Siemens Surge Protection Devices (DPS) - 5SD7

Introduction to Surge Protection

Modern life relies heavily on electronic equipment, making robust protection against electrical surges essential. Transient overvoltages, often caused by lightning strikes or circuit switching, can damage sensitive electronics in homes and businesses. Siemens' Surge Protection Devices (DPS) are designed to mitigate these risks by safely diverting surge currents to the ground.

The Brazilian standard NBR 5410 mandates the installation of DPS in areas prone to overvoltages. Brazil experiences a high incidence of lightning strikes, with millions occurring annually, causing significant economic damage. Effective surge protection is crucial for safeguarding electrical installations and equipment.

Understanding Transient Overvoltages

Transient overvoltages are sudden, short-duration increases in voltage that exceed the nominal level of an electrical installation. These can be caused by:

• Direct Lightning Strikes: When lightning directly hits a building or its immediate vicinity, including the electrical grid. This is the most severe type of surge, carrying immense energy.
• Indirect Lightning Strikes: Surges that occur when lightning strikes a distant location, but the resulting electromagnetic field induces overvoltages in nearby electrical lines. This is the most common cause of damage to electronic equipment.
• Switching Surges: Overvoltages generated by the operation of electrical equipment or the grid itself.

Siemens DPS are engineered to limit these transient overvoltages and safely discharge surge currents.

Types of Surge Protection Devices (DPS)

Siemens offers a comprehensive range of DPS, including:

• Class I DPS: Designed for protection against direct lightning strikes. They are installed at the main service entrance and are built to handle high surge currents.
• Class II DPS: Primarily used for protection against indirect lightning strikes and switching surges. They are typically installed in distribution panels and are suitable for residential and commercial applications.
• Class I+II DPS: Combined devices offering the benefits of both Class I and Class II protection.
• Class I/II DPS: Similar to Class I+II but designed for installations requiring lower surge current discharge capacity.
• Class III DPS: Used for fine protection, installed close to sensitive equipment to provide an additional layer of defense.

Key Technical Specifications

When selecting a DPS, several parameters are important:

• Nominal Voltage (Un): The nominal voltage of the electrical system.
• Maximum Continuous Operating Voltage (Uc): The maximum continuous RMS voltage that can be applied to the DPS terminals without compromising its function.
• Voltage Protection Level (Up): The maximum voltage that the DPS allows to pass to the installation during a surge event. This value must be compatible with the equipment's impulse withstand capability.
• Nominal Discharge Current (In): The current value of an 8/20 µs impulse that simulates indirect lightning effects. It indicates the DPS's ability to withstand multiple surges and influences its lifespan.
• Maximum Impulse Current (Imax): The peak current value of an 8/20 µs impulse that the device can withstand, typically for a single event.
• Impulse Current (Iimp): The current value of a 10/350 µs impulse used for testing Class I DPS, simulating direct lightning effects.
• Response Time (ta): The time it takes for the DPS to react to an overvoltage.

Installation and Coordination

Proper installation is critical for the effective performance of DPS. Key considerations include:

• Grounding and Equipotential Bonding: A well-installed grounding system and equipotential bonding are essential for the DPS to function correctly and protect the installation.
• Conductor Length and Cross-Section: Connecting conductors for the DPS should be as short as possible (ideally less than 0.5m) and have an appropriate cross-sectional area based on the DPS class and system requirements.
• Coordination with Residual Current Devices (DR): When installing DPS with DRs, their placement (upstream or downstream) should follow specific guidelines to prevent nuisance tripping.
• Coordination Between DPS: If multiple DPS are used in an installation, they must be coordinated to ensure that each device operates within its intended parameters, often requiring specific distances between them.

Selection Based on Exposure Level

The selection of a Class II DPS is influenced by the local lightning exposure level (Td) and the characteristics of the power supply line. A formula is provided to calculate an exposure factor (F), which then guides the selection of the appropriate nominal discharge current (In) based on tables that correlate exposure levels with DPS ratings.

Siemens DPS Product Range

The document provides detailed selection tables for various Siemens DPS models, categorized by class (Class I, Class I+II, Class II, Class III) and application (e.g., photovoltaic systems). These tables include specifications such as:

• Model Code
• Poles
• Application
• Nominal Voltage (Un)
• Maximum Continuous Operating Voltage (Uc)
• Impulse Current (Iimp)
• Nominal Discharge Current (In)
• Maximum Discharge Current (Imax)
• Response Time (ta)
• Backup Protection
• Remote Signaling
• Earthing System