The primary purpose of rating an electrical machine is to give the user an idea of what he may expect from the unit which he purchases. It is the purpose of this paper to propose a method of rating arc-welding generators and transformers which will give a truer picture of their working ability than is afforded by the present one-hour rating. Such a method of rating will be beneficial both to the customer who buys and uses arc welders and to the manufacturers who produce and market the units. The user will be better able to select a machine which will do the job to be performed, and at the same time he will be assured that he is not purchasing a machine unduly large for his requirements. The present custom is to give welding transformers and generators a one-hour rating, specifying the current they can deliver for a one-hour period, starting cold, without exceeding the permissible temperature rise. The plan here proposed is to give them a current rating indicative of their normal operating capacity, or short-time welding ability; and an additional service factor rating, indicative of their continuous current capacity, as limited by thermal considerations. All electric apparatus has these two major limitations on its output, one a ``size'' limit expressed by breakdown torque, commutation limit, or voltage drop; and the other a thermal limit expressed by the degrees temperature rise permissible for the type of insulation used.
THE rapid growth of a-c arc welding in the last ten years has resulted in a-c welding becoming a large fraction of all arc welding rather than a negligible proportion. As power loads due to a-c arc welding become larger, questions arise in the minds of users and power-supply authorities about power requirements of a-c welders and the effect of a-c welders on power circuits. In some instances arc welding has been confused with resistance welding, although the two are entirely different from the standpoint of power supply. This paper presents data useful for determining the effects of a-c arc-welding loads on electric power circuits.
THE rapid growth of a-c arc welding in the last ten years has resulted in a-c welding becoming a large fraction of all arc welding rather than a negligible proportion. As power loads due to a-c arc welding become larger, questions arise in the minds of users and power-supply authorities about power requirements of a-c welders and the effect of a-c welders on power circuits. In some instances arc welding has been confused with resistance welding, although the two are entirely different from the standpoint of power supply. This paper presents data useful for determining the effects of a-c arc-welding loads on electric power circuits.
A dynamic modeling study and field validation of a cooling tower serving a chiller are performed in this study to evaluate the efficiency of the cooling tower under various conditions. The dynamic model examines the losses and thermal capability of the cooling tower. The cooling tower used in this study for field validation is located at Cookeville, Tennessee, USA. The whole setup is fully instrumented to record the water and air flow rates and temperature; make-up water and blow down water flow rates; power consumption of pump; fan and chiller; weather data; etc. with one-hour resolution. The outcomes of the model are validated with the recorded data of the cooling tower and the test condition data. Furthermore, the effects of using Variable Frequency Drive (VFD) on the cooling tower’s fan power consumption are investigated. Additional recommendations on improving the energy efficiency and reducing the water losses are suggested based on the modeling data.
The primary purpose of rating an electrical machine is to give the user an idea of what he may expect from the unit which he purchases. It is the purpose of this paper to propose a method of rating arc-welding generators and transformers which will give a truer picture of their working ability than is afforded by the present one-hour rating. Such a method of rating will be beneficial both to the customer who buys and uses arc welders and to the manufacturers who produce and market the units. The user will be better able to select a machine which will do the job to be performed, and at the same time he will be assured that he is not purchasing a machine unduly large for his requirements. The present custom is to give welding transformers and generators a one-hour rating, specifying the current they can deliver for a one-hour period, starting cold, without exceeding the permissible temperature rise. The plan here proposed is to give them a current rating indicative of their normal operating capacity, or short-time welding ability; and an additional service factor rating, indicative of their continuous current capacity, as limited by thermal considerations. All electric apparatus has these two major limitations on its output, one a "size" limit expressed by breakdown torque, commutation limit, or voltage drop; and the other a thermal limit expressed by the degrees temperature rise permissible for the type of insulation used. These two limits are usually quite independent of each other, so that no single number, such as a one-hour rating, can fully describe the usability of the apparatus. The proposed service factor rating gives both of these limits, and therefore gives the user the data for applying the apparatus to a variety of duty cycles. In conclusion, it is suggested that welding generators and transformers be designed for a service-factor rating of 75 per cent, since this corresponds best to typical welding duty cycles. It is also proposed that the standard AIEE values of temperature rise by resistance for continuous rated machines, 60 degrees centigrade for class A, or 80 degrees centigrade for class B insulation, be recognized as the limiting values in continuous operation at the service-factor rating. Rating for Welding Service Before proposing a method of rating, it is advisable to consider the purpose of rating. "The rating of a machine or other equipment is a set of performance characteristics which are subject to verification by test under specified conditions and which by mutual agreement between buyer and seller may serve as a basis of specifications and contracts covering the purchase and sale of the machine or other equipment. The rating is used by the manufacturer in the design and fabrication of the equipment and is used by the purchaser as the basis for application; therefore, the terms in which the rating is stated should be definite, easily verified, of such a nature as to permit intelligent use of the equipment, and as far as possible inclusive of usual conditions as found in practice." 1
