KoCoS Blog

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 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.

Since this is a blocking of protection functions, the inrush stabilization testing has to be part of the protection testing. For this purpose, test quantities that are within the tripping range of the protection device have to be superimposed with corresponding proportions of harmonics and the reaction of the relay has to be evaluated. With the VD-Monitor of the ARTES 5 testing software, such test sequences can be created in a simple manner. The ratio between the fundamental signal and the superimposition can be kept constant or changed in steps by means of ramp definition. Thus, combining several test sequences with different settings enables phase-selective testing of the inrush stabilization in a single test routine.

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 R_CON of the connection over the overlap length l_CON to the resistance R_REF of the bus bar of the same length l_REF.

     K = R_CON/R_REF

     R_CON: Resistance of the connection
     R_REF: Resistance of the bus bar

The vacuum inspection systems from KoCoS, which have been tried and tested in practice all over the world, monitor a wide variety of containers such as bottles, jars and cans for leaks in-line during the production process. Containers with insufficient vacuum are reliably detected and removed fully automatically. Highest reliability and easiest handling characterize the processor controlled inspection systems and are the first choice for many food manufacturers.

INDEC VD 100 vacuum testing systems are also increasingly used in Spain for cap inspection. In response to numerous requests by customers at this region, KoCoS decided to develop a Spanish user interface for INDEC VD 100 system and to integrate it as standard in the new firmware. This new Spanish user interface is now available for all new orders for INDEC VD 80 / VD 100 series since spring 2022. Of course, this software update can also be retrofitted in already delivered INDEC VD 100 units.

Users of the INDEC VD 100 can now simply choose their preferred language version between the four user interfaces in German, English, French and Spanish. This significantly simplifies the operation of this INDEC series. Even untrained personnel are now able to generate the relevant sensor parameters (recipes) on the INDEC VD 100. This measure also improves the safety of operation and the acceptance of the INDEC VD 100 series.