Communication-capable Circuit Breakers

WL Circuit Breaker

ZSI Module

To use the ZSI function with the WL Circuit Breaker, the external CubicleBUS ZSI module must be implemented.

The zone selective interlocking (ZSI) module provides the complete range of selectivity with the short

delay time of tZSI = 50 ms, irrespective of the number of levels

and the location of the short-circuit in the distribution system. Its benefits become even more apparent, the higher the number of levels in large systems and the longer the resulting delay times.

By shortening the time, the ZSI module significantly reduces stress and damage in the event of a short- circuit in the switchgear.

Operating principle

If the ZSI module is used in a distribution system comprising several levels, each circuit breaker affected by a short-circuit interrogates the circuit breaker directly downstream, to ascertain whether the short-circuit also occurred in the next level below:

•If the short-circuit did occur in the downstream level, the upstream circuit breaker delays tripping to ensure that the circuit breaker directly upstream of the short- circuit has enough time to interrupt the short-circuit.

•If the circuit breakers in the downstream level do not report a short-circuit, the short-circuit occurred between the two levels in question. In this case, one of the two upstream circuit breakers interrupts the short-circuit once

the programmed delay time of tZSI = 50 ms has elapsed.

Example as illustrated in Graphic 2-6.

This shows a section of a power distribution system that has been installed with the ZSI module. WL Circuit Breakers are implemented at different levels.

Short-circuit at 3:

Circuit breakers -Q5, -Q3, and -Q1 establish that a short-circuit has occurred. -Q5 blocks -Q3 by means of the ZSI signal and, as a result, -Q1 too, so that they do not trip in 50 ms. Since -Q5 does not receive a blocking signal from a subordinate circuit breaker, it is responsible for interrupting the short-circuit as quickly as possible. If this does not take place, because the circuit breaker is no longer operational due to an overcurrent, -Q3, as a backup, trips after the time-discriminating response time of 150 ms.

Short-circuit at 2:

-Q1 and -Q3 establish that a short- circuit has occurred; -Q5 does not. For this reason, -Q3 does not receive a blocking signal from -Q5, but provides a blocking signal for -Q1. This information tells -Q3 that it is closest to the short-circuit and trips with a delay of tS = 50 ms instead of tsd = 150 ms. Time saved = 100 ms.

Graphic 2-6This graphic illustrates the operating principle of the ZSI function using an example in a power distribution system. It is also a connection diagram that shows how the ZSI module must be wired if the WL Circuit Breakers are used.

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WL MODBUS Communication and Electronic Accessories • January 2005

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Siemens UL 489, UL1066 specifications ZSI Module, Operating principle, Example as illustrated in Graphic
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UL 489, UL1066 specifications

Siemens UL1066 and UL489 are essential components in the landscape of electrical equipment, specifically in circuit protection and control. These standards ensure reliability, safety, and efficiency in various applications, including industrial, commercial, and residential settings.

The Siemens UL1066 is primarily focused on disconnect switches. These devices are designed to isolate electrical circuits, ensuring the safety of both personnel and equipment during maintenance or in case of faults. One of the key features of UL1066 disconnect switches is their high breaking capacity, enabling them to handle significant fault currents without failure. This characteristic is crucial in protecting downstream equipment from damage caused by short circuits. The UL1066 switches are also known for their robust construction, often featuring a metal enclosure that enhances durability and environmental resistance. Additionally, these switches can be operated manually or remotely, offering flexibility in operation and control.

On the other hand, Siemens UL489 circuit breakers provide comprehensive protection against overcurrents and short circuits. These devices not only interrupt fault currents but also protect connected devices from damage due to overload situations. Key features of UL489 circuit breakers include adjustable trip settings, which allow users to customize the response to overcurrent conditions based on specific application requirements. This adaptability makes them suitable for a wide range of environments, from large industrial plants to smaller commercial buildings.

Both UL1066 and UL489 products are constructed with advanced technologies, such as thermal-magnetic or electronic trip mechanisms in UL489 devices, ensuring precise and timely interruption of fault currents. These technologies promote energy efficiency and stability within electrical systems. In addition, many of these devices are equipped with indication features, providing clear visual status cues for quick assessment in emergency situations.

In terms of characteristics, both UL1066 and UL489 devices adhere to rigorous testing and certification processes to meet UL standards. This compliance assures users of their performance and reliability. Furthermore, the devices are designed to accommodate a wide range of operating temperatures and environmental conditions, making them versatile choices for various applications.

In summary, Siemens UL1066 and UL489 devices are paramount in ensuring safety and efficiency in electrical circuits. Their advanced features and robust construction make them indispensable in protecting both personnel and equipment in an array of industrial and commercial applications.
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