Practical applications of power protection systems (III) [Part 2/2: Diesel/gas static UPS systems for LCD panel production lines]

Diesel/gas static UPS systems

Diesel/gas static uninterruptible power supply systems (D/G SUPS for short) have been around since the beginning of the 2010s. Description of their topology and operating principle can be found as far back as 2011. They were developed to take care of the increasing power quality problems and energy efficiency requirements of equipment and facilities that conventional solutions like diesel rotary UPS systems (DRUPS for short) could not handle.

Diesel/gas 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 mission critical facilities and continuous production processes.

Functions

Diesel/gas static UPS systems combine the functionalities and benefits of various power protection, power quality improvement, energy storage and standby generation 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 and provide long term emergency power generation. In addition, they can take care of several other power quality problems, support the development of clean energy and provide few ancillary services by combining different control functions in a single device.

Connection

A diesel/gas 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, diesel/gas 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.

D/G SUPS for LCD panel production lines

A liquid crystal display (LCD for short) is a flat-panel display or other electronically modulated optical device that uses the light-modulating properties of liquid crystals combined with polarizers. Liquid crystals do not emit light directly but instead use a backlight or reflector to produce images in colour or monochrome. LCDs are available to display arbitrary images (as in a general-purpose computer display) or fixed images with low information content.

LCDs are used in a wide range of applications including LCD televisions, computer monitors, instrument panels, aircraft cockpit displays, and indoor and outdoor signage. Small LCD screens are common in LCD projectors and portable consumer devices such as digital cameras, watches, calculators and mobile phones.

Requirements

Background

In order to ensure sensitive manufacturing equipment is protected from voltage sags and interruptions, a continuous power supply must be maintained at the production lines of a LCD manufacturing plant. The plant owner wants to install a power protection system that would protect the production lines to ensure that production is not brought to a standstill by power supply problems. At the same time the owner would like to improve the power quality and the energy efficiency of the plant.

The requirements from the owner of the manufacturing plant for this project can be summarised as:

• Protection against voltage sags and interruptions.
• Power factor improvement.
• Harmonics mitigation.
• High availability of critical machinery.
• Optimised energy consumption.

System description

LCDs are manufactured in cleanrooms borrowing techniques from semiconductor manufacturing and using large sheets of glass. Several displays are manufactured at the same time and then cut from the sheet of glass, also known as the LCD glass substrate.

The power for the critical machinery of the production line is supplied from the electric utility and from a rooftop solar PV power plant.

Solution

Analysis

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

The measurement results show that the production line suffers from short interruptions few times per year. The measurements also show that the production line is suffering from other power quality and energy efficiency problems. The harmonic level in the installation is high (THDi = 24%) and the power factor is low (PF = 0.92).

Proposed solution

Based on the analysis of the measurements, the owner of the production plant decided to install a dedicated power protection system for the LCD panel production line. A diesel/gas static UPS system rated 2 MW 2.2 MVA was chosen. It uses supercapacitors as the energy storage media coupled through an energy storage inverter to enable the protected equipment to ride through short interruptions of up to 15 seconds, which allows enough time for the standby diesel generator to start.

Footprint and losses were very important factors taken into consideration when choosing the solution. The D/G SUPS provides an smaller footprint and also lower losses when compared to conventional diesel rotary UPS systems (DRUPS for short).

Based on the values monitored, the following functions are proposed for the D/G SUPS.

Conclusions

Due to various circumstances, sometimes unpredictable, critical process industries are often exposed to power quality and energy efficiency problems including voltage sags and swells as well as interruptions. These problems have serious consequences since a possible shutdown of the facility or a production line involves lost production time, lower production quality or damaged equipment, which leads for example to late delivery to customers, revenue loss and productivity loss.

The benefits of using diesel/gas static UPS systems for LCD panel production lines can be summarised as:

• Modular and scalable architecture simplifies future expansion of the production lines.
• High energy efficiency, over 99%.
• Small footprint.
• Can protect the full production line or just selected sensitive machinery.
• Allow critical machinery to ride through common power quality problems increasing yield, reducing product wastage and improving productivity.

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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.