Name: three-phase synchronous motor starting and v-curves
Uploaded: 2023-04-30T06:43:16.000Z
Duration: 11 min 19 s
Channel: JoVE

K12 Standards

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South Carolina College and Career Ready Science Standards

High School

Physics

motion-and-stability-forces-and-interactions

Motion and Stability: Forces and Interactions

P-PS2-6.

AC Synchronous Machine Characterization

1. DC Test
<ol>
	<li>Turn on the low-power DC power supply with a short circuit across its terminals.
	<ol>
		<li>Limit the current on the low-power DC power supply to 1.8 A.</li>
		<li>Turn off the supply and disconnect the short circuit.</li>
	</ol>
	</li>
	<li>Connect the supply terminals across ports 1 and 4 of the synchronous motor.
	<ol>
		<li>Turn on the supply and measure the DC voltage and current. Vary the voltage as needed to reach a current of 1.8 A.</li>
		<li>Turn off the supply, then repeat the previous two steps for ports 2 and 5 and ports 3 and 6.</li>
	</ol>
	</li>
	<li>Disconnect the low-power DC power supply.</li>
</ol>
2. Synchronous Machine Start-up
<ol>
	<li>Make sure the three-phase disconnect switch, synchronous motor switch, and DC motor switch are all off.
	<ol>
		<li>Check that the VARIAC is at 0%.</li>
		<li>Wire the VARIAC to the three-phase outlet, and connect the setup shown in Fig. 1.</li>
		<li>Remember to set the 1 to 1000 scaling of the digital power meter current probe.</li>
	</ol>
	</li>
	<li>Check that the "Start/Run" switch is in the "Start" position.</li>
	<li>Turn on the three-phase disconnect switch.</li>
	<li>Quickly increase the VARIAC output until the digital power meter reads around 115 V.</li>
	<li>Measure the armature current IAC1, armature voltage VAC1, real power, and power factor.</li>
	<li>Remember that the phase (line-to-neutral) voltage and phase current on phase "a" are being measured, so the power factor measurement on the power meter is correctly reflecting the per-phase power factor.</li>
	<li>Measure the torque and speed of the machine.</li>
	<li>Turn on the 125 V DC power supply. Make sure all connections are clear from the supply terminals.
	<ol>
		<li>Press the supply "Start" button and set the supply output to 125 V.</li>
	</ol>
	</li>
	<li>Flip the "Start/Run" switch to the "Run" position. Pay attention to how the machine sound changes. The machine sound becomes smoother as the rotor magnetic field locks to the stator rotating magnetic field.
	<ol>
		<li>Record the armature current IAC1, armature voltage VAC1, real power, power factor, and the field voltage and current from the DC power supply display.</li>
		<li>Measure and record the torque and speed of the machine.</li>
	</ol>
	</li>
	<li>Turn off the DC power supply, flip the "Start/Run" switch to the "Start" position, and set the VARIAC back to 0%.</li>
	<li>Turn off the three-phase disconnect switch. Leave the rest of the circuit intact.</li>
</ol>
<img alt="Synchronous motor diagram with variac, DC power supply; mechanical coupling to DC dynamometer." src="/files/ftp_upload/10168/10168fig1.jpg" data-altupdatedat="1761830439000" data-alt="Figure 1"> 
Figure 1: A schematic of the setup to start the synchronous motor. <a href="//cloudfront.jove.com/files/ftp_upload/10168/10168fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
3. Effect of Load on Torque Angle
<ol>
	<li>Make sure the three-phase disconnect switch, synchronous motor switch "S1," and DC motor switch "S2" are all off.
	<ol>
		<li>Note that while "S1"is on the synchronous motor side, it is used to connect/disconnect the "RL" load across the DC machine terminals.</li>
		<li>Check that the VARIAC is at 0%.</li>
	</ol>
	</li>
	<li>Connect the setup shown in Fig. 2 and set "RL" to 200 Ω.</li>
	<li>Check that the "Start/Run" switch is in the "Start" position.</li>
	<li>Turn on the three-phase disconnect switch.</li>
	<li>Quickly increase the VARIAC output until the digital power meter reads around 115 V.</li>
	<li>Turn on the 125 V DC power supply. Make sure all connections are clear from the supply terminals.</li>
	<li>Press the supply start button and set the supply output to 125 V.</li>
	<li>Flip the "Start/Run" switch to the "Run" position.</li>
	<li>Record the armature current IAC1, armature voltage VAC1, real power, power factor, and field voltage and current from the DC power supply display.</li>
	<li>Measure and record the torque and speed of the machine.</li>
	<li>Keep the strobe light on near the shaft and measure the initial angle δo.
	<ol>
		<li>To set up the strobe light, plug it into a regular power outlet and turn it on.</li>
		<li>With the Coarse knob, adjust the speed reading on the strobe light to be close enough to 1,800 RPM, which is the synchronous speed of 1 four-pole 60 Hz machine. Synchronous speed is calculated in rounds per minute (RPM) as n=120xf/P where f is the frequency and P is the number of poles.</li>
		<li>Place the strobe light to face the motor shaft's edge, and adjust the Fine knob until the shaft appears stationary. The human eye is tricked to see the shaft as stationary by having the strobe light frequency (or speed reading) match the shaft speed.</li>
	</ol>
	</li>
	<li>Turn on "S1" and repeat steps 3.9 to 3.11, but measure the new angle as δ1.</li>
	<li>Turn on "S2" and repeat steps 3.9 to 3.11, but measure the new angle as δ2.</li>
	<li>Turn off "S2" and change "RL" to 100 Ω.</li>
	<li>Turn on "S2" and repeat steps 3.9 to 3.11, but measure the new angle as δ3.</li>
	<li>Turn off the DC power supply, flip the "Start/Run" switch to the "Start" position, turn off "S1"and "S2," and set the VARIAC back to 0%.</li>
	<li>Turn off the three-phase disconnect switch. Leave the rest of the circuit intact.</li>
</ol>
<img alt="Synchronous motor setup diagram with VARIAC, DC power, mechanical coupling, and dynamometer system." src="/files/ftp_upload/10168/10168fig2.jpg" data-altupdatedat="1761830439000" data-alt="Figure 2"> 
Figure 2: A schematic of the setup to study the effect of load on torque angle. <a href="//cloudfront.jove.com/files/ftp_upload/10168/10168fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
4. Effect of Field Current on Power Factor
This section investigates one side of the V-Curve.
<ol>
	<li>Make sure the three-phase disconnect switch, synchronous motor switch S1, and DC motor switch S2 are all off.</li>
	<li>Check that the VARIAC is at 0%.</li>
	<li>Connect the setup shown in Fig. 3, which is only different from Fig. 2 by adding the series field resistor "RF," and set "RL" to 200 Ω.</li>
	<li>Set "RF" to the 10 Ω position. "RF" does not require measurement for this experiment, since the goal is to vary field current only.</li>
	<li>Check that the "Start/Run" switch is in the "Start" position.</li>
	<li>Turn on the three-phase disconnect switch.</li>
	<li>Quickly increase the VARIAC output until the digital power meter reads 115 V.</li>
	<li>Turn on the 125 V DC power supply. Make sure all connections are clear from the supply terminals.</li>
	<li>Press the supply start button and set the supply output to 125 V.</li>
	<li>Flip the "Start/Run" switch to the "Run" position.</li>
	<li>For "RF" = 10, 6, 3, and 1, record the armature current IAC1, armature voltage VAC1, real power, power factor, field voltage and current from the DC power supply display.</li>
	<li>Measure and record the torque and speed of the machine.</li>
	<li>Reset "RF" to 10 Ω.</li>
	<li>Turn on "S1," and repeat steps 4.11 to 4.13.</li>
	<li>Turn on "S2," and repeat steps 4.11 to 4.13.</li>
	<li>Turn off "S2" and change "RL" to 100 Ω.</li>
	<li>Turn on "S2," and repeat steps 4.11 to 4.13.</li>
	<li>Turn off the DC power supply, flip the "Start/Run" switch to the "Start" position, and set the VARIAC back to 0%.</li>
	<li>Turn off the three-phase disconnect switch and disconnect the setup.</li>
</ol>
<img alt="Three-phase VARIAC and synchronous motor diagram for mechanical coupling with DC dynamometer." src="/files/ftp_upload/10168/10168fig3.jpg" data-altupdatedat="1761830439000" data-alt="Figure 3"> 
Figure 3: A schematic of the setup to study the effect of changing the field current. <a href="//cloudfront.jove.com/files/ftp_upload/10168/10168fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Synchronous machines are common in applications requiring constant speed on the motor's shaft with very tight speed regulations. Such applications include electrical clocks and hard disk drives, but extend to synchronous condensers, which are synchronous motors operating in the leading power factor region to provide reactive power to a load. Power factor correction is another term used with synchronous condenser applications. Note that the most common synchronous motors are permanent magnet motors, while the most common ...

ac synchronous machine characterization

Source: Ali Bazzi, Department of Electrical Engineering, University of Connecticut, Storrs, CT.
Three-phase wound-rotor synchronous motors are less popular than permanent magnet rotor synchronous motors due to the brushes required for the rotor field. Synchronous generators are much more common and available in most existing power plants, as they have excellent frequency and voltage regulation. Synchronous motors have the advantage of almost 0% speed regulation due to the fact that the rotor speed is exactly the same as the stator&#39;s magnetic field speed, causing the rotor speed to be constant, irrespective of how much the motor&#39;s shaft is loaded. Thus, they are very suitable for fixed speed applications.
The objectives of this experiment are to understand the concepts of starting a three-phase synchronous motor, V-curves for various loads where the load affects the motor power factor, and the effect of loads on the angle between the terminal voltage and back e.m.f.

The DC phase resistance can be estimated from the DC test as the ratio of DC voltage to DC current when applied between a phase terminal and the neutral. The field resistance can be measured in a similar manner by applying DC voltage to the field winding and measuring the field current. The synchronous reactance (Xs), back e.m.f. of the machine (EA), and its related constant kφ can be found from the real power (P3<...

Source: Ali Bazzi, Department of Electrical Engineering, University of Connecticut, Storrs, CT.
Three-phase wound-rotor synchronous motors are less ...

Synchronous motors are ideal in applications requiring constant rotor speed independent of varying shaft load, and are almost ubiquitous in power plants for regulating frequency and voltage. Synchronous machines consist of an inner rotating core called the rotor and an outer stationary ring called the stator. The rotor magnetic field is fixed and is generated using either permanent magnets or a DC power source. In three phase synchronous motors, current flows to the machine's stator with each phase connected to its own separate set of stator coils. This produces a separate rotating magnetic field that corresponds to oscillations in the supply line current. The stator and rotor magnetic fields are coupled or locked, causing the rotor to spin at a speed exactly the same as the stator magnetic field's rotation rate. The overall goal of this video is to introduce three phase synchronous machines, demonstrate protocols for starting and locking the rotor and stator magnetic fields, and illustrate a protocol for finding the effect of motor loads on torque angle.To overcome initial inertia before the stator and rotor fields are aligned, a three phase synchronous machine is initially run as an induction motor. In this procedure, the stator's rotating magnetic field induces current in the squirrel cage rotor, subsequently creating a magnetic field around the rotor and inducing rotation. Once the machine speed approaches synchronous speed, a DC voltage is applied across the field winding. From this point on, electromagnetic excitation controls the rotor magnetic field. With the rotor magnetic field fixed, the rotor and stator magnetic fields become locked to achieve rotor-stator synchronism. Consequently, the synchronous motor's speed is controlled by the stator magnetic field rotation speed, and is independent of load. While rotor load does not affect the rotor's speed in a synchronous motor, it does cause the rotor pulls to fall slightly behind the stator pulls. While the motor continues to run at synchronous speed, the angular displacement is called the torque angle, which is smaller at lower loads and larger at higher loads. As the mechanical load increases, torque angle increases until the angle is so high that the rotor is pulled out of synchronism. This high mechanical load is therefore above the limit to which the motor can handle, and is called the breakdown torque. Now that synchronous motors have been introduced, we will demonstrate procedures for startup, synchronization, and characterization.Before starting the synchronous motor, test the DC power supply used to lock the rotor and stator magnetic fields. First, short-circuit the low-powered DC power supply and turn it on. Reduce the current on the supply to one point eight amps, and then turn off the supply and disconnect the short-circuit. The DC test measures the stator winding resistance. First, connect the DC supply terminals across ports one and four of the synchronous motor, and turn on the supply. Then, record the DC voltage and current across these ports. Vary the voltage as needed to reach a current limit of one point eight amps. Record the voltage and then turn off the supply. Repeat the voltage and current measurements as described across ports two and five, and then for ports three and six. Finally, disconnect the DC supply to complete the DC test.In the next step of the protocol, the synchronous machine is started in induction motor mode, and then the rotor and stator magnetic fields are locked. First, check that the three phase disconnect switch, synchronous motor switch, and DC motor switch are all off. Then, check that the variac is set to zero percent output voltage. With the equipment shut off, wire the variac to the three phase outlet, and connect the setup as shown. Then, attach a small piece of tape to the AC synchronous machine rotor shaft. Finally, set the five to 100 A-scaling of the digital power meter current probe. Now, start the motor by powering the equipment on. First, check that the 'Start-Run' switch is in the 'Start' position. Second, turn on the three phase disconnect switch. Third, quickly increase the variac output until the digital power meter reads around 115 volts. These measurements correspond to phase A, the line to neutral phase voltage and current so that the power factor measurement correctly reflects the per phase power factor. Then, measure the motor torque in induction mode. Finally, measure motor speed using the strobe light technique. Please refer to the Science Education video, "DC Motors" for more information on this technique. With the machine started, and initial parameters measured, it is ready for synchronization. First, turn on the 125 volt DC power supply. Then, flip the 'Start-Run' switch to the 'Run' position. Pay attention to how the machine sound changes. As the rotor magnetic field locks to the stator rotating magnetic field, the machine sound becomes smoother. With rotor and stator magnetic fields locked, or synchronized, measure the armature current and voltage, power, and power factor. Then, measure the field voltage and current from the DC power supply display. Next, measure the mechanical characteristics, torque, and speed. Finally, turn off the equipment starting with the DC power supply. Then, flip the 'Start-Run' switch to the 'Start' position, and set the variac back to zero percent output. Last, turn off the three phase disconnect switch.When a DC motor is mechanically coupled to the synchronous machine to provide a mechanical load, the torque angle in the synchronous motor can be modified by the shunt field current in the DC motor. This protocol examines the relationship between motor field load and torque angle. With the equipment shut off, connect the set up as shown, and set the shunt load resistor to two kilo ohms. Now, power up the equipment as described previously. Record the electrical and mechanical parameters as before. Next, record torque angle with the shunt field loaded. To do so, use the strobe to visually freeze the shaft of the synchronous motor. Adjust the strobe frequency using the 'course' nob to approximately match 1800 RPM, the synchronous speed of four pull 60 hertz machine. Then, aim the strobe light at the motor shaft's edge, and adjust the 'fine' nob until the shaft appears stationary Initially, measure the torque angle with RL set to 200 ohm, and switches S1 and S2 off. Then, repeat the angle measurements with the shunt field loaded as follows. Flip S1 on and measure angle delta one, then turn S2 on and measure angle delta two. Last, turn off S2, change RL to 300 ohm, and turn S2 back on. Finally, turn off the equipment as described previously.The DC phase resistance was estimated from the DC test as the ratio of DC voltage to DC current when applied between a phase terminal and the neutral. Phase resistance contributes to losses in the machine, and causes voltage drop across the armature. The field resistance was measured in a similar manner by applying DC voltage to the field winding and measuring the field current. Field resistance controls field current. Field voltage can be varied with a fixed field resistance to vary field current. Finally, the torque angle became larger with increased mechanical load modified by varying the shunt field current in the DC motor. The real power of the machine is then related to the torque angle as shown. This tells us that the output power is highest when the torque angle is zero.Synchronous machines are common in applications requiring constant speed on the motor's shaft with very tight speed regulations. Three phase wound rotor synchronous generators are the main source of electrical power worldwide. In order to connect the generator at one plant to the electrical grid, three factors in the generator output voltages must match those of the grid, magnitude, frequency, and phase sequence. While automatic synchronizers are usually utilized in large power plants, a simple method is demonstrated for manual synchronization in the Science Education video, "AC Synchronous Machine Synchronization." Synchronous motors are often used for simple devices such as ball mills. A ball mill is a device that blends and grinds materials by rotating a cylinder containing small metal balls. The impact of the balls grinds the materials placed within the cylinder. These grinders are used frequently to blend materials such as paints, or to pulverize materials such as plant grain.You've just watched Jove's introduction to AC synchronous machine characterization. You should now understand how AC synchronous machines work, how to start and synchronize the machine, and recognize the effect of motor loads on torque angle. Thanks for watching.

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Electrical Engineering

three-phase synchronous motor starting and v-curves

Three-phase synchronous motors and generators are important AC machines. Wound-rotor synchronous motors are less common than permanent magnet rotor synchronous motors because the rotor field uses brushes. Synchronous generators are much more common. They are used in most existing power plants because they provide excellent frequency and voltage regulation.

A synchronous motor runs at the same speed as the stator magnetic field. This gives it almost 0% speed regulation, so the rotor speed stays constant even when the shaft load changes. That makes synchronous motors a good choice for fixed-speed applications.

This experiment focuses on starting a three-phase synchronous motor and on V-curves. A V-curve shows how load changes the motor power factor. The study also looks at how load changes the angle between the terminal voltage and the back e.m.f. (electromotive force, or induced voltage).

Three-Phase Synchronous Motor Starting and V-Curves

three-phase-synchronous-motor-starting-and-v-curves

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AC synchronous generators are a major source of electrical power worldwide. They are three-phase, wound-rotor machines that are used in many power plants. These generators need a prime mover and an exciter to produce power. A prime mover is the device that spins the generator, often a turbine driven by fluid. That fluid can come from water flowing from a dam through a long nozzle or from steam made by burning coal. Most power plants use synchronous generators, including coal, nuclear, natural...

Three-phase synchronous motors and generators are important AC machines. Wound-rotor synchronous motors are less common than permanent magnet rotor synchronous motors because the rotor field uses brushes. Synchronous generators are much more common. They are used in most existing power plants because they provide excellent frequency and voltage regulation. A synchronous motor runs at the same speed as the stator magnetic field. This gives it almost 0% speed regulation, so the rotor speed stays...

electrical engineering

This collection starts with an electrical safety video that introduces the best practices for commonly used equipment in an electrical laboratory. Subsequent videos introduce elements such as inductors, transformers, convertors, rectifiers, and inverters.

Explore how three-phase synchronous motors start, why they keep nearly constant speed, and how V-curves show the effect of load on power factor and back e.m.f.

Three-Phase Synchronous Motor Starting and V-Curves | JoVE K12

Ali Bazzi

Overview

Principles of AC Synchronous Motors

DC Test

Starting the AC Synchronous Machine

Effect of Load on Torque Angle

Results

Applications

Summary

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The ...

Apply scientific and engineering ideas to design, evaluate, and refine a device that minimizes the effect of a force on a macroscopic object during a collision.

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Gravitation

In the years before Newton, a general belief prevailed that different laws governed objects in the sky than objects on Earth. When Kepler wrote down the ...

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Newton's Law of Gravitation

Our everyday observation tells us that all objects close to the Earth naturally tend to fall to the ground. Early philosophers assumed that this downward ...

gravitation-between-spherically-symmetric-masses

Gravitation Between Spherically Symmetric Masses

The gravitational potential energy between two spherically symmetric bodies can be calculated from the masses and the distance between the bodies, ...

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Gravity between Spherical Bodies

Newton&#39;s law of gravitation describes the gravitational force between any two point masses. However, for extended spherical objects like the Earth, ...

Coulomb's Law

Experiments with electric charges have shown that if two objects each have an electric charge, they exert an electric force on each other. The magnitude ...

comparison-between-electrical-and-gravitational-forces

Comparison Between Electrical And Gravitational Forces

There are four fundamental forces in nature: the gravitational force, the electromagnetic force, the strong nuclear force, and the weak nuclear force. To ...

Newton's Law of Gravitational Attraction

Sir Isaac Newton established the universality of the law of gravitational attraction based on empirical evidence and inductive reasoning. He published his ...

Newton's Law of Universal Gravitation

Source: Ketron Mitchell-Wynne, PhD,&#160;Asantha Cooray, PhD, Department of Physics &#38; Astronomy, School of Physical Sciences, University of ...

Use mathematical representations of Newton's law of gravitation and Coulomb's law to describe and predict the gravitational and electrostatic forces between objects.

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Types of Forces

In most situations, forces can be grouped into two categories: contact forces and field forces.&#160; Contact forces occur as a result of direct physical ...

Magnetic Fields

Source: Yong P. Chen, PhD, Department of Physics &#38; Astronomy, College of Science, Purdue University, West Lafayette, IN
Magnetic fields can be ...

Electric Charge in a Magnetic Field

Source: Andrew Duffy, PhD, Department of Physics, Boston University, Boston, MA
This experiment duplicates J.J. Thomson's famous experiment at the end of ...

Electric Fields

Source: Yong P. Chen, PhD, Department of Physics &#38; Astronomy, College of Science, Purdue University, West Lafayette, IN
An electric field is generated ...

Electromagnetic Fields

Electric fields generated by static charges, often referred to as electrostatic fields, are characteristically different from electric fields created by ...

Magnetic Field Due to Two Straight Wires

Consider two parallel straight wires carrying a current of 10 A and 20 A in the same direction and separated by a distance of 20 cm. Calculate the ...

Energy Carried By Electromagnetic Waves

Anyone who has used a microwave oven knows there is energy in electromagnetic waves. Sometimes, this energy is obvious, such as in the summer sun&#39;s ...

Energy Stored in Capacitors

A parallel plate capacitor connected to a battery develops a potential difference across its plates.
By integrating the equation relating voltage and ...

Power and Energy

Energy is the total work required to drive the current through the circuit.
A rise in voltage results in more work done, passing more current, resulting ...

Voltage

The movement of electrons in a conductor requires some form of energy or work, usually provided by an external force, like a battery. This force is called ...

Electromotive Force

Electromotive force (emf) is the force that causes current to flow from a higher to a lower&#160; potential. The term &#34;electromotive ...

Electrical Energy

Using electric appliances for a longer period of time consumes more electrical energy and results in a higher electric bill. The energy produced by the ...

Electrical Current

Electrical current is defined as the rate at which charge flows. When there is a large current present, such as that used to run a refrigerator, a large ...

Electric Potential Energy

When an electric field accelerates a free positive charge q, it is given kinetic energy. The process is analogous to an object accelerated by a ...

Electrical Power

Electric power is the product of current and voltage, represented in units of joules per second, or watts. For example, cars often have one or more ...

Plan and conduct an investigation to provide evidence that an electric current can produce a magnetic field and that a changing magnetic field can produce an electric current.

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sources-and-properties-of-electric-charge

Sources and Properties of Electric Charge

All objects we see around us consist of atoms, which combine to form molecules. The lightest element in the universe is hydrogen, and a hydrogen atom ...

Electric Charges

From lightning during thunderstorms to electronic devices, the phenomenon of electromagnetism is all around us. The electromagnetic force is one of the ...

Electron Behavior

Electrons are negatively charged subatomic particles attracted to and orbit around the positively-charged nucleus of an atom. They reside in spaces ...

Electronic Structure of Atoms


An atom comprises protons and neutrons, which are contained inside the dense, central&#160;core called the nucleus, with electrons present around the ...

Atomic Structure

All matter is composed of atoms, the smallest individual units of elements. Each atom is made up of three subatomic particles: protons, neutrons, and ...

Communicate scientific and technical information about why the molecular-level structure is important in the functioning of designed materials.

Three-Phase Synchronous Motor Starting and V-Curves

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