Ungrounded System Research Articles

Levels of Functional Equivalence in Reverse Bioengineering

Both Artificial Life and Artificial Mind are branches of what Dennett has called engineering: Ordinary engineering attempts to build systems to meet certain functional specifications; reverse bioengineering attempts to understand how systems that have already been built by the Blind Watchmaker work. Computational modeling (virtual life) can capture the formal principles of life, perhaps predict and explain it completely, but it can no more be alive than a virtual forest fire can be hot. In itself, a computational model is just an ungrounded symbol system; no matter how closely it matches the properties of what is being modeled, it matches them only formally, with the mediation of an interpretation. Synthetic life is not open to this objection, but it is still an open question how close a functional equivalence is needed in order to capture life. Close enough to fool the Blind Watchmaker is probably close enough, but would that require molecular indistinguishability, and if so, do we really need to go that far?

配電線における分散電源単独運転時の鉄共振過電圧現象の発生様相と対策

Ferroresonant overvoltages can occur on an isolated feeder connected to Distribution System Generators (DSGs). This paper analyzed the overvoltages and the following results are obtained.(1) The overvoltages occur on a three-phase four-line wye-grounded system such as 400V class distribution lines but do not occur on a three-phase three-line ungrounded system such as 6.6kV distribution lines.(2) The overvoltages can occur when DSGs are separated from the utility source not at the primary side but at the secondary side of a delta-wye grounded transformer connected to the feeder.(3) The saturated reactances of transformer excitation circuit and the phase-to-neutral capacitances on the isolated feeder eatablish the ferroresonance circuit.(4) The ferroresonance generates the phase-to-neutral voltages of 2.6 pu. The voltages are suppressed to 1.8 pu with installation of surge-absorbers but continue. The DSGs have to be disconnected from the islanding system by overfrequency or overvoltage relays to drop the continuing overvoltages.

Grounding transformer applications and associated protection schemes

Various aspects of the purpose, protection philosophy, application and specifications of different types of grounding transformers and two governmental system case studies illustrating improperly applied grounding transformers and associated ground fault protection systems are discussed. The first case study involves the use of an incorrect value of resistance in grounded neutral wye-broken delta grounding transformers associated with a 2400 V ungrounded system. Detailed calculations are given to correctly size the grounding transformer resistance value necessary to limit the magnitudes of transient overvoltages caused by restriking ground faults. The second case involves ground fault tripping deficiencies caused by utilizing only a single zig-zag grounding transformer with an associated neutral resistor on a multibus 2400 V ungrounded system. It is stressed that a single grounding transformer is not adequate for use with a multibus configuration. A protection scheme for use on a multibus arrangement is presented. >

System Grounding of Electric Submersible Pumps

Summary To ground or not to ground? That is the question. This paper assists in answering that question. Proper system grounding of electrical submersible pumps has long been an issue for debate. Some believe that an ungrounded system is best, whereas others are equally convinced that the opposite is true. Many are not aware of how important the correct answer may be.

The Detection of Induced Polarization with a Transient Electromagnetic System

The study of two-dimensional TEM models consisting of a cylinder in a conductive host using measured rock properties show that TEM surveys are capable of detecting induced polarization (IP) effects. A case history showing a comparable type of response is presented. The IP effects manifest themselves in extreme cases as negatives in the response and in other cases as anomalously high apparent resistivities. The models used allow a study of the variation of responses produced by varying the Cole-Cole constant for the cylinder properties. The results suggest that the different parameters produced distinct effects in the response. If the rock properties reported in the literature are correct, it appears quite feasible to observe IP effects via TEM using an ungrounded system. There may also occur a set of negatives in the response of a cylinder which are associated with high-conductivity contrasts and geometrical effects. In the cases studied these two groups are readily distinguished. IP effects might be interpreted from a family of zero responses (when these occur), apparent resistivity/time sections or by stripping away the host rock response and comparison with a uniform polarizable ground. There is a great deal of geometrical information about the scattering body at early times our of reach of many contemporary instruments.

High-Resistance Grounding

High-resistance grounding of electrical power systems offers many of the advantages of both solidly grounded systems and ungrounded systems, including practical suppression of transient overvoltages, practical reduction of equipment damage due to ground fault, and the ability to continue to operate a system with a ground fault present on one phase. The design, application, packaging, and field testing of high-resistance grounding systems, including a practical method of fault location, are described.

Ground Fault Tests on High-Resistance Grounded 13.8-kV Electrical Distribution System of Modern Large Chemical Plant---I

Actual ground faults were applied to a high-resistance grounded 13.8-kV electrical distribution system supplying power to a large chemical plant. These tests show that such a system will restrict overvoltage transients and reduce damage to equipment under ground fault conditions. Such a system is inherently safer and more reliable than an ungrounded system and offers some operating features not possible with a low-resistance grounded system. The maximum overvoltage transient recorded during many ground faults, involving several different ground conditions imposed on the system during six hours of testing, was about 2000 V. The effect of these ground faults on the 13.8-kV electrical distribution system supplying an operating plant was negligible. In fact, the operating personnel, anticipating the worst, were not aware that the tests had been performed.

Trends and Practices in Grounding and Ground Fault Protection Using Static Devices

Grounded and ungrounded systems are in general use in both commercial and industrial distribution systems. Proponents of each type of system have established valid points to defend their position. This paper briefly identifies the types of systems in use in each category and lists some of the main advantages and disadvantages of each. With the advent of higher voltage levels in our low-voltage distribution systems and the trend towards solidly grounded systems, problems resulting from the lack of proper ground fault protective devices have caused some severe equipment burndowns. The need for adequate protection has been recognized by the 1971 National Electric Code. This recognition is being complemented by Underwriters' Laboratories with the introduction of appropriate standards. With the passing of the Occupational Safety and Health Act of 1970, more emphasis than ever before will be placed on adherence to the preceding code and standards. This paper will review the various methods of detecting ground faults using static devices and describe some of the equipment available for these applications.

Three-Phase Subharmonic Oscillations in Symmetrical Power Systems

This work makes a three-phase TNA study of the most commonly observed subharmonic oscillation, that is, the 1/3-order subharmonic. Symmetrical Y-connected systems are studied wherein the neutral is firstly solidly-grounded, and secondly resistively-grounded. The influence on the subharmonic performance of this, and other system parameters, is determined. The belief that 1/3-order subharmonic oscillations could not occur in ungrounded symmetrical systems is shown to be incorrect.

The Problem of Arcing Faults in Low-Voltage Power Distribution Systems

Many cases of electrical equipment burndown arising from low-level arcing-fault currents have occurred in recent years in low-voltage power distribution systems. Burndown, which is the severe damage or complete destruction of conductors, insulation systems and metallic enclosures, is caused by the concentrated release of energy in the fault arc. Both grounded and ungrounded electrical distribution systems have experienced burndowns, and the reported incidents have involved both industrial and commercial building distribution equipment, without regard to manufacturer, geographical location, or operating environment.

Fourteen Years of Data on the Operation of One Hundred Ungrounded 240-and 480-Volt Industrial Distribution Systems

A discussion is given of the data found over a fourteen-year period of 240-and 480-volt ungrounded industrial distribution system operation at Kodak Park Works, Eastman Kodak Company. An advantage of the ungrounded system over the grounded system is the higher degree of reliability that is attainable. One drawback of the system is the problem of locating a ground when it occurs. Practical and successful tracing of grounds with power on are possible and, when combined with systematic detecting and clearing, the ungrounded system may offer further advantages over the grounded system.

Sensitive Ground Relay Protection for 6900-Volt Motors on a High-Resistance Grounded Chemical Plant Distribution System

In a large chemical plant built in 1946, a 6900-volt ungrounded primary distribution system was installed initially. After approximately ten years of operation, in which the plant electrical load had increased to approximately twice its original value, it was decided to convert to high-resistance grounding on the 6900-volt system. Shortly after the installation of the high-resistance grounding system, a number of large (700 to 2250 hp) induction motors were installed in the plant. The addition of these motors and their associated surge protection capacitors made it necessary to increase the capacity of the 6900-volt high-resistance grounding bank. The increase in this grounding bank capacity, and the corresponding increase in the maximum 6900-volt ground fault current to approximately 30 amperes, resulted in the need to develop a relaying system which was sensitive enough to protect the large 6900-volt induction motors adequately for ground faults. A number of relay schemes employing both conventional electromechanical and static relays were investigated. A relaying scheme which protects these 6900-volt motors for ground faults as low as approximately 1 ampere was developed and installed at this plant to supplement the normal complement of relays which had originally been installed on the motors.

High-Resistance Grounding of 2400-Volt Delta Systems with Ground-Fault Alarm and Traceable Signal to Fault

A method is described which has been used to reduce the difficulties encountered on several old delta-ungrounded systems. Data are included which will help in applying this to any particular power system. The scheme gives an alarm whenever a ground fault occurs, permits everything to keep running even more assuredly than with an ungrounded system, and provides a method for quickly locating the fault. Circuit diagrams and photographs of actual equipment are included, and operating practice is summarized.

Advantages of ungrounded marine electric systems

FOR MANY YEARS there has been a great deal of discussion and interest expressed concerning the possibility of grounding the neutral of marine electric systems. It is the purpose of this paper to consider the numerous theoretical and practical considerations accumulated over the years with regard to industrial and electrical utility plants1?15 from the viewpoint that the ungrounded system is superior. In addition to a review of the literature, some field test work has been performed.

Grounding of Power Station 4,160-Volt Auxiliary Systems

As the size of power station units has increased, it has become economical to raise the voltage on auxiliary systems to 4,160 volts. Almost universally, 2,400-volt systems have been operated ungrounded. With the higher voltage, the question again arises whether the system should be grounded and if so, whether there should be neutral impedance. It is apropos then to enumerate the advantages and disadvantages of each mode of operation and then select the one that appears most justified for power station auxiliary supply. An exact answer cannot be expected; the probabilities can be weighed and the best possible decision made. To simplify the study, the question is divided into two parts: a comparison between grounded and ungrounded systems, and a discussion as to what mode of grounding is best suited to the problem. For the sake of completeness, a discussion of resistor rating and the type and performance of ground relays is included.

Abnormal Overvoltages on Ungrounded Systems Having Wye-Grounded Potential Transformers

Abnormal Overvoltages on Ungrounded Systems Having Wye-Grounded Potential Transformers

System neutral grounding for chemical plant power systems

THE chemical industry, because of its continuous processes, has always demanded reliable performance from its electrical power system. Observation of electrical practices will show that care has been exercised in the selection and application of electrical equipment. The scope of this paper is to review the influence which system neutral grounding has on the performance of electrical apparatus, something of the history of grounded and ungrounded systems and why they have been selected, and a discussion of the methods of system neutral grounding with suggestions on how the over-all performance of the power system and the connected equipment can be improved by the operation of some form of system neutral grounding.

Arcing Grounds on Ungrounded Systems

Arcing Grounds on Ungrounded Systems

Transmission and Distribution Grounding in The Hydro-Electric Power Commission of Ontario

Accepted grounding methods have been modified for use in areas having difficult grounding conditions. Satisfactory transmission line grounding in rocky areas is obtained economically where the improved methods are followed. Long rods are effective in reducing distribution neutral voltages to an acceptable sustained maximum of 15 volts, which introduces a negligible hazard. Measurements taken on an air-switch installation showed the superiority, over that with rods alone, of a grounding arrangement incorporating a mat or grid. On the basis of these tests, it is proposed to use such a mat to control the potentials possible between switch handle and ground. Personnel and equipment at generating stations under construction are protected from fault currents by connecting all equipment on the ungrounded distribution system to a common metallic circuit. Ground detectors are used if this arrangement is not practical. Completed stations are safely grounded both for power-frequency system faults and lightning surges. In most instances, separate grounding arrangements are necessary for each type of installation.

Field Investigations of Lightning

In the investigation described in this paper, measurements have been made and statistical data obtained on the multiple character and wave shape of the currents in direct strokes and the currents discharged by lightning arresters. These data, in conjunction with other data on the field performance of arresters, have revealed definite differences between the nature of direct strokes and the currents they produce in arresters. 1. Arrester discharge currents have fewer components than found in direct strokes. Only about 30 per cent were found to be multiple and not over 8 components were recorded, while from 50 to 70 per cent of direct strokes were multiple with as many as 32 components recorded. 2. Components of arrester discharges are of lower crest magnitude. Only 30 per cent of those measured exceeded 1,000 amperes, while for direct strokes 50 per cent exceeded 5,000 amperes. 3. The initial high current portions of the components of arrester discharges do not vary greatly in wave shape and are similar to those of direct strokes, having for both types of discharges times to half value which, in general, lie between 25 and 100 microseconds and average about 50 microseconds. 4. The long duration low magnitude portions of direct strokes vary over wide limits, both in magnitude and duration. However, for arrester discharges they are seldom present to any appreciable degree. This portion of the discharge may have current magnitudes as high as 1,000 amperes and measurable durations from 50 to 20,000 microseconds in direct strokes, while lightning discharges through arresters seldom last more than 300 microseconds. 5. There is definite evidence that system neutral ground conditions influence the currents discharged by arresters on systems, and that the most severe duty is imposed on arresters on ungrounded systems, while the least severe service conditions appear on four-wire grounded neutral circuits. This is shown by the fact that no long duration surge components have been recorded on four-wire circuits, while about 50 per cent of the records obtained on ungrounded circuits had components of long duration. It is also shown by the performance record of the new Autovalve lightning arrester. With over 40,000 arrester years service this arrester has experienced only 18 lightning failures or a lightning failure rate of 0.045 of one per cent. Of 27,000 arrester years experience on four-wire systems there have been no failures, while of 4,500 arrester years of service on ungrounded circuits there have been 11 lightning failures. 6. There is indication that one of the factors influencing the nature of a lightning stroke is earth resistivity or geological structure. Observations lead to the inference that lightning discharges of long duration are more prevalent in regions of high earth resistivity and ancient geological structure than elsewhere. Thirteen of the 14 long duration arrester current records and 16 of the 18 arrester failures due to lightning occurred on four systems in two regions of high earth resistivity for which there was only 1,078 arrester years experience. 7. These data indicate that it is only with a combination of high earth resistivity and type of system for which the transformers cannot absorb the long duration portion, that appreciable long duration arrester discharges and accompanying severe duty on arresters is obtained. The data on which this is based are not yet conclusive, but the indications are sufficiently definite that this probability should not be overlooked.