Practical applications of power protection systems (II) [Part 1/2: Single conversion static UPS systems for liquid filling lines]

Single conversion static UPS systems

Single conversion static uninterruptible power supply systems (SC SUPS for short) have been around since the 2000s. Description of their topology and operating principle can be found as far back as 2005. They were developed to take care of the increasing power quality problems and energy efficiency requirements of equipment and facilities that conventional solutions like power and voltage conditioners, double conversion or delta conversion static UPS systems or rotary UPS systems could not handle.

Single conversion static UPS systems can be applied to small, medium or large installations in a wide range of segments. Thanks to their flexibility and their availability in a wide range of power and voltage ratings, they have many low and high voltage potential applications where their use offers many benefits including continuous production processes, mission critical facilities, sensitive machinery, and their integration together with standby generators to build continuous power supply systems.

Functions

Single conversion static UPS systems combine the functionalities and benefits of various power protection, power quality improvement and energy storage technologies into a single robust system without the drawbacks of conventional solutions. They can fully protect equipment and facilities from short and long duration voltage variations of any magnitude. In addition, they can take care of several other power quality problems and support the development of clean energy by combining different control functions in a single device.

Connection

A single conversion static UPS system is a power electronics-based device connected in series with the equipment or facility that has to be protected, that is generating power quality problems or that has issues to comply with certain grid code and energy efficiency requirements. 

By their connection capability to the electric power system, they can be classified into 3-wire or 4-wire devices.

• 3-wire devices are typically used in industrial applications.
• 4-wire devices are typically used for applications in buildings.

When connected to an AC electric power system, single conversion static UPS systems are offered in a range of voltages. Most common range is 200 V up to 690 V as the energy storage inverters are usually built using low voltage IGBT switches. It is possible to connect these devices to higher voltages using a suitable step-up transformer for the energy storage inverter.

SC SUPS for liquid filling lines

Packaging machinery is used throughout all packaging operations in many industries from primary packages to distribution packs. These packaging operations include several processes like fabrication, cleaning, filling, sealing, combining, labelling, overwrapping and palletizing. Choosing the right packaging machinery for a certain product includes an assessment of technical capabilities, labour requirements, electric power system integration, maintainability, serviceability, reliability, capital cost, floorspace, flexibility, energy efficiency, productivity and return on investment, to name a few.

Filling machines (or fillers) are used mainly for food and beverage packaging to fill either a bottle or a pouch. The type of food or beverage filling machine to be used in a process is usually determined by the type of product to be filled, speed requirements, quality and shelf life expectations, and technology feasibility. The type of products may range for example from solid to semi-solids, from liquids to frozen, from hot to cold and from free flowing to highly viscous products.

Liquid filling machines (also known as flow fillers) are designed for liquids, oils and thin food products. These filling machines are designed so that when they fill a bottle that enters the machine, they eject the open bottle back onto another conveyor for sealing. This is a fast and continuous process that requires an uninterrupted supply of high quality power.

Requirements

Background

A beverage processing plant produces several thousands of filled bottles per day in a high speed liquid filling line. The plant is subject to voltage variations that cause major disruptions to the liquid filling line. When the filling line suddenly stops because of these voltage disturbances, product processed at that moment has to be disposed and machinery cleaned and sterilized before restarting the process. This is very costly for the plant and can take several hours even though the voltage disturbance may last for only a small fraction of a second.

The management of the plant is looking for a solution that would protect the operation of the liquid filling line against short duration voltage variations and improve the overall power quality and energy efficiency of the installation.

System description

The electric utility is supplying 400 V to the beverage processing plant via a 11 kV medium voltage distribution line.

The automatic high speed liquid filling line is formed by several machines synchronised together including bottle washing machines, turn tables, bottle visual inspection machines, liquid filling machines, cap sealing machines, labelling machines and packing conveyors.

Solution

Analysis

To be able to dimension a solution it is necessary to collect power quality measurement data from the liquid filling line over a period of time by using a power quality analyser.

The measurement results show that the liquid filling line suffers from voltage sags and interruptions lasting from several milliseconds to up to 2 seconds. The measurements also show that the liquid filling line is suffering from other power quality and energy efficiency problems. The harmonic level in the installation is high (THDi = 20%) and the power factor is low (PF = 0.87).

Proposed solution

Based on the analysis of the measurements, the plant’s management decided to install a dedicated power protection system for the high speed liquid filling line. A single conversion static UPS system rated 120 kW 120 kVA was chosen to take care of the power quality problems and improve the energy efficiency. Based on the measurement results, supercapacitors providing a backup time of 4 seconds were selected as the energy storage media.

Based on the values monitored, the following functions are proposed for the SC SUPS.

When a voltage sag or interruption is detected, the SC SUPS disconnects the liquid filling line from the utility supply using a static switch, and at the same time supplies the liquid filling line with energy from the supercapacitors via the energy storage inverter. The inverter converts the supercapacitors DC voltage to three-phase AC voltage. The switch occurs within a fraction of a cycle (the transfer time is less than 1.8 ms) and allows the liquid filling line to continue to operate without disruption.

When the supply voltage is restored to normal, the SC SUPS will close the static switch and synchronise the liquid filling line with the utility supply, restoring the liquid filling line to normal operation, again within a fraction of a cycle.

When the voltage is within allowed parameters, the SC SUPS will take care of the power quality and energy efficiency problems of the installation. It will reduce the harmonics produced by the liquid filling line and at the same time it will improve its power factor.

Conclusions

The worldwide demand for commercial beverages continues to grow. Successful beverage production requires getting the most out of raw materials and maintaining desired end-product characteristics through safe, cost-effective, energy efficient and sustainable multi-stage processing.

In this case, the single conversion static UPS system continuously monitors the voltage of the liquid filling line and corrects even minor variations in real time. It provides a steady constant voltage to the liquid filling line and at the same time takes care of other power quality and energy efficiency problems affecting its operation.

The benefits of using single conversion static UPS systems in beverage processing plants can be summarised as:

• Increased production yields and maintained long running times through high availability and uptime levels.
• Decreased ingredient and product loss levels by getting more out of raw materials.
• Reduced consumption of utilities, such as energy and water.

If you would like to receive any of my publications on the topic or to explore how #PowerProtectionSystems can benefit your application, feel free to reach me at pedro.esteban@meruspower.com. 

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About the author:

Pedro Esteban is a versatile, multicultural and highly accomplished marketing, communications, sales and business development leader who holds since 2002 a broad global experience in sustainable energy transition including renewable energy, energy efficiency and energy storage. Author of over a hundred technical publications, he delivers numerous presentations each year at major international trade shows and conferences. He has been a leading expert at several management positions at General Electric, Alstom Grid and Areva T&D, and he is currently working at Merus Power Plc.