Full Load Rate Research Articles

A Better Approach to Motor Circuit Protection

Over the years, various approaches including both thermal magnetic breakers and several types of fusible devices have been used in motor circuit protection schemes with acceptable results. Evidence reported in the trade magazines indicated that the level of protection from these types of devices was not totally effective. For the first time, with the printing of the 1968 National Electric Code, the application of instantaneous trip circuit breakers (without time delay) was allowed provided the pickup could be adjusted above 700 percent to a maximum of 1300 percent of the motor full-load ampere rating. After extensive testing the first product complying with these requirements was introduced to the market in 1969. Experience in motor failures indicates that most faults occur at relatively low levels of fault current just above lock rotor values rather than at higher levels. With rapid clearing of faults in the low-level range such as can be accomplished with the use of instantaneous trip circuit breakers, extensive damage to motors as well as to control equipment can be greatly reduced. By combining low-level protection obtained with the high interrupting capabilities of specially designed current limiters, a full range of coordinated protection is available for both high-and low-level faults.

Alternators for operation on a transmission line

When laying out the design of ah alternator that will be used to transmit power over a long transmission line, it is necessary to consider several factors in addition to the specified full-load rating before one can decide on the relative electric and magnetic loadings of the machine, or even the frame size on which it should be built.In attempting a survey of the problem, the paper was divided into six sections, which may be summarized as follows :—(1) General discussion of the possible instability of an alternator connected to a transmission line.(2) Varying-voltage and constant-voltage ' transmission lines. (3) A more detailed consideration of the alternator, showing that it is possible to determine directly from its open-circuit and short-circuit characteristics the maximum leading kVA with which it can deal at normal voltage, for complete stability down to zero voltage.(4) Effect of the exciter on the stability of the generating unit.(5) Variations in station voltage to be expected when operating the high-tension line switches.(6) Particulars of an alternator built for a 50-period line demanding a charging current equivalent to 8 100 kVA at 11 000 volts.

Present Status of Prime Movers

The paper brings out in a concise form the present status of heat engines and hydraulic turbines in commercial use today for the conversion of the energy found in fuel and water into mechanical power for the production of electric energy. The various types are compared as to relative importance, capacity, efficiency, weight, cost and economy, which are illustrated by curves plotted on kilowatt basis. (a) Reciprocating Steam Engine. (b) Steam Turbine (c) Gas Engine (d) Oil Engine (e) Hydraulic Turbine (f) Finance and Economics Curves are plotted showing the investment and fuel costs of the different heat engine units, on the basis of percentage of normal full load rating of machines.

Present status of prime movers

The paper brings out in a concise form the present status of heat engines and hydraulic turbines in commercial use today for the conversion of the energy found in fuel and water into mechanical power for the production of electric energy. The various types are compared as to relative importance, capacity, efficiency, weight, cost and economy, which are illustrated by curves plotted on kilowatt basis. (a) Reciprocating Steam Engine. (b) Steam Turbine (c) Gas Engine (d) Oil Engine (e) Hydraulic Turbine (f) Finance and Economics Curves are plotted showing the investment and fuel costs of the different heat engine units, on the basis of percentage of normal full load rating of machines.