Surge Protection for Water Treatment

Surge Protection for Water Treatment

Created by: Glen Zhu | Updated Date: November 18th, 2023

Surge Protection for Water and Wastewater Treatment

Being a fundamental source for the socio-economic development and well-being of mankind, water is one of the most crucial, if not the most, natural resources on Earth.

Therefore, the awareness of accessing clean and reliable resources becomes paramount especially in contemporary societies as people experience a significant improvement in their quality of life. Water and wastewater treatment systems are built to meet the increasing demand for high water quality.

Water and wastewater treatment, collectively referred to as water treatment, encompass any processes that promote the quality of water by removing contaminants and undesirable components or reducing their concentration to make it appropriate for a specific end-use.

The whole process includes coagulation, sedimentation, filtration, disinfection, and sometimes desalination, depending on the source of water and the desired quality standards. The aim is to remove as much suspended solids bacteria, viruses, and other contaminants as possible, ensuring the water is safe for consumption and other applications.

Threats facing water treatment systems

Modern water treatment systems consist of a large proportion of electrical automation in operating facilities, leading to a substantial investment size of up to million dollars. However, digital and electronic components are particularly susceptible to damage from lightning strikes and surges because they heavily rely on computer control systems, which poses significant threats to equipment malfunction, arousing the potential for uninterrupted operating processes, costly downtime, and even devastating fires.

Lightning strikes: When lightning strikes occur, the strikes can generate extremely high voltages and currents that are well beyond the designed standards of electrical components, greatly threatening not only the connected devices but also the structural integrity of buildings, the entire water treatment system, and the staff working within the vicinity.

Surges: Electrical surges, resulting from direct or indirect exposure to lightning, power switching on and off, improper wiring, manifest as abrupt overvoltage spikes. These surges are damaging as they can jeopardize electronic components, disrupt control mechanisms, and stress essential equipment. Consequently, the disruptions, including malfunctions, power supply interruptions, and data loss, halt the water treatment process, thereby compromising water quality and supply reliability.

Even a single lightning or minor transient event can bring about tremendous upset in terms of finance and system safety within a water treatment plant. Implementing a comprehensive lightning protection system to safeguard all equipment from lightning and surge damage can entail substantial investments, often reaching tens of thousands of dollars. Yet, choosing not to do so can just cause much greater costs in the long run.

Equipotential bonding and Earthing system

The concepts of Earthing system and equipotential bonding are always important and cannot be overlooked for any industrial plant.

Water treatment plants, responsible for purifying water for consumption, heavily rely on intricate electrical systems and equipment. The equipotential bonding, which ensures all conductive parts are at the same electrical potential, is fundamental. By implementing a comprehensive intermeshed earth-termination system, the facility ensures a uniform electrical potential across all conductive parts.

This uniformity not only neutralizes the risk of electrical shocks to personnel but also creates a stable environment for electronic devices. With a consistent electrical potential, sensitive equipment operates securely and predictably, enhancing its performance and longevity.

Equipment reliability is especially crucial in water treatment plants where any disruption can directly impact the availability and quality of the treated water supplied to communities. Improper or insufficient bonding can lead to electrostatic discharge and ground loops, resulting in equipment malfunctions, data corruption, and even permanent breakdowns.

Additionally, the Earthing system is crucial in lightning protection systems. Grounding systems that connect electrical installations to the Earth are essential for dissipating lightning strikes and electrical surges safely. Each separate plant building must be grounded to the Earth.

Figure 1 – Intermeshed bonding system

Sewage water plant

Sewage water plants serve as the backbone of wastewater treatment, accommodating a wide array of operational facilities, advanced instruments, and precise sensors, ensuring a consistent supply of clean water for various end uses. Whereas, sewage plants, often situated in remote areas and characterized by their substantial size, are highly vulnerable to damage caused by lightning strikes and electrical surges. Lightning strikes pose a significant threat, potentially disrupting operations, interrupting water supply, as well as threatening plant safety. To safeguard the sewage plants and mitigate risks, implementing robust surge protection measures is imperative.

Figure 2 – Block diagram of sewage water plants

Pumps and lifts

Each separate pump and lift is adjacent to direct lightning, and ground potential rise and is protected by a type 3 TLP-60 (60v) surge protector to divert excess energy and safeguard the pumps from surges that may occur within the immediate vicinity.

In addition to this, pumps within sewage plants are typically located outdoors, increasing the likelihood of experiencing a ground potential rise. Therefore, a standard sewage plant configuration involves the strategic installation of Type 1 AC surge protection devices (SPDs) FLP25-275/3S+1 at the main electrical service entrance to counter direct lightning strikes and manage lightning-induced ground currents effectively.

Type 1 surge arresters are specifically designed for large-scale applications, providing comprehensive protection against both direct and indirect lightning strikes. FLP25-275/3S+1 Din-Rail pluggable SPD is developed as the best solution available to protect service entrances at an industrial site that can withstand an impulse current of up to 25kA (10/350 μs).

Furthermore, type 2 Surge arrester SLP40-275/3S+1 is integrated into the main distribution panels directly connected to the pumps to redirect any remaining transients away from the motor systems. The entire comprehensive surge protective device approach ensures the redirection of any remaining transients away from the motors, thereby safeguarding sensitive components and ensuring their uninterrupted operation.

For measuring sensors and instruments connected to pumps and lifts, FRD2-5 one-pole telecom surge protector is installed to the panel entering sensors and instruments to prevent electrical hazards.

Power supply

Power and data networks within the water treatment plant are particularly sensitive to switching and lightning transients due to a combination of factors. Heavy electrical equipment like pumps and motors cause abrupt switching, amplified by intricate systems involving transformers and control panels, will spread disturbances across networks. The vulnerability to lightning strikes, coupled with lengthy cable runs acting as antennas for external electromagnetic interference, further heightens the risks.

The installation of a type 1+2 surge protector, namely FLP12,5-275/3+1 for 3-phase for three-phase setups, is mandatory at the main panels for data centers and power grid.

And at distribution panels, type 2 surge protectors, SLP40-275 for three-phase must be installed in place at service entrance to guarantee uninterrupted power supply.

 These certified devices, approved by TUV and CB, utilize top quality metal oxide varistor. It also has a Rockwell hardness of 105 degrees and materials used comply with RoHS 2.0 standards, ensuring environmental safety and adherence to regulations.

Control system

The facility control system is equipped with various computer-based monitoring components, including CAMbus control, security cameras, lighting control systems, motor control systems, etc. CAMbus (Control Area Network bus) is a communication protocol used in the automation and control industry. It is a robust and real-time network protocol designed for connecting various control devices within a water treatment plant. To protect the control system from being damaged, FLP25-275/3+1 is chosen to withstand extra overvoltage transients induced by all kinds of sources. The unique design makes it effectively extinguish the arc and release the trigger when the temperature rises at a certain level to avoid a potential fire.

Data network

Sensor data and measurements are crucial components to sewage management transmitted through telecontrol signals. The data holds immense value, often surpassing the worth of the facilities themselves because losing data renders all the effort invested in its collection futile, demanding months or even years to regain the lost insights. The telecontrol systems are protected by combined lightning current and surge arresters capable of carrying lightning currents with an appropriate voltage protection level for terminal equipment and minimum requirements space. For example, FLP12,5-275/3+1 is capable of withstanding surges and transients for the use of telecontrol protection.

Shied earthing at both ends of the short wires from the measuring transformer to the ultrasonic sensors is paramount. Placed underneath the water to monitor both water and wastewater, sensors and flow meters are constantly exposed to a challenging and potentially hazardous setting, adding the likelihood of short circuits occurring. Shield earthing acts as a protective barrier, providing a direct and controlled path for excess electrical current to dissipate harmlessly into the ground, minimizing the risk of short circuits.

Data lines are integral components in modern sewage plants, facilitating efficient monitoring and control. Utilizing data line surge protectors can prevent voltage spikes from damaging data communication equipment. Moreover, wireless telemetry systems, relying on RF coaxial connections, can be protected using specialized wireless telemetry-RF coaxial surge protectors.

4-20 mA signal and Profibus

Within water treatment plants, 4-20 mA signals are commonly used to monitor and control ensure the smooth operation of various processes. Profibus, or “Process Field Bus”, stands out as a widely used industrial communication protocol tailored for process automation applications.

To safeguard both 4-20 mA signals and Profibus communication, shield earthing at both ends of the wires is mandatory from measuring transformer to the ultrasonic sensors and power supply connection respectively. The shield of the bus cable must be consistently routed and grounded with low impedance both via the sensor and surge protective devices. Shielding procedures have to be adhered to standard IEC 60079-14.

Figure 3 – 4-20 mA power supply

Figure 4 – 4-20 mA EX (i) surge protection for measuring equipment

The pH value and temperature are transmitted to the sewage plant control as two independent 4-mA signals, each functioning as independent channels for their transmission. Shield earthing is placed at both ends of the lines from the measuring transformer to the electrode of the hose fitting, eliminating the risk of electrical interference.

The challenge escalates when dealing with explosive atmospheres (Ex). When the measuring transformer and explosive environment isolation amplifier are placed at a distance from each other, Ex (i) surge protection devices are installed at both ends of the connecting cable in such scenarios. Additionally, outside the explosive environment zone, surge arresters are deployed to uphold the integrity of the 4-20 mA signal and the power supply system beyond.

Figure 5 – Profibus and power supply system

Figure 6 – Profibus PA Ex (i)

Within hazardous zones prone to explosive atmospheres, level measuring sensors are connected to control systems through intrinsically safe PROFIBUS PA unit. Given the absence of an external power supply, the emphasis is placed on securing the bus connector, Ex(i)-type SPDs have to be housed into the metal enclosure, positioned upstream of the measuring sensor.

Switchgear cabinets with PLCs

Switchgear cabinets are electrical cabinets used to control, protect, and isolate electrical equipment. They contain switches, fuses, circuit breakers, and other devices to manage electrical power distribution and prevent electrical faults. The cabinet must be grounded to the earth in case of any surges induced by external or internal lightning. One of the key components of surge protection is metal grounding, particularly the grounding of cabinet doors, due to their conductive nature. By establishing a direct and low-resistance connection between the metal doors and the grounding system, the surge energy finds a pathway to dissipate harmlessly into the earth.

Figure 7 – Switchgear cabinet

Type 1 surge protective devices are typically installed at the main electrical service entrance and the point where the main power supply enters the facility, safeguarding the entire facility. Closer to the equipment, type 2 SPDs are responsible for handling moderate surges generated internally, often due to switching operations within the facility.

For Programmable Logic Controllers (PLCs), type 3 SPDs provide localized protection for sensitive electronic devices. The SPDs can be installed at the power supply input of the PLC panel. Additionally, communication lines, such as RS-485, connected to the PLC should be protected using type 3 SPDs designed for data lines.

Any signal lines entering from outdoors into the system via cables (except for optical cables), PLC power lines, power lines for instruments leading from indoors to outdoors, and signal lines all require the installation of lightning protectors and surge protection devices. After installing the SPDs, there is no impact on the existing lines, and they are easy to install and use. They can be repeatedly used, and their functionality can be restored after a lightning strike.

Figure 8 – PLC programmable logic controller

Power over Ethernet

Ethernet serves as a ubiquitous communication protocol utilized extensively in numerous sectors. In water treatment plants, Ethernet networks can be wired or wireless depending on different facilities. Power over Ethernet (PoE) is a technology that enables both data and electrical power to be transmitted over a single Ethernet cable.

The DT-CAT 6A/EA is certified to support the highest transmission speeds and cabling categories utilized in PoE networks. Notably, it is also suitable for Ethernet networks with lower categories. The DT-CAT 6A/EA surge protector is utilized in signal network applications where data transmission speeds reach up to 10 Gbps. Its transient protection circuit employs high-energy gas discharge tubes (GDT) and a network of fast-response silicon avalanche diodes (SAD) to swiftly and sharply clamp very large surge events.

It is recommended to practice protection and bonding on every Ethernet line as close as possible to the sensitive controllers, switches and routers.

Maintenance and inspection

Timely maintenance and regular inspection of surge protective devices can’t be overlooked to ensure the optimal performance and longevity of water treatment facilities. One critical reason for this diligence is the inherent nature of Metal Oxide Varistors (MOVs), which are fundamental components integrated into SPDs. MOVs are designed to divert excess voltage away from sensitive equipment during power surges. However, their effectiveness can be compromised over time due to wear and tear, particularly after encountering significant electrical events.

Perform regular visual inspections to identify damage, loose connections, or overheating in SPDs. Conduct quarterly functional tests to ensure MOVs are diverting surges effectively. In addition to that, Arrange an annual professional inspection for a comprehensive evaluation by certified technicians.

For SPDs installed at equipment and facilities that are exposed to lightning without the protection of combined SPDs, conducting more frequent inspections at vulnerable sites is imperative to ascertain the system’s operational integrity. Monitoring the visible window, denoted by its green hue, serves as an indicator of proper functionality. The visible window turns red indicating varistor failure resulting from substantial energy exceeding its designated threshold. LSP DIN rail pluggable SPDs facilitate the replacement of failed poles within the SPD, ensuring seamless restoration through the installation of new components.

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