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37

Chapter 4

Motor Loads

Introduction

This section provides examples that you can use to troubleshoot induction
motors with and without an adjustable speed drive.

Figure 4. Distribution System: Motor Loads

Содержание 43B

Страница 1: ...Fluke 43B Power Quality Analyzer Applications Guide April 2001 2001 Fluke Corporation All rights reserved Printed in The Netherlands All product names are trademarks of their respective companies...

Страница 2: ...Testing Continuity 11 Measuring Resistance 12 Measuring Capacitance 13 Testing a Diode 14 2 Receptacle Branch Circuits 15 Troubleshooting Electrical Distribution Systems 15 Detecting Transients Phase...

Страница 3: ...asuring Voltage Harmonics 50 Adjustable Speed Drives 51 Checking Current on Phases 51 Measuring Fundamental of Motor Voltage 52 Measuring Frequency of Motor Current 53 5 Scope Mode 55 Introduction 55...

Страница 4: ......

Страница 5: ...he manuals Obey posted instructions Never assume that a circuit is de energized Check it first Always set up the measurement first then connect the test leads to the circuit Use only test leads and te...

Страница 6: ...to problems with receptacle loads and transformers Chapter 3 contains applications related to lighting systems Chapter 4 focusses completely on motors and motor drives Chapter 5 explains the scope fun...

Страница 7: ...How to use this Manual 3 SAGS SWELLS Pages 9 19 OHMS CONTINUITY CAPACITANCE Pages 11 12 13 14 TRANSIENTS Page 16 RECORD Page 26 INRUSH CURRENT Pages 34 44 SCOPE Page 55...

Страница 8: ...e 43B off and proceed as follows 1 Press and hold 2 Press and release The Fluke 43B turns on and you should hear a double beep indicating that the reset operation was successful Figure 1 Resetting the...

Страница 9: ...provides easy to do measurements which you can perform almost anywhere Begin with these examples to get started with the Fluke 43B Note It is a good idea to reset the Fluke 43B before you start a new...

Страница 10: ...connections as shown below The rms voltage should be close to the nominal voltage for example 120V or 230V The waveform should be smooth and sinusoidal The frequency should be close to 50 or 60 Hz Th...

Страница 11: ...d to a load in this example a hair dryer 1 Open the main menu 2 3 Make connections as shown below 4 Turn on the hair dryer When the hair dryer is turned on the current from the outlet increases Notice...

Страница 12: ...the influence of the load current on the voltage 1 Open the main menu 2 3 Make connections as shown below The rms voltage should stay within reasonable limits The current increases when the copier is...

Страница 13: ...rrent always use SAGS SWELLS Basically it does the same as the RECORD key but it can record faster fluctuations Use the RECORD key for all other combinations of readings you want to record Use the cop...

Страница 14: ...sag or swell In this example the high peak current from the copier caused the voltage to drop voltage sag In general if you find voltage sags the next step is to look for devices which may cause them...

Страница 15: ...r open connection 1 Open the main menu 2 3 Select continuity 4 Make connections as shown below When the Fluke 43B beeps and shows a beep icon the fuse is closed When the Fluke 43B shows OL Over Load t...

Страница 16: ...sistor 1 Open the main menu 2 3 Select ohm 4 Make connections as shown below Observe the resistance A typical reading on the display should be between about 150 and 500 If the reading seems too high t...

Страница 17: ...acitance of a capacitor 500 F 1 Open the main menu 2 3 Select capacitance 4 Make connections as shown below Observe the capacitance The display shows the measured value of the capacitor Compare the me...

Страница 18: ...ntact 1 Open the main menu 2 3 Select diode 4 Make connections as shown below Observe the voltage in forward direction A It should read about 0 5V Now turn the diode in reverse direction B and look at...

Страница 19: ...shoot electrical systems is to begin at the load and work towards the building s service entrance Measurements are taken along the way to isolate faulty components or loads This chapter describes typi...

Страница 20: ...ssary to monitor the system for a period of time to find them You may look for voltage transients impulses or spikes when for example computers are resetting spontaneously 1 Open the main menu 2 3 A t...

Страница 21: ...ceptacle Branch Circuits Detecting Transients Phase to Neutral 2 17 5 Make connections as shown below 6 The Fluke 43B starts capturing up to 40 transients 7 Press HOLD to stop capturing transients STA...

Страница 22: ...screen you want to analyze 9 Move the cursor to a transient Observe the measured maximum or minimum peak voltage If the peak voltage reading indicates OL Over Load repeat the measurement at a higher v...

Страница 23: ...ion system may cause lights to flicker Deviations of only a few cycles waveform periods may result in visible dimming The SAGS SWELLS function measures the rms voltage over each cycle and displays dev...

Страница 24: ...l the maximum voltage Observe the time when it occurred Determine where the sag or swell came from When the voltage decreases and the current does not change or only slightly the source of the problem...

Страница 25: ...by measuring the Total Harmonic Distortion on the voltage 1 Open the main menu 2 3 Select VOLTS 4 Make connections as shown below 5 Scale the harmonics spectrum screen to see more or less details Look...

Страница 26: ...Current Harmonics Non linear loads produce current harmonics which may cause voltage distortion 1 Open the main menu 2 3 Select AMPS 4 Make connections as shown below 5 Scale the harmonics spectrum sc...

Страница 27: ...ether the THD and individual harmonics comply with national standards like IEEE 519 It is incorrect to apply such standards to specific loads Zero sequence harmonics 3rd 9th 15th add in neutral conduc...

Страница 28: ...wn the value kVA1 The symbol of a Capacitor or an Inductor is shown to indicate capacitive or inductive loads 4 Repeat the measurement on phase 2 and phase 3 keep the black test lead connected to the...

Страница 29: ...tacle Branch Circuits Measuring the Load on a Transformer 2 25 transformer If this is impossible the transformer should be replaced by a unit with a higher kVA or K rating if harmonic currents are pre...

Страница 30: ...t if there are specific moments during the day that the transformer may become overloaded 1 Open the main menu 2 3 Open the RECORD menu Select the desired record time 4 5 Select the first reading to r...

Страница 31: ...ic shutdown during recording 8 The Fluke 43B starts recording the kVA reading Wait for 8 hours or press the HOLD key to stop the recording Look for high kVA readings during the day 9 Select CURSOR 10...

Страница 32: ...cations Manual 28 Note Note that the kVA of only 1 phase was recorded Record the other two phases before drawing conclusions Tip Press SAVE to save the screen in memory for later documenting and analy...

Страница 33: ...rents High harmonic orders influence the K factor more than low harmonic orders 1 Open the main menu 2 3 Select AMPS 4 Make connections as shown below Measure the K factor under full load Observe the...

Страница 34: ...r must replace the transformer by a transformer with a higher K rating or reduce the maximum load on the transformer When choosing a replacement transformer use the next trade size higher than the hig...

Страница 35: ...31 Chapter 3 Lighting Loads Introduction This chapter provides applications of problems and phenomena that are likely to occur in a lighting system Figure 3 Distribution System Lighting Loads...

Страница 36: ...2 3 Select AMPS 4 Make connections as shown below Turn all lights on Look at the harmonics spectrum and read the THD value If the current THD is less than 20 the harmonic distortion is probably accept...

Страница 37: ...1 Open the main menu 2 3 Make connections as shown below Look at the W reading It shows the real power consumption of the lights Look at DPF cos reading Low DPF means that corrective measures have to...

Страница 38: ...ents that may cause voltage sags in a weak lighting system A system is considered weak when it has a high impedance 1 Open the main menu 2 Set the expected maximum current during the inrush 3 4 Set th...

Страница 39: ...oads Measuring Surge Current 3 35 7 Make connections as shown below 8 9 Turn on the lights If nothing happens Press HOLD to stop Repeat the measurement at a lower value for MAXIMUM CURRENT in step 3 a...

Страница 40: ...rsor to the end of the inrush Read the peak current It indicates the maximum current during the moment the lights were turned on Tip Perform a sags and swells measurement see chapter 2 Monitoring rapi...

Страница 41: ...7 Chapter 4 Motor Loads Introduction This section provides examples that you can use to troubleshoot induction motors with and without an adjustable speed drive Figure 4 Distribution System Motor Load...

Страница 42: ...oltage imbalance causes high unbalanced currents in the stator windings resulting in overheating and reduced motor life 1 Open the main menu 2 3 Make connections as shown below Write down the voltage...

Страница 43: ...argest deviation ___ VDEVIATION V1 2 VAVERAGE ___ V c Finally calculate the voltage imbalance Voltage Imbalance ___ VDEVIATION x 100 _____ ___ VAVERAGE Voltage imbalance for three phase motors should...

Страница 44: ...gle phasing complete loss of power on one of the phases feeding the motor may cause overheating in the two other phase windings 1 Open the main menu 2 3 Make connections as shown below Run the motor a...

Страница 45: ...Example a 33 A1 29 A2 34 A3 96 ATOTAL 32 AAVERAGE 3 b 33 A1 32 AAVERAGE 1 A 29 A2 32 AAVERAGE 3 A Largest value 3 ADEVIATION 34 A3 32 AAVERAGE 2 A c 3 ADEVIATION x 100 9 4 32 AAVERAGE Note To detect s...

Страница 46: ...oximately the same voltage and current on all three phases and must be wired in a wye or delta configuration The balanced load makes it possible to calculate 3 phase power from one current and one vol...

Страница 47: ...ER to return to the main menu The voltage and current waveforms are displayed with a phase shift of 90 This is due to the fact that voltage and current are measured in different phases This phase shif...

Страница 48: ...of motors can cause breakers to trip or fuses to open 1 Open the main menu 2 Set the maximum expected current during the inrush This might be 6 to 14 times the full load current of the motor 3 4 Set...

Страница 49: ...Loads Induction Motors 4 45 7 Make connections as shown below 8 9 Turn the motor on If nothing happens Press HOLD to stop Repeat the measurement at a lower value for MAXIMUM CURRENT in steps 3 and 4...

Страница 50: ...r to the end of the inrush Read the peak currents at the cursors Can fuses and breakers withstand these currents Are conductors properly sized Read the time between the cursors Can fuses and breakers...

Страница 51: ...wer loss in the transmission lines Grounded Y Connection with Balanced Load For balanced motors with a grounded Y connection you can read the Power Factor directly from the screen To test for a ground...

Страница 52: ...ulate the Power Factor for a 3 phase grounded delta connected motor or for floating sources 1 Open the main menu 2 3 Make connections to phase 1 and 3 as shown below Run the motor under normal full lo...

Страница 53: ...r measurement results ___ kW1 ___ kW2 ___ kWTOTAL _____ 3 ___ kVA ___ kVA Example Measured kW1 170 kW kW2 68 kW kVA 188 kVA 170 kW 68 kW 238 kWTOTAL 0 73 1 73 188 kVA 325 6 kVA Poor power factor can b...

Страница 54: ...Total Harmonic Distortion of the voltage supplied to an induction motor should not exceed 5 Look at the harmonic spectrum Negative sequence harmonics 5th 11th 17th etc will cause most heating because...

Страница 55: ...alance see Checking Voltage Imbalance Then check the current on all three phases feeding the motor 1 Open the main menu 2 3 Make connections as shown below Run the motor at full load If no current is...

Страница 56: ...full speed and full load Read the voltage of the fundamental The voltage should be slightly less than the line voltage If the voltage is significantly lower than the line voltage it indicates an impro...

Страница 57: ...ke connections as shown below Vary the speed of the motor and look at the frequency and the waveshape of the current The frequency of the current should correlate with the speed of the motor 4 Repeat...

Страница 58: ...Fluke 43B Applications Manual 54...

Страница 59: ...available to display voltage waveforms while channel 2 can be used to display current waveforms via the clamp on AC current probe This chapter gives a step by step explanation of the most important sc...

Страница 60: ...minal line voltage for example 120V or 230V The waveform should be smooth sinusoidal and in the vertical middle of the screen Fluke 43B is in the Auto mode This function optimizes the position range t...

Страница 61: ...use Fluke 43B just has been reset The scope mode offers more readouts As an example selection of the frequency readout Hz is given Also the meaning of the other readouts are explained 1 Select SETUP 2...

Страница 62: ...dout of the duration of the negative going part of the input signal usually a square wave Duty Readout of the duration of the positive going part of the input signal usually a square wave as a percent...

Страница 63: ...o mode is then switched off the indication AUTO in the header of the SCOPE screen changes to 1 2 AUTO 1 Select RANGE 2 Press the left button to increase the number of periods 3 Press the right button...

Страница 64: ...ess the upper button to enlarge the waveform amplitude In this example the waveform amplitude is higher than the screen Rescale the amplitude within the screen area to view the whole waveform In the s...

Страница 65: ...evel Note that the Fluke 43B is capable of capturing signal details occurring prior to the trigger point This is a feature that is not offered in analog scopes The default is to display 2 divisions pr...

Страница 66: ...tomatically optimizes position range time base and triggering to a stable and well defined display of nearly every type of waveform Here is how to return the Fluke 43B to AUTO mode To select AUTO proc...

Страница 67: ...ak a voltage sag will be observed The dual channel mode can be used to observe current and voltage simultaneously The scope mode gives many possibilities to zoom in on signal details so that every pha...

Страница 68: ...ained how to adapt amplitude and vertical position of both waveforms so that they do not cover each other Use RANGE to adjust waveform amplitudes to 2 4 divisions each Use MOVE to position one wavefor...

Страница 69: ...current increases causing a well defined trigger condition 1 Press SETUP 2 3 BACK Input 2 is selected for triggering the trigger icon is on waveform 2 now Time base is still in NORMAL mode and the dis...

Страница 70: ...rent increases rapidly and voltage drops due to the load of the motor After the motor has started up current stabilizes to a lower steady state value and as a result the voltage rises If Fluke 43B doe...

Страница 71: ...by using FlukeView software is also explained Screens are saved in a format that allows for post processing This makes it possible to use a cursor on a recording that has been saved With the cursor po...

Страница 72: ...ve a screen while all memories are filled you will see a message telling that you first must delete one or more memories Viewing and Deleting screens 1 Open the main menu 2 3 Select a screen 4 Press V...

Страница 73: ...ndling Screens and Data Viewing and Deleting screens 6 69 8 Select a screen that has been saved in memory Press VIEW 9 Press RECALL to restore the data on screen as it was at the time that it was save...

Страница 74: ...er as shown in the picture below 2 Print the actual screen To print a saved screen view it first see previous section Viewing and Deleting Screens If the printer does not print refer to the Users Manu...

Страница 75: ...on getting started are given on the CD ROM package The FlukeView SETUP procedure installs a predefined report with the name QREPORT DOC 1 Connect the Fluke 43B to the PC see FlukeView Users Manual 2...

Страница 76: ...extended period of time For example recording current harmonics over 24 hours will give insight in load variations on your system 1 Setup the Fluke 43B for measuring current harmonics 2 Connect the F...

Страница 77: ...lukeView will display the actual reading and in the background all the readings are logged in memory 7 Click this button to stop recording 8 Click this button to save the recorded values in an ASCII f...

Страница 78: ...Fluke 43B Applications Manual 74...

Страница 79: ...ent power Displacement Power Factor is the cosine of the phase angle between the fundamental current and the fundamental voltage cos Inductive loads cause current to lag behind voltage while capacitiv...

Страница 80: ...un the motor faster than fundamental negative sequence harmonics try to run the motor slower than fundamental In both cases the motor looses torque an heats up Order F 2nd 3rd 4th 5th 6th 7th 8th 9th...

Страница 81: ...oltage Also the presence of harmonic currents decrease the Power Factor The power factor uses the total rms value thus including all harmonics for its calculation see also Displacement Power Factor PF...

Страница 82: ...age of the total RMS value THD R or as a percentage of the fundamental THD F It is a measure of the degree to which a waveform deviates from a purely sinusoidal form 0 indicates that there is no disto...

Страница 83: ...75 Displacement Power Factor Measuring 33 Documenting 71 Downstream 20 DPF Cos 75 Dropout 75 F Frequency Of Motor Current Measuring 53 Frequency Measuring 6 Fundamental Of Motor Voltage Measuring 52 F...

Страница 84: ...26 Sags and Swells 9 Report Creating 74 Resistance Measuring 12 S Safety Precautions 1 Sag 77 Sags Swells Recording 9 19 Saving Screens 68 Scope Reading 58 Screens Deleting 68 Printing 70 Saving 70 Us...

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