By Steve Evans
If you were in a hospital in southern Florida in hurricane season, you might just find it comforting to know that the emergency power system works! Last winter, the University of Miami's Miller School of Medicine opened a new ten-story, 500,000 square foot expansion facility, with parking for 1400 cars and 15,000 square feet of retail space. Southern Florida’s notoriously hot climate and such a large building required the second largest chilled water plant in Florida and a major upgrade to its emergency power system. The ground floor parking garage is hurricane proof and filled with the chilled water plant and three 2.8 MW Kohler 2800REOZDB diesel generators, with room for two future units.
“The facility was built on-time, within budget, and will provide the medical school with emergency power for many years to come,” said Mark Schwartz, Sr. Project Manager, Facilities Design and Construction for the University of Miami's medical campus.
The entire building is state of the art and in compliance with the university's green building standards. Ron Bogue, assistant vice president for facilities and services at the Miller School of Medicine, says it may contain the only green cooling tower in the whole of South Florida. The gensets, switchgear and control systems are designed to bring all three generators on line within ten seconds in the event of an outage to meet the requirements of NFPA 110. Approvals are pending to allow these generators to respond to requests from the local utility for load shedding during high demand periods or peak shaving to limit demand charges.
“The new facility at the Miller School of Medicine is quite a place,” says Greg Porter, senior project manager for Elcon Electric Inc. of Pompano Beach, FL, the electrical contractor on the job. “There is nothing like it in Florida.”
The Miller School of Medicine’s massive new building is using a new twist on an old fashioned technology, thanks to the latest generation of control systems that utilize the power of the micro processor to execute advanced power management features.
Evolution of Control Systems: Power generation is not just for the utilities anymore
A combination of factors over the past decade has led to a boom in decentralized power production and renewable energy sources in order to meet the growing electrical demand in an environmentally conscientious way. These include a measurable shift in environmental awareness leading to greater use of cogeneration systems, combined heat and power systems, and green energy sources. In the past, the utilities were the only companies allowed to sell electricity commercially. The liberalization of the power sector started with the first energy crisis in the 1980’s and is now opening up generation to entities other than traditional public utilities. Greater demand now exists for emergency power plants, as data centers, hospitals, and many industrial processes require uninterruptible power sources. Even smaller businesses and some homes have on-site power generation. Addressing the lack of widespread utility acceptance of IEEE 1547 intertie standards and billing standards is the next critical step to enable many more co-gen and combined heat and power systems to come onto the grid.
In order to be remotely controlled and dispatched by the utility network as either an Interruptible Rate Plan generator or as cogeneration, the control of decentralized and emergency power plants demands highly advanced and very specialized technology. Utilities often offer a lower year-round rate, typically known as Interruptible Rate Plan, if the consumer agrees to be off the grid within a short period of time. Co-gen sites parallel with the utility for extended periods of time in various modes including peak shave, import/export control, base load, or zero power transfer modes. To start these units, they must also be able to communicate with external control systems using a range of protocols: from the common industrial ones such as serial MODBUS, Profibus and CAN-open to the more advanced TCP/IP Modbus or GSM modems and integrated web servers that allow data to be communicated over the Internet, cell phone, or satellite systems.
Systems like the one at the University of Miami rely upon new, easy to use, advanced power management systems, like the DEIF Automatic Genset Controller. Rather than being limited by equipment design with older discrete components, the software can be easily customized to meet the unique needs of a particular location. Then changing power management functionality is a simple matter of updating the programming or settings. While the ideas are not new, technological advances have highly automated these control systems and replaced the discrete components like synchronizers, load share modules, power factor / VAR controllers, PLC’s, and protective relaying devices with integrated controllers capable of all these functions in one ‘box’.
This latest generation of digital genset controllers gives operators greater control over the operation and safety of the gensets, helping to improve fuel efficiency and reduce emissions. Since they have fewer components and less wiring than older analog systems, they require less maintenance and have a higher MTBF (mean time between failure).
One more key factor facing the power industry is the severe shortage of experienced personnel. It is often a requirement to make the control system as robust and easy to operate as possible by automating such things as synchronizing and load management that used to be done by hand. Today’s advanced systems can interface to multiple models of gensets, even from multiple vendors, thus decreasing the learning curve for operators. This makes it faster to spot problems, easier to train personnel, and safer for equipment and personnel.
Three Levels of Control
There are three levels of controls in a complex power generation system.
Level 1 consists of the control systems located on the engine. The Engine Control Unit or Engine Control Module (ECU/ECM) provides the basic functions for the single engine, including primary engine protection, crank/start/stop control, fuel management, injector and emissions control. These systems have grown in complexity due to more stringent emissions requirements.
The second level, traditionally located at the generator switchgear, includes synchronization, active and reactive load sharing, power factor control, primary generator protection and sometimes back up engine protection (this is a requirement in the shipping industry, for example). With several discrete components, this historically took a complete switchgear section, lots of wiring, and extra labor.
The third level controls are typically located at the utility tie point circuit breaker and were often done by a PLC, or, in older systems, analog devices and control relays. Add to this the protective relaying, and another section of the switchgear would be dedicated to the intertie controls. The functionality is limited only by the programmer and the budget, and might include:
- Peak shave, electrical demand cost control.
- Import/ Export control.
- Run time management or generator priority.
- Close Before Excitation.
- AMF/ATS (automatic mains failure / automatic transfer switch) operation.
- Fuel optimization.
- Load dependent start/stop and Heavy Consumers management.
- Load shed/load add.
- Multiple utility or main breakers and tie breakers.
- Remote Control / Remote Monitoring.
Today’s advanced controls can combine all three Levels of Control into one device often called an advanced power management controller. Modern electronic engines dictate that the proprietary Level 1 control must be done by the ECU/ECM on the engine. With the ECU/ECM on the engine and the Level 2 and Level 3 controls in the advanced power management controller at the engine/generator or at the switchgear, the switchgear can be much simpler with reduced the wiring, programming, and construction costs.
Let’s discuss each of these functions in more detail and look at some real world applications where they are being done with a modern automatic power management system.
Peak Shave and Import/Export Control
With real time data on electrical market conditions, generator owners can cut their utility bills by switching to their own generation during afternoon peak periods, thus saving demand costs or even become a revenue source by selling power back to the utility. Participating in such markets requires control systems that can respond to a signal from the utility or market operator. For more details, see remote control case study. The new digital controls can communicate with a host computer to automate the starting, synchronizing, and ramping up the power produced to make a fast, unattended, and smooth transition.
Run Time Management
Run time management is the replacement for what used to be called run time equalization. With run time equalization, the usage of multiple gensets was monitored and managed so they were all run approximately the same amount of time. While this approach solved some problems by preventing the early demise of over utilized units, it created another: all generators required maintenance at the same time. The trend now is to manage the run time so that certain machines accumulate the hours first and hit their preventive maintenance (PM) intervals before the other units. Then, while that genset is undergoing maintenance, the other gensets with lower usage can reliably take over the load. This approach staggers the maintenance work and expenditures, ensuring that at any given time there are more machines available for use that are not approaching the end of their maintenance schedule.
Close Before Excitation
When multiple generators need to be brought on line at one time, established operating methods dictated they be synchronized one at a time to each other. Sometimes, however, that is not an option. NFPA 110: Standard for Emergency and Standby Power Systems requires that critical facilities such as hospitals have their emergency power on line within ten seconds. This is impossible to achieve when the critical load demand exceeds the capacity of one generator under that operating protocol.
The only way to achieve this quick response is to use an old method of synchronizing gensets where the prime mover is started, the circuit breaker closed right above crank speed connecting the generator to bus with the excitation off. As the speed approaches synchronous, the excitation is turned on and the generator pulls into sync as the voltage build up. Then the generator is gradually brought up to rated output. The University of Miami, for example, simultaneously brings three gensets fully on line within ten seconds using this method (see case study). Close before excitation might require an extra component or two to turn on the excitation, but the control feature can be embedded into an advanced power management controller. Also, multiple controllers can talk to each other to start up to 16 gensets simultaneously using this method. No extra control systems are required.
For NFPA 110 compliance, the controllers can execute the control functions needed to operate with Automatic Mains Failure/Automatic Transfer Switch systems. All that is needed in addition to the controller are external power switching devices like circuit breakers or contactors. When there is a utility or mains failure, the transfer switch will signal the generator(s) to start then switch to the emergency generator power when available.
There are four different types of transfer schemes: 1) open transition, 2) close transition, 3) 100 ms or closed transition, and 4) extended parallel operation. In an open transition transfer switch, the generator and the utility remain isolated: the switch breaks the connection with one power source before connecting the second. Close transition systems can either use active synchronizers to pull the generator in sync with the utility or simply wait until they drift together so the switches can swap sources very quickly, often fast enough not to drop out motor controls. Closed transition switches, also called in sync transfer, keep the utility and the generator contacts running in parallel for extended periods of time. A variation on this is the momentary closed transition, or “100ms parallel”, that will parallel sources for a maximum of 100ms, preventing motors from stopping or lights flashing before opening one of the switches. 100ms is short enough that control systems and utility agreements can be simplified.
Oil prices have dropped sharply from the $150 per barrel they were running last summer and natural gas prices have also fallen, but that doesn't mean anyone can afford to waste fuel! Fuel optimization systems can maximize efficiency by running engines at their most efficient level, only running the minimum number of engines for the required load and paralleling different size gensets. Fuel optimization will, for example, run one generator when the system demand is at one level. As the demand increases and another generator is required to handle the load, the fuel optimization controls will decide which generator or generators can provide the best fuel economy to meet the demand, automatically starting and stopping engines as needed. Most of engines are run at their optimum efficiency point and one is left to handle the remaining load, not equal loading like standard load share systems.
On the ship Kommandor Subsea 2000, this means getting better fuel efficiency out of its five generators: two 840 kW Cummins KTA 38; two 450 kW Cummins K19 D1 and one 300 kW Cummins NTA 855 G-M engine. The generators power all the propulsion motors: two 600 kW main propulsion motors, one 400 kW stern tunnel thruster and two 400 kW bow tunnel thrusters. A loss of power could mean disaster. See the Case Study for more details.
Load Dependent Start/Stop, Heavy Consumer Management, and Load Shed/Load Add
Load depended start/stop, heavy consumer management, and load shed/load all function basically the same way – regulating the spinning reserve – load dependent start/stop and heavy consumer management dealing with the starting and stopping of the generators and load shed/load add dealing with switching loads off and on.
First, by controlling the generators: like fuel optimization, increased efficiency has payoffs in fuel costs, environmental impacts (carbon footprint, waste heat), engine life, and maintenance. The basic principal is to only run the generators necessary at their most efficient level to handle the load. In older systems, load dependent start/stop automatically added or subtracted generators as the frequency changed. Today’s automatic controllers regulate the spinning reserve, the difference between the total load KW and the KW available from each generator, holding the frequency constant. They must know the KW from each generator and the expected KW from each load in order to function at their best.
Heavy consumer management effectively increases this spinning reserve set point to allow large loads to be started. A start request is issued that raises the spinning reserve set point, thus starting generators as necessary. When there is sufficient spinning reserve, the load is allowed to start.
The other side of the coin is managing the load, including ensuring that the higher priority functions are kept running when there is not enough power available to service all loads. The advanced power management system manages loads in a priority, dropping lower priority loads when the spinning reserve drops and keeping the higher priority loads energized. If there is no load shed function, the entire system could collapse on under frequency, like the August 2003 outage in the Northeast and Canada.
Multiple mains and ties
As more organizations are installing connections to multiple utilities to improve uptime, the power management systems must be able to monitor and control multiple main breakers and tie breakers, as well as the backup generators when neither main is functioning. Advanced power management provides an integrated, simpler, faster and more reliable means of controlling multiple main and tie breakers than older PLC based systems.
In February 2009, Kolding Hospital, a 300 bed facility in Kolding, Denmark, commissioned a multi-mains control system. This control system includes five Automatic Genset Control (AGC) units to monitor, control and protect the five incoming mains, two AGC units for the two 1.4 MVA emergency generator sets, and special unit for the bus tie breaker.
Remote Control/ Remote monitoring
Although modern advanced power management controllers can control the entire critical power system, a host computer often monitors the power system for monitored for faults, alarms, or status updates. This is not a new concept, but technological advancements are making this easier and opening up more possibilities. Rather than relying on analog phone lines, the latest systems can operate the plant via secure Ethernet or even worldwide on the Internet. MODBUS is a technology that is almost 40 years old, still widely in use today, but now can cover greater distances on fiber optics than the old 485 twisted-pair copper standard. CAN bus communications are fast becoming the new standard with broad acceptance. The use of radio frequency (RF) links between the I/O and the controller and between the controller and the Human/Machine Interface (HMI) has also gained popularity as a way to reduce wiring costs.
When Maersk Oil & Gas wanted to commission a Power Management System for the DAN-F oil platform complex in the North Sea, for example, it specified a single advanced power management system that would share loads between one diesel generator, seven gas turbine generators and 12 bus tie breakers on three interconnected platforms. A traditional approach would have featured analog governor technology, 1–5 Volt DC signals and individual controls at each genset. In practice, the 1-5 Volt signals were unusable due to the distances and grounding issues between the three platforms.
The answer in this case was to install a digital solution featuring advanced power management controllers ‘talking’ on a local area network interconnected to the customer’s SCADA software. All power management controllers, including KW and KVAR share, are on this same digital network. An HMI visual display unit is connected to each genset, offering the operator a complete plant overview of the power system and the ability to control any generator from any HMI. Software in the controllers detects a loss of the network and shifts the systems to the old “isochronous droop” mode, thus keeping the system operating if the network should fail.
Bringing Out the Best
Many customers are demanding more complete control over generators and their entire operating environment, as well as the capability of taking part as a distributed energy provider in a deregulated market.
“The distributed generation part of the market has taken off tremendously for us and the entire industry,” says Tom Ferry, Sales Manager for Kohler, WI-based Kohler Power Systems’ Americas-Systems Group. “Nobody wants power plants built in their areas, therefore utilities and end users are looking to this type of project for the potential to assist in demand reduction. Approximately 50 percent of the projects we design now have the capability to parallel to the utility.”
Advanced Power Management systems give operators greater flexibility in designing systems to meet their own particular needs, yet this is only a small sampling of what can be achieved. Utilizing “the power of the processor” offers many benefits and features – cut fuel consumption, boost efficiency, improve reliability, increase functionality, improved flexibility, ease of use, reduce maintenance costs, and even create new revenues – today’s new advanced power management control systems can bring out the best in your power system.
- AGC controller makes Brazil Greener
- Distributed Embedded Power Generation
- Old School Synchronization
- Kommandor Subsea
Steve Evans is the CEO and General Manger of DEIF’s North American operation based in Fort Collins, Colorado. He has been in transmission, protection, generation, distribution, conversion, and control of electrical power for over 28 years.