Find structure in confusion
March 1, 1999 By Pulp & Paper Canada
PROTECTION, design and control strategies were the focus of the electrical engineering session held Thursday.Network alphabet soup, the presentation of Eric Byres, Artemis, aimed to demystify communic…
PROTECTION, design and control strategies were the focus of the electrical engineering session held Thursday.
Network alphabet soup, the presentation of Eric Byres, Artemis, aimed to demystify communication network terminology in the pulp and paper industry.
Byers explained that computer jargon comes from protocols, rules that determine how computers or controllers communicate with each other. Using a cooking analogy, Byers said that even with the development of industry standards it is not possible for any one person to understand all the details about all the protocols that exist.
“Anyone who has worked in this field knows there’s too much going on,” he said. “You don’t have to know all the soup recipes to be the best cook.”
Using the OSI Reference Model is a way for users to structure this confusion and better understand how different network protocols inter-relate. This model explains protocols in layers. The physical layer is the first layer of protocols and describes how raw data signals is transmitted physically over the network, and includes standards for cables, modulation and transmission rates. Byres said this layer is the most important in terms of troubleshooting and accounts for 80% of all network problems.
The middle layers represent transport protocols, such as TCP/IP, which ensure messages can find their route through a complex network.
The upper layers represent the most vague and diverse of the protocol layers. File transfer protocols, e-mail, telnet and applications such as Windows NT, Novell NetWare or OLE, fall into this category.
Once these relationships are defined practical decisions on reducing the number of protocols on site can be made. When purchasing software, Byres recommends buying all upper layer software from one vendor in a package because cabling for supporting separate networks is complex, expensive and can lead to high maintenance costs.
Pierre Nader of SPN Consultants, discussed winder drive control strategies implemented on two-drum winders. He focused on winder finishing equipment and functions at high speeds relating it to practical experience in the industry. He made suggestions on different parameter adjustments including speed and web tension control, drum torque differentials control, lead-in roll speed matching, inertia calculations and other compensations.
Nader said web tension represents the most important control area and has direct consequences on winder runnability and roll quality. During steady state operation, the acceleration/deceleration periods should be kept as short as possible and the transition from transient to steady state must be as soft as possible to maintain sheet stability.
If we have to choose a tension level its better to go towards a higher tension than a lower one, said Nader.
In controlling torque differential, the differential control accuracy should be better than 1.0% throughout the set. To ensure tight winding it is necessary to transfer some of the pull force to the front drum.
Nader also recommends driving the lead-in roll to avoid sudden web tension disturbances during deceleration.
Shoaib Khan, Sandwell Inc., addressed electrical protection systems using power generators. In his presentation Electrical aspects of paper generation in industrial plants: Protection considerations he described individual aspects in a power protection scheme and outlined the important applications and utility of these elements.
Many accidents, he said, are often the result of human fault that could’ve been easily prevented by initiating some of these schemes.
Khan also looked at synchronization. He said that successful synchronization involves matching phase angle, frequency and voltage parameters, with a certain tolerance, prior to breaker closing. Khan said that excessive phase angle differences across the breaker tends to sharply bump the machine, and that along with a slight frequency difference, this can lead to a synchronizing accident that results in machine damage.
In the selection of protection relays, Khan recommends the system be tested to ANSI/IEEE standards, show proven experience for a minimum of three years period and include a digital integrated protection scheme that is microprocessor based.
William Jackson, GE Canada Inc., examined the design of refiner motors to withstand twitching voltage transients. Stator winding insulation systems are important component affecting overall motor reliability. He said that as refiners grow larger, higher voltage requirements are adversely affecting the insulation of the machine and leading to motor damage.
Jackson’s presentation outlined different mechanism to avoid these problems such as using corona resistant materials and impulse testing stator coils individually after installation. He also said adding capacitors, arrestors and resistors aren’t required if the turn to turn insulation is properly designed to meet the 3.5 unit surge factor, but that capacitors and arrestors do act as a good insurance against power system surges. Adding series resistors however, negatively affects motor reliability.
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