Power Monitoring and Control Systems Mean No More Whistling in the Dark

Although much has been written about power monitoring and control systems (PMCS) lately, little has been said that clearly shows why plants should invest in them. We became convinced at the Shell Chemical plant in Norco, La., a couple of years back that PMCSs were the wave of the future and have recently introduced a system into our plant. To better understand the benefits of such a system, one should consider the issues at the Norco plant, the selection process we went through in choosing the best system for us, and the benefits we have realized and what we see for the future of our PMCS.

When we first started investigating PMCSs in 1993, we quickly learned that technology within the electrical industry had become high tech. While electrical systems are an integral part of the plant’s process, they had played second fiddle to process instrumentation equipment which is often computerized and loaded with state-of-the-art instrumentation for efficient control.

 As a result, electricians, operators, inspectors, and engineers work with much too little data to make the most intelligent decisions concerning their electrical system. They just don’t have the instrumentation to be able to look at a motor and see if it is running overloaded, grounded, or if it tripped on an overload or an electrical fault.

Maybe the lack of information and flexible control were less important 25 years ago, but today with increased emphasis on reducing cost, information is crucial for monitoring energy consumption and identifying ways to improve system and equipment efficiency. The widespread use of energy-efficient motors helped reduce costs, but until intelligent PMCSs are also accepted as part of the formula, energy and operational expenses will continue to remain unnecessarily high.

Whistling in the Dark

 Like others around the country, the Shell Chemical’s Norco plant had no monitoring equipment capabilities on the electrical system. Monitoring the quality of electrical power throughout the plant was limited. For example, the monitoring of incoming plant power from the local utility company was limited to analog voltage and current meters; breaker protective devices provided no pre-fault or post-fault data; on-line motor conditions had to be manually gathered; and system power factor status was unknown.

 This lack of information resulted in certain non-optimum maintenance procedures being the accepted norm, perhaps not only at Norco but industry-wide. Preventative maintenance and equipment surveillance are two examples.

Preventative maintenance frequencies were based on time which was set based on experience and gut feeling rather than real-time data. Every three to five years, motors and motor starters at the site were cleaned and checked as part of a preventative maintenance program. Data such as running hours, number of starts, and number of trips on each piece of equipment was not available. The cost of performing unnecessary preventative maintenance equated to four or five hours of electrician’s time.

Equipment surveillance was limited to the electrical inspector who made daily rounds to nearly a dozen substations to see if there were any abnormal conditions. But if something went wrong five minutes after he left, it’s possible no one would know about it until the next day. If there was a problem, maintenance could only guess at the cause until they made one or more trips to the field, and sometimes they could only speculate as to what went wrong and in what sequence events occurred.

 Failure in the electrical system could result in a complete loss of power to the entire plant within minutes. Within minutes the entire facility would be down costing several million dollars in lost production. This catastrophic failure of the electrical system could also cause significant safety and environmental concerns. This has never happened, but without adequate information about the electrical system, it was a worst-case scenario that we could not ignore.

Shell has two plants at Norco, referred to as the East Site and the West Site (Chemical Plant). The incoming power to the West Site comes from the East Site via four 13.8KV feeders. The West Site comprises 10 different operating units that produce various resins and solvents, a biotreater plant, incineration facilities, and a utilities unit which provides steam, air, and treated water to the entire plant. The West Site has nearly 800 induction motors ranging from 4160 volts down to 480 volts. The entire load of the West Site averages 12 megawatts of power. The monthly power bill from the local utility is supplied to the East Site and is based on the total load of both sites. The West Site’s portion of the bill is based on information obtained by metering equipment at the East Site. The West Site did not have equipment necessary to determine that accuracy of it’s electrical bill and could not accurately distribute the total cost of each production unit. This no doubt meant some units were being charged more for their electrical consumption and others less.     Capacitor banks located on incoming 13.8KV feeders are required to maintain voltage levels on the 13.8KV system at acceptable levels. Occasionally fuses or capacitors would fail resulting in a significant voltage drop which would go undetected until the electrical inspector would make his rounds. This reduction in the voltage posed a problem for starting of large induction motors and could result in a major power dip which could cause on-line equipment to shutdown. It became apparent that it was important to monitor the voltage level and provide low voltage alarming.

Looking for the Answer

The vision for the future of Shell Chemical Company is to be the premier producer and preferred supplier of customer product needs. This includes being a world class performer in safety, health, environment, customer satisfaction and applied technology. Local management recognized this meant taking advantage of new technology, so we were encouraged to take risks along this line. With this support, we initiated a project to replace 1950’s vintage electrical equipment (switchgear, motor control centers, transformers, bus ducts, etc.) which provided electrical power to the plants utilitie infrastructure. Included in the project was a rudimentary PMCS. The first step was putting together a conceptual design team. The team consisted of electrical engineer discipline leader Billy Wright, Carl Reed, senior electrical inspector at the West Site, and Mark Plagens with Parsons, SIP, an Engineering, Procurement and Construction firm based in Houston.

We analyzed the plant's electrical system and determined its needs. To avoid possible equipment conflicts we decided to stay with a single supplier for the switchgear, motor control centers, and PMCS. A list of approved suppliers was developed and a preliminary evaluation was performed. The list was narrowed to Westinghouse Cuttler-Hammer, General Electric and Siemens Energy and Automation. In addition to the typical product literature, we received on-site presentations and, where available, visited other companies that had installed similar systems. We reviewed each from the standpoint of data collection, user friendliness, expandability and ability to interface with our existing components. We decided to stay with a Microsoft Windows based system with which our people were familiar. User friendly was a key issue for us. We wanted the system to be used and maintained, and that meant the people using it had to be able to learn it and keep it evergreen. We then developed location-specific Engineering Guidelines and Specifications which were included in the bid packages that were submitted to the three candidates.

Siemens was just introducing its WinPM software when we approached Gerry Thomas, Siemens industrial sales engineer based in nearby LaPlace. WinPM is an all-in-one, user friendly, menu-driven software that includes Dynamic Data Exchange to import and export data between itself and other software, and which uses standard Windows bit maps for graphics.

We liked the quality and availability of the equipment and parts as well as the company stability, the price offered, and the general direction Siemens was taking. They also impressed us with their enthusiasm, experience, and commitment, so the bid was awarded to Siemens. But now came the hard part*making it work for us and in a way that justified the change and outlay.

Blazing a Trail

We began working with the WinPM software at Norco in September 1994. As expected, the software was new and needed some bugs ironed out, so we were in regular phone contact with the Siemens people. We provided feedback and recommendations and they responded with product improvements. Visits to the Siemens factory provided opportunities for us to learn more about the program and again later, to test the software when the equipment was ready. After they installed the system, Siemens sent technicians to Norco and also troubleshot the system over the modem. One of our concerns had been that the manufacturer would continue to maintain and update its software; we gained assurances from Siemens when they committed to an additional 1.5 years of software support.

The motor installation proceeded on schedule but took a year to complete because it was being done hot. We had to swap over loads on tight time frames while making sure the old and new systems ran together smoothly. Out of 180 pieces of equipment switched, the only problem we had was one motor that ran in reverse and spun an impeller into a pump.

The System

For hardware, we located a computer with printer and monitor in a Retalle PC enclosure in one of the plant's substations and connected it via twisted pair wires to two switchgear units, each with 11 feeder breakers and six MCCs .

The computer is connected via fiber optic cable and modems to all the other substations in the site. Several isolated multi-drop RS232 to RS485 converters link different comm ports inside the console with Siemens Advanced Motor Master System (SAMMS), ACCESS I/O relays, 4720 meters and Static Trip III units in the switchgear and MCCs that make up the Siemens ACCESS PMCS.

The SAMMS units are solid state overload relays with integrated control logic designed to protect low and medium voltage motors. A sensor takes RMS current measurements and combines them with user-programmed full load amperes, service factor and trip class to prevent overload. Among other functions, they also protect motors from phase imbalance, load loss and ground fault.

 The solid-state, addressable I/O relays allow remote control of contactors and breakers, while providing information on the status of field devices.

The 4720 power meters monitor the four incoming feeder lines as well as the medium and low voltage lines. These digital 4720s offer numerous metering functions, from min/max values and waveform capture to snapshot memory. They can also be used for a variety of control functions, such as load shedding and breaker tripping.

The Static Trip III devices are microprocessor controlled, RMS sensing over current protective relays with zone interlocking as a standard feature, for use in low-voltage switchgear. ISGS (Intelligent SwitchGear System) relays are provided for medium voltage applications, providing time delay trip and optional instantaneous trip for phase and ground elements.

By communicating with twenty-two 480V feeder breakers, eight MCCs and two enunciators that represent a total of 180 addressable devices, this one computer enables electrical personnel at the site to remotely program, monitor and control the electrical system within two substations.

A computer in another substation is running a separate system on WinPM, Impact, Excel and Multilin Relay Comm software that are tied together by the ACCESS system. This computer communicates with Siemens multi-drop converters which are looking at 4720s and ISGS relays inside that substation, as well as Westinghouse devices and Multilin meters and motor management relays.

The plan is to link both systems together over our LAN as soon as Siemens finalizes the networkability of its WinPM software. When that happens, the chemical facilities' electrical system will be accessible from any Shell facility in the country.

The Payback

So what has ACCESS done for us? The system counts utility kWH pulses and we now know exactly how much energy we are using. This means we can verify and correct any discrepancies in billings.

A big plus for maintenance is that they can take the initiative instead of reacting to problems. By looking at the number of starts, the number of trips, and comparing the data to the manufacturer's recommended maintenance schedule, for instance, they can execute wise maintenance instead of operating on set schedules and hunches. The result is useful work, rather than inadequate or unnecessary maintenance carried out.

 Trying to operate without a PMCS in the years ahead will be like commuting in a horse and buggy on a New Jersey freeway. In the old days, for instance, a motor that kept tripping would have required someone clipping a recording amp meter on the motor and returning a couple of days later to pick the charts off the floor and decipher them. With ACCESS, we simply take snap-shot recordings of the amperage on all three phases on that motor at one-minute intervals and plot them on a graph for a couple of days. We did that recently and the process people looked at the graph and realized they had a filter that was clogging and drawing more load. We set a pre-alarm that alerted them when it was time to check their filters. End of story.

Another time an alarm showed a battery charger with a ground fault. An electrician isolated and fixed the problem straight away. A maintenance repair ticket arrived the next day. By comparison, our maintenance repair cycle time has been reduced by 50-75 percent already.

The supervisor no longer does his daily rounds of the substations. All he does are look at the WinPM Event Log and follow up on anything significant.

 We also discovered something interesting about the power supply: We had assumed the voltage level on the incoming 13.8kV feeders was fairly constant until we connected the 4720s. The min/max data showed the voltage tolerances swinging all over the place, so we knew we had to correct that problem.

Min/max values have proven useful in answering other questions, too, such as tracing voltage spikes or finding out how much the voltage sags when starting large motors. One transient overvoltage condition caused MOVs to blow on three variable speed drives and shut down another drive and a compressor. We checked the min/max values on the WinPM software and saw a maximum voltage of 15kV on the 13.8kV system just when the drives went down. We realized that energizing the primary of the transformer had caused a spike down to the 480V level. Before the days of ACCESS, there was no way we could have traced why those MOVs went out. But now, knowing we had an RLC circuit with a lot of resonance, we were able to take the capacitors off line temporarily before closing that transformer. This kind of in-depth and rapid root-cause analysis is exactly what makes a PMCS earn its keep.

Two of our incoming feeders have capacitor banks protected by fuses. The 4720s monitoring these lines go into alarm mode when a fuse blows and this information is passed on immediately to the utility company: it is vital that these capacitor banks stay on line so as to prevent voltage drops on process equipment when we start our large motors.

At the moment, we have only tapped a small part of the system's capabilities. Harmonics analysis, for instance, hasn't been touched on yet. We are only beginning to evaluate problems we have been looking at for a while, such as where to place capacitors on the 480V level to improve the power factor, whether it is more economical to use steam or electricity, whether starting a particular motor at a particular time will create a new peak demand, or how to accurately allocate energy cost.

It will take another year before we are fully utilizing all the features of the system. Most of the benefits will be realized when networking provides operators with the information at their fingertips in the control rooms. System growth can also be properly planned when the need arises.

To promote partnership and growth with Irrigation Craft, Siemens assisted Irrigation Craft in training their dealers and converting their drawings and PLC programs. “Siemens is willing to come in and perform educational services, and that is more than the other manufacturers would do,” Neff said. “So Siemens has taken an interest in our business and in our industry.

A Time to Change

What motivates people to stick their necks out by introducing a new technology into the plant when they could play it safe and just change out the old gear? The answer is that technology is changing, and the only way to reap the benefits is to make a move. Remeber, there was a lot of resistance to PLC technology in the plants. People were comfortable with the existing technology, seeing relays clicking in and out and fixing things they could understand. But then someone handed them a little black box. If they are going to move ahead, though, they have to invest in new technology.

The only difficulty in an industry that is typically conservative, is making people aware of what is available, letting them kick the tires and take a test drive. It's a learning curve for the whole industry, and it may take years to get to the point where plants can access this information and start to reduce costs and inventory, minimize downtime and improve maintenance. Although it is hard to quantify the rate of return accurately on an energy management system, because you also get abstract pay outs, we strongly endorse this kind of system to other plants. ACCESS and systems like it are the trend of the future. As a colleague is fond of saying, If you’re tired of whistling in the dark, try turning on the lights.

Billy Wright is Electrical Engineer Discipline Leader Shell Chemical’s West Site in Norco, Louisiana

Mark Plagens is a consulting specifying engineer with Parsons SIP, an Engineering, Procurement and Construction firm in Houston