Created by: Glen Zhu | Updated Date: January 9th, 2024
Electrical power distribution boards are as essential as any electric equipment, serving as the central hub in delivering electricity to different compounds and facilities. They are indispensable components, functioning as the heart of the electrical systems. Comprising highly integrated plants and intricate wiring, the protection to the system from lightning and surges has consistently been a significant challenge.
When subjected to attack from transient overvoltages, the aftermath extends beyond the potential damage to distribution board, there exists a high risk of harm to downstream equipment connected to the boards. To guarantee both equipment functionality and the safety of individuals.
The necessity of surge protection to power distribution boards can never be overstated. Among all protective measures, surge protection devices (SPDs) is an important aspect and is wildly applied in todays’ electric systems.
What is a surge?
A power surge occurs when the voltage in an electrical circuit exceeds its normal operating range for a brief period. A sudden surge in voltage can be catastrophic, bursting delicate components or overloading and crippling connected appliances. Designed for a precise range, electrical systems can falter under excessive strain, leaving behind a trail of malfunction and damage.
This phenomenon can happen due to various factors, including lightning strikes being the most common and direct causes, power switching activities, improper wirings, etc.
Within the framework of power distribution boards, while circuit breakers can protect against sustained overcurrents, they may not be effective against the short-duration high voltage spikes associated with power surges. Thus, adequate and effective surge protection measures are essential to ensure the integrity and longevity of the electrical system.
What is surge protection?
Surge protection is a mechanism designed to safeguard electronic devices, electrical equipment, and systems from voltage spikes or surges. Any protection alone cannot effectively defend the target area, the effectiveness of protection lies in the collective integration of various components designed to work synergistically.
Surge protection, for example, involves a combination of devices such as surge protectors, lightning rods, and suppressors strategically placed within an electrical system. It encompasses concepts such as equipotential bonding, emphasizing the importance of maintaining uniform electrical potential across connected equipment and structures.
All in all, to effectively secure the protected area, a holistic strategy is significant for the whole system.
SPDs, an abbreviation for surge protective devices, meaning protective equipment intended to prevent electrical and electronic systems from potential damage caused by voltage spikes or transients. SPDs operate as miniature dams within the electrical system, monitoring voltage levels and diverting excess energy away from vulnerable circuits. When operating under normal conditions, Surge Protection Devices (SPDs) exhibit high impedance, allowing the regular flow of electricity without interference.
However, when a surge event occurs, the characteristics of SPDs rapidly change. In response to the surge, SPDs transition to a low-impedance state, allowing them to effectively divert and dissipate the excess energy to the ground.
Power Surge Protection Devices (SPDs) come in various types, each serving a distinct role in fortifying electrical systems against transient voltage surges.
In application of power distribution boards, they can be classified as follows:
Composed of Metal Oxide Varistors (MOVs) and Gas Discharge Tubes (GDTs) as primary components, surge protection devices (SPDs) employ a dynamic mechanism to enhance electrical systems against transient voltage surges.
MOVs, with their nonlinear voltage-current characteristics, swiftly respond to surges by conducting excess voltage to the ground, limiting its impact on the connected equipment. On the other hand, GDTs act as fast-responding switches that trigger when the voltage surpasses a certain threshold, providing an additional layer of protection.
For seamless integration into existing electrical systems, DIN-rail Surge Protective Devices (SPDs) shine. Their compact design, ideal for space-constrained distribution panels, effortlessly adapts to standard equipment racks. Modular construction permits convenient expansion or module replacement, simplifying maintenance within power distribution setups.
Furthering ease of use, internationally standardized DIN-rails guarantee compatibility across diverse configurations, streamlining procurement and installation. DIN-rail SPDs actively protect against overvoltage within power distribution environments by effortlessly aligning with established structured wiring systems.
Beyond practicality, DIN-rail electric power SPDs lend a touch of elegance to their surroundings. The streamlined appearance enhances the organization and aesthetics of critical electricity supply systems installations.
Selecting suitable Surge Protective Devices for electrical distribution systems is critical to have reliable protection of electrical and electronic equipment. The choice of SPDs involves considering various factors to effectively clamp and withstand high-energy transients, preventing disruption, downtime, and equipment damage.
An ideal SPD for distribution boards should exhibit a low-residual voltage during high-energy surge events and possess a higher nominal discharge current, crucial for equipment protection. Achieving both UL Recognition and IEC compliance in a single part number streamlines global utilization, reducing inventory size and simplifying part allocation.
Key features to look for in SPDs for distribution boards include an interlocking tab mechanism for vibration resistance, compact size for flexible panel design, and a visual life indicator for quick module replacement status checks, preventing a loss of protection and saving time.
Remote contacts enable the connection of the SPD to a programmable logic controller, allowing for quick alerts about the device’s health. Pluggable modules facilitate fast and simple replacements, minimizing maintenance and downtime without the need for tools.
Incorporating thermal protection in SPDs eliminates catastrophic failure, ensuring long-term reliability. An IP2+ rating, where the first number is 2, provides protection against solid objects up to 12 mm, enhancing worker safety and overall effectiveness in diverse environments.
These features collectively contribute to the optimal performance of SPDs in distribution boards, safeguarding equipment and maintaining operational efficiency.
Understanding the key features of a reliable surge protective device is only the first step; it doesn’t automatically translate into the ability to select the right product for specific protected areas.
IEC standards 60364-4-44 and 60364-5-53, published in September 2015, mandate the use of Surge Protective Devices (SPDs) not only in commercial and industrial facilities but also in residential buildings. SPDs must be installed at the facility’s supply point, typically the main distribution board (MDB)/low voltage main distribution, to guard against common-mode interference.
For lightning protection, facilities with external lightning protection require a combined arrester, with type 1 SPDs mandated for MDB/low voltage main distribution to meet specific discharge, short-circuit withstand, and follow current extinguishing criteria.
Selecting the appropriate surge arresters entails addressing critical aspects within your systems, including the power type, grounding reference, and the various types of voltages involved.
For those cognizant of their system’s grounding reference, panel designers can furnish an SPD aligning with the precise clamping voltage requirements. However, the SPD shopping landscape may not always boast customers well-versed in their system’s grounding specifics. In such instances, erring on the side of caution entails selecting an SPD with a Maximum Continuous Operating Voltage (MCOV) surpassing the system’s Line-to-Line (L-L) voltage by a conservative 25%.
The MCOV takes center stage, dictating the SPD’s threshold before clamping kicks in. In cases where the grounding reference eludes clarity, opting for an MCOV exceeding the system’s L-L voltage serves as a safeguard against worst-case scenarios. Inappropriately sized SPDs, whether excessively low or high, usher in consequences impacting vulnerability to overvoltages, longevity, and overall protective efficacy.
Mitigating risks calls for ensuring that the SPD’s clamping voltage maintains a cushion of at least 15% above the circuit’s peak working voltage.
An often overlooked aspect is the size of surge arresters, determined by the secondary side of the upstream transformer rather than the load connection method. Oversized SPDs may pose challenges in distribution board installation, while undersized ones may compromise effective surge protection. Achieving the right balance ensures both space efficiency and optimal protection.
The reference to ground in an electrical system is a crucial aspect that influences the choice of equipment and protection measures. below are eight types of electrical systems, each has different grounding configurations, and the choice of grounding method affects the system’s behavior in terms of safety, fault tolerance, and equipment protection. Here’s a brief overview of each type:
3-Phase, 3-Wire Systems:
No neutral wire, and all three phases are balanced.
3-Phase, 4-Wire Systems:
Includes a neutral wire in addition to the three phases.
Figure 1 – 3-Phase, 4-Wire Systems
3-Phase, 3-Wire Corner-Grounded Delta Systems:
A variant of the delta configuration where one of the corners is grounded.
Figure 2 – 3-Phase, 3-Wire Corner-Grounded Delta Systems
Ungrounded Delta Systems:
Delta configuration without intentional grounding.
Figure 3 – Ungrounded Delta Systems
Impedance-Grounded Wye Systems:
Wye (star) configuration with intentional grounding through impedance (resistor or reactor).
Resistance-Grounded Wye Systems:
Wye configuration with intentional grounding through a resistor.
Single-Phase (Split-Phase) Systems:
Commonly used in residential settings, consists of two conductors with a voltage potential between them.
Figure 4 – Single-Phase (Split-Phase) Systems
High-Leg Grounded Delta Systems:
A delta system with one of the legs grounded, also known as “wild-leg” or “stinger” configuration.
Figure 5 – High-Leg Grounded Delta Systems
When designing electrical panels, panel designers should prioritize selecting the lowest possible voltage protection rating for Surge Protective Devices (SPDs). It ensures a lower clamping voltage, emphasizes the importance of utilizing short lead lengths or short wires for enhanced SPD performance. Longer wires or bent configurations can diminish the protective capabilities of SPDs, making it essential to avoid excessive wire lengths and bends.
Additionally, the installation of surge protection at the main service entrance is paramount, which aims to offer comprehensive defense against transient voltage surges. For larger facilities where critical loads are distant from the main service entrance, employing cascaded protection for sub-panels and equipment is recommended. Careful consideration of wire sizes and configurations during the design and installation process is necessary to optimize the overall effectiveness of the surge protection system.
Incorporating Surge Protective Devices (SPDs) into distribution equipment carries several risks. To minimize the potential for collateral damage to the distribution equipment, those integrating SPDs should place them in distinct and isolated compartments within the distribution equipment. Below is an illustration of the typical internal installation of an SPD within a switchgear assembly. The design and construction of switchgear and switchboards share many similarities, with differences limited to specific components and applications.
Figure 6 – Backward sequence diagram of SPD switchgear installation
In Figure 7, the switchgear assembly is equipped with a primary disconnect (item 1), directing power into the internal bus bars. Item 2 encompasses mechanical, rack-type circuit breakers with adjustable trip mechanisms, strategically placed throughout the remaining switchgear compartments, alongside a dedicated cable compartment.
The presence of separate cable compartments isn’t universal, leading to configurations where conductors share space with the internal bus bars. Within the switchgear, the surge protective device occupies its own compartment, denoted as item 3. This deliberate isolation serves to confine potential collateral damage to the distribution equipment in the event of a catastrophic failure.
While some SPDs feature internal overcurrent protective devices like fuses, others depend on external counterparts, such as fuses or circuit breakers, for short circuit current protection. Regardless of the overcurrent protective device’s location, SPDs are typically installed with a disconnect upstream.
The upstream disconnect, often an external circuit breaker, not only ensures short circuit current protection for the SPD and the upstream conductors but also acts as a means to disconnect the SPD.
Figure 7 – Front view of SPD switchgear installation
The location of circuit breakers often necessitates lengthy conductor runs. This seemingly minor detail can significantly impact the performance of SPDs and even raise safety concerns.
The issue boils down to conductor length. In complex switchgear installations, reaching neutral and ground bus bars, critical connection points for SPDs, can involve conductor runs exceeding 48 inches. Even phase bus bars, dictated by the circuit breaker’s placement, may require considerable conductor lengths to connect with the SPD. These extended journeys come at a cost.
Firstly, longer conductors exhibit higher impedance, a technical term reflecting how much they resist the flow of current. This increased impedance leads to a phenomenon called “let-through voltage.” Simply put, even after activating, the SPD allows some surge voltage to pass through. It compromises the overall protection level, potentially leaving connected equipment vulnerable to damaging voltage spikes.
Secondly, long conductor runs raise safety concerns. Increased impedance can contribute to voltage drop, impacting equipment operation and potentially leading to malfunctions. Additionally, longer conductors generate more heat, increasing the risk of overheating and potential safety hazards.
To address these challenges, several strategies can be employed:
Beyond these measures, remember that every installation is unique. Different equipment has varying surge tolerance levels. Sensitive loads demand prioritized protection, which may influence the selection and placement of SPDs. Additionally, local regulations may dictate maximum allowable lead lengths for SPD installations. Ensuring compliance with relevant regulations is crucial for both safety and legal considerations.
In cases where the Surge Protective Device (SPD) within the main distribution board (MDB)/low voltage main distribution falls short of ensuring the necessary rated impulse withstand voltage level, the incorporation of additional type 2 and type 3 SPDs becomes imperative.
The supplementary SPDs are essential not only within the main distribution board but also in subsequent distribution boards throughout the system. It is necessary to have a energy-coordinated arrangement, as depicted in Figure 8, to optimize the overall effectiveness and reliability of the surge protection system.
Figure 8 – Coordinated energy SPDs located downstream of the primary distribution board.
In complex installations with significant conductor lengths or sensitive equipment, consulting qualified professionals is highly recommended. They can provide expert insights into optimal SPD placement, conductor routing, and compliance with regulations, helping to create a system where efficient protection and optimal performance coexist seamlessly.
To minimize the impact of Surge Protective Device (SPD) failures on electrical distribution equipment, it is recommended to place the SPD in a separate compartment within the switchgear or switchboard. Routine maintenance is crucial for all equipment, with circuit breakers requiring servicing every two years, electrical connections tightening annually, and SPDs needing attention due to transient attenuation or random component failures.
Working on energized equipment within switchgear or switchboard assemblies necessitates a thorough justification and analysis according to NFPA 70E. Article 130.1 of NFPA 70E emphasizes the need to establish an electrically safe work condition before employees operate within the Limited Approach Boundary. However, de-energizing the entire assembly for SPD maintenance may not be feasible due to interconnected critical systems. While live work is possible, adherence to proper safety processes, such as obtaining a “hot work” permit and wearing rated Personal Protective Equipment (PPE), is essential.
Accessing switchgear and switchboard assemblies when energized, particularly in high short-circuit current environments, demands Category 3 or higher PPE. Performing maintenance on energized equipment requires a “hot work” permit, involving an investigation into arc flash, voltage, mechanical hazards, and management approval. Some organizations additionally mandate potential problem analysis to identify adverse actions and implement preventive measures for personnel safety and process downtime minimization.
Table 1 – Personal protective equipment levels
If a connection version is chosen that avoids voltage drop to the SPD when using an SPD set with an integrated backup fuse, considerations for this are unnecessary. The inductivity of a circular conductor in the specified cross-sectional area (16-50 mm²) is approximately 1 μH/m.
Assuming an impulse current of 10kA 8/20 μs, this results in a voltage drop of around 1 kV/m. For a main distribution board with a 4 kV rated impulse withstand voltage, connecting a surge protective device with an additional cable length of approximately 1 m is feasible (Figure 7). Adjustments should be made for higher or lower values than 25 kA 8/20 μs by linearly reducing or increasing cable lengths
Figure 9 – Surge arresters installed in main distribution boards
If local conditions prevent meeting these requirements, users have several options to address the issue, including selecting an SPD with a lower protection level, or opting for an SPD with an integrated backup fuse. Alternatively, installing a second coordinated SPD at the equipment to be protected in series, incorporating additional local equipotential bonding (e.g., through the metal enclosure of the switchgear installation) is a viable solution.
In a TN-C system fed into a main distribution board with the central earthing point at the separation of the PEN conductor to the PE and N conductor, another SPD in a 3+0 configuration can be installed at a maximum distance of 0.5 m.
It is a key to install surge protection devices for both cables and communication systems connected to the distribution system to sustain their optimal performance and longevity.
Failure to implement proper and adequate protection may result in coupled interference, potentially leading to disruptions and damage.
Specifically, for cables, the FRD 2 series offers effective surge protection, mitigating the risks associated with transient events. In the realm of communication systems, the POE surge protector DT-CAT 6A/EA emerges as an exemplary choice, providing protection against power surges and ensuring the integrity of data transmission.
LSP’s reliable surge protection devices (SPDs) are designed to meet the protection needs of installations against lightning and surges. Contact our Experts!
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