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In our latest blog, we provide exciting insights into the use of our PROMET R600 micro-ohmmeter at the renowned company TRUMPF Laser-und Systemtechnik GmbH. Read how our micro-ohmmeter helps to minimize electrical losses and thus also ensures longer ranges for electric vehicles.

The requirement: Reduction of contact resistances

In e-mobility, systems and components must be one thing above all else: extremely efficient. Every kilometer counts and vehicles with a long range have the edge. Even the smallest components often have a major influence on this - such as copper contacts. These so-called busbars are often used in inverters and conduct the current from the battery to the drive, for example. They are usually screwed together. However, this reduces conductivity: a lot of energy is transferred via the contacts. The force-fit connection using a screw leads to a high contact resistance and therefore to power losses. To make matters worse, although copper is very conductive, it oxidizes quickly. The oxide layer on the surface also causes energy losses at the connection points. In electric vehicles, this affects the range, reduces performance and shortens the service life of the components. Reducing the contact resistance of billions of connections in e-vehicles worldwide offers enormous savings potential here.

The solution: Structuring the joint with a laser
TRUMPF takes this into account with a specially developed laser process. With its TruMicro7070 lasers, the Ditzingen-based company structures the copper busbars at the connection point before screwing them together. The laser removes any impurities and the old oxide layer and also creates a specific surface topography. The resulting new, pure oxide layer protects and preserves the condition of the surface in the long term. During screwing, the resulting structure leads to micro-deformations, resulting in a significant reduction in electrical losses - even over several screwing and unscrewing cycles.    
The laser removes the old oxide layer from the copper surface and ensures better conductivity at the screwed points thanks to the structuring.

The proof: measurement with the PROMET R600 micro-ohmmeter
The electrical conductivity can be determined by measuring the contact resistance. A lower resistance in the contact leads to lower electrical losses in the system and therefore also to a longer service life of the contact.

TRUMPF uses our high-precision micro-ohmmeter PROMET R600 for this measurement.

The PROMET R600 is a precision measuring device for determining resistances in the μΩ to mΩ range. Due to the measurement in four-wire technology and the output of high test currents up to 600 ADC, the resistance measuring device meets the highest accuracy requirements. The use of state-of-the-art power electronics and the robust design guarantee maximum reliability for stationary and mobile use in industrial environments such as at TRUMPF.

The contacts are evaluated both on the basis of the absolute measurement of the contact resistance and by measuring the so-called quality factor. The resistance in the contact is compared with the resistance in the homogeneous conductor.

By equipping the systems with three voltage measurement inputs, the resistances can be determined and compared in parallel at two measuring points at the same time. The quality factor K is calculated as the ratio of the resistance RCON of the connection over the overlap length lCON to the resistance RREF of the busbar of the same length lREF.

The result allows a direct comparison of different qualities of electrical transitions.

Conclusion
Copper contacts can be structured quickly and efficiently using laser technology. The result is a significantly reduced contact resistance, which is activated when the two metal components are screwed together. The KoCoS precision resistance meters PROMET R300/R600 are an ideal tool for characterizing such connections for high current and low resistance due to their measurement in four-wire technology and the ability to accurately measure both current and voltage.

Information on Trumpf's laser process can be found in the white paper "Laser structuring of copper busbars" at https://www.trumpf.com/de_DE/loesungen/branchen/automobil/e-mobility/laserschweissen-von-leistungselektronik/

Do you have any questions or additions regarding resistance measurement or our measuring devices? Then contact us via the comment function here in the blog or by email to info(at)kocos.com.

Compact motor and coil testing system for switchgear testing

KoCoS Messtechnik AG now offers the compact, portable EPOS MC4 test system for the supply, testing and analysis of motors and trip coils of switching devices.
In addition to its use as a powerful AC/DC source, EPOS MC4 records the operating currents of spring tensioning and pump motors as well as release coils and displays the motor and coil currents as numerical results on a 5" touchscreen.

The voltage source is based on state-of-the-art power electronics and is insensitive to interference in the power supply due to the synthetic generation of the output variables. Test sequences can therefore always be carried out under the same conditions, which enables a direct comparison of the results.

The EPOS MC4 can be operated and controlled via the integrated operating unit with high-resolution, resistive 5" touchscreen, rotary selector switch and function keys or in combination with the ACTAS test systems. EPOS MC4 can be conveniently integrated into switchgear tests via the ACTAS test software. A remote control unit is also available for controlling motor and coil outputs.

EPOS MC4 provides additional functions for analyzing switchgear:

  1. Analysis of motor running and coil tripping
  2. Determination of the coil resistance
  3. Determination of the minimum tripping voltage
  4. Testing undervoltage releases

The evaluation of the results is simple and conclusions about the condition of coils, motors and mechanics can be drawn immediately. The integrated measuring functions therefore guarantee meaningful analyses for maximum operating times and minimum maintenance effort.

EPOS MC4 enables the direct connection of a PC/notebook. The measurement results stored in the device can be read out and managed using easy-to-use software.

The test system is housed in a handy, extremely robust and hard-wearing hard case. Waterproof and dustproof to IP67 when closed, the case absorbs even hard knocks without sustaining damage. The robust test system is just as suitable for demanding outdoor use as it is for use in production or in the laboratory.

A special feature of the EPOS 360 three-phase signal generator is the operating unit for on-site operation. All basic operating and parameterization tasks, such as changing amplitude, phase angle or frequency, can be performed via the operating unit with touch screen, function keys and jog wheel. In addition, information about system states and an overview of the set signal values are displayed.

The jog wheel enables fast and precise changes of values and is used for setting as well as for controlling the device. The integrated illuminated ring provides a clearly visible display of the system states, acoustic signals provide additional information and feedback during settings and output.

The states and the operating modes of the inputs and outputs of the EPOS 360 are further signaled by numerous LEDs in the front panel. A quick glance is enough to see which outputs are active and which states are present at the binary inputs and outputs.

The function keys are used, among other things, to start/stop tests and to accept settings as well as to confirm memory prompts.

The VD-Static and Symmetric monitors are available for local operation. Amplitude, phase and frequency can be set independently. The output can be started directly and the signals can be changed stepwise during the output.

The function of changing the output values in specified step sizes allows simultaneously increasing or decreasing the values for voltage, current, frequency and angle in one step via the jog wheel.

The settings for a symmetrical three-phase system are to be made via the Symmetric monitor. For example, when setting the voltage value, the setting for all three voltage phases is adopted.

In the VD-Static monitor the settings for an unbalanced three-phase system are to be made. In this monitor the parameters for each phase are to be set independently.

It is possible to choose between different views for the monitors. The numerical view NUM gives an overview of the parameters and states of the outputs. In the VD view, the signals are displayed in a vector diagram. The right status bar shows the current status of all binary inputs and outputs.

The control of the output of the voltage and current amplifiers can be done in static or dynamic mode. In static mode, changes to the output values are only accepted and output after confirmation.

In dynamic mode, changes are accepted immediately. Thus, dynamic adjustment of the output values is possible without having to confirm them beforehand.

In addition, it is possible to store up to ten individual parameter sets for each output mode, giving the user the option of easily accessing predefined values.

With the high-resolution 5" touchscreen with Smart-Touch technology, function keys and a ergonomic jog wheel, three-phase signals can be output quickly and easily with the EPOS 360 signal generator, even without connecting an external PC. The clear user interface guides the user intuitively to the target.

Do you have any questions about our measuring devices?

Then contact us via phone +49 5631 95960 or by mail to info(at)kocos.com.

By:
Brian Burke, Application Engineer, KoCoS America LLC
Guy Wasfy, Managing Director, KoCoS America LLC
Jürgen Dreier, Product Manager, KoCoS Messtechnik AG

Bonding connections and ground connections are an essential component for the safe functioning of power and communications engineering systems and for ensuring personal and equipment safety.
Unwanted voltage potential differences are to be avoided by means of ground connections and grounding procedures. These voltage potential differences can occur between metallic components and ground, which can endanger human safety and/or technical equipment.
Metallic components must be connected to ground potential to prevent dangerous voltages. Voltage drops are reduced by grounding all non-voltage-carrying parts and by extensive ground potential equalization (grounding system). It is important to make sure these grounding connections have a low resistance. Resistance measurements must be made at both potential and ground connections to ensure that a sufficiently good low resistance connection is achieved and maintained.

Below is an example of application in power distribution where grounding and equipotential bonding and their good connection are important.  However, there are many other applications where grounding and equipotential bonding must be taken into account (Rail vehicles, aviation industry and aircraft maintenance, etc.). Typical applications for equipotential bonding and grounding are found in power distribution substations in low and medium voltage networks and especially in high voltage substations. The grounding of all non-voltage-carrying parts and extensive ground potential equalization reduce voltage drops that can occur due to capacitive or even inductive voltage coupling.

An example of these non-voltage-carrying parts is the mechanical disconnect switches used to remove a switchgear from service. Due to the need for human interaction with these physical switches, it is critical their grounding connection is not compromised. These straps are metallic braids secured via bolts to the switch and ground connection point. These straps can become poor conductors due to corrosion or physical damage. A compromised strap could lead to improper grounding of the switch causing a hazardous touch potential when the switch is to be used. To ensure the straps are functioning accordingly, the connection across them can be tested with a micro-ohm measurement. A failing strap will have a high resistance reading where as a properly conducting strap will have a low resistance reading. High resistance of the connection or, in the worst case, a failing strap could require the bolted connection points being cleaned and reconnected or the strap being replaced entirely.

Aside from bolted ground straps, the grounding connections can be bonded through exothermic welds. These welds result in superior mechanical and electrical bonding. Especially for conjoining dissimilar metals, such as joining a copper grounding rod to a galvanized metallic structure in a substation. These welds, when done properly, create a solid and reliable connection (Figure 2) Due to improper heating or unwanted moisture, the welds can have pitting or gaps (Figure 3) and be considered poor quality both mechanically and electrically. Performing a micro-ohm resistance measurement across these connections can give insight into the weld quality. The more solid the weld connection is, the lower the resistance reading will be. A poor quality weld could result in a less reliable grounding connection.

The resistance measuring instruments from KoCoS Messtechnik AG are ideal for measuring equipotential bonding and earth connections. The PROMET SE precision resistance measuring instrument is used to determine low-resistance in the μΩ and mΩ range. With adjustable test currents of up to 200 A, in conjunction with a four-wire measurement method, the systems provide measurement results for the highest accuracy requirements. The use of state-of-the-art power electronics and the robust design guarantee maximum reliability for mobile use.

The PROMET SE is ideal because it is battery operated and does not require a mains connection. Some of the connections described may be at height so that the tester is standing on a ladder or similar. Without the battery operation, the meter would also require a portable generator. Finally, the PROMET SE is very lightweight and easy to transport.  It weighs less than 5 pounds and can be conveniently transported on-site to test the many ground connections.

If you have questions or additions to the resistance measurement or to our measuring devices? Then contact us via the comment function here on the blog or by mail to info(at)kocos.com.

When distributing electrical energy, it must be remembered that poor current connections cause losses that must be compensated for by additional power from the power generator.

The power loss at the contact point depends on the current and the resistance: P = I²·R

When transmitting high currents, the aim must therefore be to achieve the lowest possible contact resistance at the connection points. The contact resistance is influenced by several variables and increases in the course of the operating time due to aging. By testing at the installation site, a faulty connection can be detected and eliminated.

The quantity for assessing an electrical connection is the resistance. The resistance of an electrical connection is in the micro ohm range. These small resistance values require special measurement technology, such as resistance measurement in four-wire technique (Kelvin method).

In order to assess the quality of a connection, the PROMET SE and PROMET R300/R600 resistance measuring instrument is able to determine the quality of a connection. Due to two voltage measurement inputs, a simple and quick determination of the quality, e.g. of screw connections on bus bars, is possible. The determination is made via the quality factor. This is defined by the ratio of the resistance of the connection over the overlap length to the resistance of the bus bar of the same length.

The quality factor K is the ratio of the resistance RCON of the connection over the overlap length lCON to the resistance RREF of the bus bar of the same length lREF.

     K = RCON/RREF

     RCON: Resistance of the connection
     RREF: Resistance of the bus bar

Therefore, when making an electrical connection, care must be taken to limit aging and provide a low-maintenance and reliable connection.

By determining the resistance or quality of a connection, the correct connection can be verified during installation and maintenance and a reduction in electrical losses, an extension of service life and an increase in plant safety can be achieved.

Do you have questions or additions to the resistance measurement or to our measuring devices? Then contact us via the comment function here on the blog or by mail to info(at)kocos.com.