Monitoring transformers key to predictive maintenance

Mike Dickinson, Pacific Coast Transformers, www.pacificcresttransformers.com

Transformers serve as a hub for collection and distribution of energy changing the voltage level at different locations of the grid. They are a key component of the Smart Grid, loosely defined as an automated, widely distributed energy delivery network, characterized by a two-way flow of electricity and information, and capable of monitoring everything from power plants to customer preferences to individual appliances.

There is some ways to go before the vision of the Smart Grid is realized, but recently monitoring transformers has taken a leap forward, as energy production sites seek solutions to lower maintenance costs. Remote monitoring is seeing increasingly wider use especially remote wind farms and solar-powered production sites where having someone present to monitor transformers at fixed intervals is a costly proposition. As more renewable energy production sites come online, utilities have been investing in monitoring technology that keeps labor costs to a minimum.

Predictive maintenance gains favor over preventive

Remote monitoring and communication capabilities let utilities conduct “predictive” maintenance of transformers, which means conducting maintenance only when a parameter starts deviating from a pre-set standard. This typically does not occur at a pre-determined interval. Remote management let operators“see” how a transformer is operating and send someone to fix it only when it’s necessary.

Daniel Lambert, of Vizimax, a Montreal, Canada-based company that offers remote monitoring and control systems for public utilities and the industrial and private sectors, notes that remote management is being widely embraced, especially as operators need more profitable maintenance functions. “It is similar to today’s cars that tell you when to change your oil or conduct other maintenance based on specific driving habits,” said Lambert. “Rather than changing your oil at 6,000 mile intervals, electronic sensors can determine if you do mainly city or highway driving and signal the need for an oil change accordingly. That basic principle has been adapted for use in monitoring transformers.”

When maintenance is done purely in preventive mode, operators have no idea what is really happening inside and next to the transformer, and may tend to unnecessarily shorten intervals between each maintenance activity. With predictive monitoring, utilities can save money by having a real understanding of the key transformer parameters, which include temperature, liquid level, pressure vacuum, outgoing voltage, and ingoing voltage.

Utilities that conduct preventive maintenance programs usually use either time or quantity of energy consumed as the determining factor. Once they install remote monitoring capabilities, most switch to predictive-maintenance modes. Payback on the investment in remote monitoring equipment is estimated between 9 and 15 months.

Among those moving in the direction of this type of remote monitoring are GE, Siemens, Alstom Grid (Areva T&D), Schneider Electric, BHEL, Crompton Greaves, New York Power Authority, National Grid, Power Grid of India, and Hydro-Quebec, among others.

Building transformers that incorporate digital monitoring

Many transformer manufacturers are recognizing this growing demand for online transformer monitoring products and diagnostic services, and investing in building them, especially for step-up transmission, high-voltage transformers.

These technologies will be critical for improving grid reliability and helping utilities avoid transformer failures and resultant blackouts. They will also reduce maintenance costs and defer capital expenditures by extending a transformer’s useful life.

In addition to monitoring vital statistics such as temperature, pressure, and vacuum levels, there has also been a burgeoning interest in conducting dissolved gas analysis (DGA) of the oil in transformers. A DGA takes samples of an oil’s exhaust gases to determine if events have occurred that might be detrimental to the transformer and reduce its life. Industrial transformer maintenance people and utilities are setting up these planned sampling programs, using online devices that can monitor oil quality.

This can greatly improve reliability, because users will know in advance when something has to be replaced, rather than risk unscheduled outages. For food-processing plants and mills, which can lose millions of dollars when power is interrupted, this type of sampling program is being undertaken to ensure reliable power.

Transformers in place now are already using various smart devices for load switching. In the 21st century, the move will be towards monitoring systems that promote transformer reliability. Ensuring reliability on the grid by replacing equipment before it fails and anticipating upcoming problems is what transformer manufacturers will be focusing on.

Remote monitoring equipment

The latest technology used for remote transformer monitoring includes a combination of a remote terminal unit, a programmable language controller, a gateway (a network node equipped for interfacing with another network that uses different protocols), and a protocol converter. The complete monitoring system is usually placed in service by a system integrator or a power manufacturer.

An example of one such system is Vizimax’s RightWON, a secure, modular, rugged automation remote terminal unit (RTU), programmable logic controller (PLC), gateway, communication conversion protocol platform that connects circuit breakers, transformers, IEDs, meters, sensors, control and monitoring devices at the substation level or anywhere on the distribution network. In addition to energy applications, the monitoring devices are used in water and telecommunications monitoring.

The unit is for remote management applications, providing support for equipment through its data acquisition, monitoring, control and remote maintenance functions. At renewable energy sites, the system shuts down and locks circuit breakers (CBs) and inverters remotely, which avoids traveling to an energy-production site for distribution-line maintenance. The production site is still operational while maintenance is occurring on the network.

The unit is often used in substations, where it usually connects to transformers, circuit breakers, intelligent electronic devices (IEDs), protective relays, and meters through the electric utility’s private network. In some instances, in can be used strictly for monitoring transformers in substations, using wireless connectivity (through GSM, GPRS, 3G or CDMA networks). Parameters such as temperature, liquid level, pressure vacuum, outgoing voltage, and ingoing voltage will be measured and transferred to a utility’s supervisory control and data acquisition (SCADA) system. Wireless monitoring calls for specialized Web service interfaces.

The system makes it economical to conduct monitoring, because it can convert older controls and sensors already implemented to newer communication protocols without having to replice or modify them. The monitoring system connects to the SCADA using fiber optic cables or web interface through a wireless device. It offers a remote and local view on event logs charting key assets status changes and alarm signals about exceeding thresholds.

Remote access is made possible through networking, security, and telecommunication functions, and is supported by a broad range of integrated interfaces. These interfaces support a wide variety of industrial protocols (IEC 61850, DNP3, ModBus, and IEC 60870) as well as Web access and remote maintenance functions. The information collected is easily viewed on smart phones from anywhere, any time. The system supports sending notifications by email, text messages, or pager. Users who receive a message can access the system using a Web browser to view the data and operate the site remotely.

The system is IEC 61850 KEMA certified and can also be used for a variety of other Smart Grid applications, including remote default detection and automated reclose/disconnect operations within distribution networks, and alarms and operational data broadcast and commands, usually to or from the SCADA of power utilities, IPPs, integrators and equipment manufacturers’ team management applications.

Monitoring equipment also used in re-energizing transformers

In addition, new flux management monitoring technology is being deployed more at the end of transmission lines during re-energizing a transformer, a regular process that takes place every time a production site connects to the grid. The need to re-energize varies considerably, but there are always times when required maintenance requires stopping the connection between the production site and transmission lines. When maintenance is completed, the transformer must be re-energized.

The flux management units avoid network inrush that may create network outages while transformers are re-energized, something that in the past had been a frequent occurrence. This is extremely important, because several hours of lost revenue in a month can mean the difference between a profitable energy production site and an unprofitable one.

The system calculates the residual flux while a transformer is reenergized at the last operation, and ensures that the next transformer operation is performed at the exact millisecond such that residual flux is identical to the previous operation, which minimizes current inrush and stress on both the high voltage transformer and circuit breaker.

The unit measures relevant parameters from the transformer and sends a command to the circuit breaker of the transformer to achieve this operation. Using this equipment increases the quality of the network, decreases network outages, and decreases the frequency and the cost of maintenance operations.

Last thoughts

Remote monitoring makes it possible to manage maintenance of remote power equipment in the field in a predictive mode instead of the more traditional and more expensive preemptive or preventive mode. By remotely monitoring power equipment in remote locations, electric utilities now only must execute maintenance operations on their equipment when it is required. This is going a long way to cutting costs for the many renewable energy production sites that are coming online.

Pacific Crest Transformers
http://www.pacificcoasttransformers.com

Transformers pass severe shake (earthquake) test

The manufacturer of liquid-filled distribution transformers says its transformer designs has withstood rigorous seismic testing performed at an independent engineering testing laboratories. The testing showed that units from Pacific Crest Transformers (PCT) are suitable for mission critical applications, including hospitals, command centers, and generation stations.

The same transformer was subjected to tests simulating six violent earthquakes over two days, each equating to real potential events from different extreme seismic zones of the country. The transformer was energized during the tests. The final two tests simulated the worst potential earthquake in the US – the New Madrid Fault, located under Arkansas, Missouri, Tennessee, and Kentucky, but with the potential to affect an even larger region. In each test, the transformer continued to operate throughout and sustained no internal or external damage. The transformer passed Hi-Pot tests and IEEE Routine tests performed before and after the shake table testing, which showed it withstood the shake tests without diminishing its operational performance.

The testing program was conducted by Wyle, an experienced qualification testing operations which provides services to a wide range of industries, as well as the aerospace and U.S. Department of Defense arenas. PCT conducted the testing at Wyle’s Huntsville, Alabama laboratory, which specializes in testing and qualifying equipment for the energy and nuclear power industries, automotive companies, other high-technology industries, as well as DoD missile, aviation, ground applications, and NASA.

Following the devastating effects of the recent earthquake in Japan, organizations are reviewing their list of assets to ensure that they can withstand the potential for earthquake damage. The company’s transformers feature circular windings that evenly spread radial forces over their circumference and have cooling ducts throughout the coils, eliminating hot spots that lead to premature breakdown and ultimately transformer failure. Coil-end blocking with heavy duty 3-gauge steel bracing and proprietary pressure plates contain the axial forces exerted during a fault condition. These forces can cause telescoping of the coils, shortening transformer life. The innovative design includes round coils, a cruciform, mitered core with heavy-duty clamping and a proprietary pressure plate design, as well as a premium no-load tap changer.

“No one transformer would be expected to experience more than one of these events over its lifetime and PCT’s transformer survived the entire gamut of possible events,” said Curt Collins, Pacific Crest Transformer’s Vice President of Sales and Marketing.

Pacific Crest Transformer

www.Pacificcresttrans.com

This transformer includes terminal lugs

 

All standard, ventilated Jefferson Electric transformers (75 kVA and smaller) now include terminal lugs. The mechanical lugs on units from the Franklin, Wisc. company are electro-tin plated and UL listed to 90°C. Lugs are required to connection wires to the transformer terminals. Providing lugs with the transformer lets the installer complete the installation faster and eliminates having to purchase lugs separately.

Many transformers ship without lugs. The type required can change depending on the type and size of the wire. On some installations lugs may be provided on the wires. Larger transformers may be connected with a single large wire (requiring one large lug) or multiple smaller wires more easily installed with multiple lugs on a single terminal.

They support aluminum and copper wires up to a 600V connection, and have a chamfered wire entry for easy installation of wires. Lugs are attached at the factory and lug kits are also available for purchase separately to support common voltage and kVA combinations. Attachment hardware is included with kits.

Liquid-filled division Pioneer Transformer, a sister company to Jefferson Electric, produces utility transformers to step-up turbine output voltages to useful levels before distribution to the power grid. Pioneer Transformer designs and manufactures liquid-filled units up to 25 MVA at 69 kV (350 kV BIL)  and is based out of Granby Quebec.

Jefferson Electric
www.jeffersonelectric.com

http://pioneertransformers.com/

What are the electrical & electronic components in a wind turbine?

Motors and drives: nacelles on utility scale turbines are filled with motors and drives. The latter devices are part of the turbine controls that tell motors what to do. Generally, electric motors pitch the blades on turbines with less than 1.5 MW outputs and point nacelles in appropriate directions. Utility-scale turbines can have up to eight yaw drives. Motor outputs on these turbines range from 2.2 to 22 kW. They attach to speed reducers to produce output torques from 2,000 to 50,000 nm.

 

Blade-load sensing leads to rotor monitoring and load measuring on the turbine hub. Such a system can be designed-in during manufacturing or retrofitted. The system detects operation and maintenance issues such as blade icing, in which the system lets operators predict when they ought to shut down turbines because “ice throw” is possible. Signaling when the ice has been shed from a blade also lets operators restart sooner.

 

Such controls and sensors would allow for adjustments to:

 

• Yaw misalignments. When running below rated power, a 10° yaw misalignment reduces power output by about 5%.

• Rotor imbalance. Sensors that provide data on mass and aerodynamic imbalances allow early action to maximize power generation and avoid damage.

• Blade damage. Sensors can detect damage affecting the structural or aerodynamic performance of a blade, allowing early remedial action.

 

Inverters

 

The output from a generator has three electrical characteristics: voltage, current, and frequency. Because wind speed changes constantly, a generator would produce these at variable rates as well. Hence, the inverter’s job is to steady two of the characteristics, and let only one of them vary. These electrical devices turn the variable current or voltage coming out of a generator into steady voltage and frequency that can contribute to power on the grid.

 

Transformers

 

These allow raising or lowering voltage in ac transmission lines. Transformers for wind turbine generators switch with solid-state controls to limit inrush current. While potentially aiding the initial energization, these electronic controls contribute damaging harmonic voltages that, when coupled with non-sinusoidal wave forms from the turbine, also contribute to overheating.

 

Standard voltage alternates at 60 Hz. When the transformer frequency differs, voltage peaks do not line up and do not produce the required amplification that would come from in-synch frequencies. The transformer tries to pass its voltage through the circuit, thereby causing extra loading. All electronics today send spikes on line. Transformers must handle the higher loading in frequency disturbances and spikes.

 

To handle potentially hazardous heat, one transformer manufacturer winds coils on a cruciform- mitered core. Circular windings have coolant flow ducts throughout which evenly spread radial and axial forces over their circumference, eliminating hot spots that lead to premature breakdown and ultimately transformer failure.

 

Transformers for wind turbines are usually designed so their voltage exactly matches the wind turbine’s output voltage. Generator output current is monitored at millisecond intervals. Operational limits allow up to 5% over-current for 10s before controls take a generator off the system. Because transformers used with wind turbine generators are intended to match generator output without overload sizing, the generator must function without extra capacity.

 

When using a rectifier-chopper system (the electronic controller in wind turbines) the transformer must handle harmonics similar to rectifier transformers. These harmonics are called “dirty” because they may contain high frequencies that wind-farm owners do not want to send to the grid because they affect other equipment.

 

 

300 ton transformers, heaviest yet, head by rail to west Canada

A milestone in project cargo movement was recently reached at the Head of the Lakes as crews handled the heaviest Canadian Pacific (CP) direct, single-line rail move from the Port of Duluth-Superior to western Canada. Two, 300-ton transformers arrived at the Clure Public Marine Terminal in Duluth on Nov. 5. Both units were manufactured in Germany and shipped from Rotterdam along with multiple crates of accessories. Crews from Lake Superior Warehousing Co. discharged the high, wide, and heavy cargo directly onto specialized railcars waiting dockside

One of those specialized cars, a new 20-axle railcar, was recently introduced into American service. A train comprised of this car and eight others (including a 16-axle railcar) left Duluth and made its way along a 1,200-mile CP clearance route northwest to Lethbridge, Alberta, where the transformers will be installed to power the Montana Alberta Tie Line – the first international merchant transmission line in North America.

“When fully operational in 2011, the 214-mile transmission line will connect the electricity markets of Alberta and Montana,” said Paul Kos, Director of Engineering for Montana Alberta Tie Ltd, “opening a huge potential for development in renewable energy projects in both countries.”

“The Port of Duluth factored into this single-line rail move,” said David Walker, Senior Manager, CP Logistics Solutions. Since 2005, CP has handled most of wind energy components inbound to southern Alberta for wind energy projects in that region. “This transmission line will transform renewable energy into power for customers on both sides of the border. CP is excited to have brought the two heaviest transformers through the Port of Duluth, one of our premier transloading partners.”

CP completed upgrades to bridge infrastructure in Minneapolis-St. Paul a couple of years ago to accommodate the movement of more large cargo through Duluth. “When it comes to designing end-to-end transportation,” noted Walker, “using Duluth’s multimodal facility makes possible a single-line, cross-border rail haul that creates huge benefits for our customers.”

“This is a CP-served facility, with on-dock rail and intermodal transloading capabilities – the farthest inland port on the Great Lakes St. Lawrence Seaway,” said Jonathan Lamb, Vice President and General Manager of Lake Superior Warehousing Co., terminal operator for the Duluth Seaway Port Authority’s Clure Public Marine Terminal. “Our location lets us collaborate with key marine and railway companies involved in transportation logistics, for a transmission line project like this and for renewable energy companies across the heartland.”

“This move has proven to be a great example of the innovative collaborations being forged today,” added Walker, “shared efforts to provide solutions for the efficient, specialized transport of high/wide and heavy project cargo from its point of origin to an installation site halfway around the world.”

Why do wind turbine transformers fail so often?

Small power transformers handle 5 to 15 MVA

The recent line of small power transformers is customized for use in municipal power substations. The utility-focused smaller power transformers, from Pacific Crest Transformers, Medford, Oregon, are rated from 5 to 15 megavolt-amperes. They are ruggedly built, using disk-wound coils with cruciform miter-cut cores and proprietary 360° cooling ducts. The design improves reliability because it increases the transformer’s capability to handle the axial and radial forces exerted on the transformer during periods of short circuits and heavy loads.

“With our design, each and every turn in the windings is directly in contact with the insulating fluid, improving the transformer’s cooling characteristics, reliability, and thereby reducing its total cost of ownership,” says Pacific Crest Transformer’s VP Tom Steeber. The company welcomes plant visits for those with power-station-transformer requirements.

In addition, the transformers will be on display in booth 622 at the 2010 Northwest Power Association’s Engineering & Operations Conference & Tradeshow, from March 29th to April 2nd, Hotel Murano/Marriott Courtyard in Tacoma, Washington.