Low-voltage Air Circuit Breakers Research Articles

Equilibrium Composition of a Plasma in the Low Voltage Air Circuit Breaker Contaminated by the Vapor of AgSnO<sub>2</sub> Alloy Electrical Contacts

When the circuit breaker cuts the electric current, an electric arc is created between its electrodes. The success or failure of breaking the electric current by the circuit breaker depends strongly on the physico-chemical properties of the electric arc created, such as the composition of which depends on the material of the electrical contacts. In this work, we determine the equilibrium composition of the electric arc in the low voltage air circuit breaker with silver tin dioxide alloy contacts, in a temperature range from 500 K to 15,000 K and at atmospheric pressure. We use the Gibbs free energy minimization method and develop a computer code to determine the equilibrium composition of the created plasma. The analysis of the results obtained shows that O2 particles with a dissociation energy of 5.114 eV, NO with a dissociation energy of 6.503 eV, and N2 dissociation 9.756 eV dissociate around 3500 K, 5000 K, and 7500 K, respectively. We note that the electro-neutrality is established between the electrons and the cations: Ag+ and NO+, for temperatures lower than 6500 K. For temperatures higher than 6500 K, the electro-neutrality is established between the electrons and the cations: N+, O+, and Ag+. The numerical density of the electrons increases when the proportion of the vapor of the electrical contacts increases in the mixture, in particular for temperatures lower than 11,000 K.

Numerical Modeling of Arc Root Transfer During Contact Opening in a Low-Voltage Air Circuit Breaker

A 3-D model of an arc in a low-voltage circuit breaker is used to simulate arc root transfer from the moving contact to the arc runner, as the contact is opened.

High speed x-ray radiography diagnostic of current interruption in circuit breakers

High-speed x-ray radiography is used for the imaging of internal components of a low-voltage air circuit breaker during fast current interruption events. A continuous x-ray source was used to irradiate the circuit breaker during interruption, while a fast camera imaging system recorded the output visible light from the x-ray image intensifier up to a maximum rate of 4000 frames per second. Detailed time-resolved images were obtained of the movable contact position and tripping mechanism components of the circuit breaker during the interruption event. Experimental observations were used to validate numerical simulation results obtained using electromagnetics and dynamics/kinematics analysis software. In addition to imaging of the circuit breaker mechanism, molten metal streams and droplets ejected from the electrodes were also observed. Tracking of these metallic particles can provide valuable information about contact phenomena and gas flow fields in circuit breakers.

Life Testing of a Low-Voltage Air Circuit Breaker to Assess Age-Related Degradation

This paper reports that a DS-416 low-voltage air circuit breaker manufactured by Westinghouse is mechanically cycled to identify age-related degradation in the various breaker subcomponents, specifically in the power-operated mechanism. This accelerated aging test is performed on one breaker unit for over 36 000 cycles. Three separate pole shafts, one with a 60-deg weld, one with a 120-deg weld, and one with a 180-deg weld in the third pole lever, are used to characterize cracking in the welds. In addition, during the testing, three different operating mechanisms and several other parts are replaced as they become inoperable. Among the seven welds on the pole shaft, welds 1 and 3 are found to be critical ones whose fracture can result in misalignment of the pole levers. This can lead to problems with the operating mechanism, including the burning of coils, excessive wear in certain parts, and overstressed linkages. Furthermore, the limiting service life of a number of subcomponents of the power-operated mechanism, including the operating mechanism itself, is assessed.

Static overcurrent tripping device for low-voltage breakers

In an effort to overcome some of the outstanding shortcomings of presently used electromechanical tripping devices, a static type using semiconductors has been developed. Advantages include greater accuracy, simplified field testing, greater flexibility, and reduced maintenance Low-voltage air circuit breakers rated at 600 volts and less are used as protective and switching devices on plant distribution systems. They may be installed in metal-clad switchgear, on switchboards, or they may be separately mounted. Designed to interrupt currents of 15 to 100 kiloamperes at 600 volts (and higher at lower voltages), these breakers are necessary for complete system protection where the greatest degree of service continuity is desired.

Protecting A-C motors with low-voltage air-circuit-breaker series trips

LOW-VOLTAGE air circuit breakers are sometimes used alone as motor starters, since they provide in a single device the various elements of a motor-branch circuit as required by the National Electrical Code. The purpose of this paper is to discuss the effectiveness of the direct-acting series trips used on such breakers as a means of protecting squirrel-cage motors in the event of: 1. Locked or stalled rotor, either during starting or running. 2. Overheating due to prolonged moderate overloads. 3. Short circuits in the motor or in connections to it.

Co-ordination of Current-Limiting Fuses and Low-Voltage Air Circuit Breakers [includes discussion

Co-ordination of Current-Limiting Fuses and Low-Voltage Air Circuit Breakers [includes discussion

Introduction of Hydraulic Operation to Low-Voltage Air Circuit Breakers [includes discussion

The designer of low-voltage switchgear is continually confronted with two conflicting demands: first, the requirement for reducing the space occupied by the switchgear; and second, the requirement to increase the interrupting capacity of the circuit breakers which must be installed in the allotted space of the switchgear enclosures. However, higher interrupting capacity is accompanied by the need to be able to close against higher momentary ratings. This requires a more powerful operating mechanism, which usually occupies a greater portion of the allotted space. The a-c solenoid, which is still the conventional power source for low-voltage circuit breakers, requires exceedingly high currents to supply even marginal closing effort in the small available space. It is natural, then, that high-pressure hydraulics, which has proved so successful in aeronautical and automotive practice and more recently1,2,3 has proved equally successful in high-voltage circuit breaker operators, should be extended to the low-voltage circuit breaker field where it can solve the problem of great power in small space and because of its ability to respond without heavy shock to abruptly changing loads during breaker closing stroke. This paper describes the design and development of a simple and unique hydraulic system which has been co-ordinated with a time-tested and proved mechanically trip-free linkage arrangement adapted to fulfill the requirements imposed by the extremely arduous load characteristic of low-voltage high-current-interrupting-capacity air circuit breakers.

New Line of Low-Voltage Air Circuit Breakers [includes discussion

ANEW LINE OF AIR CIRCUIT breakers, having interrupting ratings of 50,000, 75,000, and 100,000 amperes, has been developed to meet the requirements of modern low-voltage electric systems.

New line of low-voltage air circuit breakers

ANEW LINE OF AIR CIRCUIT breakers, having interrupting ratings of 50,000, 75,000, and 100,000 amperes, has been developed to meet the requirements of modern low-voltage electric systems.

New low-voltage air circuit breaker

THE GROWTH of modern low-voltage systems has advanced so far that now the low-voltage air circuit breaker must meet requirements which were unheard of ten years ago.

New Low-Voltage Air Circuit Breaker with 50,000 Ampere Interrupting Capacity at 600 Volts A-C

New Low-Voltage Air Circuit Breaker with 50,000 Ampere Interrupting Capacity at 600 Volts A-C

An Air Delayed Selective Overcurrent Tripping Device for Low-Voltage Air Circuit Breakers

An Air Delayed Selective Overcurrent Tripping Device for Low-Voltage Air Circuit Breakers

An improved low-voltage air circuit breaker

ANEW 225- and 600-ampere frame size air circuit breaker incorporating the recent war improvements is now available. The principal advantages offered in this design over older ones specifically are 1. An improved arc chute of reduced size. 2. Long-lived contacts with momentary ratings equal to interrupting ratings. 3. Flexible and rugged overcurrent devices capable of necessary precision timing for selective tripping systems, but equally suitable for simple overload protection. 4. A 30 per cent reduction in size. 5. Longer life and lower maintenance from improved design.

An Improved Design of Low-Voltage Panel-Mounted Air Circuit Breaker

Close co-operation with the Navy during the war in working out solutions for rapid improvement of pre-war standards of protection and control of low-voltage distribution circuits, gave the group that developed these circuit breakers an enviable background of experience to fit them for the program just discussed. The results of their efforts have been outlined and can be summarized by saying that industry is offered a new circuit breaker in which high inrush and momentary currents are easily handled, with an increased contact life. Accurate and proved timing elements have been provided giving a variety of desired time-current characteristics. A wider application on motor and other repetitive duty high inrush current circuits is assured by longer contact and mechanism life and accurate delayed tripping obtained with the fluid displacement timing elements. Dependable selective operation can be obtained without the additional expense of current transformers and relays. Contacts and coils which will stand the high momentary currents, while tripping is delayed with an accurate mechanical timing device, make possible dependable selective operation, so unquestionably proved on the Navy's major ships.

Selective Tripping of Low-Voltage Air Circuit Breakers

Selective or sequential tripping in low-voltage air circuit breaker application provides for removal from the system of a faulted part only, leaving the rest of the system in operation. Present standard circuit breakers generally are not suitable. Solution of the problem is through direct-acting series tripping means with distinct current-time characteristics in ranges of overcurrent and fault current, with minimum time to complete interruption the objective. This subjects the circuit breaker to the very severe duty of having to carry short-circuit currents for appreciable times, whereas standard circuit breakers have been designed to open instantaneously. Modified standard circuit breakers may be applied to selective tripping, with limitations of application based upon (1) rated interrupting capacity and (2) series trip coil rating. As tests show that modified standard circuit breakers will carry short-circuit current for necessary times, they also may be applied with relay schemes requiring delayed tripping. In systems using cascade or backup arrangements of circuit breakers, little is gained by selective tripping. It is recommended that for a particular installation choice be made between selective tripping and cascade arrangement, according to relative importance of advantages of each.

Improved selective tripping of low-voltage air circuit breakers

Improved selective tripping of low-voltage air circuit breakers

Improved selective tripping of low-voltage air circuit breakers

SINCE the first devices for interrupting short-circuit currents in electric systems were invented, the problem of having them operate to clear faults without removing energy from normal circuits has existed. Many devices, both separate and as parts of the interrupters, have been developed and good results obtained. Systems having potentials below 600 volts alternating current normally use air interrupting devices designed particularly for this service.

Improved Selective Tripping of Low-Voltage Air Circuit Breakers

SINCE the first devices for interrupting short-circuit currents in electric systems were invented, the problem of having them operate to clear faults without removing energy from normal circuits has existed. Many devices, both separate and as parts of the interrupters, have been developed and good results obtained. Systems having potentials below 600 volts alternating current normally use air interrupting devices designed particularly for this service.

A 500,000-Kva 7.5-Kv Air Circuit Breaker for Steel-Mill Service

WITH the advent of the first 15-kv power air circuit breakers for central station service in 1929,1,2 it was soon recognized that an air circuit breaker was much more desirable for highly repetitive steel-mill motor switching than was the conventional equipment universally used at that time. Interrupting tests showed that the air circuit breaker could withstand many operations on considerable power without requiring maintenance, as compared to the high maintenance necessary on oil switching equipment of that period. This was somewhat to be expected in view of the fact that low-voltage air circuit breakers and contactors had demonstrated this ability for years. It was also believed that the air circuit breaker was highly desirable for steel-mill-substation service because of the additional severity of steel-mill operating conditions, as compared to the duty on corresponding equipment in central-station service.