Surge Protection for Industrial Control Panels

Surge Protection for Industrial Control Panels

Created by: Glen Zhu | Updated Date: December 07th, 2023

Industrial Control Panels Surge Protection

Surge protection for industrial control panels is not just a recommended practice, but a crucial necessity dictated by regulations and mandatory for safeguarding electrical systems.

[NFPA 79: 2021] 7.8.1 illustrated industrial machinery with safety circuits not effectively protected from the effects of over-voltages due to lightning or switching surges shall have surge protection installed. IEC 60634 standard requires compulsory surge protective devices installation for commercial and industrial facilities as well as residential buildings.

Surge protection has become a general rule for installing the power supply point of any important facilities. This could be easily implemented in residential buildings since the size of the backup fuse is sufficient, there is no requirement for additional fuse protection.

However, the situation varies for large-scale main power distributions. The common industrial control panels are equipped with a backup fuse larger than 315A, and surge protection devices for electrical panels work functionally with a backup fuse. This backup fuse has a high demand for cable lengths and protection levels, thus it is worth paying attention to the installation of surge protective devices.

The Importance of Surge-Protecting Control Panels

Control panels could be seen as a central power hub that connects with various electrical equipment, when lightning, and surges can easily cause equipment damage, surge disruption, and downtime losses. Here are the key benefits of industrial control panel surge protection.

Equipment protection: Surge protection helps prevent unwanted over-voltages passing through the control panels and reaching to electrical infrastructure at the incoming supply. The service life of the equipment is extended, being safeguarding from costly damage and disruptions.

Downtime Prevention: Surge protection helps avoid surge-induced failures to maintain uninterrupted operations of industry and households. Large facilities can run continuously and prevent unnecessary downtime loss, especially in some industrial spots.

Safety Assurance: Surge protection promises the safety of personnel by reducing incidents of fires and injuries due to electrical surges. That is the priority no matter what the condition is.

Cost Reduction: Surge protection proves its substantial cost savings over time by reducing equipment replacement costs, downtime-related losses, and maintenance expenses while involving an initial investment.

Considering these favorable conditions, the installation of surge protection devices in distribution boards is necessary.

Cascaded Surge Protection

Installing a surge protection device in the main distribution box could discharge the most overcurrent, but it is insufficient to fully protect the whole system as the fact that residual energy could pass to damage the sensitive electronics. Therefore, the terminal surge protector is always mounted close to the equipment.

Additionally, short-circuit protection is necessary depending on the scale exposure and sensitivity of the equipment. This means only the combination of several surge protection devices can ensure effective protection for whole control panels.

SPDs are installed at all levels of the electrical distribution system by what IEEE called “protection in depth”. IEEE Standard 1100 recommends cascading levels of protection from the service entrance to distribution and branch panels, and even protection for individual critical loads. The closer to the service entrance, the more robust the device should be. This protection in-depth strategy protects the facility and critical loads.

Figure 1 – Cascaded surge protection for the control panel

The statement from IEEE emphasizes that achieving a protection level of 99.5% is a practical choice. This level of protection significantly reduces the incidence of direct lightning strokes, making it a reasonable compromise between protection and practicality.

Location and Types of Surge Protective Devices

Providing proper surge protection to a facility and its equipment requires more than a single SPD located at the service entrance. We recommend cascaded SPDs with a proper surge current rating for each location. of system protection.

Comprehensive protection can be classified into three levels: main protection, circuit protection, and terminal protection. This provides superior suppression for a service panel or critical load. A single SPD, no matter how big or expensive, will not provide the same level.

Figure 2 – Location and types of surge protection devices

The protection at the origin of the power supply shunts most of the incident energy to the equipotential bonding system and to the earth. Type 1 combined surge protector is installed in the main distribution box, 80% overcurrent could be dissipated safely.

Type 1 Surge Protection Device SPD for Control Panels

Installing surge protectors at the entrance point, act as the first line of defense against voltage spikes and surges entering the electrical system. This primary protection helps prevent surges from propagating further into the building’s wiring and reaching sensitive electronic devices.

The shorter the distance between the surge protector and the main power source, the more effective the protection. Installing surge protectors at the entrance minimizes the length of wiring that is exposed to potential surges, reducing the risk of voltage spikes reaching sensitive equipment.

However, it is impossible to discharge 100% overvoltage at once, type 2 surge protector is added close to the electrical equipment to precisely protect sensitive equipment.

The faster a surge protector can respond to a transient event, the better it can divert the excess energy away from the equipment. Installing surge protectors close to the equipment shortens the distance the surge has to travel before encountering the protective device.

Voltage drop can occur over long wiring distances. By placing surge protectors close to the equipment, the impact of voltage drop is minimized, ensuring that the protective device can effectively respond to surges without a significant reduction in its effectiveness.

Type 2 Surge Protection Device SPD for Control Panels

Surge protectors can be tailored for specific circuits or pieces of equipment. Installing them close to the equipment allows for a more targeted approach to protection based on the specific needs of each circuit or device.

In case the surge protection device exceeds its limitation capacities, it may be destroyed by short-circuiting itself. Additional protective devices must be installed in series upstream of the surge protection device.

Short circuits occur when an unintended low-resistance connection is established between two conductors in an electrical system. SPD must have a short-circuit withstand capacity (ISCCR) at least equal to the short-circuit current at the point of connection.

Another SPD in a 3+0 configuration is required at a maximum distance of 0.5m when the main distribution box is powered by a TN-C system.

Figure 3 – Surge protection devices installed in the main distribution box

Protection of Information Technology Cables

IEC standards do not cover data and telecommunications cable protection, but it’s recommended for complete surge protection.

In contemporary buildings, numerous functional modules are equipped with both main power supply and telecommunications connections. Consequently, interference can potentially be transmitted through both of these channels. This applies particularly to typical information technology cables that are intended to be connected.

Various cables like telephone, DSL, data lines, building automation, etc., should be considered for protection as well.

Installation of Surge Protection

Incorrectly installed surge protection exposes the whole control panel and connected devices to a higher risk. Surge protection works correctly when cable length, the distance between SPDs and devices, and the cross-section are regulated.

If the cable length between SPD and the device is over 10m, extra protection measures are required.

The protection level (Up) of SPD should not exceed 80% of the rated impulse withstand voltage of electrical equipment. Consideration of voltage drop on connection wires with a max length of 0.5m.

Excessive long cables increase the effective voltage protection level in the switching device to a level that is no longer adequate.

Figure 4 – Cable lengths and voltage protection level in a switching device

The voltage protection level Up between the active conductors and the protective conductor shall not to exceed the necessary rated surge voltage Uw.

For normal residential buildings, the household equipment usually meets the rated surge voltage of 1.5 kV or 2.5 kV, but in a large main power distribution, all the equipment is up to 4 kV or 6 kV.

Voltage Drop on the connecting cables

Voltage drop is often underestimated but must be taken into consideration when evaluating the overall effective voltage protection level. The voltage drop over the connecting cables can quickly reach a value that is higher than the voltage protection level of the SPD.

To minimize voltage drop, it is advisable to use larger conductors with lower resistance or increase the voltage supplied to compensate for the drop. Calculating voltage drop is crucial in designing electrical systems to ensure that the voltage at the load (end of the circuit) remains within acceptable limits for proper and efficient operation.

Table 1 – Voltage drop in connection cables with different impulse current loads

Surge protective devices are not always connected with cables, copper rails are typically installed for industrial control panels, they have a lower inductance than cables due to their geometric shape.

The inductance of a mounting plate is significantly lower than that of a cable, resulting in a considerably reduced voltage drop during a pulse surge current. However, it is essential not to overlook the voltage drop across the mounting plate, and careful consideration should be given to the connections on the plate.

For instance, when dealing with a pulse surge current of 10 kA (10/350 µs), a straight 1-meter conductor may experience a voltage drop of approximately 1 kV. However, large switching devices often use type 1 Surge Protective Devices (SPDs) with discharge capacities of 25 kA per position and up to 100 kA in total – exceeding the normative 10 kA figure. The tenfold increase in di/dt results in a tenfold voltage drop, turning the initial 1 kV into a rapid 10 kV.

Table 2 – Voltage drop on different geometry of the connection for various pulse surge currents

Refer to Table 2, you can roughly determine the overall protection level in an electrical system depending on different dimensions and materials of connections.

Effect of a Backup fuse on the voltage protection level

The actual voltage protection level of the SPD adds up the partial voltages across all connecting parts between the line conductor and the protective conductor. When dealing with a type 1 SPD, the backup fuse must have a high rating to safely handle the nominal surge current of 25 kA per position without tripping.

Figure 5 – Voltage protection level in a switching device with a backup fuse

The SPD with external fusing and integrated fusing varies in how the overcurrent protection is implemented. The external fusing is a separate component from the SPD and is often installed upstream or in line with the SPD.

It is responsible for interrupting the current in the event of a sustained overcurrent or fault condition. It protects both the SPD and the connected electrical system.

In contrast, an SPD with integrated fusing incorporates the overcurrent protection directly within the SPD housing. The fusing mechanism is part of the SPD unit itself.

It is designed to interrupt the current if the surge protection device is exposed to a high-level surge or experiences a fault. This design simplifies installation as the protection is contained within a single unit.

The choice between SPDs with external fusing and integrated fusing should be taken into account for the whole installation.

Follow these guidelines of surge protection installation in distribution boards, take the return of investment.

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