Uninterruptible Power Supply for Telecommunications and Remote Control Systems – How to Design a System for Power Outages

A modern electrical substation must maintain control, monitoring and communication capabilities even when the primary 230 V AC power supply fails.

During a power outage, devices such as controllers, communication equipment, protection relays, routers and radio transceivers should continue to operate. They are essential for maintaining communication with the supervisory system, monitoring the status of the facility and performing specific automation functions.

The problem arises when these devices are powered directly from the 230 V AC mains. When the mains voltage fails, they lose power precisely when their operation may be most critical.

That is why such installations require more than a standard 230 V AC/24 V DC power supply. The system must supply the connected loads, keep the batteries fully charged and automatically switch to battery power when the primary supply fails.

This function is provided by a floating-operation power supply.

When designing a backup power system, the first question is usually:

How long should the battery supply the loads?

This is an important parameter, but it is not the only one.

Proper battery management is equally important. For VRLA batteries, the charging voltage should take the operating temperature into account. For batteries commonly used in this type of system, a typical compensation value is approximately −4 mV/°C per cell relative to the reference temperature of 25°C.

Another challenge is the variety of connected loads.

For example, a single cabinet may contain a controller requiring a 24 V DC supply and a radio device requiring 13.2 V DC.

Using a separate power supply for each voltage increases the number of devices, connections and components that require maintenance.

Backup power alone is not enough if the operator does not know the status of the system.

A primary power supply failure, battery problem or incorrect voltage should not only be detected during an on-site inspection.

That is why, in telecontrol systems, it is important to be able to transmit power system status information to a supervisory monitoring system.

Depending on the model, the ZEM series offers features including:

• floating power supply for DC loads,
• battery charging and monitoring,
• temperature compensation of the charging voltage,
• protection against excessive battery discharge,
• independent outputs for different load groups,
• timed disconnection of a selected output,
• an additional 13.2 V DC output for radio equipment,
• RS485 communication,
• DNP 3.0 protocol support in the ZEM200 model,
• initial charging of batteries with a low state of charge in the ZEM100 model,
• relay outputs for transmitting alarm signals.

Not every system requires all of these functions. The model should therefore be selected based on the actual requirements of the installation.

For the end user, the most important consideration is not which features the power supply itself offers, but how the entire system will behave during a power failure.

A properly designed system can provide:

• continuity of telecontrol operation – automation devices can continue performing their functions after the primary power supply fails,
• maintained communication – communication devices can use the same backup power system,
• more efficient use of battery capacity – less critical loads can be automatically disconnected,
• remote diagnostics – power supply and battery status information can be transmitted to the supervisory system,
• a simplified power supply arrangement – a single system can supply loads requiring different voltages,
• easier servicing – the cold-start function allows the system to be started from the battery even when the mains supply is unavailable.

For photovoltaic farms and other renewable energy facilities, an additional benefit is the ability to maintain communication with the supervisory system even when the auxiliary power supply is lost.

In telecommunication and telecontrol systems, a floating-operation power supply does much more than provide a specified amount of power.

It should provide power when the primary supply fails, manage the battery correctly, account for different load priorities and, where required by the installation, transmit information about its status to the supervisory system.

Therefore, the key selection criterion is not a single power supply parameter, but how well the entire system meets the functions that need to be maintained during a power failure.

The MERAWEX ZEM series combines DC power supply, battery backup, control and monitoring functions. This makes it possible to build power supply systems tailored to the requirements of automation, telecontrol and communication equipment used in power infrastructure.

Once the loads, their requirements and the required backup time are known, the selection process can begin with an analysis of the specific system. MERAWEX can help determine the appropriate power supply model and battery configuration based on these requirements.