Electric Power Interruptions

On November 9, 1965, at 5:16 p.m., a back-up relay failed at one of the five main transmission lines at No. 2 station near Toronto, Canada. As the load had shifted to the other four lines, they became overloaded, and as a result the relays failed in all four lines. The failure resulted in the load being shifted to the other plants in the system. The plants got overloaded, which caused them to shut down. Within minutes, power plants in Canada, New York, and the New England states got out of service. The blackout affected 30 million people and covered an area of 306,000 sq. m. In some areas, such as New York City, power was not restored for about 13 hours.

This massive power blackout resulted in the construction of the national Electric Reliability Council in June 1958. This council sets standards for the design, operation, and maintenance of generating and transmission systems. These standards serve to prevent a failure in one power system from spreading to other systems. Yet local system failures cannot be avoided.

Nowadays in some European countries and in the US there are from 60 to 80 power interruptions per year, in which there is a loss of service for customers for more than 15 minutes. Mostly these interruptions are caused by weather conditions - ice, freezing snow, lightning or storms. There can be also failures of equipment - transformers, relays, insulators and so on. However, the reliability of electric service is extremely high.

Have you been a witness to an electric service failure? Describe it, please.

 

Read and translate the text. What do you think is meant by «Member countries»?

Give the new units for the following: röntgen, rad, rem, curie.

Quantities and Units

For many years, special measurement units for quantities of interest in radiation protection were used, which were not coherent with the International System of Units (SI). These old units (röntgen, rad, rem and curie) have been superseded in the last few years by a new set of units which are coherent with the SI system.

These new units, the gray for absorbed dose, the sievert for dose equivalent, and the becquerel for activity of radioactive materials, have been progressively adopted in Member countries, although some residual cases of use of the old units are still being observed. The relationships between the new SI units and those previously used are shown in the following table:

Quantity	SI Unit	New Name and Symbol	Old Unit and Symbol	Conversion Factors
Exposure	kg-1	-	röntgen (R)	1 C kg-1 = 3876 R 1 R = 2.5 × 10-4 C kg-1
Absorbed dose	J kg-1	gray (Gy)	rad (rad)	1 Gy = 100 rad 1 rad = 10-2 Gy
Dose equivalent	J kg-1	sievert (Sv)	rem (rem)	1 Sv = 100 rem 1 rem = 10-2 Sv
Activity	s-1	becquerel (Bq)	curie (Ci)	1 Bq = 2.7 × 10-11 Ci 1 Ci = 3.7 × 1010 Bq

 

Read the text and find in it the answers to the questions that follow it.

Electric Power Plants

The two main types of power plants traditionally have been the fossil-fuel steam-electric plant and the hydroelectric plant. Other types, including internal-combustion-engine plants and nuclear plants also have been built. The selection of a particular type of generating plant and its location involves consideration of a number of factors such as plant, fuel, and transmission line costs; availability of cooling water, and environmental considerations.

Fig.24. Cross-section through the main structures and units of hydroelectric power plant

For several reasons, the relative importance of the various types of power plants has been shifting. Good sites for new hydroelectric plants have become scarce in many countries. Distribution networks have been extended so that less expensive power from large steam-electric stations has been replacing power from smaller diesel-generator units. Nuclear-electric power plants have been built instead of fossil-fuel steam-electric plants because the cost of coal and oil has been increasing.

In the United States in 1970, fossil-fuel steam-electric plants accounted for 76% of the power generated, hydroelectric plants for 16%, and nuclear plants for 2%.

In 2000 45% of the electric power in the United States is generated from fossil-fuel steam-electric plants, 45% from nuclear plants, and 10% from hydroelectric plants.