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The Impact of UPS in a Control System Using Power Line Communication


The installation of an Uninterruptible Power Supply (UPS) system plays a crucial role in tunnel lighting. In the event of a power outage, the UPS not only provides electricity to power the lights but also to the control system. Whether a tunnel is under or over-illuminated, it increases the risk of accidents. Choosing a UPS in a power line communication control system presents specific challenges because some of its characteristics can interfere with lighting control, affecting the proper functioning of the systems. This paper explores the issues related to lighting control and the desired characteristics to ensure optimal communication when the UPS comes into action during power outages or fluctuations.

1. Challenges

The harmonic noise generated by electrical power sources, including UPS units, is the main obstacle to effective power line communication. Noise in the frequency range used for communication can disrupt transmission continuously or intermittently, depending on electrical activity on the network. To address this issue, the technical team at Nyx Hemera Technologies has developed unique expertise over the past years, mastering harmonic management with specific filters. These filters ensure optimal communication over the electrical wires powering the lights. Impedance also poses a challenge for power line communication. When impedance is low at the frequencies of interest, the transmitted signal is automatically altered. The technical team at Nyx Hemera Technologies has developed tools to assess the impedance of UPS units. If isolating the impedance of UPS units with dedicated filters is not possible (in existing installations), it is possible to determine where gateways or signal amplification routers should be installed to ensure optimal transmission. Therefore, it is imperative to qualify each UPS model used for each project, as the quality of the emitted signal varies from one installation to another.

2. Different Types of UPS

UPS units, used as secondary power sources to take over in case of power outages, are essential for the safety of tunnel lighting. All UPS units share the same basic components, including power inputs, one or more inverters, power outputs, batteries, and a power control system in case of a main power source failure. There are three categories of UPS units:

  • Standby/offline: The system activates within a few milliseconds during a power outage.
  • Line-interactive: It also manages current fluctuations using a voltage-regulating autotransformer.
  • Online/double conversion: It is used in systems where no power variation is tolerated.

This last model is preferred to supplement any other source of electrical power in tunnel lighting control because it ensures system stability, which is essential for user safety.

3. Battery Lifespan

The lifespan of a UPS can reach up to 10 years, but it’s different for batteries, whose longevity depends on the model. Several factors influence battery lifespan, including battery chemistry, ambient temperature, usage, maintenance, and their quality. Since tunnel lighting is crucial for safety, it is essential to monitor the battery status in real-time. For this purpose, an effective monitoring tool is indispensable, providing alerts when maintenance is required.

4. Different Forms of Alerts

There are several types of alarms to monitor the status of UPS batteries, including audible, visual, and remote alarms. In a tunnel context, the first two options are often impractical. Ideally, when the tunnel has an external connection, the alert signal should be integrated into the tunnel’s SCADA (Supervisory Control and Data Acquisition) system or the lighting control system’s SCADA. Such communication allows Nyx Hemera Technologies’ team to integrate information about the UPS status into TLACS-SCADA via TCPIP or SNMP access, offering precise management of the UPS and its batteries.

5. Modularity

The modularity of the UPS is particularly important to ensure lighting power in case of an outage. The flexibility of voltage ranges and the choice of the number of inverters allow adapting the UPS according to real needs, especially those specific to power line communication. Modular UPS components also integrate better into a lighting control enclosure, optimizing design and reducing the space required in installations.

6. Characterization

The use of power line communication in tunnels has proven its robustness, reliability, and ease of installation in more than 150 installations worldwide. The key to this performance lies in mastering and controlling the environment by an expert team. Each tunnel is unique, and to ensure control of its environment, it is essential to understand it by characterizing the components that could affect the signal. If a UPS is already installed, on-site characterization is performed using oscilloscopes to evaluate noise and determine the necessary filters to isolate the transmission signal. Nyx Hemera Technologies’ technical team has also developed tools to locate impedance on a network, allowing for the installation of injection points at strategic locations, in addition to repeaters already integrated into each LPC (local controller installed in each luminaire). In cases where the UPS is not yet installed, it is highly recommended to let Nyx Hemera Technologies’ engineering team select the UPS based on installation characteristics, voltage ranges, the number of luminaires, tunnel length, planned UPS installation location, etc.


The installation or upgrade of a lighting system comes with uncertainties, mainly due to the integration of components from different suppliers. UPS units are undoubtedly among the elements with the most influence on the quality of power line communication transmission. According to Nyx Hemera Technologies, the best choice is a model that is:

  • Online/double conversion.
  • Equipped with batteries offering maximum lifespan or connected to a generator in case of a power outage to minimize battery usage.
  • Equipped with a remote alarm.
  • Modular to match changing needs and components.
  • Sourced from the same supplier as the control system for smooth integration before on-site installation.

Over 30 years’ experience of Nyx Hemera Technologies team members guarantees the best possible choice of equipment. This decision will save time in characterization, installation, and SCADA communication integration. Moreover, a series of tests can be performed at Nyx’s facilities before on-site installation, reducing risks and costs related to uncertainty and unplanned interventions. For further information, please contact