Waste water treatment plants (WWTP) play a vital role throughout the world. Making water safe for industrial and human consumption, controlling water pollution, and reducing the chance of waterborne illness are just a few responsibilities that WWTPs take on each day. To make things even more difficult, WWTP operators are now feeling the pressure to perform the same duties while significantly reducing their energy consumption.
Waste water treatment plants use a substantial amount of electricity to operate efficiently. Old electrical architecture did not originally take into account the need to conserve energy and were focused solely on maximizing productivity.
Today, unpredictable energy costs and environmental concerns are raising the stakes for WWTP operators. It is now critical that plant operators and electrical network designers work together to implement electrical distribution architecture that optimize plant production. By doing so, waste water treatment plants can become as safe and efficient as possible.
Rising Challenges for Waste Water Treatment Plants
Both electrical engineers and WWTP operators are feeling the pressure to make waste water treatment plants safer and more efficient. With rapidly changing regulations, energy markets, and new technologies, designing a successful electrical architecture for WWTPs is now more important than ever before.
WWTP Operator Challenges
While advancements in technologies have helped waste water treatment plants, operators still find themselves struggling to overcome a few challenges. One of the biggest challenges is that of energy conservation. As one of the largest expenses of a waste water treatment plant facility, operators are constantly looking for ways to lower their energy consumption while improving performance operations. In addition, keeping on top of rapidly changing local and federal regulations and adhering to them can be difficult.
Plant operators are now working closely with electrical engineers in order to tackle some of their biggest challenges. By establishing superior electrical networks in their facilities, operations can become safer, more efficient, and more cost-effective than ever before. It is also an area that plant operators can’t neglect if they don’t want to run into big problems later. Because of this, investing in electrical distribution equipment is a smart and cost-effective method of significantly improving a plant’s performance.
Electrical Network Designer Challenges
Electrical network designers also face some challenges when creating an electrical distribution system for WWTPs. Not only must the electrical network design allow operations to be efficient, reliable, and scalable, but it must also do so while cutting operating costs.To do this, it is important that electrical network designers establish the best electrical distribution architecture by inspecting the WWTP closely and performing an in-depth analysis of operations. Other factors that electrical engineers must keep in mind include the following:
Reliability:
First and foremost, a WWTP’s electrical network needs to be able to minimize downtime and be as safe as possible.The safety of those working at the plant is paramount and needs to be the first consideration when installing an electrical distribution system.
Cost-effectiveness:
After reliability, cost-effectiveness is the WWTP operator’s biggest priority. This can be difficult because it requires electrical engineers to find the balance between cutting significant costs while still retaining a high degree of operational safety. In addition to capital expenditures, it is important for electrical engineers to consider operational expenses over the WWTP’s lifetime.
Scalability:
Because of continually changing codes and standards, electrical network designers must make the electrical network system scalable. Being able to easily upgrade a WWTP’s electrical system when the time comes will help reduce downtime and cut costs.
Efficiency:
Maximizing the efficiency of a waste water treatment plant is the ultimate goal of any plant facility. To do so, electrical engineers will need to recommend the right electrical configurations and the best electrical equipment to go with it.
Environmental concerns:
Many WWTP operators are looking to improve the sustainability of their processes by reducing their CO2 emissions. This can benefit plant operators in the long run by helping them stay ahead of ever-changing codes and regulations. Electrical engineers can suggest waste monitoring systems that can be easily integrated into the plant’s electrical network.
Electrical Distribution Architecture Networks
for Waste Water Treatment Plants
In order for electrical network designers to recommend the proper architecture and equipment for WWTPs, it is helpful to classify them into four main groups based on the size of each plant. The size of the plant is determined by the number of dwellings treated, the volume of water that is treated at the plant per day (m3/per day), and by each plant’s power demand. The four sizes are described below:
T1 Plant:
These plants are small, autonomous, and less complex, serving anywhere from 1,000 to 10,000 dwellings and treating 1,000 to 5,000 m3/per day. Their power demand is 25 to 125 kVA.
T2 Plant:
T2 plants are small-sized plants that serve 10,000 to 100,000 dwellings and treat anywhere from 5,000 to 50,000 m3/per day. Their power demand is 125 to 1250 kVA.
T3 Plant:
T3 plants are medium-sized plants that serve 100,000 to 500,000 dwellings and treat 50,000 to 200,000 m3/per day. Their power demand is 1.25 to 5 mVA.
T4 Plant:
These plants are large or very large waste water treatment plants that serve 500,000 1,000,000 dwellings and treat 200,000 to 1,000,000 m3/day.
Electrical Network Architecture Recommendations
Based on Plant Types
In order for each WWPT to operate in a safe and cost-effective manner, it is essential that the correct electrical network architecture and equipment is chosen. This will enable plant facilities to cut down on energy usage and enhance the plant’s longevity. It is also important for electrical network designers to take other factors into account, such as the plant’s availability, reliability, and maintainability.
T1 Plant Recommendations
Because T1 plants have low power demands and a single radial feeder configuration provided by a utility company, it would be a low-cost means of power distribution. However, as one of the simplest system topologies, single radial feeder systems come with one significant drawback. If the feeder fails, there would be no alternative source to the transformer and, therefore, would result in a loss of power and equipment failure.
The power supply could also be interrupted in the case of transformer failure, in which the radial feeder system would be ineffective until a replacement transformer was acquired. This will need to be taken into account when choosing an electrical distribution architecture.
Recommended architecture:
Because T1 plants use less than 125 kVA, they require a simple electrical distribution architecture that will reduce operational expenses and save space. A radial single feeder with low-voltage electrical network is recommended.
Additional equipment:
Equipment for this architecture would include a low-voltage (LV) switchboard, variable speed drive controller, soft starter (for fixed speed pumps), and power meters.
T2 Plant Recommendations
T2 plants are not autonomous, but they are still smaller plants with power requirements ranging from 125 to 1250 kVA. These plants will need a low to medium-voltage (LV/MV) supply as part of their electrical distribution system. Because of the additional motors, T2 plants can have voltage harmonic problems, which can lead to equipment failure.
Recommended architecture:
A radial double feeder with a simple medium-voltage electrical network.
Additional equipment:
This electrical architecture would work best with at least one low-voltage switchboard to supply your process units, two redundant transformers, a fixed low-voltage capacitor bank, intelligent motor control center (MCC), an Uninterruptable Power Supply (UPS), and power meters with communication abilities that can send information to your local Supervision Control and Data Acquisition (SCADA) system.Active harmonic filters are also recommended.
T3 Plant Recommendations
T3 plants are large and have high operating costs, in addition to a greater impact on the environment. As such, these plants require a medium-voltage electrical network architecture that enhances reliability and performance. This electrical network should be carefully monitored with specific systems. Superior motor control systems are required, as well, due to the greater number of motors that often use variable speed drives.
For plants of this size, a ring-circuit service can be used from the WWTP’s electric utility that will feed the medium-voltage system. A radial single feeder system could be used, but plant facilities will have better availability with a medium-voltage loop architecture. However, plant downtime must be avoided, making it important to install a few ML/LV transformers that can help stabilize normal operations in the case of transformer failure. LV switchboards should be used to supply process units.
Recommended architecture:
Medium-voltage electrical network with a radial single feed or an open MV loop architecture.While the radial single feed architecture is less costly, it does not provide as much power availability asthe open MV loop architecture. Because of this, the open MV loop may be a better choice for larger plant facilities
Additional equipment:
For a plant of this size, it is best to install multiple LV/MV transformers in the case of transformer failure. Other equipment includes an MV switchboard or a ring main unit (RMUs) for tough environments, MV protection relays, LV/MV transformer, MCC, capacitor banks, variable speed drive controller, harmonic filters, a UPS system, and a power meter.
T4 Plant Recommendations
With power demands ranging from 5 to 25 mVA, plants of this size will need a large installed power base. With higher operating costs and energy usage, it is particularly important that these WWTPs are managed properly. Large WWTPs will have many motors that use variable speed drives, making it necessary to have intelligent motor control systems in place.
Recommended architecture:
Feed the MV system with a double supply service (in case of malfunction) from the waste water treatment plant’s electric utility.The primary MV switchboard would ideally be located in the main electrical room. An open MV loop is recommended for a plant of this size, as it offers more reliability and can be easily upgraded or made cheaper. It can also be controlled using an automatic reconfiguration system for faster and safer operations.
Additional equipment:
Multiple transformers are recommended in the case of LV/MV transformer failure. Other equipment includes a ring main unit, MV switchgear, MV protection relays, motor control centers, capacitor banks, variable speed drive controller, and harmonic filters.
Electrical Distribution Architecture for All WWPTs
All WWPTs should consider using the following in order to make their plant as efficient and reliable as possible:
- Efficient metering architecture that is adjusted based on plant size.
- Uninterruptible power supply (UPS) unit (if power failure is not acceptable).
- Power factor correction capacitors.
- Motor protection and control systems.
- Motor starters.
- Power monitoring and control systems.
Securing Power Supply
It is extremely important that all waste water treatment plants have power that they can depend on. UPS units and back-up generators are essential to WWTPs that must keep their equipment running safely without the loss of power.
UPS units:
UPS units are battery-operated and can prevent power loss occurring for a limited time. UPS systems are frequently used with back-up generators to maintain power supply for longer and can be used with systems that are sensitive to voltage disturbances as well.
Back-up generators:
Back-up generators are used in the case of an outage and are key pieces of equipment for T3 and T4 plant facilities. While back-up generators do not normally run on medium voltage, there are a few exceptions.
Combining both UPS units and back-up generators with monitoring and control systems is critical to securing your WWTP’s power supply and can also be used for preventative maintenance purposes. By testing back-up equipment regularly and monitoring it, operators will be able to save themselves money and improve their operations. Additionally, monitoring and control systems help ensure the safe operation of your plant while also helping increase its efficiency.
Conclusion
Effective treatment of water waste is critical to preventing disease and providing communities with safe water consumption. With unpredictable energy costs and environmental concerns, WWTPs are looking to implement more efficient electrical distribution networks that can reduce energy consumption while maximizing their plant’s operations.
To accomplish this goal, electrical engineers will have to understand the best practices for designing and selecting electrical distribution architecture and equipment for each individual plant. By doing so, WWTP operators can expect a greater return on investment and safer operations at their plant facility.