Alltec Corporation News & Articles
Why Protecting Wind Turbines from Lightning is Critical
News by Alltec Corporation
Tuesday December 29, 2009
Exactly when and where lightning will strike is an unpredictable act of nature. If scientists could calculate the exact location of future lightning, the United States would be able to avoid the $2 billion in annual property damage due to this awesome yet terrifying natural phenomenon. However, the fact that lightning usually strikes the highest point is indisputable. Height, shape and isolation are all leading factors in determining the place where lightning will choose to strike. One of the worst possible courses of action during a storm is to stand under a tree; in fact, this is the number one leading cause of death or injury from lightning strikes. Wind turbines act in a similar manner, as they are the tallest point and sustain a high probability of being struck by lightning. Therefore, it is often not a matter of “if” but “when” a wind turbine will be struck by lightning or experiences other types of overvoltages and currents.
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Protecting Variable Frequency Drives
Articles by Alltec Corporation
Thursday October 29, 2009
Surge Protection Devices (SPDs)
Sophisticated and highly susceptible microprocessor based electronics and data communication networks are integrated across every sector of today’s fast paced business world. Preserving these mission-critical systems from the damages of surges, spikes, and transients ensures that these systems are protected from equipment destruction, disruption in service, and from costly downtime. How to properly stage these SPDs can be as important as actually making the decision to purchase them.
Protection of Drives
The use of various types of drives to control motors is very common. The purpose of the drive is to increase the efficiency or to manage the speed of the motor being controlled. Through various processes and control mechanisms, the drive often reshapes the sinewave to provide a signal to the motor that allows for greater efficiency or varies the frequency of the signal to control the speed of the motor.
Due to the action of the drive, the power quality of the electrical environment can be compromised. That is, the drives can create voltage surges and harmonics on the system.
There are various technologies available that aid in correcting these issues. This application note focuses on applying surge protective devices (SPDs) to a drive system to mitigate the damage that can occur due to voltage surges while considering the effects of the harmonics on the surge protective device.
Application of SPDs
To aid in the description of the application of SPDs to a drive system, please refer to Figure 1.
This figure illustrates a typical drive layout. The incoming power is usually delta configured (3 phases and ground).
Often the incoming voltage is 480 V, but other voltages may be used. The incoming power is usually stepped down to a lower voltage (typically 120 Vac) that provides power to the control circuit. The control circuit contains sensitive electronics. Once the power is acted upon by the drive the output is fed to the motor.
As noted, there are five opportunities for protecting the typical drive system—each are labeled with a circled number and are described below.
Drive Input
Protecting the drive input is an essential step in protecting the drive system. Providing protection at this location prevents surge damage due to events propagated on the electrical system from upstream sources, external events such as lightning and switching surges created by the utility, and the interaction of multiple drives on the same system.
At this location, a parallel connected, voltage responsive circuitry device is appropriate (one without frequency responsive circuitry). Frequency responsive circuitry is not recommended for this location due to the fact that this location is typically more susceptible to impulse transients as opposed to ring wave transients.
Inverter Input
The inverter input is one of the most sensitive and critical areas of the drive itself. It is at this location that care must be taken and the proper survey conducted. You may install a parallel connected, frequency responsive circuitry device provided you have confirmation that within this drive that no additional capacitors have been installed to mitigate harmonic currents.
IF THEY HAVE, then at this location, a parallel connected, voltage responsive circuitry device is appropriate (one without frequency responsive circuitry). Frequency responsive circuitry would not be recommended for this location due to the high harmonic content that necessitated the installation of additional capacitors. Installation of frequency responsive circuitry devices at this location will lead to failure of the SPD.
Control Circuit
The control circuit contains sensitive electronics that can be damaged by the environment created by the drive or by surges from external sources. Protection at this location is essential.
Since this circuit is isolated by a step down transformer and it feeds sensitive electronics, a series connected SPD with frequency responsive circuitry is recommended for this location.
Drive Output
Protecting the immediate drive output is recommended when the length of the connection between the drive and the motor is longer than 50 ft (15 m) or if the connection is routed along an external wall or outdoors.
One reason for protecting at the immediate output when the length of the connection to the motor is long is due to reflected waves that can occur as the signal (often higher frequency) from the output of the drive reaches the motor and is then reflect back and forth between the drive and the motor. This action can create "voltage piling" – the reflected voltage adds to the nominal voltage and other reflected waves. The SPD will aid in reducing the voltage peaks of the reflected waves.
More importantly, if the connection between the drive and the motor extends outdoors, along a path that is exposed to the environment or close to the building’s steel structure, protection at this location is important to diminish the effects of direct lightning or induced voltage surges due to nearby lightning. These surges can cause damage to the drive, even if protection is provided at the motor input.
At this location, a parallel connected, voltage responsive circuitry device is appropriate (one without frequency responsive circuitry). Frequency responsive circuitry is not recommended for this location due to the high harmonic content of the signal due to the normal operation of the drive. Installation of frequency responsive circuitry devices at this location will lead to failure of the SPD. Utilizing a voltage responsive circuitry device at this location will eliminate this possibility.
Motor Input
Protecting the motor input is an essential step in protecting the drive system. Providing protection at this location prevents surge damage due to events propagated from the drive output to the motor input. Providing protection at this location aids in extending the life of the motor as the SPD helps to prevent damage to the windings and bearings of the motor due to surges.
Further, if the connection between the drive and the motor extends outdoors, along a path that is exposed to the environment or close to the building’s steel structure, protection at this location is important to diminish the effects of direct lightning or induced voltage surges due to nearby lightning. These surges can cause damage to the motor, even if protection is provided at the drive output.
At this location, a parallel connected, a voltage responsive circuitry device is appropriate (one without frequency responsive circuitry). Frequency responsive circuitry is not recommended for this location due to the high harmonic content of the signal due to the normal operation of the drive. Installation of frequency responsive circuitry devices at this location will lead to failure of the SPD. Utilizing a voltage responsive circuitry device at this location will eliminate this possibility.
Overall, properly installed surge protective devices reduce the magnitude of random, high energy, short duration electrical power anomalies. These occurrences are typically caused by atmospheric phenomena (such as lightning strikes), utility switching, inductive loads, and internally generated overvoltages. The ultimate goal of our approach is to keep sites and systems operating safely and reliably. PowerTrip® Surge Protection Devices incorporate "Frequency Responsive Circuitry" technology years ahead of any other devices on the market today. Utilizing proprietary electro-chemical encapsulation, PowerTrip® SPDs dissipate large amounts of surge energy to prolong service life.
Signal Reference Grids: Grounding Solutions with Exceptional Results
News by Alltec Corporation
Friday October 2, 2009
Proper bonding and grounding are essential factors in today’s quest for ultimate power quality, and it is critical to have a system that is driven by both safety and performance. Alltec Corporation’s Signal Reference Grids (SRGs) are used around the world in communication/data centers to reduce static and noise and to protect equipment. SRGs are cost-effective, easy to maintain, and very successful at protecting equipment from voltage surges.
The Need for an Equipotential Plane
Electronic equipment is typically affected when there is a potential difference between devices. Proper grounding and bonding of sensitive electronic systems, including computer installations, require careful consideration of all frequencies. Alltec’s SRGs provide an equipotential plane for equipment where all electronic and electrical equipment connected can rise and fall together. These signal reference grids (SGRs) reduce or eliminate high frequency transients by achieving a common ground reference for all equipment within an adjoining area. The equipotential grid significantly decreases potential differences and diminishes current flow, thereby eliminating the adverse affect on logic circuits.
Requirements
Signal Reference Grid installation is normally required when:
- The logic ac-dc power supplies used in the electronic equipment are installed with one of the terminals connected to the equipment’s metal frame. This prevents damage to inter-unit signal units by providing a low-inductance, and hence, effective ground reference for all externally installed AC and DC power, telecommunications, or other signal level line to-ground chassis connected Surge Protection Devices that may be used with the associated equipment.
- The signal-level circuits and logic ac-dc power supply common terminals are OEM dielectrically insulated or galvanically isolated from equipment against recommended practice and are instead connected to an insulated “ground” terminal that is intended for connection to an externally installed signal reference circuit.
- There are actual performance problems occurring with the equipment which can be assigned to common-mode electrical noise; they are used to prevent or minimize damage to inter-unit signal-level circuits and equipment power supplies when a power system ground-fault event occurs.
- Low-impedance return path for RF noise currents
- Containment of EM (noise) fields between their source and the plane
- Increased filtering effectiveness of contained EM fields
- Shielding of adjacent circuits or equipment
- Conductive grid embedded in, or attached to, a concrete floor
- Metallic screen under floor tile
- Ceiling grid above equipment
- Supporting grid of raised access flooring
Signal Reference Grids as Grounding Solutions
The purpose of Signal Reference Grids is to enhance the overall reliability of the signal transfer between interconnected items of equipment by reducing the inter-unit common mode electrical noise over a broad band of frequency. All metallic enclosures, conduit, and ductwork should be bonded to the Signal Reference Grid for it to function properly.
Advantages of a well designed Signal Reference Grid
Forms of available Signal Reference Grids
Alltec Corporation designs and manufactures copper ground grids for grounding applications. Typical ground grids are manufactured from #6 solid copper wire on a 6” spacing or grids can be made from 2” wide soft copper strap on a 24” spacing. All connections are welded with silver brazing or wire grids can be exothermically welded for an additional cost. Copper ground grids are available with a continuous perimeter wire or with extended grid wires for making connections to additional grids.
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Protecting Cultural Heritage Landmarks from Lightning Strikes
News by Alltec Corporation
Tuesday September 22, 2009
The Secret of Protecting Cultural Heritage: Humayun Tomb in Delhi, India
Humayun Tomb is located in Delhi, India and is a unique piece of archeological history. Built in 1570 AD, this historic masterpiece inspired several major architectural innovations, including the legendary Taj Mahal. It was designed by renowned Persian architect Mirza Ghyas, and the red sandstone combined with ornate colored tiles signifies the beginning of a new design era known as Mughal architecture. Humayun Tomb is also the first garden-tomb on the Indian subcontinent, as the Mughals brought with them an affinity for gardens and fountains. This monument is forever honored as a UNESCO World Heritage site.
Originally built by Emperor Humayun’s grieving widow, the burial place not only houses Humayun himself, but also many other distinguished members of the Mughal dynasty. The tomb towers a height of 154 feet and is 300 feet wide, with a marble dome standing approximately 140 feet from the base of the terrace. The structure is topped with a copper pinnacle, and the two adjoining cement peaks support and are protected from lightning by Alltec’s Early Streamer Emission devices.
Alltec Protection Systems Pvt. Ltd. (Alltec’s South Asia Regional Headquarters) was awarded the lightning protection project for the Humayun Tomb, Delhi in the summer of 2009. Due to the cultural and natural significance of the site, prospective clients chose Alltec based on international reputation and comprehensive experience. By safeguarding this historical landmark from the dangers of lightning strikes, Alltec Protection Systems has aided in the role of ensuring that this monument’s splendor will be enjoyed for generations to come.
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Telecommunication Towers for the Military Industry
News by Alltec Corporation
Friday September 4, 2009
International Towers & Alltec Corporation Achieve Construction & Grounding Success with the Twenty-Nine Palms Project
As "Solution Providers for an Energized World™" Alltec Corporation offers a comprehensive facility protection approach to solving some of the world’s most difficult lightning, grounding, and power quality problems. For this reason, International Towers contacted Alltec to help facilitate its site protection for one of their most complicated and unique communication tower projects. The Marine Air Ground Task Force Training Command (MAGTFTC) OC3 Remote Mountain Top Tower Build for the US Marine Corps at Twenty-Nine Palms, California was initially a challenging task. However, combining dynamic expertise, International Towers and Alltec Corporation achieved total project success without any hesitation.
International Towers has been an integral part of the communications industry for more than 30 years, and they are responsible for tower development around the world. The Twenty-Nine Palms project involved a remote mountain-top tower built portion of the OC3 Backbone Infrastructure Upgrade for the MAGTFTC positioned at a very secluded and demanding desert location. It consisted of a tower installation at each of five remote mountain-top sites and was the initial effort as part of a larger multi-phase approach to build the Information Technology (IT) infrastructure at Twenty-nine Palms.
The Twenty-Nine Palms IT Infrastructure Expansion project will extend and augment the existing range infrastructure to seven sites. By expanding and upgrading these sites, a redundant IP network will be established to allow existing and future data traffic to support Marine Corp training across the range. The existing data traffic is generated by the Weapon Impact Scoring Systems (WISS), Strafe Scoring System (SSS), Integrated GPS Radio System (IGRS), standard Global Positioning System (GPS) and Vehicle Acoustic Warning Surveillance (VAWS) system.
The upgrade at five remote sites provided sufficient platforms to mount radio antennas and microwave dishes, to provide Line of Sight (LOS) communications between connecting microwave repeaters and to have vertical clearance of existing structures. Without sufficient platforms, the system described will not function. NSWC Corona FT31 provided the engineering design, oversight, and vendor selection for this effort.
CACI/ITI were the successful bidders in this unique design build opportunity, developing proprietary design and solutions to meet the needs of the MAGTFTC. Alltec Corporation provided the grounding design and materials for this unique assignment. In many cases, constraints such as air transportation costs, a lack of utilities other than solar power, and the use of only military specs could have inhibited the job completion. However, Alltec Corporation and International Towers formed a dynamic task force for total site success with the Twenty-Nine Palms IT Infrastructure Expansion project.
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