Monitoring in low voltage

Description

Stadtwerke Kempen set up a new network control centre in 2016 and has since been steadily expanding the telecontrol technology for monitoring and controlling the 10 kV network and for monitoring its gas and district heating network. In doing so, they have relied on SAE’s telecontrol technology throughout. Various variants of the FW-5 device series are being used in the Kempen municipal utility network for expansion, depending on the required application solution.

A new requirement of Stadtwerke Kempen is a system for monitoring and network supervision in the low-voltage level of its secondary unit substations. The data from the secondary unit substations will help to identify critical network states and possible faults in advance, to evaluate transformer loads, to archive network loads for later analyses and to support network expansion planning with real load values.

For this purpose, the voltages, currents, active and reactive power values of the transformer, as well as the outgoing currents (single-phase) of all low-voltage outgoing feeders of a transformer station are transmitted as measured values to the network control center. The RTU model FW-5-GATE-4G with integrated LTE modem and the extension I/O cards PM-1 and 8DI are used to solve this task.
In addition, devices from Janitza and Horstmann are also connected to the RTU in the transformer stations using the Modbus RTU protocol – in total, the following information is transmitted:

• Short-circuit and earth fault direction messages from the Compass B
• Short-circuit messages via indicator with rotor system
• Transformer measurement values voltage, currents, active and reactive power via Janitza UMG 605
• Outgoing branch currents in the low voltage by means of SAE PM-1 module
• Other operating messages directly via additional module 8DI

The measured values are pre-selected in the FW-5-GATE-4G and provided with a hysteresis curve and threshold values in order to keep the amount of data transmitted via LTE and IEC 60870-5-104 protocol as lean as possible.

SAE offers a so-called T-Bus extension for the connection of remote expansion modules. With this, the distance of a good 7 meters between the RTU in a plant and the PM-1 modules for measurement at the Rogowski coils in the low voltage could be bridged very efficiently. Even longer distances between the RTU and the low-voltage outgoing feeder measurement do not pose any technical problem.

The measured values are then visualized and archived in the new control center of Stadtwerke Kempen. From a total of 250 secondary unit substations, 44 stations have already been connected.
Every week, the degree of expansion and thus the SAE telecontrol technology in the network of Stadtwerke Kempen grows.

Practical experience
As a result of the comprehensive network monitoring, the staff discovered that a low-voltage outgoing feeder of a specific transformer station showed a short-term but regular network overload early in the morning.
Subsequently, a local butcher’s shop, which had used a single-phase cutter without start-up current limiter for shredding pork sides, could be detected as the cause. Such disturbances show how important it can be to observe and monitor low-voltage outgoing feeders.

From the parameterization of the telecontrol systems with the parameterization software setIT, the creation of the system visualizations by using visIT to the installation and commissioning of the telecontrol technology, all tasks are carried out independently by the employees of Stadtwerke Kempen.

The use of redundant communication paths and the SAE master stations reduce possible communication disturbances to a minimum. The use of VPN encryption with IPsec (IKEV2) increases the IT security of the entire system and was also very helpful for the successful certification of Stadtwerke Kempen’s ISMS.

Conclusion
Particularly with view on the upcoming expansion of the charging infrastructure for e-mobility, it is essential to closely monitor and supervise network utilization in our low-voltage network.
An appropriate measurement and the transmission technology are key issues. With SAE as our partner, we are well positioned for the future.