RELIABILITY OF POWER CONNECTIONS

Reliability requirements
Basic feature of electrical contacts
Connector design
Degradation of electrical contacts
Mitigating measures
New trends in electrical contact design

ELECTRICAL CONTACT REQUIREMENTS

Electrical: low power losses, no signal distortion, no overheating;
Mechanical: stable contact force during closing and opening, high wear resistance;
Ecological: resistance to environment factors, minimal pollution to the environment under fabricating, operating, and recycling conditions;
Ergonomic: simplicity of design and fabrication, simple maintenance repair and replacement, possibility of combining units;
Economical: minimal content of noble and deficient non-ferrous

FACTORS AFFECTING CONTACT RELIABILITY

BASIC FEATURES OF ELECTRICAL CONTACTS

Surface Topography
Contact Area
Electrical Current at an Interface
Constriction Resistance
Influence of Mechanical Load
Effect of Surface Roughness on Contact Resistance

BASIC FEATURES OF ELECTRICAL CONTACTS

Surface Topography

BASIC FEATURES OF ELECTRICAL CONTACTS

• Electrical Current at Interface

BASIC FEATURES OF ELECTRICAL CONTACTS

•Constriction Resistance

CONNECTOR DESIGN

Types of Power Connectors

CONNECTOR DESIGN

Types of Power Connectors

CONNECTOR DESIGN

Comparison of different connection techniques

CONNECTOR DESIGN

Mechanical Connectors

Advantages

Inherent resilience of the connector components permits follow- up of creep and reduces the stresses due to thermal expansion that tend to cause excessive
Ease of installation (sockets, wrenches, screwdrivers, etc) and removal, simple to use, require minimal training to install
Can be disassembled without damage to the connection components and may be reusable if in good condition

Electrical performance of mechanical connectors meets or exceeds the industry requirements for which they are designed, thus not compromising the performance.

CONNECTOR DESIGN

Mechanical Connectors

Disadvantages

Specific torque requirements must be followed to provide the proper clamping force needed for a sound electrical
Inconsistency of forces applied over identical mechanical installations is not generally repeatable due to use of uncalibrated torque
Because of relatively low mechanical holding strength, these connectors can not be used as full tension connections and in areas of high vibration; more maintenance and periodic inspection may be
Owing to their geometry, installing mechanical connectors on insulated conductors is usually difficult and

CONNECTOR DESIGN

Compression Connectors

Advantages

Low cost, relatively reliable performance, use of recommended tools and/or dies removes the human element during
Connector construction provides better conductor encirclement while retained oxide inhibiting compound protects the contact area from the atmosphere, thus assuring a maintenance free
High localized and consistent forces imparted by the installation tool break down the oxides and establish contact points (a-spots) for reduced contact resistance and electrically and mechanically sound
The softness of compression connector material relative to the conductor prevents spring back and contact
Due to their geometry, compression connectors are considerably easier to insulate or tape than mechanical
These connectors are most suitable in areas of wind, vibration, ice

CONNECTOR DESIGN

Compression Connectors

Disadvantages

Proper installation tooling for a compression system program involves potentially high capital investments due to a large variety of different types of compression tooling to select
Accurate die and tool selection is essential for proper installation of a compression
Due to the need for specific tools and dies to install a compression connection, installers must be trained how to use the proper techniques and maintain these
In some compression connections, manually operated tools require greater physical exertion to install, thus when installing numerous
connections, installers can become fatigued and possibly not complete the specified number of

CONNECTOR DESIGN

Wedge Connectors

CONNECTOR DESIGN

Wedge Connectors

Advantages

Powder actuation provides consistent, uniform performance and requires low physical exertion from an operator to complete a
Rapid mechanical wiping action as the wedge is driven between the conductors breaks down surface oxides and generates superior contact points thus reducing overall contact
Installation is accelerated with the use of lightweight, portable tooling with simplified loading and engaging
The spring effect of the ‘C’ body maintains constant pressure for reliable performance under severe load and climatic conditions whereas a large connector mass provides better heat
Electrical performance of fired-on wedge connectors are excellent due to the low contact resistance developed during

CONNECTOR DESIGN

Wedge Connectors

Disadvantages

Dedicated nature of powder actuation require full support from the user in terms of training, maintenance and
Precautions and specially trained and qualified installers are required for safe and proper installation of wedge
Mechanical wedge connectors installed with wrenches, require more physical exertion for installation, show more inconsistent performance due to discrepancies caused by contaminants on the hardware and wide tolerances of shear-off
Mechanical wedge spring bodies are typically manufactured by casting which produces much less spring action to maintain the

Wedge connectors are restricted to non-tension, out-door applications and suited only for a limited range of conductors

CONNECTOR DESIGN

Types of Power Connectors

INSULATION PIERCING CONNECTOR

CONNECTOR DESIGN

Insulation Piercing Connectors

Advantages

Low installation costs since no special tooling is required as they can be installed with a basic
No insulation stripping or application of oxide inhibitor is required when making connections to insulated
These connectors incorporate contact teeth designed to penetrate conductor insulation and make electrical contact, and are pre-filled with an oxide inhibiting compound to fill voids where contamination may
Insulation piercing connectors are insulated and require no tape or special cover once the connection is
Relatively safe and easy installation on energized

CONNECTOR DESIGN

Insulation Piercing Connectors

Disadvantages

Limited scope of applications; recommended for low voltage (600V and below) secondary distribution applications where insulated conductors are
The nature of the connection device limits their application to functions such as taps, although some parallel splices can also be
These connectors are intended for use in non-tension applications only and should never be used on bare
These connectors may not be suitable for conductors with very thick, very thin, or very hard insulation materials as they could damage the conductor or not make electrical contact at all

CONNECTOR DESIGN

Exothermic (Thermite) Connectors

Exothermic welding is a process in which an electrical connection is made by pouring superheated, molten copper alloy on and around the conductors to be
The process requires no external source of heat or current and is completed within few seconds in a semi-permanent graphite mold in which the molten copper alloys causes the conductors to melt.
The result of a reaction between a metal oxide and aluminum is liquid metal that acts as the filler metal and flows around the conductors making a molecular
The following chemical reaction occurs in the welding of copper conductors:

3Cu₂2O + 2Al = 6Cu + Al₂2O₃3 + Heat (1060 kJ)

The thermite welding is extensively used for making grounding connections between copper

CONNECTOR DESIGN

Exothermic (Thermite) Connectors

Advantages

Excellent current-carrying capacity equal to or greater than that of the conductors, high stability during repeated short-circuit current pulses, excellent corrosion resistance and mechanical

Disadvantages

Cost, lack of repeatability, numerous mold requirements, potential down–time caused by inclement weather or wet conditions, safety risks to personnel and
The intense heat damages both the conductor and its insulation, anneals the conductor so that exothermic connections can not be used in tension
The resultant weld material exhibits lower conductivity and physical properties than the conductor, being similar to cas

CONNECTOR DESIGN

Friction Welded Connectors

Friction welding is a solid–state welding process in which the heat for welding is produced by direct conversion of mechanical energy to thermal energy at the contact interface without the application of external electrical energy or heat from other
Friction welds are made by holding a non–rotating work–piece in a contact with a rotating work–piece under constant or gradually increasing pressure until the interface reaches welding temperature and then the rotation is interrupted to complete the
The frictional heat developed at the interface rapidly raises the temperature of the work–pieces, over a very short axial distance approaching but bellow the melting
During the last stage of welding process, atomic diffusion occurs while the interfaces are in contact, allowing a metallurgical bond to form between the two

CONNECTOR DESIGN

Friction Welded Connectors

RICTION WELDED HEXAGONAL COMPRESSION DEEP STEPPED INDENTATION

DEGRADATION OF ELECTRICAL

CONTACTS

Oxidation
Corrosion
Fretting
Stress Relaxation / Creep
Differential Thermal Expansion
Formation of Intermetallics