SINGLE-PHASE INDUCTION MOTORS (Electric Motor)
There are many types of single-phase electric motors. In this section, the discussion will be limited to those types most common to integral-horsepower motor ratings of 1 hp and higher.
In industrial applications, three-phase induction motors should be used wherever possible. In general, three-phase electric motors have higher efficiency and power factors and are more reliable since they do not have starting switches or capacitors.
In those instances in which three-phase electric motors are not available or cannot be used because of the power supply, the following types of single-phase motors are recommended for industrial and commercial applications: (1) capacitor-start motor, (2) two-value capacitor motor, and (3) permanent split capacitor motor.
A brief comparison of single-phase and three-phase induction motor characteristics will provide a better understanding of how single-phase motors perform:
1. Three-phase motors have locked torque because there is a revolving field in the air gap at standstill. A single-phase motor has no revolving field at standstill and therefore develops no locked-rotor torque. Anauxiliary winding is necessary to produce the rotating field required for starting. In an integral-horsepower single-phase motor, this is part of an RLC network.
2. The rotor current and rotor losses are insignificant at no load in a three-phase motor. Single-phase motors have appreciable rotor current and rotor losses at no load.
3. For a given breakdown torque, the single-phase motor requires considerably more flux and more active material than the equivalent three-phase motor.
4. A comparison of the losses between single-phase and three-phase motors is shown in Fig. 1.11. Note the significantly higher losses in the single-phase motor.
The general characteristics of these types of single-phase induction motors are as follows.
A capacitor-start motor is a single-phase induction motor with a main winding arranged for direct connection to the power source and an auxiliary winding connected in series with a capacitor and starting switch for disconnecting the auxiliary winding from the power source after starting. Figure 1.12 is a schematic diagram of a capacitor-start motor. The type of starting switch most commonly used is a centrifugally actuated switch built into the motor. Figure
FIGURE 1.11 Percent loss comparison of single- and three-phase motors.
FIGURE 1.12 Capacitor-start single-phase motor.
1.13 illustrates an industrial-quality drip-proof single-phase capacitor-start motor; note the centrifugally actuated switch mechanism.
However, other types of devices such as current-sensitive and voltage-sensitive relays are also used as starting switches. More recently, solid-state switches have been developed and used to a
FIGURE 1.13 Capacitor-start single-phase motor. (Courtesy Magnetek, St. Louis, MO.)
limited extent. The solid-state switch will be the switch of the future as it is refined and costs are reduced.
All the switches are set to stay closed and maintain the auxiliary winding circuit in operation until the motor starts and accelerates to approximately 80% of full-load speed. At that speed, the switch opens, disconnecting the auxiliary winding circuit from the power source.
The motor then runs on the main winding as an induction motor. The typical speed-torque characteristics for a capacitor-start motor are shown in Fig. 1.14. Note the change in motor torques at the transition point at which the starting switch operates.
The typical performance data for integral-horsepower, 1800-rpm, capacitor-start, induction-run motors are shown in Table 1.6. There will be a substantially wider variation in the values of locked-rotor torque, breakdown torque, and pull-up torque for these single-phase motors than for comparable three-phase motors, and the same variation also exists for efficiency and the power factor (PF). Note that pull-up torque is a factor in single-phase motors to ensure starting with high-inertia or hard-to-start loads. Therefore, it is important to know the characteristics of the specific capacitor-start motor to make certain it is suitable for the application.
Two-Value Capacitor Motors
A two-value capacitor motor is a capacitor motor with different values of capacitance for starting and running. Very often, this type of motor is referred to as a capacitor-start, capacitor-run motor.
The change in the value of capacitance from starting to running conditions is automatic by means of a starting switch, which is the same as that used for the capacitor-start motors. Two capacitors are provided, a high value of capacitance for starting conditions and a lower value for running conditions. The starting capacitor is usually an electrolytic type, which provides high capacitance per unit volume. The running capacitor is usually a metallized polypropylene unit rated for continuous operation. Figure 1.15 shows one method of mounting both capacitors on the motor.
The schematic diagram for a two-value capacitor motor is shown in Fig. 1.16. As shown, at starting, both the starting and running
FIGURE 1.14 Speed-torque curve for a capacitor-start motor.
capacitors are connected in series with the auxiliary winding. When the starting switch opens, it disconnects the starting capacitor from the auxiliary winding circuit but leaves the running capacitor in series with the auxiliary winding connected to the power source. Thus, both the main and auxiliary windings are energized when the motor is running and contribute to the motor output. A typical
TABLE 1.6 Typical Performance of Capacitor-Start Motors3
|hp||Full-load performance||Torque, lb-ft|
a Four-pole, 230-V, single-phase motors. Source: Courtesy Magnetek, St. Louis, MO.
speed-torque curve for a two-valve capacitor motor is shown in Fig. 1.17.
For a given capacitor-start motor, the effect of adding a running capacitor in the auxiliary winding circuit is as follows:
Increased breakdown torque: 5-30% Increased lock-rotor torque: 5-10% Improved full-load eciency: 2-7 points
FIGURE 1.15 Two-value capacitor, single-phase motor. (Courtesy Magnetek, St. Louis, MO.)
FIGURE 1.16 Two-value capacitor, single-phase motor.
Improved full-load power factor: 10-20 points Reduced full-load running current Reduced magnetic noise Cooler running
The addition of a running capacitor to a single-phase motor with properly designed windings permits the running performance to approach the performance of a three-phase motor. The typical performance of integral-horsepower, two-value capacitor motors is shown in Table 1.7. Comparison of this performance with the performance shown in Table 1.6 for capacitor-start motors shows the improvement in both efficiency and the power factor.
The optimum performance that can be achieved in a two-value capacitor, single-phase motor is a function of the economic factors as well as the technical considerations in the design of the motor. To illustrate this, Table 1.8 shows the performance of a single-phase motor with the design optimized for various values of running capacitance. The base for the performance comparison is a capacitor-start, induction-run motor with no running capacitor. Table 1.9 shows that performance improves with increasing values
FIGURE 1.17 Speed-torque curve for a two-value capacitor motor.
of running capacitance and that the motor costs increase as the value of running capacitance is increased. The payback period in years was calculated on the basis of 4000 hr/yr of operation and an electric power cost of 6^/kWh. Note that the major improvement in motor performance is made in the initial change from a capacitor-start to a two-value capacitor motor with a relatively low value of running capacitance. This initial design change also shows the shortest payback period.
The determination of the optimum two-value capacitor motor for a specific application requires a comparison of the motor costs and the energy consumptions of all such available motors. It is
TABLE 1.7 Typical Performance of Two-Value Capacitor Motors3
a Four-pole, 230-V, single-phase motors. Source: Courtesy Magnetek, St. Louis, MO.
recommended that this comparison be made by a life-cycle cost method or the net present worth method (outlined in topic 7).
The efficiency improvement and energy savings of a specific product line of pool pump motors when the design was changed from capacitor-start motors to two-value capacitor motors are illustrated by Table 1.9 and Figs. 1.18 and 1.19. Based on the same operating criterion used above, i.e., 4000-hr/yr operation at power costs of 6^/kWh, the payback period for these motors was 8-20 months.
TABLE 1.8 Performance Comparison of Capacitor-Start and Two-Value Capacitor Motors
|Type of motor|
|Capacitor start||Two-value capacitor|
|Running capacitor, MFD||0||7.5||15||30||65|
|Input watts reduction, %||0||10.1||11,5||13,3||15|
|Approximate payback period||—||1.3||1.0||1.8||2.9|
a Leading power factor.
TABLE 1.9 Efficiency Comparison: Standard and Energy-Efficient 3600-rpm, Single-Phase Pool Motors
|hP||Standard efficient motors||Energy-efficient motors|
FIGURE 1.18 Efficiency comparison of energy-efficient and standard pool pump single-phase motors. (Courtesy Magnetek, St. Louis, MO.)
FIGURE 1.19 Annual savings for a 1-hp energy-efficient pool motor operating 365 days/yr. (Courtesy Magnetek, St. Louis, MO.)
Permanent Split Capacitor Motors
The permanent split capacitor motors, a single-phase induction motor, is defined as a capacitor motor with the same value of capacitance used for both starting and running operations. This type of motor is also referred to as a single-value capacitor motor. The application of this type of single-phase motor is normally limited to the direct drive of such loads as those of fans, blowers, or pumps that do not require normal or high starting torques. Consequently, the major application of the permanent split capacitor motor has been to direct-driven fans and blowers. These motors are not suitable for belt-driven applications and are generally limited to the lower horsepower ratings.
The schematic diagram for a permanent split capacitor motor is shown in Fig. 1.20. Note the absence of any starting switch. This type of motor is essentially the same as a two-value capacitor motor
FIGURE 1.20 Permanent split capacitor single-phase moto
operating on the running connection and will have approximately the same torque characteristics. Since only the running capacitor (which is of relative low value) is connected in series with the auxiliary winding on starting, the starting torque is greatly reduced. The starting torque is only 20-30% of full-load torque. A typical speed-torque curve for a permanent split capacitor motor is shown in Fig. 1.21. The running performance of this type of motor in terms of efficiency and power factor is the same as a two-value capacitor motor. However, because of its low starting torque, its successful application requires close coordination between the motor manufacturer and the manufacturer of the driven equipment.
A special version of the capacitor motor is used for multiple-speed fan drives. This type of capacitor motor usually has a tapped main winding and a high-resistance rotor. The high-resistance rotor is used to improve stable speed operation and to increase the starting torque. There are a number of versions and methods of winding motors. The most common design is the two-speed motor, which has three windings: the main, intermediate, and auxiliary windings. For 230-V power service, a common connection of the windings is called the T connection. Schematic diagrams for two-speed T-connected motors are shown in Figs. 1.22 and 1.23. For
FIGURE 1.21 Speed-torque curve for a permanent split capacitor motor.
high-speed operation, the intermediate winding is not connected in the circuit as shown in Fig. 1.23, and line voltage is applied to the main winding and to the auxiliary winding and capacitor in series. For low-speed operation, the intermediate winding is connected in series with the main winding and with the auxiliary circuit as shown in Fig. 1.23. This connection reduces the voltage applied across both the main wind ing and the auxiliary circuit, thus reducing the torque
FIGURE 1.22 Permanent split capacitor single-phase motor with a T-type connection and two-speed operation.
the motor will develop and hence the motor speed to match the load requirements. The amount of speed reduction is a function of the turns ratio between the main and intermediate windings and the speed-torque characteristics of the driven load. It should be recognized that, with this type of motor, the speed change is obtained by letting the motor speed slip down to the required low
FIGURE 1.23 Permanent split capacitor single-phase motor with a T-type connection and a winding arrangement.
speed; it is not a multispeed motor with more than one synchronous speed.
An example of the speed-torque curves for a tapped-winding capacitor motor is shown in Fig. 1.24. The load curve of a typical fan load is superimposed on the motor speed-torque curves to show the speed reduction obtained on the low-speed connection.
FIGURE 1.24 Speed-torque curves for a permanent split capacitor single-phase motor with a tapped winding.
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Single phase induction motors are traditionally used in residential applications such as ceiling fans, air conditioners, washing machines, and refrigerators. These motors consist of the split phase, shaded pole, and capacitor motors.
An AC (alternating current) motor is an electromechanical device that converts electrical energy into mechanical movement through the use of electromagnetism and the changing of the frequency and voltages produced by the utility company or motor controller.
AC motors are at the heart of the electrical consumption in the world because they do so much and with very little human intervention. The AC motor is by far the easiest and cheapest motor used in industry.
Fig.1: Motor Stator and Rotor
There are very few parts that make up an AC motor, so long as they stay within their operating characteristics they can run as long as 100 years with very little maintenance here and there. The main parts of the AC motor are the rotor and stator, as seen in figure 1.
A rotor is a rotating part of the AC motor that is supported by a set of bearings to allow flawless rotation housed inside the end bells. The bearings are pressed into the set of end bells which are filled with a lubricant to allow fluid motion.
The stator is the fixed or stationary part of the motor in which the end bells are attached and the windings are wrapped around the laminate sheets of iron that creates an electromagnetic rotating field when the coil is energized.
Motors are very versatile electromechanical components because they can be sized, configured, and constructed to fit any situation or perform any duty. A large percentage of the motors using industry are a single-phase and three-phase motors, as seen in figure 2.
Fig.2: Three Phase induction motor (Image Courtesy: Wikipedia)
Single Phase Induction Motors
A single phase induction motor is an electric motor that operates on a single waveform of alternating current. Single-phase induction motors are used in residential applications for AC motor appliances in single, or multiple dwellings. There are three types of single phase induction motors which are the shaded pole, split phased, and capacitor motors.
Shaded pole Motor
Shaded Pole motors, as seen in figure 3, are single-phase induction motors found operating small cooling fans inside refrigerators in computers. They belong to the family of induction squirrel cage motors that are used in limited applications that require less than 3/4 horsepower, usually ranging from 1/20 to 1/6 horsepower.
The heaviest load a shaded pole motor can turn component that is very light in weight and able to spin in low density, Usually when shaded pole motors go bad they are thrown in the recycle bin and a new one is purchased.
Fig.3: Shaded Pole Motor
Fig.4: Shaded Pole Motor Wiring Diagram
The stator poles are equipped with an additional winding in each corner called a shade winding as shown in fig.4. These windings have no electrical connection for starting but uses induced current to make a rotating magnetic field.
The pole structure of the shaded pole motor enables the development of a rotating magnetic field by delaying the buildup of magnetic flux. A copper conductor isolates the shaded portion of the pole forming a complete turn around it. In the shaded portion, magnetic flux increases but is delayed by the current induced in the copper shield. Magnetic flux in the unshaded portion increases with the winding current forming a rotating field.
Split Phase Motor
A split phase induction motor is a single phase induction motor that has two windings called the run winding and a secondary start winding and a centrifugal switch as shown in figure 6. Split phase motors usually operates at 1/20 HP TO 1/3 HP.
These squirrel cage motors are a step above the shaded pole motors, because they can to a little more work with a heavier load attached to the shaft of the rotor.
Fig.5: Split Phase Motor
Fig.6: Split Phase Motor Wiring Diagram
The split phase motor can be found in applications requiring 1/20 HP up to 1/3 HP, meaning it can turn anything from blades on a ceiling fan, washing machines tubs, blower motors for oil furnaces, and small pumps.
The centrifugal switch is a normally close control device that is wired into the start winding. The purpose of this configuration is that the motor start winding would be taken out the circuit once the motor reaches 75 to 80% of its rated speed. Even though it is considered to be a reliable motor this centrifugal switch is a moving part that sometimes fails to reengage when the motor stops spinning.
How Split Phase Motors Operate
- To start a split phase motor the start and the run windings has to be connected in parallel
- At 75% full speed the centrifugal switch opens, disconnecting the start winding.
- Since the start winding is disconnected from the circuit, the motor is operating through the run winding.
- To remove power from a split phase motor at 40% full load speed the centrifugal switch closes. Powering off the motor.
Single phase capacitor motors are the next step in the family of single phase induction motors. Capacitors motors contain the same start and run winding as a split phase motor does with the exception of the capacitor which gives a motor more torque on startup or when it is running. The purpose of the capacitor is to return voltage to the system when there is no voltage being produced and DAC sine wave of a single phase system.
In the AC single phase system there is only one voltage wave form and during one cycle of the sick 60 cps that it takes to produce voltage no voltage is produced at two points. It is the job of the capacitor to fill this void so the motor is always seeing a voltage which means a lot of torque is produced when the motor is running.
The three types of capacitor motors are capacitor start, capacitor run, and capacitor start and run motors.
Capacitor Start Induction Motor
Capacitor start induction run motors, as seen in figure 7, is a single phase induction motor with the capacitor is connected in series with the start winding and the centrifugal switch of the motor. This configuration gives the motor past starting power but the application does not require a lot of power doing the runtime. During the runtime the inertia of the load plays a big part in the motor operation when there is a problem with the motor it is usually due to a bad capacitor. The motor will generally not rotate unless an outside force spins the shaft; once it is started it will continue to operate fine until power is removed from the motor.
Capacitor start motors are generally found in AC units, large blower motors, and condenser fans. The capacitor of these motors are sometimes built onto the motor or located remotely away from the motor primarily making it easier to replace.
Fig.7: Capacitor Start Motor
Capacitor Motor Operation
- Has a start winding, run winding, and centrifugal switch that opens at 60 to 80% full load speed, as seen in figure 8.
- The start winding and the capacitor are no longer in use once the centrifugal switch opens, as seen in figure 9.
- The capacitor is only used for high torque starting.
Fig.8: Start Capacitor
Fig.9: Centrifugal Switch
Capacitor Run Induction Motor
Capacitor run induction motors, as seen in figures 10 and 11, are much like the capacitor start induction run with the exception of the start winding and run winding stay in the circuit at all times. This type of motor requires low starting torque but needs to keep a constant torque while running. This type of motor can sometimes be found in the air-conditioning compressor. The start winding is permanently connected to the capacitor in series.
Fig.10: Capacitor Run Motor
Fig.11: Capacitor Run Motor
Capacitor Run Operation
- Uses a lower rated capacitor because the capacitor is in the circuit at full load speed at all times.
- Used for higher running torque.
Capacitor Start-Capacitor Run Induction Motor
Capacitor start capacitor run induction motors are single phase induction motors that have a capacitor in the start winding and in the run winding as shown in figure 12 and 13 (wiring diagram). This type of motor is designed to provide strong starting torque and strong running for applications such as large water pumps.
Fig.12: Capacitor Start and Capacitor Run Motor
Fig.13: Capacitor Start-Capacitor Run Motor Wiring Diagram
Capacitor Start-Capacitor Run Motor Operation
- Consist of two capacitors
- One capacitor is connected in series with the start winding; the other capacitor is connected in series with the run winding.
- Both capacitors have different values.
- Capacitor start and run motor has the same starting torque and higher running torque because there is more capacitance.
- Larger value capacitor to start, and lesser value capacitor to run.
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Start capacitor run capacitor or permanent capacitor. Single phase motor wiring diagram with capacitor start.
Capacitor start motor because it uses a capacitor to start itself.
You can find out more Diagram below
Single phase motor capacitor connection. One often used method is the split phase motors. Weg motor capacitor wiring diagrams schematics and baldor diagram in. 5 hp electric motor single phase wiring diagram beautiful single.
Three phase motors with single phase frequency inverter should be used for frequent onoff switching. A direct current dc single phase motor starts turning automatically once electricity is connected but an alternating current ac single phase motor needs a capacitor to initiate rotation. How to wire single phase motor with capacitor.
Another method is the capacitor start induction run motors. Frequent stopstarts andor changing of the direction of rotation will damage the motors capacitors and winding. However we use mostly in our homes and for small work the one phase motor in this post you will learn about the single phase motor wiring with contactor motor starter.
Reconnect the termination on the terminal block. Centrifugal switch is connected with starting capacitor and this. Capacitor start induction run motors as seen in figure 7 is a single phase induction motor with the capacitor is connected in series with the start winding and the centrifugal switch of the motor.
This motor is called. You will find out how to identify to main and auxilliary winding and change motor rotation. Types of single phase induction motors electrical a2z single phase induction motors are traditionally used in residential applications such as ceiling fans air conditioners washing machines and refrigerators single phase motor wiring with contactor diagram the plete guide of single phase motor wiring with circuit breaker and contactor diagram.
The reconnection must be carried out by qualified electrician. This configuration gives the motor past starting power but the application does not require a lot of power doing the runtime. These designs operate by creating a rotating magnetic field.
Some single phase ac motor designs use motor run capacitors which are left connected to the auxiliary coil even after the start capacitor is disconnected by the centrifugal switch. The single phase induction motor can be made to be self starting in numerous ways. The single phase motor are those motor which is working one phase and neutral ground supply for doing his duty and a 3 phase motor required 3 phase power source.
Baldor single phase motor wiring diagram collections of weg motor capacitor wiring diagrams schematics and baldor diagram in. Baldor reliance industrial motor wiring diagram new wirh baldor. This is because ac current alternates about 60 times a second so without a capacitor the motor would simple vibrate rather than rotate.
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