2. Mejores prácticas de medida para localizar averías en
motores y variadores de velocidad
• Gracias a estos ejercicios aprenderá a conectar y configurar
correctamente los instrumentos de medida y verificación para
mejorar sus habilidades en la localización de averías en variadores
de velocidad y motores
• Estos ejercicios le permitirán practicar medidas clave utilizando
un variador de velocidad y un motor en un entorno de laboratorio
controlado
Abril de 2011 2Ejercicios prácticos - motores y accionamientos Fluke
3. Índice
• Puntos de medida eléctrica de la unidad de demostración
– Perspectiva general rápida del sistema
de demostración
• Módulo B- Ejercicios prácticos de entrada
del accionamiento
– Simular la señal de control del accionamiento
• Simular señal de control de 4 – 20 mA
• Simular señal de control de 0 – 10 V
– Medidas en la entrada del variador de velocidad
utilizando el Fluke-435
• Medidas de tensión básicas
• Medida de armónicos
• Captura de corriente de arranque
• Potencia y energía
• Módulo C- Ejercicios prácticos del accionamiento
y de salida
– Medidas en el variador utilizando el ScopeMeter
Fluke 190-204
– Captura de la señal PWM en la salida del variador
• Nivel de salida de señal PWM
• Medida de tensión pico PWM
• Observación de detalles de la señal PWM
• Medida de corriente de salida del variador
• Medida de voltios por hercio de salida del
variador
• Voltios por hercio TrendPlot™ de salida
del variador
• Módulo D – Ejercicios prácticos del motor y el tren
• de transmisión
– Medidas en el variador utilizando un multímetro
digital y pinza
• Carga del motor
• Medidas de corriente - funcionamiento
monofásico del motor
– Pruebas de vibraciones del tren de transmisión
del motor
Abril de 2011 3Ejercicios prácticos - motores y accionamientos Fluke
4. Puntos de medida eléctrica de la unidad de demostración
Ejercicio práctico
• Fusible de entrada
[5 A, 250 V 1,25 pulg. (3 cm)]
• Entrada tensión CA línea (L1),
neutro (N) y tierra (GND)
• Bus de CC salida positivo
y negativo
• Entrada corriente CA
• VFD CA salida corriente/tensión
trifásica
• Entrada analógica
Abril de 2011 4Ejercicios prácticos - motores y accionamientos Fluke
5. Funcionalidad clave de la unidad
de demostración
Abril de 2011 5Ejercicios prácticos - motores y accionamientos Fluke
7. Simular una señal de control del variador
Ejercicio práctico
Demuestre cómo las herramientas de procesos de Fluke pueden
utilizarse para generar/simular una señal analógica en un variador
de velocidad para controlar la salida a un motor de CA trifásico
Determine rápidamente si el problema se encuentra en la señal
de control o en el propio variador
Herramientas de procesos que pueden generar/simular mA o Vcc
705, 707, 715, 719, 725, 726, 74x, 772, 773, 787, 789
Abril de 2011 7Ejercicios prácticos - motores y accionamientos Fluke
8. Simulación de la señal de control
del variador
• Configuración inicial
1. Conecte el interruptor “POWER” del kit de demostración,
tras unos segundos la pantalla del variador pasará de
forma predeterminada a una lectura de “0,0 Hz”
2. Para una entrada de 4-20 mA, pulse “Esc” hasta que
“d001” aparezca y la “d” parpadee mientras está en el
estado de programación activo
3. Pulse la tecla arriba/abajo hasta que aparezca la letra “P”
4. ” y se activará el dígito más a la derecha
5. Pulse las flechas arriba/abajo hasta que la pantalla indique
“P038”
6. ” y a continuación las flechas arriba/abajo introduciendo “3”
y “Enter”
7. Pulse “Esc” 3 veces y la luz verde encima de “Start” debe
encenderse
Abril de 2011 8Ejercicios prácticos - motores y accionamientos Fluke
9. Simular una señal de 4 - 20 mA
Ejercicio práctico
1. Conecte una fuente de 4-20 mA a las tomas
“ANALOG SIGNAL” debajo del VFD en el kit
(positivo – rojo, negativo – negro)
2. Pulse el botón “Start” en el VFD y genere
4-20 mA
– 4 mA = 0,0 Hz = 0 RPM,
– 12 mA = 30 Hz = ~900 RPM,
– 20 mA = 60 Hz = ~1800 RPM
3. Introduzca “0” en “P038” para que
el potenciómetro accione el motor
– Este es el ajuste predeterminado
necesario para el resto de los ejercicios
prácticos
Abril de 2011 9Ejercicios prácticos - motores y accionamientos Fluke
10. Simular una señal de 0 - 10V
Ejercicio práctico
1. Para entrada de 0-10 V CC cambie “P038” a “2”
2. Mueva el conductor rojo al terminal “13” en las
entradas analógicas verdes bajo la cubierta
superior del variador.
3. Conecte una fuente de 0 – 10 V a las tomas
“ANALOG SIGNAL” debajo del variador en el kit
(positivo – rojo, negativo – negro)
4. Pulse el botón “Start” en el variador y genere 0 –
10 V
– 0V = 0,0 Hz = 0 RPM,
– 5V = 30 Hz = ~900 RPM,
– 10 V = 60 Hz = ~1800 RPM)
5. Introduzca “0” en “P038” para que el potenciómetro
accione el motor
– Este es el ajuste predeterminado necesario
para el resto de los ejercicios prácticos
Abril de 2011 10Ejercicios prácticos - motores y accionamientos Fluke
11. Medidas en la entrada del variador
Ejercicio práctico
• Con unas cuantas conexiones simples, el Fluke-435 puede verificar
completamente el estado del suministro eléctrico al variador.
– Tensión y corriente de entrada
– Armónicos
– Corriente de arranque
– Potencia y energía
Abril de 2011 11Ejercicios prácticos - motores y accionamientos Fluke
12. Medidas en la entrada del variador utilizando el Fluke-435
• Configuración del instrumento
1. Asegúrese de que el sistema de
demostración esté apagado antes
de realizar las conexiones
2. Restablezca el 430 a los valores
predeterminados de fábrica
• Pulse la tecla de menú SETUP
• Pulse F4 SETUP USER PREF
• Pulse F1 para los valores
predeterminados de fábrica
• Confirme los menús emergentes
• Pulse F5 para confirmar la
configuración.
3. Conecte el 430 a la alimentación
de entrada del variador,
4. Utilice el canal A para la tensión y
la corriente (esta medida es sólo
monofásica).
5. Conecte el adaptador de alimentación
Conductores de
tensión, negro a
entrada de tensión A,
blanco a neutro
Pinza de
corriente
a entrada A
Conexión de
tierra verde
¡No olvide
el adaptador de
alimentación!
Abril de 2011 12Ejercicios prácticos - motores y accionamientos Fluke
13. Mediciones en la entrada del variador utilizando
el Fluke-435
• Configuración del instrumento
1. En la pinza de corriente i400s
seleccione en el interruptor en
el interior de la empuñadura
la posición del conmutador
para 10 mV/40 A,.
2. Esto garantizará una señal
con una resolución razonable
para fines de visualización.
3. La pinza debe colocarse
alrededor de la espira del
cable de entrada del variador
Abril de 2011 13Ejercicios prácticos - motores y accionamientos Fluke
14. Medidas de tensión básicas
Ejercicio práctico
• Encienda el instrumento. Cuando el instrumento
se enciende, debe aparecer esta pantalla con los
siguientes detalles:
– Configuración: 1Ø + neutro, 230 V, 50 Hz
– Pinza: debe ser 10mV/A
• Aplique alimentación al variador y pulse el
interruptor de encendido, ahora ponga en marcha
el variador.
• Pulse el botón SCOPE para mostrar la tensión y
la corriente:
• Seleccione Volts Amps Hertz en el MENU
principal para ver las lecturas digitales integrales:
– Observe los valores de CF (factor de cresta)
para tensión y corriente, un CF de la corriente
elevado indica una distorsión importante.
Abril de 2011 14Ejercicios prácticos - motores y accionamientos Fluke
15. Medida de armónicos
Ejercicio práctico
• Seleccione la pantalla de medida de
armónicos del MENU.
• Los gráficos de barras de los armónicos
de corriente muestran la envergadura de
la distorsión de la corriente.
• Ahora observe las lecturas digitales
integrales:
– Observe los valores de CF (factor de
cresta) para tensión y corriente, un CF
para la corriente elevado indica una
distorsión importante.
Abril de 2011 15Ejercicios prácticos - motores y accionamientos Fluke
16. Captura de la corriente de arranque
Ejercicio práctico
– Pulse MENU para acceder a INRUSH,
utilice la tecla DOWN del cursor,
seleccione INRUSH con ENTER.
– La tendencia de la corriente medida se
desplaza transversalmente por la pantalla
pero estos datos no se almacenan
permanentemente hasta que se activa el
disparo.
– Una vez activado el disparo, la tendencia
se desplaza transversalmente y
posteriormente se congela para permitir
la visualización y la medida.
Abril de 2011 16Ejercicios prácticos - motores y accionamientos Fluke
17. Potencia y energía
Ejercicio práctico
• La pantalla de potencia muestra la potencia
y las variables de energía más importantes,
– Para la demostración, los valores A y los
totales son los mismos
– Para los circuitos trifásicos, el total será
la suma de las fases A, B y C.
• La potencia se totaliza con el tiempo para
indicar la energía utilizada durante una
prueba.
• La medida normal de la energía es en kWh
• La tendencia de potencia puede ser útil
cuando el accionamiento se utiliza bajo
diferentes condiciones de carga.
Abril de 2011 17Ejercicios prácticos - motores y accionamientos Fluke
This module describes what measurements you can make when troubleshooting the input side of a motor drive along with when and why to use each measurement type.
!! Take care when connecting, these sockets have 120V on them!!.
The power input to the drive a 120V single phase. A three wire connection is made to the power input to phase A, neutral and ground – note: the motor chassis is not connected to the ground of the power input. During the demonstration the instrument should be powered by the power adapter to keep the battery charged. The voltage leads simple go into the input sockets near the power switch matching the meter input connections N to N Va to L1 and Gnd to Gnd,
On the i400s current clamp choose the 10mV/40A switch position, the switch on the inside of the handle. This will ensure a signal with reasonable resolution for display purposes. The clamp should go around the turns of wire, the arrow indicated on the inside of the current clamp should be pointing towards the location of the input (towards the back of the drive case).
Once the measuring leads and the current clamp are in place the power may be applied to the drive.
The instrument powered with the green button on the bottom left hand side of the instrument. On start-up the instrument shows how the instrument is currently configured in terms of the circuit type, voltage setting, frequency and the current clamp settings.
To get the correct readings the settings should be 1Ø + neutral, the voltage is 120V, 60Hz. If the settings are incorrect press the SETUP button, each settings field can be selected using the cursor key to move up and down and left to right as required. After the correct item is chosen confirm with the ENTER key. To get good current readings it’s important to select the correct probe. As previously we discussed how to set the current clamp correct we must now set the instrument. Scroll down to the Clamp table at the foot of the screen, when highlighted press ENTER in the column PHASE, select the Amp clamp setting, this should be 10mV/A (this means that 10mV output from the clamp will register 1A). There is no need to set the NEUTRAL current clamp as it’s not used in the demo. Once the setting is correct press OK (function key F5).
The drive can now be powered, plug the drive in, press the red power switch in the case. Now display current and voltage, on first pressing SCOPE the display will phase A voltage and neutral voltage, this automatically appears as the single phase circuit option has been selected. To view the voltage and current simultaneously press function key F1 until A is selected. Now both voltage and current appear as a waveform and have digital values on screen too, at this point the current will be very low as the inverter does not consume very much energy. The drive can now be started, plug the drive in, press the red power switch in the case, start the drive using the Start button on the inverter.
In most installation the frequency of the voltage at the input should be very stable, occasional large drives may exhibit frequency effects where the frequency drops when the high starting current of the drive affects the supply. Typically drive are designed to operate over a wide frequency range, 48Hz to 62Hz is not unusual; frequencies outside of this range are quite unusual.
Note the RMS voltage and peak voltage, these are different due to the way they are calculated, note the value CF (Crest Factor), for a pure sine wave this should be 1.414. It’s likely that the value displayed won’t be exactly 1.414, it will be slightly higher or lower, that depends on the voltage supply.
Taking a look at the current you will see typical distortion caused by a non-linear electronic loads. Note that the RMS current is around 6A and the peak current is ~23A and the crest factor is ~3.7, this indicates that the current is somewhat distorted. This is typical, as long as the voltage crest factor is not too high this should have little effect on the power system. We can dig further in to the details of the distortion using the harmonics measurement screens.
Select the harmonics measuring screen, press the MENU button and select harmonics using the cursor keys and ENTER. The opening screen shows the voltage harmonics bar graph, for an electronic load the predominant harmonic is 5th, for this drive the 5th harmonic voltage will be around 3% of the fundamental, for clarity the inter-harmonics function should be switched off by pressing F4 so the OFF text is highlighted. To get a clear view of the harmonics press the cursor UP or DOWN buttons so that the harmonics fill as much space as possible on screen. A key number on this screen is the voltage THD (Total Harmonic Distortion) shown at the top of the screen. This indicates the overall distortion, for reliable operation of equipment this should be less that 6%.
The absolute value of each harmonic can be indicated by using the LEFT and RIGHT cursor buttons, the associated bar values are displayed at the top of the screen.
Now take a look at the current harmonics, press function key F1 until the current bar graph appears. You will immediate notice that the current harmonics are much bigger. You will need to set the y-axis scale to 100% by pressing the UP cursor key. There are two possible current THD readings - %f where the reading is a %age of the fundamental or %r where the reading is a %age of the rms value. In the case of %f it is possible have THD readings that are greater than 100% due to the mathematics of calculation.
On this screen at the top right a value AK is displayed, this value K-factor when measured at the transformer, is a weighting of the harmonic load currents according to their effects on transformer heating, as
derived from ANSI/IEEE C57.110 standard. This value is useful for users who may be experiencing overheating transformer, it is an indication of what affect the load may have on a transformer. User can make decisions about the type of transformer that should be used for the measured load.
For a more detailed view of simultaneous of voltage and current a press of the F3 (METER) key and F1 (until V&A are highlighted), this provides the harmonics table.
One of the frequent problems experienced on drive and motor loads is the failure of circuit breakers during equipment start up. The usual reason for this is that the breaker is either the wrong size or has the wrong characteristics for the connected load. To discover what is happening during start up the INRUSH capability of the 430 can be used to find out exactly what’s happening. Press MENU to access INRUSH, use the cursor DOWN key, select INRUSH with ENTER.
Select a duration of 7.5 seconds, this drive is fairly small and starts relatively quickly, on some small direct on-line motors the starting cycle is even short, 7.5 seconds is the minimum setting for the 430 series. Larger motors typically have longer starting periods, ideally the starting period is optimized so that as few problems with high inrush current and voltage dips occur.
Select a Nominal Amps current of 1.0A using the LEFT / RIGHT cursor keys; set the threshold at 200% (2.0A) and leave the hysteresis at 2%.
These settings are suitable for this drive, other drives will require different settings.
The 7.5 second setting will show 7.5 seconds of activity on the display when INRUSH is captured.
The setting of the nominal current at 1.0A allows the drive to be powered without the motor running, the inverter takes some current, the chosen 1.0A nominal is about the current drawn by the inverter. The threshold setting is that value that will activate the INRUSH capture. The hysteresis setting is not applicable in this case; hysteresis is the setting of the range around the trigger for inrush, the trigger remains active if the measured value drop slightly below the trigger point.
To capture INRUSH press START, as long as the trigger setting is not exceeded a trend of the measured current will scroll across the instrument screen. Now press START on the drive, you will see the current increase, once trigger current is exceeded the trend will continue scrolling across the screen for 7.5 seconds and then stops. After capture the current profile for phase current and neutral is displayed, as neutral is not of interest here use the ZOOM function to show the phase current profile with higher resolution by pressing the DOWN cursor key. Now activate the measurement cursors by pressing F2 (CURSOR ON/OFF); one cursor stays in the same position all the time, this is the trigger cursor, a second cursor can be scrolled across the captured graph using the LEFT / RIGHT CURSOR keys. As the cursor is moved detailed measurement data appears at the top of the screen. On the example here the maximum inrush current is selected at the cursor, at that point the current was 10.2A, after the maximum is reached the current settles to a lower running value of 6.6A. The characteristic of the starting current of drives is typically defined by the software running in the drive, often this characteristic can be changed depending on the application of the drive.
This simple example of the key measurements is readily applicable across a many drives troubleshooting applications, by considering these simple principles it’s possible to quickly get to the root cause of drives issues. These simple tests can be used to confirm the correct performance of the drive and can be used as a benchmark for deploying multiple drives across an enterprise. These measurements take the guess work out of whether things will work OK once the drive is commissioned and if problems are occurring eliminates some of the possible causes of those problems.
One of the key reasons for installing drives over simple direct online motors is the potential to control the amount of energy used. The drive can easily be controlled so that it uses less power when needed, consider control of air handling units or air compressors. Motors in a drive system are more efficient as they operate at optimum voltage levels, the electronics in the drive take care of that. A motor connected directly to an electrical distribution system is affected by the changes on the electrical system that usually happen. Many utilities offer incentives to their customers to install drives systems in place of direct online motors, there’s a number of reasons for this, firstly, as the drives are more efficient the overall load to the customer can be reduced – the utility doesn’t need to install costly new infrastructure as the users power needs grow. The control offered with drives prevents voltage dips experienced with very large direct online motors which can affect other connected users.
From the users point of view the control of the drive can prevent peak demand charges. A well designed drive is optimized for power factor which can further reduce the cost of energy for the drive. In the simple example here we can view the single phase power used by the drive, the key measurements being power (kW), apparent power (kVA), reactive power (kVAR), power factor (PF) and displacement power factor (DPF).
In this example the power factor is quite poor at 0.47, this is typical for a low cost single phase drive, as the load is small it’s not as critical as on a large drive. The DPF provides an indication of the effects of harmonics on the measured power.
The power trend is really useful in seeing how power consumption is affected by different load situations, this graphing can quickly show the effect say opening a damper on an air handling unit or changes in viscosity of liquid being pumped.
As part of the overall justification of investing in these technologies typically before and after measurements are made, a typical method used would be to run the load through typical cycles and compare the results before the installation of the drive and after installing the drive.
