Author: Georg Halfar
Infraserv Höchst is responsible for the electricity supply to the Höchst Industrial Park in Frankfurt am Main, where there are many critical manufacturing plants that operate in the chemical and pharmaceutical sectors. These sectors have always had particularly stringent requirements for security of supply, but energy suppliers with customers in other demanding industries can also profit from the experiences of Infraserv Höchst, particularly in relation to their discerning use of unfamiliar, proven technologies.
The Höchst Industrial Park is home to more than 90 companies with a total of 22 000 employees. Many of the companies operate in the chemical and pharmaceutical sectors and have especially demanding requirements for the security of their energy supplies. For this reason, they give close attention to the testing and maintenance of critical supply system components, such as low-voltage circuit breakers, and they insist on detailed and accurate test and maintenance records.
Digitization is increasing dependence on secure supplies
The IT industry, the Internet, online banking and even private households with their smart homes and widespread Wi-Fi networks are creating requirements for security of supply that are comparable with those in chemical and pharmaceutical sectors. These requirements will become even more pressing with the growing spread of ‘autonomous driving’, electric vehicles with their new battery charging infrastructure and, last but not least, ‘smart grids’. And, to makes things even more challenging, today’s power distribution networks are far more difficult to manage than they were in the times of centralized large-scale generation. Against this background, concern about declining security of supply is justified, and this affects almost every energy supplier.
Figure 1: Switchboard with withdrawable low voltage circuit breakers and double busbars
Figure 2: Inserting a breaker into a test station equipped with an ODEN AT
Infraserv Höchst’s experience can benefit all distribution system operators
Infraserv Höchst has had much experience of carefully evaluating data collected over many years from low voltage circuit breakers and trip systems supplied by a range of manufacturers. This experience has shown that accurate testing of switching times and the synchronization of the main contacts in low voltage circuit breakers is of central importance for safety, because safe operation is only possible if the main contacts operate simultaneously. Investing in employee training, time and test equipment needed to ensure and confirm correct operation of circuit breakers has proved to be a very successful strategy for Infraserv Höchst.
Low voltage circuit breakers
In its supply networks, Infraserv Höchst uses low voltage circuit breakers with high operating currents and high short-circuit currents, the latter being greater than 30 kA in some cases. In the event of a fault, the trip circuit in these circuit breakers is designed to trip the breaker in a fraction of a second. If, however, the release mechanism does not react to short-circuit or thermal overload events within the specified tripping times, this can result in considerable damage to the supply system.
In addition, such a failure may cause the operation of back-up protection devices, which is likely to lead to the disconnection of consumers who were not affected by the original fault. Finally, when a circuit breaker fails to trip correctly, there is significant risk of fire. Correct functioning of the tripping systems in low voltage circuit breakers therefore makes an important contribution both to safe operation and to security of supply.
Why Infraserv Höchst relies on the Megger ODEN AT
The Megger ODEN AT provides true short-circuit currents of the order of 2000 to 14 000 amperes in a format that is transportable by hand with a trolley! These high currents are needed for primary injection testing of circuit breaker protection systems. The alternative is secondary injection testing, which uses much lower currents but does not test all of the components of the protection system. Whichever approach is used, the tests must cover overload, delayed short-circuit and instantaneous shortcircuit protection.
Figure 3: Short-circuit testing of a low voltage circuit breaker
Testing with the ODEN AT has important advantages for Infraserv Höchst
- True primary injection testing, rather than secondary injection testing
- Unbiased data analysis; tests are independent of the circuit breaker manufacturer and are held to consistent measurement and evaluation
- Results are reliable and easy to understand
- The test set is easy to use
- The cost of buying, storing and learning how to use a plethora of manufacturer-specific test equipment is eliminated
(RIGHT) Figure 4: The ODEN AT has proved to be indispensable at Infraserv Hochst
The Megger ODEN AT replaces manufacturer-specific test equipment
Test equipment supplied by a circuit breaker manufacturer can only be used to test that manufacturer’s circuit breakers so, if a network incorporates breakers from several manufacturers, multiple test sets must be purchased. This is not just a cost issue: there’s also the inconvenience to cope with multiple user interfaces and having to make sure that each test set is always calibrated, updated with the latest software and enhancements. Opting to use the ODEN AT, which works with breakers from any manufacturer, therefore saves Infraserv Höchst time and money.
Figure 5: Synchronization testing of main contacts with a TM1700
Figure 6: The Megger B10E provides power for the breaker opening and closing coils, and for the spring charging motor
Checking synchronization with the Megger TM1700 circuit breaker analyzer
The three main contacts, one contact per phase, in a low voltage circuit breaker are operated via a common drive shaft. The contacts in every type of breaker have different operating characteristics, as is shown by the systematic analyses that Infraserve Höchst performs with a Megger TM1700 circuit breaker test set. These regular synchronization checks have now become indispensable.
The Megger TM1700 is suitable for use in electrically noisy environments, as it incorporates input and output circuitry designed to minimize the effect of interference. Moreover, the TM1700 measures the main contact times of all three phases simultaneously, which is time saving and makes it very easy to identify issues with synchronization between the phases. Infraserv Höchst uses the TM1700 in conjunction with a Megger B10E, which supplies power to circuit breaker opening and closing coils as well as to the charging motor for the spring-release mechanism. This means that no manual spring charging is needed. This test set up allows Infraserv Höchst engineers to test all types of circuit breakers.
Double busbar systems and withdrawable circuit breakers
Type-tested double busbar systems and withdrawable circuit breakers are the backbone of Infraserv Höchst’s high-availability supply systems. These double busbar systems facilitate maintenance, service and repair. Both sets of busbars are energized. To perform a busbar changeover, the coupling switch is turned on and, subsequently, trained personnel can unlock and change the busbars over. The circuit breakers are built into the panels as withdrawable units. This considerably speeds up the workflow during maintenance or repairs in the event of a fault. A similar design in the test station allows the low voltage circuit breaker to be quickly connected to the Megger ODEN AT tester.
In summary, distribution grid operators can maximize their supply reliability by testing and systematically analyzing low voltage circuit breakers with the Megger ODEN AT and TM1700 test sets, as part of a dynamic maintenance strategy that systematically records and integrates all new insights. With double busbar systems and modern slide-in systems, fast, certain and safe repairs can be made in an emergency.