N. Hawkins

“ In construction, the relay consists of a special motor with a short circuited armature and a split field. Under normal conditions, the fields are separated from each other and the motor armature does not revolve. The force tending to pull the two faces of the field together is opposed by a spring, the compression of which determines the number of amperes necessary to cause the relay to begin operation. The motor structure performs the whole work and the motor itself un-meshes and meshes the gears without the aid of any external device. ”

“ It is a principle in electromagnetics that a conductor carrying a current in a magnetic field will tend to move in a direction at right angles to the field. The arc set up on breaking a circuit constitutes a conductor, and in magnetic blow out circuit breakers, as generally manufactured, there is an electromagnet, energized by the current to be broken, which produces a field in the neighborhood of the arc, with the result that the arc moves outward, and so becomes attenuated and is finally extinguished. ”

“ The magnetic circuits formed by the cores of the pressure and current coils are so arranged that they exert a high torque upon the disc of the rotating element in order that minute variations in the friction of the moving parts, which are likely to occur will not cause any appreciable error in the registration of the meter. The iron case surrounding the electrical elements protect that part of the meter from the effects of external stray fields, while the astatic arrangement of the permanent magnets tends to prevent any influence on the damping system. ”

“ The current at start with full voltage applied is usually higher in an induction motor owing to the fact that the total impedance of the stator and rotor are less due to the greater distribution of the windings and the lower resistance of the squirrel cage. The high magnetizing current of a synchronous motor should not be lost sight of as it is a very important consideration in starting the machine. Even though the motor can be brought practically to synchronous speed while still on the compensator, if line voltage be thrown on, there will be a very heavy rush of current. ”

“ Series resistance limits the discharge current to such an extent that an arrester with series resistance fails to protect against destructive rises of voltage when the conditions are severest. Graded shunt resistance responds to all frequencies and opens a discharge path for excessive voltage when the frequencies are high as well as when they are low. Its further effect in withholding the line current from the gaps after the relieving discharge has occurred, is to aid the non-arcing quality of the metal cylinders in quickly suppressing the arc that follows a discharge. ”

“ Fig. 2,438.—Diagram of connections of General Electric pole type regulator. The operation of the regulator is obtained by means of a small single phase motor which is in continuous operation, and which by mechanical means may be connected to the regulator shaft. The control of the mechanism is obtained by means of a voltage relay. The operating motor, which is of the drawn shell type, is provided with a starting clutch and will consequently start up with full load. Under actual operating conditions it will, of course, be comparatively seldom that the motor will be called upon to start up. ”

“ When the current reaches a point where it overcomes the weight of the armature and lifts the same, the magnetic force tending to raise the armature is opposed by the vacuum created in the interior of the cylinder. As the magnetic force continues the vacuum is overcome due to the leakage of air past the plunger and the armature gradually moves up until it reaches the point where it trips the circuit breaker. If at any point of the armature travel, the current drop back to normal, the armature immediately resets itself by means of a ball valve in the top of the brass cylinder. ”

“ The no voltage trip, receives energy from a high resistance or fine wire coil which is arranged to be placed directly across the line, but in contradistinction to the shunt trip type, in which the coil is momentarily energized to trip the breaker, the no voltage coil is constantly energized and a decrease or failure of pressure trips the breaker. It can be used as a remote control device the same as the shunt trip. Its general use, however, is to cause the circuit breaker to open when the voltage of the line fails from any cause. ”

“ This has the effect of reducing the resistance of the rotor winding to some extent and causing the motor to have less slip with a given load. The gain from this source is small, however, in most cases, as the self-inductance of the field winding is so high as to allow very little current to flow even if the field be short circuited so that the total effective resistance of the rotor winding is not materially reduced. In some cases where the torque is nearly sufficient, however, enough gain may be obtained to take care of the conditions. ”

“ When the motor has accelerated and has come partially up to speed the starting lever is quickly thrown to the running position in which position the field windings are connected in delta. The effect of connecting the field winding in star at starting is to reduce the voltage applied to each phase winding, while in the running position each phase of the field winding has full line voltage impressed upon it. ”

“ NOTE.—The author adheres to the term virtual because in mechanics the adjective effective is used to denote the difference of two opposing forces; for instance, at any instant in the operation of a steam engine, effective pressure = forward pressure - back pressure, hence, to be consistent in nomenclature, the term effective cannot be used for the forward or virtual pressure, that is, the pressure impressed on an electric circuit. ”

“ Induction motors and other inductive apparatus take a component of current which lags behind the line pressure, and thereby lowers the power factor of the system, while a non-inductive load, such as incandescent lamps, takes only current in phase with the voltage and operates at unity power factor. ”

“ The facility with which alternating current can be transformed from one voltage to another, thus permitting high pressure transmission of electric energy to long distances through small wires, and low pressure distribution for the operation of lighting systems and motors, gives a far greater variety of systems of transmission and distribution than is possible with direct current. ”

“ The non-arcing metals ordinarily employed are alloys of zinc and copper. Plain multi-gap arresters as here shown operate satisfactorily with the smaller machines and on circuits of limited power, but for large machines of close regulation, and therefore of very large momentary overload capacity, especially when a number of such are operated in parallel, such arresters were found insufficient, the line current following the lightning discharge frequently was so enormous that the circuit did not open at the end of the half wave, that is the arrester held the arc and was destroyed. ”

“ In many power plants direct current, three wire, power service is furnished by "high voltage" two wire dynamos operating in connection with balancer sets consisting of two "low voltage" machines on a common shaft. With this combination of machine, a short circuit or heavy overload on one side of the system will shift the neutral considerably, and the lamps on the opposite side may "burn out". To protect the lamps, a differential relay operating on 15 volts unbalancing, is commonly used ”

“ The function of a circuit closing relay is to close an electrical circuit, usually direct current, through a trip coil on an oil switch or circuit breaker, or it may short circuit a low voltage release coil, and thereby open the oil switch or circuit breaker on occurrence of the condition upon which the relay is designed to operate. Direct current at 125 or 250 volts taken from exciter bus bars or storage battery system is generally used for the tripping circuit. ”

“ As shown in the diagram, the instrument embodies the principle of a short circuited transformer, consisting of a primary or exciting coil A, a secondary or closed coil B, linked in inductive relation to the primary by a laminated iron core C, constructed to give a completely closed magnetic circuit, that is, without air gap. The secondary is so mounted with respect to the primary as to have a movement under the influence of their mutual repulsion when the primary is traversed by an alternating current. ”

“ If current transformers are to be used on the same circuit for other purposes, and have sufficient capacity to supply energy for operating relay coils, then secondary relays would be more economical, otherwise the series relays are much less expensive. By means of a specially treated wooden rod, the relay operates a tripping switch, closing a separate tripping circuit, usually 125 or 250 volts direct current. Relays and switches are for mounting on flat surfaces. Series relays are essentially the same as secondary relays except in the coil winding and insulation. ”

“ The field for relays is more extensive for alternating current than for direct current power circuits, the latter being generally confined to much smaller and simpler systems and areas of distribution, and generally sufficient selective action can be obtained by the use of fuses or circuit breakers arranged with instantaneous trip. ”

“ Choke Coils.—A lightning discharge is of an oscillatory character and possesses the property of self-induction, accordingly it passes with difficulty through coils of wire. Moreover, the frequency of oscillation of a lightning discharge being much greater than that of commercial alternating currents, a coil can [Pg 1709] readily be constructed which will offer a relatively high resistance to the passage of lightning and at the same time allow free passage to all ordinary electric currents. ”

“ Current is flowing through the shunt coil continuously, even when no energy is being taken, and the higher the inductance of this coil, the smaller will be the energy component of the constant flow. The series coil causes a loss of energy proportional to the square of the current flowing. It also causes a drop in voltage, both inductive and resistive, hence, the resistance and inductance of the series coil of the meter should be as low as possible. ”

“ When the machines are running at the same frequency and in phase the pointer is stationary at the marked point. In construction, it is like a small, two phase, bipolar synchronous motor, the field being supplied with alternating instead of direct current. ”

“ For very large motors the switching device is generally separate from, the compensator itself and consists of triple and four pole switches for three phase and two phase motors respectively. One double throw switch or two interlocked single throw switches are required for the motor and a single throw switch for energizing the compensator, the running side of the motor circuit being provided with fuses or automatic circuit breakers, or the switches provided with low voltage and overload release attachments. ”

“ In plants in which two or more banks of transformers are operated in parallel between high and low voltage busses, it is desirable to have for each transformer bank, an automatic circuit breaker equipment which will act selectively and disconnect only the bank in which trouble may occur. With a circuit breaker on each side of transformer bank, selective action may be secured in two ways as follows:
1. By means of an instantaneous differential relay connected in the secondaries of current transformers installed on both the high and low voltage sides of each transformer bank. ”

“ Alternating Current Systems.—The saving in the cost of transmission obtained by using alternating instead of direct current is not due to any difference in the characteristics of the currents themselves, but to the fact that in the case of alternating current very high pressures may be employed, thus permitting a given amount of energy to be transmitted with a relatively small current. ”

“ The choice of a tap giving so low a voltage as to require over one minute for starting should be avoided so as to prevent the overheating to which starting compensators, in common with other motor starting devices, are liable if left in circuit unnecessarily long, or if the motor be started several times in rapid succession. ”

“ The plunger compresses the spring and further motion is prevented by a stop, making the relay practically independent of the amount of the overload, only the stored energy of the spring, if the overload continue, applies power, dependent on its own mechanical strength, to the diaphragm. The time limit therefore becomes practically a constant for any given setting under ordinary conditions of overload or short circuit. ”

“ If the field be decreased a lagging current flows which in turn magnetizes the field bringing the density back to its original value. Therefore, with a constant line voltage, the iron losses in a synchronous motor are approximately constant irrespective of the field excitations with the exception that the internal voltage will vary slightly due to the armature I R drop, the density being a trifle lower at full load than at no load. ”

“ The resistance thus interposed between the ground and the conductor is such that any voltage very much in excess of the maximum normal will cause a discharge to ground, whereas at other times the conductor is ungrounded because of the air gap. ”

“ In construction, the control magnet is connected in series with the alternating current control magnet on the regulator and the contacts are connected in series with the rheostat shunt circuit. Then, should the voltage rise beyond a certain value, predetermined by the setting of the thumb screw supporting the plunger of the control magnet, the contacts of the relay are tripped open which, by inserting all the resistance in the exciter field, reduces the exciter voltage which in turn reduces the alternating current voltage. ”

“ In an arrester for a grounded neutral circuit, each stack of cones normally receives the neutral pressure when the arrester discharges, but if a phase become accidentally grounded, the line voltage is thrown across each of the other stacks of cones until the circuit breaker opens the circuit. ”

“ The magnet is mounted on the current carrying stud of the circuit breaker between the back of the panel and the first contact or supporting nut, and is placed in a vertical position. The contacts are insulated from the magnet permitting the use of an auxiliary circuit for the tripping device, independent of the circuit controlled by the circuit breaker. The magnet is excited by the current flowing through the stud, and the armature is connected across the line in series with suitable resistance. Rotation of the armature in the normal direction is prevented by a stop. ”