Grammar: Non-finite forms of the Verb. The Complex Sentences

Word List:

1. motor losses	потери в двигателе
2. stray losses	потери на рассеяние
3. core losses	потери в сердечнике
4. zero slip	нулевое скольжение (пробуксовка)
5. slip losses	потери при пробуксовке
6. tooth edges	края зубца
7. flux density	плотность потока
8. in-plant	рабочий режим (на предприятии)
9. back iron	станина
10. stator impedance	полное входное сопротивление статора
11. idle to run idle	холостой ход работать на холостом ходу
12. idle readings	значения параметров на холостом ходу
13. core teeth	зубцы сердечника
14. motor imput watts	мощность мотора на входе
15. windage	сопротивление воздуха

Evaluating Individual Losses

Three of the motor losses appear, at first glance to be easy to evaluate. Stator I²Ror “copper loss” is simply the product of winding resistance and current squared, summed up for all three phases. Both those items can thread quite accurately. With the motor running idle – that is, uncoupled from any load - only three losses are present rather than all five. Stray loss is nonexistent without load, and at essentially zero slip the rotor I²R, or “slip loss”, will not be present either. Total motor input watts will include only core loss, friction and windage, and a small stator I²R calculable from the no-load amperes. Taking idle readings of current and power as the voltage is varied permits separation of core loss and friction and windage from the total input. Unfortunately, the in-plant situation rarely permits adequate voltage variation, although in the repair shop it may be easy.

The core loss from such an idle test will not be quite the same at full load. Although the difference is slight, it can become important when small changes in loss are assigned high dollar value. Because core loss is associated with the magnetizing branch of this circuit, the value will depend upon the voltage across that branch. Under increasing load, the current through the stator increases while terminal voltage remains unchanged. Thus anincreasing voltage drop occurs in the stator impedance, lowering the voltage across the magnetizing branch and decreasing the core loss.

Separate tests for core loss have become popular in recent years, primarily to evaluate possible damage incurred during motor repair. Those tests require the motor to be disassembled. It has been claimed that one testing device will verify actual motor core loss within 10 percent. Be skeptical of that. In the first place, what we call “core loss” in an assembled running motor is not the same as the power loss within a stator core alone, magnetized by a “core loss tester”. Even if the magnetic flux density in the core iron below the slots were exactly the design value, a motor’s total core loss includes major components other than that in the so-called back iron.

One is the loss in the core teeth themselves, especially along the tooth edges near the air gap. It is not present during the usual “'core loss test” because the teeth are not magnetized. Another component is the “surface pulsation loss” caused by magnetic flux crossing the air gap to link the rotor. It, too, is obviously not present during a core loss test. Hence, using the tester toestimate possible core damage prior to rewind is one thing; trying to accurately predict overall motor efficiency is quite another.

Focused Practice

I. Answer the following questions:

1. How many losses are present when the motor is running idle?

2. What are these losses?

3. What is “copper loss”?

4. What does taking idle readings of current and power as the voltage is varied permit?

5. Why will the core loss from an idle test be quite the same at full load?

6. (What)When can the slight difference become important?

7. Why have separate tests for core loss become popular in recent years?

II. Analyse the grammar structures underlined in the above text.

III. Speak on: Motor losses

Unit 20

Grammar: The Infinitive. The Infinitive Constructions.
The Passive Voice

Word List:

1. hydraulic system design	проектирование гидравлической системы
2. computational techniques	вычислительные методы/приемы
3. pneumatic system	пневматическая система
4. fluid power	гидравлическая мощность
5. design procedures	методы  конструирования
6. feasible circuits	выполнимые, возможные схемы
7. servohydraulic circuits	сервогидравлические сети
8. selection database	база отбора данных
9. load attributes	характеристики нагрузки
10. hydraulic power unit	гидравлический энергоблок
11. KEOHPS	Knowledge Engineering on Hydraulic and Pneumatic Systems
12. tool	инструмент, средство
13. browser	браузер, просмотр
14. fire and mining	Пожаро- и взрывоопасность

Expert Systems for Fluid Power

The application of expert systems to hydraulic system design has been thoroughly studied. Hydraulic systems are made up primarily of pre-engineered components that each has a specific function. Thus, system functionality can bebroken down into its basic units. Considering that fluid power is more than a billion-dollar industry, a computational system for fluid power should carry strong market potential.

Design procedures for hydraulic systems have been well established, primarily in technical books and manufacturers’ literature. These design techniques are of paramount importance for developing expert systems, and the component-oriented nature of fluid power systems is an ideal fit. Many engineers and designers involved in fluid power technology have a background in machine design, but lack a command of computational techniques. This makes it difficult for them to realize the value of expert systems without having witnessed the demonstration of a prototype. The prototype has proven to be sufficiently useful to raise interest from a number of fluid power designers to collaborate on its enhancement.

A technology-based enterprise has been established in Florianopolis, SC, Brazil, to develop computational systems for fluid power. The enterprise is known as KEOHPS. The goal of KEOHPS is to develop computational solutions using artificial intelligence to design hydraulic and pneumatic systems. A key element of this program is that the systems are intended for both national and international markets.

The prototype is a result of an international research project involving experts from Brazil, western Europe, and the U.S. In its present form, it has the capability to:

· prompt the user to respond interactively to determine system requirements without requiring extensive knowledge of hydraulics;

· automatically generate a set of feasible circuits - based on well-proven principles of circuit design - for consideration by the designer;

· allow preliminary ranking of alternative solutions from general attributes;

· allow altering the hydraulic power unit (HPU) model and redefining component model lists;

· calculate the HPU demand based on load attributes (force, speed, torque, etc.);

· handle servohydraulic circuits;

· generate topological dynamic simulation models tailored to a specific simulation package;

· display circuit schematics and component specifications through automatically generated pages that can be viewed through an Internet browser, and

· offer a fluid selection database through which the user can search via keyword combinations, such as fire and mining.

A comprehensive prototype model was developedto demonstrate the system to as many experts as possible. The prototype was presented to individuals in the fluid power industry through visits to component manufacturers and participation at conferences and technical trade shows. Based on observations during its validation by fourth-year engineering students, the system also holds potential as an educational tool.

Focused Practice

I. Answer the following questions:

1. What are hydraulic systems made up primarily of?

2. Why is a computational system for fluid power of paramount importance?

3. Where has a technology-based enterprise been established?

4. What is the name of the enterprise and its goal?

5. What is a key element of this program?

6. What makes this research project international?

7. What does the prototype have the capability to do?

II. Analyse the grammar structures underlined in the above text.

III. Speak on: Hydraulic systems.

Unit 21