DC

DC (Direct Current) is a form of electrical current in which the direction of flow remains constant. Unlike AC, its polarity does not alternate periodically.

DC plays a crucial role in modern OT environments and is used in:

• Electronics
• Battery systems
• PLC power supplies
• Industrial control
• Data centres
• Telecom
• UPS
• Solar panels
• variable frequency drives

While large-scale energy distribution traditionally uses AC, the importance of DC is rapidly growing thanks to digitalisation, battery technology and power electronics.

⚡ Basic principle of DC

In direct current, voltage polarity remains constant.

An ideal DC voltage:

v(t)=Vv(t)=Vv(t)=V

Current direction does not change, so energy flows continuously in one direction.

Typical DC sources:

🔋 DC in industrial automation

In Industrial Automation, DC is widely used for control and electronics.

Typical voltage levels:

24V DC is the industrial standard for:

• PLC
• Sensor
• Actuator
• IO
• Relays
• Safety systems

Benefits of 24V DC:

• Relatively safe
• Reliable
• Low susceptibility to interference
• Compatible with industrial electronics

⚙️ DC power supplies

DC systems require conversion from AC networks.

Typical architecture:

AC mains      │Power supply      │24V DC bus      │PLC / IO / Sensors

Important components:

Within industrial installations, power supplies are often configured redundantly.

🔄 DC and power electronics

DC forms the basis of modern power electronics.

Applications:

• VFD
• UPS systems
• Battery storage
• EV charging stations
• Solar energy systems

Many modern systems work internally with a DC bus.

For example, inside a variable frequency drive:

AC input    │Rectifier    │DC bus    │Inverter    │AC motor

The DC bus acts as an energy buffer between rectification and inverter technology.

🏭 DC motors

Although AC motors are dominant in industry, DC motors are still used for specific applications.

Benefits:

Applications:

• Robotics
• Conveyor belts
• Servo systems
• Embedded systems

Drawbacks:

• More maintenance
• Brush wear
• Less efficient at high power levels

🌐 DC in data centres and telecom

Data centres and telecom environments frequently use DC architectures.

Common voltages:

Benefits:

• Less conversion loss
• Battery integration
• Higher efficiency
• Better energy control

In critical infrastructure, DC is often combined with:

• UPS
• Battery banks
• Redundant power supplies
• Power monitoring

🔋 Battery systems and energy storage

DC is at the core of battery technology.

Applications:

• UPS
• Emergency power
• Smart grids
• Energy storage
• EV systems

Important parameters:

In OT environments, battery systems support:

• Continuity
• Safe shutdown behaviour
• Critical control
• Alarm provisioning

⚡ Power in DC systems

DC power calculation is simpler than for AC.

The basic relationship:

P=VIP=VIP=VI

Where:

There is no distinction between active and reactive power as with AC.

🔥 DC and electrical safety

DC systems carry specific safety challenges.

Key risks:

DC arcs are dangerous because the current does not naturally pass through zero as with AC.

DC systems therefore require:

• Dedicated fuses
• DC switches
• Arc suppression
• Temperature monitoring

Important standards:

• IEC 60204-1
• NEN 1010
• NEN 3140

🛡️ OT security and DC systems

Modern DC systems are increasingly connected to OT networks.

Examples:

• Smart power supplies
• UPS management
• Battery monitoring
• Energy management systems

Risks:

• Remote sabotage
• Voltage manipulation
• Availability attacks
• Malware in power management

Energy systems are therefore also integrated into:

• IEC 62443
• Defense in Depth
• Monitoring
• Zero Trust

🌡️ Practical example: PLC power supply

In an industrial production line:

400V AC    │24V power supply    │24V DC bus    │PLC / IO / Sensors

Benefits of centralised 24V DC distribution:

• Standardised supply
• Easier maintenance
• Reliable control
• Integration with UPS systems

In case of power loss, a DC UPS can provide temporary continuity.

⚠️ EMC and DC systems

DC systems are sensitive to electromagnetic disturbances.

Common causes:

• Switching power supplies
• PWM signals
• Poor earthing
• Long cable runs

Consequences:

Mitigation:

• Shielding
• Proper earthing
• EMC filters
• Segregated cabling

🔄 DC in modern energy infrastructure

DC is becoming increasingly important in modern energy systems.

Key developments:

This creates hybrid AC/DC infrastructure in industrial environments.

📈 High Voltage DC (HVDC)

For very long energy links, HVDC is sometimes used.

Benefits:

• Lower transmission losses
• Suitable for subsea cables
• Better grid stability
• Coupling between different AC grids

Applications:

• Offshore wind farms
• International energy links
• Long-distance transmission

HVDC systems require complex power electronics to convert between AC and DC.

🔍 Monitoring of DC systems

In OT environments, DC systems are extensively monitored.

Important measurements:

Monitoring is integrated with:

• SCADA
• Historian
• Predictive Maintenance
• Industrial AI