Starting of Induction Motor and Speed Control

Some induction motors can draw over 1,000% of full-load current during starting (though a few hundred percent is more common). Small motors of a few kilowatts or smaller can be started by direct connection to the power line. Starting larger motors can cause line voltage sag, affecting other loads. Motor-start rated circuit breakers (analogous to "slow blow" fuses) should replace standard circuit breakers for starting motors of a few kilowatts. This breaker accepts high over-current for the duration of starting.

Picture 1: Autotransformer induction motor starter


Motors over 50 kW use motor starters to reduce line current from several hundred to a few hundred percent of full-load current. An intermittent duty autotransformer may reduce the stator voltage for a fraction of a minute during the start interval, followed by application of full line voltage as shown on Picture 1 above. Closure of the S contacts applies reduced voltage during the start interval. The S contacts open and the R contacts close after starting. This reduces starting current to, say, 200% of full-load current. Since the autotransformer is only used for the short start interval, it may be sized considerably smaller than a continuous duty unit.

Running 3-phase motors on 1-phase

3-phase motors will run on single phase as readily as single-phase motors. The only problem for either motor is starting. Sometimes 3-phase motors are purchased for use on single-phase if 3-phase power is anticipated. The power rating needs to be 50% larger than for a comparable single phase motor to make up for one unused winding. Single phase is applied to a pair of windings simultaneous with a start capacitor in series with the third winding. The start switch is opened upon motor start, as shown on Picture 2 below. Sometimes a smaller capacitor than the start capacitor is retained while running.

Picture 2: Starting a 3-phase motor on single phase


The circuit for running a 3-phase motor on single phase is known as “add a phase” or various other brand names. “Add a phase” supplies a phase approximately midway 90 degrees between the 180 degrees single-phase power source terminals.

Speed control with multiple fields

Induction motors may contain multiple field windings. For example, a 4-pole and an 8-pole winding corresponding to 1,800 and 900 rpm synchronous speeds. Energizing one field or the other is less complex than rewiring the stator coils, as shown on Picture 3 below.

Picture 3: Multiple fields allow speed change


If the field is segmented with leads brought out, it may be rewired (or switched) from 4-pole to 2- pole as shown above for a 2-phase motor. The 22.5o segments are switchable to 45o segments. Only the wiring for one phase is shown above for clarity. Thus, our induction motor may run at multiple speeds. When switching the above 60 Hz motor from 4 poles to 2 poles, the synchronous speed increases from 1,800 rpm to 3,600 rpm. If the motor is driven by 50 Hz, the corresponding 4-pole and 2-pole synchronous speeds would be:

Ns = 120 f/P = 120 x 50/4 = 1,500 rpm (4-pole)

Ns = 3,000 rpm (2-pole)

Speed control with variable voltage

The speed of small squirrel cage induction motors for applications such as driving fans may be changed by reducing the line voltage. This reduces the torque available to the load which reduces the speed. The torque of motor expressed in % is shown on Picture 4.

Picture 4: Variable voltage controls induction motor speed

Electronic speed control

Modern solid-state electronics increase the options for speed control. By changing the 50 or 60 Hz line frequency to higher or lower values, the synchronous speed of the motor may be changed. However, decreasing the frequency of the current fed to the motor also decreases reactance XL which increases the stator current. This may cause the stator magnetic circuit to saturate with disastrous results. In practice, the voltage to the motor needs to be decreased when frequency is decreased.

Picture 5: Electronic variable speed drive

Conversely, the drive frequency may be increased to increase the synchronous speed of the motor. However, the voltage needs to be increased to overcome increasing reactance to keep current up to a normal value and maintain torque. The inverter (Picture 5 above) approximates sine-waves to the motor with pulse width modulation outputs. This is a chopped waveform which is either 'on' or 'off', 'high' or 'low' with the percentage of 'on' time corresponds to the instantaneous sine wave voltage. Once electronics is applied to induction motor control, many control methods are available varying from the simple to complex:

Summary for Speed control:

● Scalar Control: Low-cost method described above to control only voltage and frequency without feedback.
● Vector Control (also known as vector phase control): The flux and torque producing components of stator current are measured or estimated on a real-time basis to enhance the motor torque-speed curve. This is computation-intensive.
● Direct Torque Control: An elaborate adaptive motor model allows more direct control of flux and torque without feedback. This method quickly responds to load changes.

Short Summary for Tesla Poly-Phase Induction Motors:

● A poly-phase induction motor consists of a polyphase winding embedded in a laminated stator and a conductive squirrel cage embedded in a laminated rotor.
● 3-phase currents flowing within the stator create a rotating magnetic field which induces a current, and consequent magnetic field in the rotor. Rotor torque is developed as the rotor slips a little behind the rotating stator field.
● Unlike single-phase motors, poly-phase induction motors are self-starting.
● Motor starters minimize loading of the power line while providing a larger starting torque than required during running. Starters are only required for large motors.
● Multiple field windings can be rewired for multiple discrete motor speeds by changing the number of poles.

Induction Motor Alternator

An induction motor may function as an alternator if it is driven by a torque at greater than 100% of the synchronous speed, as shown on Picture 1 below. This corresponds to a few % of “negative” slip (say, -1% slip). This means that as we are rotating the motor faster than the synchronous speed, the rotor is advancing 1% faster than the stator rotating magnetic field. It normally lags by 1% in a motor. Since the rotor is cutting the stator magnetic field in the opposite direction (leading), the rotor induces a voltage into the stator feeding electrical energy back into the power line.

Picture 1: Negative torque makes induction motor into generator


Such an induction generator must be excited by a “live” source of 50 or 60 Hz power. No power can be generated in the event of a power company power failure. This type of alternator appears to be unsuited as a standby power source. As an auxiliary power wind turbine generator, it has the advantage of not requiring an automatic power failure disconnect switch to protect repair crews. It is fail-safe. Small remote (from the power grid) installations may be make self-exciting by placing capacitors in parallel with the stator phases. If the load is removed residual magnetism may generate a small amount of current flow. This current is allowed to flow by the capacitors without dissipating power. As the generator is brought up to full speed, the current flow increases to supply a magnetizing current to the stator. The load may be applied at this point. Voltage regulation is poor. An induction motor may be converted to a self-excited generator by the addition of capacitors.

Start-up procedure is to bring the wind turbine up to speed in motor mode by application of normal power line voltage to the stator. Any wind-induced turbine speed in excess of synchronous speed will develop negative torque, feeding power back into the power line and reversing the normal direction of the electric kilowatt-hour meter.

Whereas an induction motor presents a lagging power factor to the power line, an induction alternator presents a leading power factor. Induction generators are not widely used in conventional power plants. The speed of the steam turbine drive is steady and controllable as required by synchronous alternators. Synchronous alternators are also more efficient. The speed of a wind turbine is difficult to control and subject to wind speed variation by gusts. An induction alternator is better able to cope with these variations due to the inherent slip. This stresses the gear train and mechanical components less than a synchronous generator. However, this allowable speed variation only amounts to about 1%. Thus, a direct line connected induction generator is considered to be fixed-speed in a wind turbine. See Doubly-fed induction generator for a true variable speed alternator. Multiple generators or multiple windings on a common shaft may be switched to provide a high and low speed to accommodate variable wind conditions.

Power Factor and Efficiency of Induction Motors

Power factor

Induction motors present a lagging (inductive) power factor to the power line. The power factor in large fully loaded high speed motors can be as favorable as 90% for large high speed motors. At ¾ fullload, the largest high speed motor power factor can be 92%. The power factor for small low-speed motors can be as low as 50%. At starting, the power factor can be in the range of 10% to 25%, rising as the rotor achieves speed.

Power factor (PF) varies considerably with the motor mechanical load (Picture 1). An unloaded motor is analogous to a transformer with no resistive load on the secondary. Little resistance is reflected from the secondary (rotor) to the primary (stator). Thus the power line sees a reactive load as low as 10% PF. As the rotor is loaded an increasing resistive component is reflected from rotor to stator, increasing the power factor.

Picture 1: Induction motor power factor and efficiency

Efficiency

Large 3-phase motors are more efficient than smaller 3-phase motors and most all single phase motors. Large induction motor efficiency can be as high as 95% at full load, though 90% is more common. Efficiency for a lightly load or no-loaded induction motor is poor because most of the current is involved with maintaining magnetizing flux. As the torque load is increased, more current is consumed in generating torque while current associated with magnetizing remains fixed. Efficiency at 75% FLT can be slightly higher than that at 100% FLT. Efficiency is decreased a few percent at 50% FLT and decreased a few more percent at 25% FLT. Efficiency only becomes poor below 25% FLT. The variation of efficiency with loading is shown on Picture 1 above.

Induction motors are typically oversized to guarantee that their mechanical load can be started and driven under all operating conditions. If a poly-phase motor is loaded at less than 75% of rated torque where efficiency peaks, efficiency suffers only slightly down to 25% FLT.

Nola power factor corrector

Frank Nola of NASA proposed a power factor corrector (PFC) as an energy saving device for single phase induction motors in the late 1970's. It is based on the premise that a less than fully-loaded induction motor is less efficient and has a lower power factor than a fully loaded motor. Thus, there is energy to be saved in partially loaded motors (1-φ motors in particular).

The energy consumed in maintaining the stator magnetic field is relatively fixed with respect to load changes. While there is nothing to be saved in a full- loaded motor, the voltage to a partially-loaded motor may be reduced to decrease the energy required to maintain the magnetic field. This will increase power factor and efficiency. This was a good concept for the notoriously inefficient single-phase motors for which it was intended.

This concept is not very applicable to large 3-phase motors. Because of their high efficiency (90+%), there is not much energy to be saved. Moreover, a 95% efficient motor is still 94% efficient at 50% full-load torque (FLT) and 90% efficient at 25% FLT. The potential energy savings in going from 100% FLT to 25% FLT is the difference in efficiency 95% - 90% = 5%. This is not 5% of the full load wattage but 5% of the wattage at the reduced load. The Nola power factor corrector might be applicable to a 3-phase motor which idles most of the time (below 25% FLT) - like a punch press. The payback period for the expensive electronic controller has been estimated to be unattractive for most applications, although it might be economical as part of an electronic motor starter or speed control.

NEMA Induction Motor Design Classes

Various standard classes (or designs) for motors, corresponding to the torque curves, shown on Picture 1 below, have been developed to better drive various type loads. The National Electrical Manufacturers Association (NEMA) has specified motor classes A, B, C, and D to meet these drive requirements. Similar International Electrotechnical Commission (IEC) classes N and H correspond to NEMA B and C designs respectively.

Picture 1: Characteristics for NEMA designs - Torque curves


All motors except class D operate at %5 slip or less at full load. The standard classes are:

● Class A starting torque is the same as Class B. Drop out torque and starting current (LRT) are higher. This motor handles transient overloads as encountered in injection molding machines.
● Class B (IEC Class N) motors are the default motor to use in most applications. With a starting torque of LRT = 150% to 170% of FLT, it can start most loads without excessive starting current (LRT). Efficiency and power factor are high. It typically drives pumps, fans, and machine tools.
● Class C (IEC Class H) has higher starting torque than class A and B at LRT = 200% of FLT. This motor is applied to hard-starting loads which need to be driven at constant speed like conveyors, crushers, and reciprocating pumps and compressors.
● Class D motors have the highest starting torque (LRT) coupled with low starting current due to high slip (5% to 13% at FLT). The high slip results in lower speed. Speed regulation is poor. However, the motor excels at driving highly variable speed loads like those requiring an energy storage flywheel. Applications include punch presses, shears, and elevators.
● Class E motors are a higher efficiency version of Class B.
● Class F motors have much lower LRC, LRT, and break down torque than Class B. They drive constant easily-started loads.

Speed and Torque of Induction Motors

Motor Speed

The rotation rate of a stator rotating magnetic field is related to the number of pole pairs per stator phase. The “full speed” (Picture 1 below) has a total of 6 poles or 3 pole-pairs and 3 phases. However, there is but one pole pair per phase - the number we need. The magnetic field will rotate once per sine wave cycle.

In the case of 60 Hz power, the field rotates at 60 times per second or 3,600 revolutions per minute (rpm). For 50 Hz power, it rotates at 50 rotations per second or 3,000 rpm. The 3,600 and 3,000 rpm are the synchronous speed of the motor. Though the rotor of an induction motor never achieves this speed, it certainly is an upper limit. If we double the number of motor poles, the synchronous speed is cut in half because the magnetic field rotates 180 degrees in space for 360 degrees of electrical sine wave.

Picture 1: Doubling the stator poles halves the synchronous speed: Full speed & Half speed stator windings


The synchronous speed is given by:

Ns = 120·f/P

where Ns is a synchronous speed in rpm, f is a frequency of applied power in Hz, and P is a total number of poles per phase (a multiple of 2).


Example:

The “half speed” Picture 1 above has 4 poles per phase (3-phase). The synchronous speed for 50 Hz power is:

S = 120·x 50/4 = 1500 rpm

The short explanation of the induction motor is that the rotating magnetic field produced by the stator drags the rotor around with it. The longer more correct explanation is that the stator's magnetic field induces an alternating current into the rotor squirrel cage conductors which constitutes a transformer secondary. This induced rotor current in turn creates a magnetic field.

The rotating stator magnetic field interacts with this rotor field. The rotor field attempts to align with the rotating stator field. The result is rotation of the squirrel cage rotor. If there were no mechanical motor torque load, no bearing, windage, or other losses, the rotor would rotate at the synchronous speed. However, the slip between the rotor and the synchronous speed stator field develops torque. It is the magnetic flux cutting the rotor conductors as it slips which develops torque. Thus, a loaded motor will slip in proportion to the mechanical load. If the rotor were to run at synchronous speed, there would be no stator flux cutting the rotor, no current induced in the rotor, no torque.

Motor Torque

When power is first applied to the motor, the rotor is at rest while the stator magnetic field rotates at the synchronous speed Ns. The stator field is cutting the rotor at the synchronous speed Ns. The current induced in the rotor shorted turns is maximum as is the frequency of the current (the line frequency). As the rotor speeds up, the rate at which stator flux cuts the rotor is the difference between synchronous speed Ns and actual rotor speed N (or Ns - N). The ratio of actual flux cutting the rotor to synchronous speed is defined as slip:

s = (Ns - N) / Ns

where Ns is synchronous speed and N is rotor speed.

The frequency of the current induced into the rotor conductors is only as high as the line frequency at motor start, decreasing as the rotor approaches synchronous speed. Rotor frequency is given by:

fr = s·f

where s is slip and f is stator power line frequency.

Slip at 100% torque is typically 5% or less in induction motors. Thus for f = 50 Hz line frequency, the frequency of the induced current in the rotor fr = 0.05·x 50 = 2.5 Hz. Why is it so low? The stator magnetic field rotates at 50 Hz. The rotor speed is 5% less. The rotating magnetic field is only cutting the rotor at 2.5 Hz. The 2.5 Hz is the difference between the synchronous speed and the actual rotor speed. If the rotor spins a little faster, at the synchronous speed, no flux will cut the rotor at all (fr = 0 ).

Picture 2: Torque and Current vs Slip[%]. Ns = [%] of Synchronous Speed


The above graph on Picture 2 shows that starting torque known as Locked Rotor Torque (LRT) is higher than 100% of the Full Load Torque (FLT) -- the safe continuous torque rating. The Locked Rotor Torque is about 175% of FLT for the example motor graphed above. Starting current known as Locked Rotor Current (LRC) is 500% of Full Load Current (FLC) -- the safe running current. The current is high because this is analogous to a shorted secondary on a transformer.

As the rotor starts to rotate, the torque may decrease a bit for certain classes of motors to a value known as the Pull-Up Torque. This is the lowest value of torque ever encountered by the starting motor. As the rotor gains 80% of synchronous speed, torque increases from 175% up to 300% of the Full Load Torque. This breakdown torque is due to the larger than normal 20% slip. The current has decreased only slightly at this point. But it will decrease rapidly beyond this point. As the rotor accelerates to within a few percent of synchronous speed, both torque and current will decrease substantially. Slip will be only a few percent during normal operation. For a running motor, any portion of the torque curve below 100% rated torque is normal. The motor load determines the operating point on the torque curve.

While the motor torque and current may exceed 100% for a few seconds during starting, continuous operation above 100% can damage the motor. Any motor torque load above the breakdown torque will stall the motor. The torque, slip, and current will approach zero for a “no mechanical torque” load condition. This condition is analogous to an open secondary transformer.

There are several basic induction motor designs showing considerable variation from the torque curve above. The different designs are optimized for starting and running different types of loads. The Locked Rotor Torque (LRT) for various motor designs and sizes ranges from 60% to 350% of Full Load Torque (FLT). Starting current or locked rotor current (LRC) can range from 500% to 1400% of full load current (FLC). This current draw can present a starting problem for large induction motors.

Theory of Operation of Poly-Phase Induction Motors

The construction of the Tesla induction motor was described in Tesla Poly-Phase Induction Motors article. In this article will be represented the theory of operation of the poly-phase induction motor. A short explanation of operation is that the stator creates a rotating magnetic field which drags the rotor around. The theory of operation of induction motors is based on a rotating magnetic field. One means of creating a rotating magnetic field is to rotate a permanent magnet as shown on Picture 1 below. If the moving magnetic lines of flux cut a conductive disk, it will follow the motion of the magnet. The lines of flux cutting the conductor will induce a voltage - and consequent current flow 00 in the conductive disk.

Picture 1: Rotating magnetic field produces torque in conductive disk


This current flow creates an electromagnet whose polarity opposes the motion of the permanent magnet - Lenz's Law. The polarity of the electromagnet is such that it pulls against the permanent magnet. The disk follows with a little less speed than the permanent magnet.

The torque developed by the disk is proportional to the number of flux lines cutting the disk and the rate at which it cuts the disk. If the disk were to spin at the same rate as the permanent magnet, there would be no flux cutting the disk, no induced current flow, no electromagnet field, no torque. Thus, the disk speed will always fall behind that of the rotating permanent magnet so that lines of flux cut the disk induce a current and create an electromagnetic field in the disk, which follows the permanent magnet. If a load is applied to the disk, slowing it, more torque will be developed as more lines of flux cut the disk. Torque is proportional to slip, the degree to which the disk falls behind the rotating magnet. More slip corresponds to more flux cutting the conductive disk, developing more torque.

An analog automotive eddy current speedometer is based on the principle illustrated above. With the disk restrained by a spring, disk and needle deflection is proportional to magnet rotation rate. A rotating magnetic field is created by 2 coils placed at right angles to each other, driven by currents which are 90 degrees out-of-phase. This should not be surprising if you are familiar with oscilloscope Lissajous patterns.

Picture 2: Out-of-phase (90 degrees) sine waves produce circular Lissajous pattern


On Picture 2 above, a circular Lissajous is produced by driving the horizontal and vertical oscilloscope inputs with 90 degrees out-of-phase sine waves. Starting at (a) with maximum “X” and minimum “Y” deflection, the trace moves up and left toward (b). Between (a) and (b), the two wave forms are equal to 0.707 V peak at 45 degrees. This point (0.707, 0.707) falls on the radius of the circle between (a) and (b) The trace moves to (b) with minimum “X” and maximum “Y” deflection. With maximum negative “X” and minimum “Y” deflection, the trace moves to (c). Then with minimum “X” and maximum negative “Y”, it moves to (d), and on back to (a), completing one cycle.

Picture 3: X-axis sine and Y-axis cosine trace circle


Picture 3 above shows the two 90 degrees phase-shifted sine waves applied to oscilloscope deflection plates which are at right angles in space. If this were not the case, a one-dimensional line would display. The combination of 90 degrees phased sine waves and right angle deflection results in a 2-dimensional pattern - a circle. This circle is traced out by a counter-clockwise rotating electron beam.

For reference, Picture 4 below shows why in-phase sine waves will not produce a circular pattern. Equal “X” and “Y” deflection moves the illuminated spot from the origin at (a) up to right (1,1) at (b) … back down left to origin at (c) … down left to (-1.-1) at (d) … and back up right to origin. The line is produced by equal deflections along both axes; y=x is a straight line.

Picture 4: No circular motion from in-phase wave forms (oscilloscope patern)


If a pair of 90 degrees out-of-phase sine waves produces a circular Lissajous, a similar pair of currents should be able to produce a circular rotating magnetic field. Such is the case for a 2-phase motor. By analogy, 3 windings placed 120 degrees apart in space and fed with corresponding 120 degrees phased currents will also produce a rotating magnetic field.

Picture 5: Rotating magnetic field from 90 degrees phased sine waves


As the 90 degrees phased sine waves, shown on Picture 5 above, progress from points (a) through (d), the magnetic field rotates counterclockwise (figures a-d) as follows:

● (a) φ-1 maximum, φ-2 zero;
● (a') φ-1 70%, φ-2 70%;
● (b) φ-1 zero, φ-2 maximum;
● (c) φ-1 maximum negative, φ-2 zero;
● (d) φ-1 zero, φ-2 maximum negative;

Tesla Poly-Phase Induction Motors

Most AC motors are induction motors. Induction motors are favored due to their ruggedness and simplicity. In fact, 90% of industrial motors are induction motors. Nikola Tesla conceived the basic principals of the poly-phase induction motor in 1883 and had a 400 W model by 1888.

Most large (> 1 kW) industrial motors are poly-phase induction motors. By "polyphase", we mean that the stator contains multiple distinct windings per motor pole, driven by corresponding time shifted sine waves. In practice, this is 2 or 3 phases. Large industrial motors are 3-phase. While we include numerous illustrations of 2-phase motors for simplicity, we must emphasize that nearly all poly-phase motors are 3-phase. By "induction motor", we mean that the stator windings induce a current flow in the rotor conductors like a transformer (and unlike a brushed DC commutator motor).

Construction

An induction motor is composed of a rotor (known as an armature) and a stator containing windings connected to a poly-phase energy source as shown on Picture 1 below. The simple 2-phase induction motor below is similar to the 1/2 horsepower motor which Nikola Tesla introduced in 1888.

Picture 1: Tesla poly-phase induction motor


The stator on Picture 1 above is wound with pairs of coils corresponding to the phases of electrical energy available. The 2-phase induction motor stator above has 2-pairs of coils -- one pair for each of the two phases of AC. The individual coils of a pair are connected in series and correspond to the opposite poles of an electromagnet. That is, one coil corresponds to an N-pole and the other to a S-pole until the phase of AC changes polarity. The other pair of coils is oriented 90 degrees in space to the first pair. This pair of coils is connected to AC shifted in time by 90 degrees in the case of a 2-phase motor. In Tesla's time, the source of the 2 phases of AC was a 2-phase alternator.

The stator on Picture 1 above has salient, obvious protruding poles as used on Tesla's early induction motor. This design is used to this day for sub-fractional horsepower motors (i.e., lower than 50 watts). However, for larger motors less torque pulsation and higher efficiency results if the coils are embedded into slots cut into the stator laminations. (Picture 2 below)

Picture 2: Stator frame showing slots for windings


The stator laminations are thin insulated rings with slots punched from sheets of electrical-grade steel. A stack of these is secured by end screws, which may also hold the end housings.

Picture 3: Stator with (a): 2-φ and (b): 3-φ windings


On Picture 3 above, the windings for both a 2-phase motor and a 3-phase motor have been installed in the stator slots. The coils are wound on an external fixture and then worked into the slots. Insulation wedged between the coil periphery and the slot protects against abrasion. Actual stator windings are more complex than the single windings per pole on Picture 3 above.

Comparing the 2-φ motor to Tesla's 2-φ motor with salient poles, the number of coils is the same. In actual large motors, a pole winding, is divided into identical coils inserted into many smaller slots than above. This group is called a phase belt. See Picture 4 below.

Picture 4: 3-φ distributed windings (left) and Single phase belt (right)


The distributed coils of the phase belt cancel some of the odd harmonics, producing a more sinusoidal magnetic field distribution across the pole. The slots at the edge of the pole may have fewer turns than the other slots. Edge slots may contain windings from two phases. That is, the phase belts overlap.

The key to the popularity of the AC induction motor is simplicity as evidenced by the simple rotor (see Picture 5 below). The rotor consists of a shaft, a steel laminated rotor, and an embedded copper or aluminum squirrel cage shown at (b) removed from the rotor. As compared to a DC motor armature, there is no commutator. This eliminates the brushes, arcing, sparking, graphite dust, brush adjustment and replacement, and re-machining of the commutator.

Picture 5: Laminated rotor (a): embedded squirrel cage ; (b): Conductive cage removed from rotor


The squirrel cage conductors may be skewed, twisted, with respect to the shaft. The misalignment with the stator slots reduces torque pulsations. Both rotor and stator cores are composed of a stack of insulated laminations. The laminations are coated with insulating oxide or varnish to minimize eddy current losses.The alloy used in the laminations is selected for low hysteresis losses.

List of Nikola Tesla Patents

The list of U.S. Patents of Nikola Tesla (freely available at the U.S. Patent and Trademark Office)

U.S. Patent 0,334,823 - Commutator for Dynamo Electric Machines - 1886 January 26 - Elements to prevent sparking on dynamo-electric machines; Drum-style with brushes;
U.S. Patent 0,335,786 - Electric Arc lamp - 1886 February 9 - Arc lamp with carbon electrodes controlled by electromagnets or solenoids and a clutch mechanism; Corrects earlier design flaws common to the industry;
U.S. Patent 0,335,787 - Electric arc lamp - 1886 February 9 - Arc lamp's automatic fail switch when arc possesses abnormal behavior; Automatic reactivation.
U.S. Patent 0,336,961 - Regulator for dynamo electric machines - 1886 March 2 - Two main brushes connected to helices coil ends; Intermediate point branch shunt connection for third brush;
U.S. Patent 0,336,962 - Regulator for Dynamo Electric Machines - 1886 March 2 - Auxiliary brush[es] shunting a portion or whole of the field helices coil; Regulates energy flow; Adjustable level of current;
U.S. Patent 0,350,954 - Regulator for Dynamo Electric Machines - 1886 October 19 - Automatic regulation of energy levels; Mechanical device to shift brushes.
U.S. Patent 0,359,748 - Dynamo electric machine - 1887 March 22 - Improve construction; Facilitate easier construction; Reduce the cost; Magnetic frame; Armature; Alternating current synchronous motor;
U.S. Patent 0,381,968 - Electro magnetic motor - 1888 May 1 - Mode and plan of operating electric motors by progressive shifting; Field Magnet; Armature; Electrical conversion; Economical; Transmission of energy; Simple construction; Easier construction; Rotating magnetic field principles;
U.S. Patent 0,381,969 - Electro Magnetic Motor - 1888 May 1 - Novel form and operating mode; Coils forming independent energizing circuits; Connected to an alternating current generator; Synchronous motor;
U.S. Patent 0,381,970 - System of Electrical Distribution - 1888 May 1 - Current from a single source of supply in the main or transmitting circuit induce by induction apparatus; Independent circuit(s); Electric distributor;
U.S. Patent 0,382,279 - Electro Magnetic Motor - 1888 May 1 - Rotation is produced and maintained by direct attraction; Utilizes shifting poles; Induction magnetic motor;
U.S. Patent 0,382,280 - Electrical Transmission of Power - 1888 May 1 - New method or mode of transmission; Dynamo motor conversion with two independent circuits for long distance transmission; Alternating current transmission; Includes a disclaimer; Economic; Efficient.
U.S. Patent 0,382,281 - Electrical Transmission of Power - 1888 May 1 - Improvements in electromagnetic motors and their mode or methods of their operations; Motor is wound with coils forming independent circuits on the armature; Armature is mounted to rotate between two different poles; Armature will eventually synchronize with that of the generator;
U.S. Patent 0,382,282 - Method of Converting and Distributing Electric Currents - 1888 May 1 - Related to electric distribution systems; Current is from a single main source or suitable transmitting circuit; Induction into an independent circuit; Divide the current from a single source; Transformations;
U.S. Patent 0,382,845 - Commutator for dynamo electric machines - 1888 May 15 - Relates to dynamo-electric machines or motors; Improvements on devices to collect or communicate currents; Avoids destruction and wear of machine; Avoid adjustments due to destruction and wear;
U.S. Patent 0,390,413 - System of electrical distribution - 1888 October 2 - Related to previous electric distribution systems developed by Tesla; Examples of systems in operation with motors or converters, or both, in parallel; Examples of systems in parallel; Examples of systems in series;
U.S. Patent 0,390,414 - Dynamo Electric Machine - 1888 October 2 - Related to the patents of Tesla and Charles F. Peck, numbers: US381968 and US382280; Ordinary forms of continuous and alternate current systems may be adapted to Tesla's system, with slight changes to the systems; Effects their forms;
U.S. Patent 0,390,415 - Dynamo Electric Machine or Motor - 1888 October 2 - Improvement in the construction of dynamo or magneto electric machines; Novel form of frame and field magnets that renders the machine more sturdy and compact as a structure; Requires fewer parts; Less difficulty in construction; Lower expense;
U.S. Patent 0,390,721 - Dynamo Electric Machine - 1888 October 9 - Relates chiefly to the alternate current machine invented by Mr. Tesla; Related to patents numbered US381968 and US382280; Seeks to avoid mechanical drawback of running high frequency machines; Efficient at low speeds;
U.S. Patent 0,390,820 - Regulator for Alternate Current Motors - 1888 October 9 - Improvement in the electrical transmission systems; Means of regulating and power of the motor or motors;
U.S. Patent 0,396,121 - Thermo Magnetic Motor - 1888 January 15 - Widely known that heat applied to a magnetic body will lessen its magnetizing ability; High enough temperatures will destroy the magnetic field; Mechanical power by a reciprocating action obtained from the joint action of heat, magnetism, and a spring or weight (or other force);
U.S. Patent 0,401,520 - Method of Operating Electro Magnetic Motors - 1889 April 16 - Improvements to previous instances of synchronous motors; Previous instances of synchronous motors have not been started by the alternating current generators; New discovery of simple method or plan of operating such motors;
U.S. Patent 0,405,858 - Electro Magnetic Motor - 1889 June 25 - Torque, instead of being the result in the difference in the magnetic periods or phases of the poles or to the attractive parts to whatever due, is produce to the angular displacement of the parts which, though movable with the respect to one another, are magnetized simultaneously, or approximately so, by the same currents;
U.S. Patent 0,405,859 - Method of Electrical Power Transmission - 1889 June 25 - New and useful method of bringing up the motor to a desirable speed; Forms of alternating current machines, connected to alternating current generators, can be run as synchronous motor;
U.S. Patent 0,406,968 - Dynamo Electric Machine - 1889 July 16 - Relates to class of machines referred to as "Unipolar" machine (i.e., a disk or cylindrical conductor is mounted in between magnetic poles adapted to produce a uniform magnetic field); Construction of a machine with two fields, each having a rotary conductor mounted between its poles;
U.S. Patent 0,413,353 - Method of Obtaining Direct current from Alternating Currents - 1889 October 22 - Superiority of alternating currents discussed; Delineates machines to convert alternating currents to direct (or continuous) currents at will at one or more points;
U.S. Patent 0,416,191 - Electro-Magnetic Motor - 1889 December 3 - Induction motor with two or more energizing circuits; alternating currents of differing phases are passed to produce rotation or operation of the motor; simple way consists of two circuits;
U.S. Patent 0,416,192 - Method of Operating Electro-Magnetic Motors - 1889 December 3 - Related to US401520; Alternative improvements to synchronous motors; Torque and synchronous actions in motors; different field circuit of differing induction; Windings and shunts; Increases tendency to synchronize;
U.S. Patent 0,416,193 - Electro-Magnetic Motor - 1889 December 3 - Induction motor operation with two or more windings; securing differing phase differences; Phase proportional to the induction and inverse to the resistance encountered by the current;
U.S. Patent 0,416,194 - Electric Motor - 1889 December 3 - Drawings include the motor seen in many of Tesla's photos; Classic alternating current electro-magnetic motor; Induction motor operation; Field and armature of equal strengths or magnetic quality; field and armature cores of equal amounts; Coils containing equal amount of copper;
U.S. Patent 0,416,195 - Electro-Magnetic Motor - 1889 December 3 - Induction motor operation with two or more windings; Differing phases; Structural and operational conditions; Armature operation conditions and the obedience to the energizing circuit and stator; Construction and organization principles;
U.S. Patent 0,417,794 - Armature for Electric Machines - 1889 December 24 - Construction principles of the armature for electrical generators and motors; Simple and economical; Coils of insulated conducting wire (or ribbon) may be wound or formed into bobbins; Position of the bobbins dictate the windings;
U.S. Patent 0,418,248 - Electro-Magnetic Motor - 1889 December 31 - Electric generator; Employment of an artificial cooling device; Enclosing the source of heat and that portion of the magnetic circuit exposed to the heat and artificially cooling the said heated part; Combination of an enclosed source of heat applied to a portion of said core;
U.S. Patent 0,424,036 - Electro-Magnetic Motor - 1890 March 25 - Cites then common language of his motors referred to as the "magnetic lag" motors; Another form of the induction motor with two or more energizing circuits with differing phase differences are passed to produce rotation or operation of the motor; Magnetism lags electrical parts of energizing effects;
U.S. Patent 0,428,057 - Pyromagneto Electric Generator - 1890 May 13 - Electric generator; Employment of an artificial cooling device; Enclosing the source of heat and that portion of the magnetic circuit exposed to the heat and artificially cooling the said heated part; Combination of an enclosed source of heat applied to a portion of said core;
U.S. Patent 0,433,700 - Alternating-Current Electro-Magnetic Motor - 1890 August 5 - Rotation of an electromagnetic motor is produced by the magnetic movements or the maximum of the pole's (or point's) magnetic effects from the conjoined actions (or the two energizing circuits) through which alternating currents (or similar rapidly varying currents) are passed through;
U.S. Patent 0,433,701 - Alternating-Current Motor - 1890 August 5 - Two sets of field-pole pieces of energized independently by the same source; Closed magnetic iron shunts or bridges in sets or series;
U.S. Patent 0,433,702 - Electrical Transformer Or Induction Device - 1890 August 5 - Main magnetic core and the primary and secondary coils interposed by a magnetic shield or screen between the coils or around one of the coils;
U.S. Patent 0,433,703 - Electro-Magnetic Motor - 1890 August 5 - Describes the combination, in an alternating current motor, of an energizing coil and a core composed of two parts (one being protected from magnetization from the other one interposed between it and the coil);
U.S. Patent 0,445,207 - Electro-Magnetic Motor - 1891 January 27 - Describes the combination, in a motor, of a primary energizing circuit (connected to a generator) and a secondary circuit in inductive relation to the primary; Each circuit has a different electrical character, resistance, induction capability, or number and type of windings;
U.S. Patent 0,447,920 - Method of Operating Arc-Lamps - 1891 March 10 - Abate or render inaudible sound emitted by arc lamps that are powered by (or supplied with) alternating currents by increasing the frequency of alternations (or pulsations) above the auditory level;
U.S. Patent 0,447,921 - Alternating Electric Current Generator - 1891 March 10 - A generator that produces alternations of 15000 per second or more;
U.S. Patent 0,454,622 - System of Electric Lighting - 1891 June 23 - Apparatus devised for the purpose of converting and supplying electrical energy in a form suited for the production of certain novel electrical phenomena, which require currents of higher frequency and potential;
U.S. Patent 0,455,067 - Electro-Magnetic Motor - 1891 June 30 - Alternating current motor, with field magnets and energizing circuit armature-circuit and a core adapted to be energized by currents induced in its circuit by the currents in the field circuit; Condenser connected with or bridging the armature-circuit (e.g., the rotating element of the motor);
U.S. Patent 0,455,068 - Electrical Meter - 1891 June 30 - Method of computing the amount of electrical energy expended in a given time in an electrical circuit; Operates by maintaining by the current a potential difference between two conductors in an electrolytic solution (or cell) uniform throughout the whole extent of such conductors exposed to the solution;
U.S. Patent 0,455,069 - Electric Incandescent Lamp - 1891 June 30 - Incandescent lamp consisting of two isolated refractory conductors contained in a non-striking vacuum and adapted to produce light by incandescence;
U.S. Patent 0,459,772 - Electro-Magnetic Motor - 1891 September 22 - Alternating current non-synchronizing electric motor coupled with a synchronizing alternating current motor whereby the former starts the latter and throws it into synchronism with its actuating current; Switch mechanism for directing the current through either or both of the motors;
U.S. Patent 0,462,418 - Method of and Apparatus for Electrical Conversion and Distribution - 1891 November 3 - Apparatus devised for the purpose of converting and supplying electrical energy in a form suited for the production of certain novel electrical phenomena which require currents of higher frequency and potential;
U.S. Patent 0,464,666 - Electro-Magnetic Motor - 1891 December 8 - Alternating current motor provided with two or more energizing or field circuits; One circuit connected to current source and the other (or others) in inductive relation thereto;
U.S. Patent 0,464,667 - Electrical Condenser - 1891 December 8 - Electrical condenser composed of plates or armatures immersed in oil; Plates or armatures can be adjustable;
U.S. Patent 0,487,796 - System of Electrical Transmission of Power - 1892 December 13 - Alternating current generator consisting of independent armature-circuits formed by conductors alternately disposed; Currents developed differ in phase and the field magnet poles in excess of the number of armature-circuits;
U.S. Patent 0,511,559 - Electrical Transmission of Power - 1893 December 26 - Method of operating motors having independent energizing circuits; Passing alternating currents through circuits and retarding the phases of the current in one circuit to a greater extent;
U.S. Patent 0,511,560 - System of Electrical Power Transmission - 1893 December 26 - Motor having independent energizing circuits connected with a source of alternating currents; Means of rendering the magnetic effects to said energizing circuit of difference phase;
U.S. Patent 0,511,915 - Electrical Transmission of Power - 1894 January 2 - Method of operating electro-magnetic motors; Passing alternating currents through one of the energizing circuits and inducing by such current in the other energizing circuit or circuits of the motor;
U.S. Patent 0,511,916 - Electric Generator - 1894 January 2 - Combination with the piston or equivalent element of an engine which is free to reciprocate under the action thereon of steam or a gas under pressure, of the moving conductor or element of an electric generator in direct mechanical connection;
U.S. Patent 0,512,340 - Coil for Electro-Magnets - 1894 January 9 - Effect of mutual relation self-induction exploited; Adjacent coil convolutions formed parts exists so that the potential difference is sufficient to neutralize negative effects; Object to avoid expensive, cumbersome, and difficult condensers; Bifilar coil winding technique;
U.S. Patent 0,514,167 - Electrical Conductor - 1894 February 6 - Prevent loss in line conductors; Insulate and encase conductors with a sheathing which is connected to the ground; Sheath or screen; Coaxial cabling;
U.S. Patent 0,514,168 - Means for Generating Electric Currents - 1894 February 6 - Generating and utilizing electrical energy discovered by Mr. Tesla; related to US454622 and US462418; Maintenance of intermittent or oscillatory discharges of a condenser of suitable circuit containing translating devices;
U.S. Patent 0,514,169 - Reciprocating Engine - 1894 February 6 - Provide a means of engines, which under the applied forces such as elastic tension of steam or gas under pressure, that will yield constant oscillatory movements (in wide limits); Often cited by enthusiasts as a version of the "earthquake machine."
U.S. Patent 0,514,170 - Incandescent Electric Light - 1894 February 6 - Related to US454622; Incandescent electric lamps; Particular forms of the lamp in which a light giving small body or button of refractory material is supported by a conductor entering a very highly exhausted globe or receiver;
U.S. Patent 0,514,972 - Electric Railway System - 1894 February 20 - Utilizes high potentials and high frequencies; Insulated and screened supply conductor along the line of travel; Induction bar or plate in inductive relation to the screened conductor and an electrical connection to the motor.
U.S. Patent 0,514,973 - Electrical Meter - 1894 February 20 - Method of measuring the amount of electrical energy expended in a given time in an electric circuit of alternating currents; High tension discharge through a rarefied gas between two conductors;
U.S. Patent 0,517,900 - Steam Engine - 1894 April 10 - Cylinder and reciprocating piston (with a spring) and controlling slide valve of an engine adapted to be operated by steam or a gas system under pressure of an independently controlled engine of constant period operating the said valve;
U.S. Patent 0,524,426 - Electromagnetic Motor - 1894 August 14 - Alternating current motor with energizing coils adapted to be connected with an external circuit of cores of different magnetic susceptibility so as to exhibit differences of magnetic phase under the influence of an energizing current;
U.S. Patent 0,555,190 - Alternating Motor - 1896 February 25 - Related to US381968 and US382280; Mode and plan of operating electric dynamic motor generators by progressive shifting; Magneto-electric machine; Dynamo motor conversion with two independent alternating current circuits; Transmission of energy; Rotating magnetic field principles;
U.S. Patent 0,567,818 - Electrical Condenser - 1896 September 15 - Condenser constructed or provided with means for exclusion of air or gas; Armature composed of a conducting liquid; Armatures in two separate bodies of conducting liquid insulated electrically and contained in a receptacle; Insulating liquid seal on the surface of the conductive liquids;
U.S. Patent 0,568,176 - Apparatus for Producing Electrical Currents of High Frequency and Potential - 1896 September 22 - Conversion of direct current into currents of high frequency; Combination of high self-inductance circuit, choking coil circuit controllers adapted to make and break the circuit;
U.S. Patent 0,568,177 - Apparatus for Producing Ozone - 1896 September 22 - Primarily provides a simple, cheap, and effective apparatus for the production of ozone (or such gases); Obtained by the action of high-tension electrical discharges; Related to US462418 (November 3, 1891) and US454622 (June 23, 1891);
U.S. Patent 0,568,178 - Method of Regulating Apparatus for Producing Electric Currents of High Frequency - 1896 September 22 - Cited by Tesla in "the True Wireless" (illustrated in that article as Fig. 10) in the wireless field for the concatenated tuned circuits; regulates the energy delivered by a system for the production of high-frequency currents;
U.S. Patent 0,568,179 - Method of and Apparatus for Producing Currents of High Frequency - 1896 September 22 - used in the laboratory at New York, 35 South Fifth Avenue lab for employing currents of different phase; method for producing electric currents of high frequency, which consists in generating an alternating current;
U.S. Patent 0,568,180 - Apparatus for Producing Electrical Currents of High Frequency - 1896 September 22 - an isochronous mechanical break used in the laboratory at New York, 35 South Fifth Avenue lab for employing currents of different; patent covers possible variations within Tesla's wireless systems;
U.S. Patent 0,577,670 - Apparatus for Producing Electric Currents of High Frequency - 1897 February 23. Two input circuits are each pulsed with a 25% duty cycle. Additionally, the brushes are phased so that the on states (discharges) never overlap. The output circuit has a toggled 50% output duty cycle, double the duration of the input pulse;
U.S. Patent 0,577,671 - Manufacture of Electrical Condensers, Coils and Similar Devices - 1897 February 23 - Improvements of condensers, transformers, self-induction coils, rheostats, and other similar devices; Used in areas where currents of high potentials are brought into close proximity; Method of excluding gas or air from the dielectric environment of such devices;
U.S. Patent 0,583,953 - Apparatus for Producing Currents of High Frequency - 1897 June 8 - Related to US568176; Conversion of electric current of ordinary character into high frequency and high potential; Can use either continuous (i.e., direct) or alternating currents;
U.S. Patent 0,593,138 - Electrical Transformer - 1897 November 2 - Novel form of transformer or induction-coil and a system for the transmission of electrical energy by means of the same; Improvement of electrical transformers; Develops electric currents of high potential; Corrects construction principles heretofore manufactured;
U.S. Patent 0,609,245 - Electrical Circuit Controller - 1898 August 16 - A circuit controller (see also 609245, 609246, 609247, 609250, 609251, 611719); Conductive fluid make and break circuit; Nozzle and conductor construction and their relative method of operation; Single source of power for operation; Nozzle and receptacle interaction;
U.S. Patent 0,609,246 - Electric Circuit Controller - 1898 August 16 - A circuit controller (see also 609245, 609246, 609247, 609250, 609251, 611719); Conductive fluid make and break circuit; Conductive liquid forming terminals; Two orifices with relative movement that can direct jets or streams; Two insulated compartments;
U.S. Patent 0,609,247 - Electric Circuit Controller - 1898 August 16 - A "circuit controller in which an independently-mounted terminal operated in a similar manner by a rotating body of conducting fluid may be enclosed within a gas-tight receptacle"; Conductive fluid make and break circuit;
U.S. Patent 0,609,248 - Electric Circuit Controller - 1898 August 16 - A circuit controller (see also 609245, 609246, 609247, 609250, 609251, 611719) in which one terminal body moves through jets or streams intermittently and intercepts jets or streams; Conductive fluid make and break circuit; Rotary conductor;
U.S. Patent 0,609,249 - Electric Circuit Controller - 1898 August 16 - A circuit controller (see also 609245, 609246, 609247, 609250, 609251, 611719); Conductive fluid make and break circuit;
U.S. Patent 0,609,250 - Electrical Igniter for Gas Engines - 1898 August 16 - Ignition system principles used today in automobiles; Operation of a machine that requires a spark, flame, or any other similar effect; More certain and satisfactory for use of and control by the machine or apparatus; Charging and discharging a condenser through switch or commutator.
U.S. Patent 0,609,251 - Electric Circuit Controller - 1898 August 16 - A circuit controller (see also 609245, 609246, 609247, 609250, 609251, 611719). Circuit comprising, in combination, a receptacle containing fluid, means for rotating the receptacle, and a terminal supported independently of the receptacle and adapted to make and break electric connections;
U.S. Patent 0,611,719 - Electrical Circuit Controller - 1898 October 4 - A circuit controller (see also 609245, 609246, 609247, 609250, 609251, 611719). Conductive fluid make and break circuit; The combination of a closed receptacle, of a circuit controller contained therein, and surrounded by an inert medium under pressure;
U.S. Patent 0,613,735 - Electric Circuit Controller - 1898 November 8 - A circuit controller (see also 609245, 609246, 609247, 609250, 609251, 611719). Conductive fluid make and break circuit; Combination with rigid and fluid conductors adapted to be brought intermittently into contact with each other;
U.S. Patent 0,613,809 - Method of and Apparatus for Controlling Mechanism of Moving Vehicle or Vehicles - 1898 July 1 - Tesla "Boat" patent; Art of controlling the movements and operation of a vessel or vehicle at a distance; Electromagnetic waves conveyed to vessel by the natural media and rendering by their means the controlling-circuit active or inactive;
U.S. Patent 0,645,576 - System of Transmission of Electrical Energy - 1900 March 20 - Wireless transmission of electric power;Tesla applied for a this patent in September 1897[4] This wireless power transmission scheme consisted of transmitting power between two tethered balloons maintained at 30,000 feet, an altitude where he thought a highly conductive layer of the atmosphere would exist;
U.S. Patent 0,649,621 - Apparatus for Transmission of Electrical Energy - 1900 May 15 - Related to US645576; New and useful combinations employed; Transmitting coil or conductor arranged and excited to cause currents or oscillation to propagate through conduction through the natural medium from one point to another remote point therefrom and a receiver coil or conductor of the transmitted signals;
U.S. Patent 0,655,838 - Method of Insulating Electric Conductors - 1900 October 23 - Method and practical application of insulation by freezing and solidification; Expounding on Faraday's hypothesis of freezing substances make them possess a higher dielectric level to insulate transmission conductors; Improvements in the method set out by Faraday;
U.S. Patent 0,685,012 - Means for Increasing the Intensity of Electrical Oscillations - 1900 March 21 - A method for producing a "great increase in the intensity and duration of the (electrical) oscillations excited in a freely-vibrating or resonating circuit by maintaining the same at a low temperature". Producing increase intensity and duration of electric oscillations;
U.S. Patent 0,685,953 - Apparatus for Utilizing Effects Transmitted from a Distance to a Receiving Device through Natural Media - 1901 November 5 - Heinriech Hertz methods cited; Induction method cited; Ground conduction method cited; Previous methods had limitations that result in great disadvantages for utilization;
U.S. Patent 0,685,954 - Method of Utilizing Effects Transmitted through Natural Media - 1901 November 5 -Utilizing effects or disturbances transmitted through the natural media, which consists on charging a storage device with energy from an independent source, controlling the charging of said device by the actions of the effects or disturbances;
U.S. Patent 0,685,955 - Apparatus for Utilizing Effects Transmitted From A Distance To A Receiving Device Through Natural Media - 1901 November 5 - An apparatus for transmitting signals or intelligence through the natural media from a sending station to a distant point the combination of a generator or transmitter adapted to produce arbitrarily varied or intermitted electrical disturbances or effects in the natural media;
U.S. Patent 0,685,956 - Apparatus for Utilizing Effects Transmitted through Natural Media - 1901 November 5 - Related to his Magnifying Transmitter; Used as part of Tesla's Colorado Spring receivers that posed a distributed high-Q helical resonators, radio frequency feedback, crude heterodyne effects, and regeneration techniques;
U.S. Patent 0,685,957 - Apparatus for the Utilization of Radiant Energy - 1901 November 5 - 4 illustrations; Radiation charging and discharging conductors; Radiations considered vibrations of ether of small wavelengths and ionize the atmosphere; Radiant energy throws off with great velocity minute particles which are strongly electrified;
U.S. Patent 0,685,958 - Method of Utilizing of Radiant Energy - 1901 November 5 - 2 illustrations; Ways of using radiation charging and discharging conductors; Rays or radiation falling on insulated-conductor connected to a condenser (i.e., a capacitor), the condenser indefinitely charges electrically; Radiation (or radiant energy) include many different forms;
U.S. Patent 0,723,188 - Method of Signaling - 1903 March 17 - Elevated transmitter capacitance; Coil; Earth electrode; Signal generator;
U.S. Patent 0,725,605 - System of Signaling - 1903 April 14 - Elevated transmitter capacitance; Coil; Earth electrode; Signal generator; Apparatus of and method for electrical disturbance or impulses; Transmission of intelligent messages via wireless transmission; Govern the movement of distant automata;
U.S. Patent 0,787,412 - Art of Transmitting Electrical Energy through the Natural Mediums - 1905 April 18 - Elevated transmitter capacitance; Coil; Earth electrode; Signal generator; Apparatus for generating and receiving electrical signals; Tuned resonant circuits; Physics of propagation; Non-Hertzian notes; Globe as conductor; Low frequency oscillations;
U.S. Patent 1,061,142 - Fluid Propulsion - 1909 October 21 - Transmission and transformation of mechanical power through the agency of fluid; Propelled fluid moves in a natural path; Avoids losses; Easy; Simple;
U.S. Patent 1,061,206 - Turbine - 1909 October 21 - Improvements in rotary engines and turbines; Mechanical power based on the vehicle of fluid for power; Known as the Tesla turbine; Bladeless turbine design; Utilizes boundary layer effect; Fluid does not impact the blades as in a conventional turbine;
U.S. Patent 1,113,716 - Fountain - 1914 October 13 - Improvement in the construction of fountains and aquarium displays; Large mass of fluid in motion; Display of great power; Large displacement of fluid with little expense of energy;
U.S. Patent 1,119,732 - Apparatus for Transmitting Electrical Energy - 1914 December 1 - High-voltage, air-core, self-regenerative resonant transformer; Oscillator for wireless transmission of electromagnetic energy; Tesla coil;
U.S. Patent 1,209,359 - Speed-Indicator - 1916 December 19 - Improvement that uses the adhesion and viscosity of a gaseous medium [preferably air] to measure speed [or measure the torque-transmission] between indicator and driver; Durable; Simple; Inexpensive; Reliable;
U.S. Patent 1,266,175 - Lightning-Protector - 1918 May 14 - Novel and advantageous construction of a protector in accord with the true character of the phenomena; Corrects Benjamin Franklin's hypothesis, and subsequent construction, for lightning protectors;
U.S. Patent 1,274,816 - Speed Indicator - 1918 August 6 - Speedometer that possesses the feature of: Linearly proportional torque readings; Strong low speed torsional effects; not affected by atmospheric density, temperature, nor magnetic influences; Rugged; Simple; Economical;
U.S. Patent 1,314,718 - Ship's Log - 1919 September 2 - Novel and advantageous construction of a ship's log; Instantaneous reading of knots or miles-per-hour;
U.S. Patent 1,329,559 - Valvular Conduit - 1920 February 3 - Improvement by means of a conduit or channel characterized by valvular action; Conduit has baffles, recesses, projections, enlargements, or buckets that channels the flow's movement one way more efficiently; Mechanical diode; One-way valve with no moving parts. Now known as a Tesla valve;
U.S. Patent 1,365,547 - Flow-Meter - 1921 January 11 - Related to the meter of measurement for velocity and quantity of fluid flow;
U.S. Patent 1,402,025 - Frequency-Meter - 1922 January 3 - Ascertain the periodic electric frequency and electric oscillation by the rotation or reciprocation of an electromechanical device;
U.S. Patent 1,655,113 - Method of Aerial Transportation - 1928 January 3 - VTOL aeroplane; Describes a method of achieved vertical take-off, transition to and from horizontal flight, and vertical landing, with a tilting rotor. Including transportation which consists in developing by the propelling device a vertical thrust in excess of the normal;
U.S. Patent 1,655,114 - Apparatus for Aerial Transportation - 1928 January 3 - VTOL aircraft; Includes a correction;