dangerous. So the one pieces solution has been preferred.

4) Considering the environmental and thermal requirements, in particular the Working Temperature of 200°C (continuous use) with peak at 260°C (the request was for a minimum time of 60s, but more than 60s if possible was preferable) the material chosen for the housings has been AISI 316 Passivated Stainless Steel
5) Thermal aspects are also the most important issue for the selection of the material and the finish of the contacts. An electrical connector must maintain good contact force throughout the functional life of the product. Contact force is generated by the deflection of the electrical contacts within the connector (this deflection creates stresses in the metal which then generate the force). In order to remain effective, the contacts must return to their original position when the connector is disengaged (when the connector is unmated). This means that any stress and strain in the metal due to the deflection must be elastic (recoverable). If there is any plastic (unrecoverable) strain, the performance of the connector is diminished. The key to good contact force is to achieve as high a stress as possible while ensuring that the strain remains elastic. However, if a contact is stressed to a certain point on the curve and held there for a long period of time at an elevated temperature, some of the elastic strain will convert to plastic strain. A new copper alloy (CuCrZn1) has been selected in order to have a good behavior at high temperature and at the same time good electrical properties, as low contact resistance and high conductivity (IACS%). The test performed on different prototypes have shown that a special Gold Plating is required to meet the Cleansky Project constrains. Test also showed that Silver Plating can’t be used over a temperature of 180°C.
The test performed has been the Endurance Temperature (60hr at 200°C), followed by the Accelerated Aging (33hr at 220°C, then 16hr at 260°C). During the test the after-post check parameters have been the Gauge Insertion, the Extraction Force and the Contact Resistance.
We performed other test in order to have an electrical characterization of the new connector in terms of Current Rating, considering a max Temperature of 200°C and the 4 contact powered at the same time.

6) The soft parts in the Cleansky connector are the grommet, the interfacial seal and the peripheral seal. About the soft-part material the main concerns were:
- Thermal Cycle (200°C continuous use with peaks @ 260°C)
- Aeronautic Fluids Compatibility
The most common material used for soft parts in aeronautic applications is Fluorosilicone Rubber due to its great compatibility with most of the common aeronautic fluids but it isn’t able to withstand an operating Temperature up to 200°C (for continuous use).
High Temperature is not a problem instead for a Silicone Compound but in this case the fluid compatibility has to be checked.
GLENAIR Inc. has developed a new Silicone Compound for molded parts named GPS107 which is the best compromise between the two characteristics.
GLENAIR Inc. has performed on that material some fluid compatibility test as:
•Resistance to Petroleum Lubricating Oil 70 Hours at 150°C in IRM 901 Reference Oil
•Resistance to Low Density Phosphate Esters 22 Hours at 135C in Skydrol LD-4
•Resistance to Dry Heat 24 Hours at 300°C

7) The selection of the potting and bonding material has been a critical point, due to the high temperature. The potting has to guarantee a properly sealing in the rear of connector. The bonding has to be able to permit the proper adhesion also after long time at high temperature. In order to validate the potting and the bonding materials the assembled connector has been exposed with good results to two different thermal ageing.
After both these cycles there are no presence of mechanical damages, no loosening of parts, no crack or excessive wear and no detached parts the connector passed the test with positive results.

Potential Impact:
What has been demonstrated with this Topic is in principle the feasibility to use an electrical connector together with a PWM generator mitigating the risk for partial discharges in the connector operating at higher frequencies and current levels in an environmental conditions expected during an aircraft lifetime.
This will probably help in a near future to test the complete system (PWM Generator + electrical actuators) to better simulate and test operational conditions with benefits in terms of weight and space saving on an aircraft.
Further investigations are needed by using aluminum cables instead of copper ones, used, to understand if aluminum could play a significant role on weight reduction also for PWM.What has been demonstrated with this Topic is in principle the feasibility to use an electrical connector together with a PWM generator mitigating the risk for partial discharges in the connector operating at higher frequencies and current levels in an environmental condition expected during an aircraft lifetime.
This will probably help in a near future to test the complete system (PWM Generator + electrical actuators) to better simulate and test operational conditions with benefits in terms of weight and space saving on an aircraft.
Further investigations are needed by using aluminum cables instead of copper ones, used, to understand if aluminum could play a significant role on weight reduction also for PWM
Dissemination will take place by participating to dedicated seminars and by promoting the solution within the Aerospace Industry.
Here we have a detailed plan of the dissemination activities:
- Preparation of a Product Brochure describing the requirements and proposed products;
- Preparation of Powerpoint Presentation for illustration of problematic and proposed solutions;
- Presentations:
a) Airbus Commercial – Blagnac: March 2017;
b) Airbus Helicopters – Marignane: February 2017;
c) Latecoere (Latelec) – Labege: February 2017;
d) Dassault – Saint Cloud: March 2017;
e) Safran Power & Electric – Blagnac: March 2017;
f) Safran Aircraft Engines – Moissy-Cramayel: April 2017;
g) Paris Air Show: Presentation during the conferences: June 2017.

List of Websites:
Andrea Zambetti, Project Manager

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