Power Monitoring SCADA

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Date: 2011-10-03

Power Monitoring and SCADA for Building and Facility Automation Systems:

Power MonitoringGoing green can have two meanings one from an environmental point of view and the other is green dollars or money. Money is more digital now, but getting the green still has its meaning. The use of automation and power monitoring can be instrumental in gaining both versions of green. The motivations for the monetary green, is routed in the mathematics of accounting and general self preservation. The other ”Going Green” is more socialistically oriented and motivated as part of the mass preservation goal.

Regardless of the motivations or style of going green, both can be achieved with the blended use of power (energy) monitoring and productive use of that power. Using power monitoring sensing devices and logical control devices in harmony with human endeavors is the beginning point of the beneficial quest we seek to follow. The sensing components can start with voltage, amperage and power factor. The logical control devices can be PCs, PACs or PLCs as well as any other chip driven controllers or direct relay devices.

Power quality is as important in monitoring as is power usage in quantity and when it is used. By eliminating the damage done by bad electrical power components, we eliminate the costly repair and replacement of electrical such as expensive motors and electronic such as computers, their UPS systems and system related devices. We also will improve our safety integrity with protecting fire, disaster and security systems and equipment.

As a link to the motivational component and the sought end result we have to develop a logical approach to developing our overall system. First we need to see where we are using the energy and the profitable way of using it. Eliminating the waste should be a concern as well as the damage from unwanted poor power quality. In some ways expelling one gets rid of the other.

We will start by eliminating wasted energy from non-productive consumption such as having lights on and heating/cooling when no one is there or it just does not produce any benefit at that point in time. This is where building automation comes in. With the introduction of occupancy and vacancy sensing, many wasted watts have been eliminated including the use of sleep and automatic shut down modes for computers and their peripheral devices. Hotels have saved countless dollars in maintaining environmental factors in unused or unoccupied rooms. Many businesses have benefited with lowered cost of lighting, heating and air conditioning in the office areas. Another area of wasted energy has been in the educational arena of class rooms and empty lobbies which has been reduced with sensing the lack of need and direct shut down of the components by opening the circuit that controlled them. This is a simple and relatively inexpensive on-off circuit controlling device. These have already been introduced into homes and are legally required in some states.

A more sophisticated system will include ambient light sensing from outdoors through windows and skylights and increase or decrease the power driven lighting as needed though dimming control or turning complete pre-planned banks of lights off or on. Another method is to have automatic shades block the sunlight in that it increases the ambient heat which in turn runs the air conditioning longer. This is where a trade off appears by eliminating the unwanted sunray generated heat we eliminate the wanted solar generated ambient light. That is where logical control with the use of algorithms comes in. Where is the optimum set of conditions?

We can make a more complicated system if elevators are being used. Once the door opens we shed the air conditioning load temporarily while the elevator is in use. This lowers demand levels which we will discuss later. This may include shutting down elevators when in empty mode when a fire alarm system is introduced to the overall building automation scheme including activation of alarms and evacuation messaging systems.

The first thing we need to do is know where the energy is being used and the quality of that power. This is where power monitoring devices come in. To begin lets analyze how they function. The needed information can be derived with CTs or current transformer sometimes referred to as a current transducer. Which as current goes through them it picks up the amperage and voltage being used at that specific time and with the secondary coil it sends the reduced current to a device that picks up the current and measures it. A logic device will give it a value and then some logical operation can be done. This is a simplified or general description of the operation or current transformers. There are many other factors involved.

In a power monitor, measurements are made on different lines such as in a 3 phase system. Current and voltage is measured and compare to each other and then against the neutral. Each line is called a phase and in an AC system has a wave signature. The 3 phases are compared to each other to see if they are in equal distance from each other. When an imbalance occurs you will get fluctuations in power factor which will result in lost results from the loss of effective power. A more lengthily discussion on power factor and phase imbalance would be needed and would lead us beyond the scope of this article.

Data loggers then can be incorporated with or in the power monitor to give analysis software date to make comparisons as well as provide history of the power usage and its quality. Monitoring the quality of the power and reacting to the poor conditions with reactors and capacitors can help prevent the damage of expensive motors and equipment. Monitoring the usage will help us examine where certain demands can be eliminated. The best way to do this is with power monitoring and a good SCADA system. A good SCADA system can also include process, security and safety monitoring and may be involved with a DCS system, which gives control with the use on logical devices to effectively optimize all the elements including energy usage.

Now that we have general idea how and why you would want a good monitoring and control system, we can now look as to where we can best apply them. Office buildings, educational facilities, hospitals, hotels, museums and retail areas such as malls have two common areas of major usage. These are lighting and climate control such as heating and air conditioning. Other areas include office equipment and computers. The first attack on the energy cost is shutting things down when not in use. This is where occupancy and vacancy sensors which sense when no one is in the area or room. This information can be sent to a control unit that shuts down lighting and environmental systems. This shut down could be partial or complete which will be determined as required. Dimming controls could be used for partial if for example ambient light from sky lights and windows is measured and the lighting system compensates for the needed lighting needed in an area.

Hotels lower or shut off complete rooms for air and heating and then turn them on when the room is booked. A PLC or PAC could be used to use timing functions for different time of day or days of the week when a particular area is used. Examples include offices at night or complete areas on weekends when closed. Other areas may include shutting down hot water heaters under the same criteria.

A major component in electrical cost is not the amount used but the time of day it is used. This leads to peak demand which has a higher than average use period and an off-peak which is when demand is the least. These are usually used because there are limits a power generating system can provide in electricity. Some limits are imposed by government regulation on the amount utilities can produce for the sake of the environment.

By timing as much usage during off peak as possible could generate many cost saving opportunities. Examples of this may be running systems, such as air and heat, when possible at times earlier than when the high peak demand is happening. Another peak demand area is staggering motor and heating loads so that they do not activate at the same time and create a cumulative effect such as by air handling units, elevators, and large lighting loads. The use of VFDs (variable frequency drives) or soft starters also helps in lowering start up peaks contributing to the savings.

Power monitors also help us see the quality of the power we are using. This usually pertains to the voltage. We need to watch for phase imbalances and variations in the frequencies on the individual phases. If voltages go higher than say 10% of what it should be, damages to equipment may happen. Also a phase form distortion caused by harmonics also may cause damage to many electrical and electronic components. There are other voltage characteristics that can result in costly repairs as when a system starts up or shuts down suddenly. By careful measurement and monitoring we can plan for power conditioning equipment and eliminate the damage from these variations.

In industrial environments power monitoring becomes more needed than in commercial environments do to the higher usage and the fact the components using the power are much more expensive. Motors even with VFDs have high consumption and use of energy. Being careful in startups is especially important do to the demand peaks that can be exhibited. The time of day the activities occur is also important such as power usage for steel plants and heavy fabrication. Reacting quickly to unstable and abnormal events become extremely important.

Another area is in hospitalization facilities. The loss of power needs to handled quickly for the safety and continued response needed for those under it care and those providing the care. These areas many times have expensive UPS and backup generator systems that after a sense of power loss is monitored, start up or switched to.

Banks and many stores need to detect the differences also because of computer and alarm components that need to continue running until adequate shut down modes can be implemented. As to emergency lighting and alarm systems, this is important to just about every type of facility.

Another great tool on our war against unwanted current and voltage conditions is to monitor the usage and power quality on a constant basis and keep data on when they occur. This is where SCADA software and systems become useful. With proper data acquisition and sensing we can develop a historical logging for providing data for analysis. Reoccurrences can be checked so the causes may be checked into and eliminated. Finding the culprit conditions can sometimes be difficult, but with a proper SCADA software and with data from utility companies, they can be found and in many cases routed out.

The emergence of alternative energy now offered today as well as emergency backup systems has created added dimensions in the need for power monitoring. If the lower cost alternative is not providing what is needed we need to be able to sense it and kick back into the standard power grid. If both the alternative and standard are not available we need to sense it quickly and with an ATS (Automatic Transfer Switch) go to the emergency power system which is usually a backup generator. After the other systems come back on line we then need to be able to know that it has happened and switch back to the normal power systems which are more cost effective.

David Pailley, Technical Sales Engineer, 1-888-971-9888 ext 113

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