Load Characteristics of INVERTER Fed Induction Motor

EET 3136

Electrical Drives

Experiment # 1

Load Characteristics OF INVERTER fed induction motor

Experiment # 2

Parameter Setting of an Industrial Variable
Speed Drives

Note: On-the-spot evaluation is carried out during or at the end of the experiment. Students are advised to read through this lab sheet before doing experiment. Your performance, teamwork effort, and learning attitude will count towards the marks.

Caution

This experiment deals with voltage supply of 400V,50Hz
Students will be provided with a technical manual of the system.

Experiment # 1

Load Characteristics OF INVERTER fed induction motor

Part A: (10.71.2) Setting Parameters to the Frequency Range

Part B: (10.71.4) Load Characteristic of Inverter Fed Induction Motor

Reference

ELWE – GB 51 10 062 49/99

Setting Parameters to the Frequency Range: 10.71.2

Objective

The frequency of the frequency inverter should be adjustable between 10 Hz and 70 Hz. The acceleration and deceleration should be as immediate as possible when the rotational frequency setting is changed. The other parameters should conform to the standard settings of the manufacturer. The settings required for this are to be on the frequency inverter and checked.

Requirement equipment

Experimental panel system

Unit description

1000 W

Frequency inverter control unit

10 10 076

Frequency inverter power unit

10 10 072

Connection cable LT/ST

15 10 015

Connection cable

55 00 307

Interface operator

15 10 013

Shaft-end cover

31 00 005

Three-phase squirrel-cage induction motor

30 27 600

Connection mask

31 25 601

Procedure

Connecting the motor

1.1For safety reasons, cover the motor shaft by attaching the safety guard.

1.2Connect the motor to the frequency inverter, incl. PE.

1.3How are the coils of the motor with a rated voltage 230/400 V to be connected to ensure that the motor can be operated at its rated values on the frequency inverter with one phase input to 230V mains?

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Commissioning the frequency inverter

2.1Make the basic settings described above. Connect the frequency inverter to the mains and move the mains switch to "“on"”

Describe the behavior of the motor on changing the set point value.

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2.2Describe briefly what basic settings are to be made on the frequency inverter before commissioning.

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Assigning parameters to the frequency inverter

3.1The settings which are required on the frequency inverter in order to be able complete the parameter assignment:

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3.2Enter the necessary steps in the table which will allow you to assign parameters to the frequency inverter in order to complete the task.

Settings / Display / Function
noP

-Connect control inputs for controller enabling (! Enabling direction of rotation, internal set point)

Check parameter assignment

4.1Describe the results of the check.

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4.2Disconnect the control inputs controller enabling, setting of the standard values specified by the manufacturer.

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Part B: (10.71.4) Load Characteristic of Inverter Fed Induction Motor

Objective

The dependence of the rotational frequency of a three-phase squirrel-cage induction monitor on the torque at various frequencies of the output voltage of the frequency inverter is to be examined.

Required equipment

Experimental panel system

Unit description

1000 W

Frequency inverter control unit

10 10 076

Frequency inverter power unit

10 10 072

Connection cable LT/ST

15 10 015

Connection cable

55 00 307

Interface operator

15 10 013

Pendulum machine

30 27 000

Brake control unit

67 10 611

Three-phase squirrel-cage induction motor

30 27 600

Connection mask

31 25 601

Coupling collar

31 00 000

Coupling cover

31 00 003

Shaft-end cover

31 00 005

Arrange the instruments according to the illusion.

Procedure

Putting into operation

1.1Connect the pendulum machine and the motor with help of the coupling collar.

Positioning the safety guards.

1.2Connect the brake control unit including the temperature sensor for the motor and make the following basic settings:

-Rotational frequency range 1500/ 3000 rpm

-Torque range

-Function off

1.3Switch on the brake control unit using the mains switch. Press the reset button. If the red LED is still alight now, there must be a fault in the set-up, e.g.

-the coupling safety guard is missing

-the safety guard for the shaft-end cover is missing

-the jack plug for the temperature control of the motor has not been inserted

-the motor is too hot

1.4Connect the motor according to its rated voltage to the frequency inverter with the frequency inverter being switched off, including PE.

1.5Switch on the frequency inverter and make the following basic settings:

-CP. 5Rated frequency50 Hz

-CP. 6Boost0%

-CP. 7Acceleration time0.1 seconds

-CP. 8Deceleration time0.1 seconds

-CP. 9Minimal frequency0 Hz

-CP. 10Maximal frequency100 Hz

-CP. 18Slip compensation offoff

-CP. 19Auto boostoff

-CP. 1Actual frequency display

Load capacity of the motor

2.1How does the power given off to the shaft of the motor increase with the rotational frequency whilst the load torque remains constant?

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2.2Why may a self-ventilated motor not be loaded with its rated torque permanently at low rotational frequency?

M = f ( n ) Characteristic curvesof a three-phase squirrel-cage induction motor with two pairs of poles

3.1Find the rotational frequency of the motor at the prescribed frequencies of the frequency inverter (parameters) dependent on the motor’s load. Connect controller enabling. (Release of direction of rotation F!, internal setpoint)

Set “man., nconst.” On the brake with “down” (“up”) the torque values. Enter your findings in the table.

At the end of the test series set to “off” mode and disconnect the controller release.

Boost: 0%

M

Nm
F
Hz / 0 / 0.5 / 1.0 / 1.5 / 2.0 / 2.5 / 3.0 / 3.5 / 4.0 / 4.5
10
20
30
40
50
60
70
80
90
100

Rotational frequency in rpm

3.2Repeat the series of measurements outlined in 3.1.

Boost: 25%

M

Nm
F
Hz / 0 / 0.5 / 1.0 / 1.5 / 2.0 / 2.5 / 3.0 / 3.5 / 4.0 / 4.5
10
20
30
40
50
60
70
80
90
100

Rotational frequency in rpm

3.3Draw the M = f ( n ) characteristic curves on the basis of your findings.

3.4Compare the change in slip with the motor under load in the armature range and in the field attenuation and field control range.

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3.5Compare the change in the breakdown torque in the armature range and in the field attenuation and field control range when the frequency is changed.

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3.6Why does to achievable torque of the monitor below the rated frequency without boost decrease at lower frequencies?

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3.7Why does achievable torque of the motor remains constant up to the rated frequency when a “boost” is set appropriately?

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3.8What causes the reduction of the achievable torque when the frequency is increased above the rated frequency?

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Experiment # 2

Parameter Setting of an Industrial Variable
Speed Drives

1.0THEORY

1.1Variable Speed Drives

Variable Speed Drive (VSD), in its simplest form, is a block, which can supply varying power at the terminals of a motor. When used with an AC induction motor, VSD operates based on the principle that the synchronous speed on the motor is given by

(1)

Where NS is the speed in revolutions per minute (rpm), f is the frequency in Hz and p the number of electrical poles of the motor. The VSD varies the frequency in (1) to vary the speed of the motor. A range of VSDs is available commercially for use in the industry and listed below are some of the applications, which may seem cumbersome without the use of VSDs.

Schneider Electric’s VSDs series, the ATV18 series, includes among other useful functions the 4 Preset Speeds function. This function makes use of two of the logic inputs (LI) of the ATV18 to easily select any of the four speeds combinations at which the motor may be operated. Figure 1 illustrates one of many 4 Preset Speed configurations.

Four Preset Speeds settings

LSP and HSP are low speed and high speed respectively, which are the two basic control speeds of the ATV18; SP3 and SP4 are the additional 3rd and 4th preset speeds.

1.2Conveyor Belt

Conveyor belts are used to move a continuous mass from one place to another within a compound. Conveyor belts are a necessity in many industries where use of human labor would result in degraded efficiency. The movement of the conveyor belt is driven by a motor, which in most cases allows a certain degree of control to add flexibility to the flow of the mass being transported. In mining industry conveyor belts are used to transport rocks from underground, in automobile industry parts are conveyed using belts and in food industry these belts are used to pass food through washers and driers.

1.3Ventilation

Ventilation is an air exchanging process that brings air into a building and exhausting contaminated air. Contaminated air can be hot air, cold air or even intoxicated air depending on the application. There are quite a few types of ventilation systems out there and each of these systems is composed of three main components, which are inlets, fans and controllers. The motors running as fans in these systems should, among other things, have the capability to run at different speeds and have optimum performance when operated at low speeds.

1.4Textile Machine

A textile machine transforms many single threads into a cloth. The threads, which may be of different colors and textures, are held on rods called spindles. The spinning motion of the spindles is driven by a motor, which can run at high speeds in both directions. The spindle would rotate at low speed with high load torque when it is full; and high speed with low load torque when it is almost empty. Synchronization of speed and tension between spindles is critical. Thread breakage may happen as a result of poor synchronization.

2.0APPARATUS

- ATV18-MMU

- 1.5kW Squirrel Cage Induction Motor

- Stroboscope

- Connecting Cables

3.0General Procedure

To carry out this experiment, a connection of ATV18-MMU to Power Supply and motor must be made. Please refer to the manual provided to make these connections.

1)Put all the logic input switches (SLIs) at OFF (0) position. This is necessary to prevent the motor from running unexpectedly.

2)Depress the start button(SW1) and hold for 3 seconds until the red light vanishes. If there is fault the red light will continue to glow and a fault message will be shown on the Display on the ATV18, please refer on the ATV18-MMU [page 15-16] on how to remedy the fault.

3)To RETURN all parameters to their Factory Preset Value. Go to FCS (second level parameter) and set to YES and follow by ENT. This will initialize all parameters as given in ALTIVAR 18 manual [Page 57-62]. Repeat Step 2.

4)Proceed with the experiment (Lab A-D)

Lab A: 4 PRESET SPEEDS

Note: To set the parameters, use down and up arrow, and press data button at respective parameters, use the down, and up arrow again to change the values/setting. Save the changes by pressing ENT.

Using the Keypad and Display terminal, go to LI3 and set it to PS2. Note: Since LI3 is a second level parameter, it may not appear in the menu; please refer to ATV18-MMU manual to see how to enable level 2 parameters.

Go to LI4 and set it to PS4

Go to the following parameters and set the values as stated:

ACC= 5

DEC= 13

LSP= 6

HSP= 60

SP3= 15

SP4= 30

Close SLI1, the logic input 1. (The motor will rotate at the set frequency in the forward direction). To monitor the frequency of rotation of the motor on the Display, go to rFr using the Keypad and press DATA.

Use logic input switches SLI3 and SLI4 to select different motor speeds and record their logic combinations in the table A1.

Table A1

SLI3
(1/0) / SLI4 (1/0) /

Assignment

on motor

Speed (Hz)

Measured Speed* (RPM)

Set the analog setpoint to 0 (the ref. potentiometer)
Using Stroboscope (Only for speed more than 10Hz)

LAB B: APPLICATION 1- CONVEYOR BELT

During this lab you will be introduced to most commonly used function parameters in conveyor belt system such as those that convey bottles in a factory.

In this experiment we shall look at

1) Application functions

Acceleration and decelerations ramp

Preset Speeds

2) Common problems

Resonant frequency

Fault Clearance by logic input

Procedures

Reset the VSD setting to factory presets by ENTering YES to FCS.

You will have to power up the VSD using the Start button after resetting the system to factory presets

Switch ON SLI1 and observe the rotation of the motor. You need to increase the ref (potentiometer if necessary)

Observe the acceleration (ACC) of the motor. It should accelerate in 3s since it’s a factory preset.

Start the motor again by setting SLI1 to 1 (ON), then observe the acceleration, after a while, set the L1 to 0 (OFF) then observe the deceleration. Your instructor will probably show you a simulation of what is happening.

In the bottling industry, bottles on the conveyor belt often have to temporarily stop to be filled up and then take off again. The acceleration and deceleration of the motor will determine how steady will be the bottles on the belt during those starts and stops. The factory presets are definitely not suitable for bottling application.

Increase both ACC and DEC to 6s and observe the difference from factory preset settings

Extremely high values of ACC and DEC lengthen the bottling cycle time

Bottles may have to run at different speeds in between the stops in order to optimize the bottling process. For ATV18, values set for ACC and DEC determine how well the four preset speeds are coordinated to smoothly run the process.

Factory preset setting assigns logic input LI3 and LI4 to control of preset speed. The value of these speeds of factory setting can be changed using parameters SP3 and SP4. In this case, set SP3 to 10Hz and SP4 to 35Hz.

With ACC and DEC still set at 6s, use logic switches SLI3 and SLI4 to select among the LSP, HSP, SP3 and SP4.

While observing the speed change, notice on the ATV18 display that the frequency gradually changes to the selected value and it does so with increments/decrements of 0.1 Hz. The changing frequency, while trying to reach the selected value, it may interfere with the resonant frequency of the surrounding system here degrading the conveyor’s operation. For some conveyor belt systems, the critical frequency is 43 Hz (arbitrarily chosen). Resonance frequency of conveyor system is usually determined by observing the conveyor runs at various speeds. The conveyor tends to vibrates and run noisier when it resonate.

Set JPF to 43Hz. Put both SLI3 and SLI4 at OFF positions while keeping SLI1 at ON position.

With frequency of operation displayed on the ATV18, use the analog ref to gradually vary the frequency from LSP to HSP.

Note: You can identify this frequency using parameter “ rFr ” during acceleration and deceleration.

Lab C: APPLICATION 2- VENTILATION

During this lab you will be introduced to most commonly used function in ventilation system

Application functions

Acceleration ramp

Low speed

Preset Speeds

Noise Reduction

Common problems

Catching a spinning load

Resonant Frequency

Procedures

Using the Keypad and Display terminal on the ATV18, find a second level parameter LI3 in the parameter list and set it to PS2. Assign OFF to both LI2 and LI4 parameters.

(Note: If the logic inputs-LI2, LI3 and LI4-parameters are not available in the list you may have to enable them, please refer to the manual provided).

Start the “Fan” (motor) using the logic inputs. (Recall the assignment of these logic inputs).

Write down what happen when each of logic inputs activated (logic 1).

SLI1 (LI1)………………………………………………………………………..

SLI3 (LI3)………………………………………………………………………..

In order to start the fan as quickly as possible, you can reduce the acceleration ramp. Depending to the fan inertia this may cause an erratic run up to speed. If this occurs the acceleration ramp is not followed. You can resolve this problem by extending the ramp time and modifying the gain FLG.

To simulate a high inertia fan, start the motor and let it run at 50Hz. Go to ‘LCr’ and monitor the current value while applying load to the shaft. Apply load till current value indicated is 4A. Now Stop the motor.

Set the ACC to 1s run the motor (arbitrarily count how many second it takes to reach max speed). Try to set ACC to 1s and set gain FLG to 20%. Observe the differences.

Fans are normally used for maintain good quality of the air. If the degree of pollution is low the fan runs at low speed LSP. Low speed is always relatively high to maintain efficiency.

Set the LSP to 25Hz and observe. Make sure the “ref” is set to 0.

When the degree of pollution increases (eg. Underground car park), the speed controller automatically changes the high speed HSP to enable removal of polluted air. This change the high speed is initiated by switching a logic input SLI3 (LI3) in this example.

Start the fan (SLI1). Motor runs at Low speed (LSP). Activate LI3 and Observe. Normally the LI3 will be controlled by a sensor e.g. CO2 sensor

Motor noise caused by switching frequency may be unacceptable particularly in area where comfort is a priority, for example in air-conditioning system or hospital. You have a possibility of reducing this noise level by selecting a high switching frequency using parameter SFr.

By default the switching frequency is SFr = 4kHz. Change the switching frequency from 4kHz to 8kHz and then to 12kHz..

(Note: SFr can be configured on the fly, i.e. it can be configured while the motor is running (SLI1 at logic 1)

During a short supply interruption, the fan changes the free wheel operation. When the supply comes back ON, the speed controller stops the fan to restart. This causes jolting, which may damage the machinery particularly when the inertia is high. To prevent this phenomenon you can select catching spinning load. When the supply is switch back ON the fan is restarted at the level of speed calculated by speed controller.

Using Keypad and Display terminal, set LSP and HSP to 0 and 50 Hz respectively
Start the motor in a forward direction by activating SLI1.
Increase the ‘ref’ input until the speed of the motor is at set maximum HSP.
While observing the rotational motion of the motor, depress STOP button followed by START allowing 2s between the state transitions
Using Keypad and Display terminal, find SPr parameter and set YES to it to activate the automatic spinning load catching function with speed search
Repeat step 7(d)

Lab D: APPLICATION 3- TEXTILE MACHINE