Electrical circuit

“ 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. ”

“ Fig. 2,151.—Diagram of two phase four wire system. It is desirable for supplying current for lighting and power. The arrangement here shown should be used only for lines of short or moderate length, because of the low voltage. Motors should be connected to a circuit separate from the lighting circuit to avoid drop on the latter while starting a motor. ”

“ The contacts have a long life and are easily renewed. Regulators of this type are adapted for metallurgical purposes where the regulation is effected in the primary circuit and the secondary circuit is of very low voltage but large current capacity and is used for supplying power to the furnaces. These regulators have been built in capacities up to 800 amperes at 3,300 volts. ”

“ It is designed to register the energy of alternating current circuits regardless of the power factor, and embodies the usual induction motor, eddy current generator and registering mechanism. The electrical arrangement of the meter consists of a current circuit composed of two coils connected in series with each other and in series with the line to be measured, and a pressure circuit consisting of a reactance coil and a pressure coil connected in series with each other and across the line to be measured. ”

“ Such arrangement provides a separate circuit for each unit making them independent so that they may vary in size and each one can be started or stopped without interfering with the others. Parallel circuits are largely used for incandescent lighting, and since low pressure current is commonly used on such circuits they are usually connected to step down transformers, instead of direct to the alternators. ”

“ The difficulty of operating a lamp on the alternating current circuit lies in the fact that while a current will flow freely through it in one direction, when the current reverses the negative electrode or cathode acts as an electric valve and stops the current, thus breaking the circuit and putting out the light. ”

“ Turning the primary in one direction increases the voltage induced in the secondary, thus increasing the feeder voltage like the action of a booster on a direct current circuit while turning the primary in the opposite direction from the neutral position, correspondingly decreases the feeder voltage. ”

“ Fortunately for the future delivery of energy at great distances from its source, the means to avoid the limit just discussed are not difficult. Other experiments have shown that with a given voltage and distance between conductors the loss of energy from wire to wire decreases rapidly as their diameters increase. The electrical resistance of air, like that of any other substance, increases with the length of the circuit through it. The leakage described is a flow of electrical energy through the air from one wire to another of the same circuit. ”

“ Fig. 805.—Crocker Wheeler motor-dynamo set. There are numerous cases where such a combination is useful for furnishing a circuit with a voltage different from that of the main plant or with a voltage that can be varied independently. For storage battery charging and electrolytic work, where constant current is desirable, it forms a simple means of voltage regulation. Where a circuit of special voltage is required, the set not only supplies current at the desired pressure, but insulates the special circuit, which may be subject to more severe requirements than the main system. ”

“ The determination of the power in a direct current circuit is a simple matter since it is only necessary to multiply together the volts and amperes to obtain the output in watts. In the case of alternating current circuits, this holds true only when the current is in phase with the pressure—a condition rarely found in practice. ”

“ Supposing that we consider an aerial consisting of a simple straight wire having small capacity and small inductance, such a circuit admits of being sent into electrical oscillation, not only by waves of its own natural time-period, but by the sudden application of any violent electromotive impulse. If, on the other hand, we bestow upon the circuit in any way considerable inductance, we then obtain what may be called a stiff or irresponsive circuit, which is one in which electrical oscillations can be accumulated only by the prolonged action of impulses tuned to a particular period. ”

“ The drawings and specifications show a closed circuit at the transmitting station connected with the primary of an induction coil, and embracing a source of electrical current and a circuit-closing key or other signalling device. The secondary of the induction coil is connected in a circuit which includes a spark gap or other producer of high frequency oscillations and, in a shunt around the spark gap, the primary coil of an oscillation transformer and a condenser, preferably so arranged that its capacity can readily be varied. ”

“ One and the same current
passes through all parts of a series circuit when such current is
constant.
A current being produced by electro-motive force, and electromotive
force disappearing in its production in an active circuit, there must be
some source of energy which will maintain electromotive force against
the drain made upon it by the current.
The simplest conception of an active electric circuit is a ring or
endless conductor swept through a field of force so as to cut lines of
force. A simple ring dropped over a magnet pole represents the
simplification of this process. ”

“ A protective sheath of copper, interposed between the primary and
secondary circuits of an alternating current transformer. It is
connected to the earth. If the primary coil loses its insulation before
it can leak to the secondary it is grounded. This protects the secondary
circuit from the high electro-motive force of the primary circuit. ”

“ Why when the telegraph was first invented it was necessary to double the wire lines, putting up two wires every time by way of completing the circuit. You know electrical energy will not manifest itself, or as we say, the electric current will not flow, unless there is a circuit established. ”

“ 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. ”

“ If it be imperfect, the current will leave the wire and jump to the frame and thence back to the battery without performing the work required of it. When this occurs it is known as a 'short circuit.' Electricity always travels by the easiest path, and, if it can avoid doing any work, it will do so. ”

“ When an alternating current passes through a circuit, the action termed self-induction sets up an electromotive force in the circuit that opposes the flow of current, as does the resistance of the wire, and this is called the inductance of the circuit. ”

“ On most, if not all, transmission lines the guard wire or wires, if used at all, are placed either above or on a level with the highest power conductors. With one conductor of a three-phase circuit mounted on a pin set in the top of a pole, and the two remaining conductors on a two-pin cross-arm beneath, in the method most frequently adopted for transmission lines of very high voltage, it is obviously impracticable to put guard wires either above or on a level with the power circuits. ”

“ We have seen that when too large a current passes through a wire, the wire becomes heated and may even be melted. Buildings are wired to use certain currents, and if from any cause much more current than the regular amount should suddenly pass through the service wires into the house, [120] the various smaller wires would become overheated, and perhaps melt or start a fire. An accidental short circuit, for example, would so reduce resistance that too much current would suddenly rush through the wires. ”

“ People often ask how quickly electricity travels, as if when we sent a telegraph signal along a wire a little bullet, so to speak, of electricity were shot along the wire like the carriers of the pneumatic tubes in the big drapers' shops. That is quite a misconception, for in reality the circuit of wire is more like a pipe full of electricity, and when we set a current flowing what we do is to set the whole of that [Pg 160] electricity moving at once. ”

“ If an endless wire be taken, we have the means of generating a current in it which shall run round the circuit without adding any electricity to what was previously in the wire. As far as we can judge, the electricity which appears as a current is the same as that which before was quiescent in the wire ”

“ When an open circuit was formed of a piece of copper wire, bent into the form of a rectangle, so that the ends of the wire were separated only by a short air-gap, and when this open circuit was connected by a wire with any point of a circuit through which the spark-discharge of an induction-coil was taking place, it was found that a spark passed in the air-gap of the open circuit. ”

“ The electricity excited by the action on the zinc in one cell is carried on to the next, and that again excites and transfers an additional quantity to the third cell, thus increasing in intensity to the last pair of plates in the series. The electric current, as it is called, passes along the wire, and whether the wire136 be one yard, or whether it be a hundred miles long, the generation of electricity takes place the instant that the circuit is completed, and ends the instant that the circuit is broken. ”

“ It thus seems that while two or more circuits give a greater chance of continued operation after a break in a conductor actually occurs, the use of a single circuit with larger conductors makes any break less probable. ”

“ If I connect by a wire one end or pole of the battery with the other, I, being close at hand, can see a small spark. There is now flowing through that connecting wire what we call an electric current, which passes from one end of the battery through the wire to the other end. When there is very little resistance offered to the passage of the current, there is no [Pg 90] sensible heat developed; but if I sever the wire in the middle and unite the ends by a thin platinum wire, the thin platinum wire introduced into the circuit is first raised to incandescence and then fused. ”

“ It’s just an ordinary electric circuit-breaker, the same as they use on street-cars, and it is buried in oil to keep it from arcing—as all switches are when they’re under voltages as high as ours will be. ”

“ Suppose we treat the machine as a dynamo. Bring the ends of the line wire together, thus, as we say, closing the circuit. By some external force let us cause the armature to rotate and under the influence of the magnetic field it will generate an electric current, part of which will pass through the field and part through the line circuit. We may adjust the relative amount of wire in field and line so that any portion of the current we choose will pass through the field. ”

“ But if we connect these wires to the coils of the induction apparatus and then take hold of the two ends of the secondary coil and break and close the primary circuit we should feel a painful shock at each break and close, although the actual amount of current flowing through the secondary wire is not as great as that which flows through the primary; but the voltage (or electromotive force) is higher, and thus is able to drive what current there is through a conductor of higher resistance, such as the human body. ”

“ Whenever, therefore, we find these two states of heat and magnetism present together in and round a wire, we may take it as an indication that it forms part of a circuit through which an electric current is flowing. An electric current is a physical state or condition which can only exist in or all along a closed path which is called an electric circuit. ”

“ Indeed, a close examination will show that wherever power is expended in developing current in a circuit, cutting lines of force, the energy expended is first employed in stretching the lines, which thus receive the energy required to permit them, in shortening, to cut the conductor and set up currents in the electric circuit in accordance with the potential difference developed in that circuit and its resistance. ”

“ In the arc method high voltage is essential; in the incandescent plan, current is the important consideration. In the arc, the light is produced by virtue of the break in the line of the conductor; in the incandescent, the system is closed at all times.
Supposing we have a wire A, a quarter of an inch in diameter, carrying a current of, say, 500 amperes, and at any point in the circuit the wire is made very small, as shown at B, in Fig. 118, it is obvious that the small wire would not be large enough to carry the current. ”

“ Beginning at the surface of the zinc the direction of the movement of positive electricity may be traced through the liquid to the copper plate, to the wire, to the zinc plate, to the starting point, thus completing the electric circuit. When the circuit is closed it is found that the movement of electricity starts in all parts of the circuit at practically the same instant. ”

“ The intensity may be rendered uniform by placing the secondary at a fixed distance from the primary, and keeping the current in the primary circuit constant. The constancy of the current in primary circuit is secured by the employment of an accumulator or storage cell of definite electromotive force. ”