Troubleshooting…
Troubleshooting…
Variable Frequency Drives
Variable Frequency Drives
Before I get started with this rambling I wish to explain here that this technical article is definitely Before I get started with this rambling I wish to explain here that this technical article is definitely NOT intended for the Drive Techs out there among you. It is intended to educate that poor, confused NOT intended for the Drive Techs out there among you. It is intended to educate that poor, confused soul that might be timid when it comes to dealing with these high tech appliances…Just as I once soul that might be timid when it comes to dealing with these high tech appliances…Just as I once was. I hope that this helps you all.
was. I hope that this helps you all.
Is anyone sleepy? Then welcome to VFD's 101! I've always said that if anyone has a problem Is anyone sleepy? Then welcome to VFD's 101! I've always said that if anyone has a problem sleeping just tune in the History Channel. Well, here's another sure cure.
sleeping just tune in the History Channel. Well, here's another sure cure. Let's learn about VFD's!Let's learn about VFD's! In order to troubleshoot one of these things you kind of need to know for sure what one is. So let's In order to troubleshoot one of these things you kind of need to know for sure what one is. So let's see if I can suitably define a Variable Frequency Drive. First off they call these things several different see if I can suitably define a Variable Frequency Drive. First off they call these things several different names.
names.
1.
1. VFD…My personal favorite. That's short for Variable Frequency Drive.VFD…My personal favorite. That's short for Variable Frequency Drive. 2.
2. ASD…Tha ASD…That's Adjust's Adjustable Spetable Speed Driveed Drive. This is . This is a pretty ga pretty generic teeneric term. It covrm. It covers anyers anything from ththing from the olde old
Vari-Speed (belts, pulleys, and a crank) to DC Drives to our subject, the AC Drive. Vari-Speed (belts, pulleys, and a crank) to DC Drives to our subject, the AC Drive.
3.
3. AC Drive AC Drive…a VFD.…a VFD. 4.
4. AFD…Tha AFD…That's Adjustt's Adjustable Freable Frequency Dquency Drive.rive.
5.
5. InverterInverter…People cal…People call these VFDl these VFD's…Invert's…Inverters. The inveers. The inverter is just parter is just part of the convrt of the conversion. Whaersion. What's ant's an inverter anyhow? We'll discuss this later.
inverter anyhow? We'll discuss this later.
6.
6. YouYou SORRY SORRY @*#*%!!!…@*#*%!!!…That'sThat's what we're here for!what we're here for!
Definition of a Variable Frequency Drive:
Definition of a Variable Frequency Drive: Technically…it'sTechnically…it's a device that converts a single or a device that converts a single or three phase fixed voltage and frequency to a variable three phase voltage
three phase fixed voltage and frequency to a variable three phase voltage and frequency used toand frequency used to operate an induction motor at any speed that suits a multitude of processes.
operate an induction motor at any speed that suits a multitude of processes. Basically…it's just aBasically…it's just a converter. Converts AC to DC and DC back to three phase AC. Whew! All that to turn a shaft. How converter. Converts AC to DC and DC back to three phase AC. Whew! All that to turn a shaft. How does it do that?..
does it do that?..
This is how! This is how! All VFD's
All VFD's have a bhave a bridge recridge rectifier frontifier front end. Tt end. That's tech hat's tech talk for ttalk for the input. he input. You knowYou know…where y…where youou connect the electricity. The VFD converts the AC voltage to DC voltage…first thing. Different connect the electricity. The VFD converts the AC voltage to DC voltage…first thing. Different manufacturers do this differently.
manufacturers do this differently. What's a rectifier?
What's a rectifier? The dictionary says it'sThe dictionary says it's a device, such as a diode, that converts alternating a device, such as a diode, that converts alternating current to direct current.
current to direct current. A diode is A diode is simply a dsimply a device thaevice that will allot will allow currenw current flow in t flow in one direcone direction onlytion only. A. A bridge rectifier is a set of these diodes configured in a network in such a way as to provide full wave bridge rectifier is a set of these diodes configured in a network in such a way as to provide full wave rectification. See Figure 2 to see an example of one. "Full wave" just means that both the positive and rectification. See Figure 2 to see an example of one. "Full wave" just means that both the positive and the negative portion of the AC sine wave are utilized. It makes a much smoother DC as compared to the negative portion of the AC sine wave are utilized. It makes a much smoother DC as compared to half wave, which requires half the diodes.
half wave, which requires half the diodes.
In the old days this "bridge" was a whopping big set of heat sinks with diodes that you could In the old days this "bridge" was a whopping big set of heat sinks with diodes that you could replace if they failed. Today all of the manufacturers use "hybrid bridges". They contain the same replace if they failed. Today all of the manufacturers use "hybrid bridges". They contain the same components only in a much smaller package, which aids in miniaturization and are produced in components only in a much smaller package, which aids in miniaturization and are produced in packages that are easier to test and to install. If one of these fail you just replace the whole thing. packages that are easier to test and to install. If one of these fail you just replace the whole thing. FYI…The dictionary also says that a rectifier is "
FYI…The dictionary also says that a rectifier is " a worker who blends or dilutes whiskey or other a worker who blends or dilutes whiskey or other alcoholic beverages
Please note figure 1. Here you see the power structure for one of today's VFD's. What I am calling the power structure is the portion of the drive that conducts the power that turns the motor shaft. We're not worried about the wimpy little control stuff right now. Here you see the "bridge
rectifier" on the "front end" of the drive. When the AC power is applied the first thing that happens is a conversion from AC to DC. The one thing that is not indicated here is the DC bus. That's what the DC supply is called in a VFD. The Inverter section draws its power from the DC Bus. More about the Inverter section later.
Figure 2
Figure 1
Note that there are some capacitors in parallel with the DC bus, otherwise known as bus
capacitors. These are monster capacitors and act as a battery/filter sort of thing. A capacitor acts kinda like a boss, that is it resists any change. In this case the change that it resists is voltage. If when you were young, dumb, and insane have ever played around with electrolytic capacitors and charged one up with a line, and I absolutely do not recommend that you try this , you would have probably noted the violent pop (along with blackened finger-tips) when the cap was charged. The pop is caused by the very sudden current draw when the cap is charging. The same thing happens when a cap is discharged suddenly. The caps that are used in VFD's are large enough to trip circuit breakers and blow fuses when an attempt is made to charge them suddenly…So the caps must be "soft charged".
This is where different manufacturers do this differently. In figure 1's case the caps are charged through a "precharge" resistor. You will note that there is a contact supplied by the main or
"precharge" contactor. This contact will close, removing the circuit through the resistor, when the DC bus voltage is near the fully charged state allowing the DC current to flow through the contacts as the drive is operating. The precharge resistor is sized to charge the caps for a very short duration. If the contacts fail to close, and the drive is allowed to operate, the resistor won't in very short order. Makes a really good heater for a little while.
Other manufacturers will use a hybrid bridge rectifier that utilizes SCRs otherwise known as silicon controlled rectifiers or thyristors to charge the caps. These are electronically controlled devices very similar to diodes except that they can be turned on anywhere in the positive half of the AC cycle. They turn off when the voltage reaches zero. So…the voltage required to charge the caps can be ramped up electronically with these SCRs. This can provide some other benefits, such as controlling the DC bus voltage level.
The next thing to note in figure 1 is the DC bus fuse. This manufacturer chooses to use this. Most others that I know of don't. This fuse will not keep this drive from failing! That's not what its function is. Its function is kinda like a suicide mission. It fails in order to keep the other output and control components in the VFD alive . Never change the fuse and apply the power before checking the output transistors! If you ever see that the DC bus fuse is open there is a 99% chance (no such
2 Figure 1
thing as perfect) that there is a failed output transistor and perhaps some associated electronics. The good news is that there are some good parts left because of the fuse's ultimate sacrifice.
The inverter section of the power structure of the VFD contains the output transistors. The definition of invert is 1. To turn inside out or upside down. 2. To reverse the position, order, or condition of. That's all that happens here. Looking at figure 1 again you will note that there is a
transistor above each of the output lines to the motor and one below each one. There are three sets in order to make three phases. Every positive half cycle the positive transistor conducts and every negative half cycle the negative transistor conducts. Then it all happens again, and again, and so on and so on…its just that simple! The not-so-simple part is how the transistors know when to conduct.
Figure 3
Figure 4
Figure 5
For a really simple look at what I tried to explain look at it like in figure 3. Actually, transistors are just on/off switches. If you and two buddies had a setup like this, and were real quick and coordinated, you guys could make a motor shaft turn!
In steps 1 and 2 switches A+ and B- are closed. The voltage from A to B is positive. In step 3 B- is opened and B+ is closed along with A+ making A to B zero volts. Then in steps 4 and
5 A+ is open and A- is closed sending a negative voltage to the motor. And so on and so on…until your buddies or your fingers get tired of switching those switches or the motor has completed its process.
Now…lets talk about PWM. Pulse Width Modulation is a term used to explain the process that controls the current that the drive produces and the motor uses to perform its process. This is the not-so-simple part.
In figure 5 the drawing shows the transistors in the inverter section of the drive where the switches were in figure 3. These transistors are used in most of today's drives and are called IGBTs or Insulated Gate Bipolar Transistors. Figure 4 is an example of one. This particular example is a hybrid module that contains two transistors. In fact the two transistors are the two required to make up one of the three phases in the inverter section of the drive. There would be three of these modules required to produce the three phases. Note A, B, and C in figure 5.
These IGBTs are capable of being switched on and off at up to and beyond 15,000 times a second or 15 kHz. Much faster than you and
A B C
+
your buddies! This is called the Carrier Frequency.
Let me explain this IGBT stuff. By the way…IGBT can be pronounced igbit. If you have ever been close to a motor that is being operated by a PWM drive I’m sure that you have noticed the tone, buzz, or whatever you want to call it. What causes this to happen? When the transistor is turned on the voltage isn’t ramped up like the Power Company’s power is. It just turns on. BANG…the full voltage of the DC bus is applied to the motor windings. Then just as quickly the transistor is turned off. Well it’s kinda like hitting a flagpole with a baseball bat. You hear a ring. A few years ago most PWM drives were operated at a carrier frequency of 3.5 kHz and lower, well within our audible hearing range. And it can be pretty noisy. But back then that was about all that our old transistor technology would allow. Then, as I said before, the IGBT came along and these transistors could be switched at a much higher frequency. At 15 kHz the tone is barely perceptible, unless you’re a dog or some other critter. The advantage…allows quiet operation for fans and pumps in areas where people work or play. Those high pitched whines can be pretty distracting. The disadvantages are that the high carrier frequency causes the drive and motor to run considerably hotter. It makes since…going from being hit 3,500 times to 15,000 times a second would tend to heat stuff up. Another
disadvantage is the turn to turn insulation in the motor is further stressed by both the higher temperatures involved and the abrupt voltage changes.
Lets talk about motors that are used on VFDs. Will a VFD operate an existing three phase motor even if it isn’t inverter duty? Yup...sure will! Any three phase motor can be operated with a VFD. Could I experience problems with this motor if I run it with a VFD? Yup…sure could! I always warn the customer that he could damage the motor windings with the added stresses that are caused by VFDs. Well then…should I replace my motor with an inverter duty motor? I said that you could damage the motor windings, not that you would. If that motor is performing a non-essential function, in the case of many HVAC applications, my opinion is that if there is a budgetary problem with
replacement of the motor go ahead and run it with the VFD. Personally I have experienced very few problems retrofitting existing motors with VFDs. But I didn’t say that I haven’t experienced any
problems. What I have noticed throughout my experience with AC drives is that the smaller pre-inverter duty motors, up to 10 hp, tend to throw in the towel more quickly than the larger motors. I have experienced good results recommending the application of a reactor on the output of the drive to help reduce the effect of the abrupt voltage changes on these little motors.
Figure 6
4
NOW lets discuss the PWM output that makes these drives so useful. Look at figure 6. At the beginning of the sine wave the transistor is turned on and off very quickly. The next pulse will be a little longer as will the next pulse after that and so on and so on until the transistor is on almost continuously. This is the high portion of the wave where the current is at its highest. What goes up must then come down. The voltage pulses begin to get shorter until it is time for the negative transistor to do its thing. It does the same thing only negative. We then have a complete sine wave.
Now lets look at figure7. How does the drive increase and decrease the voltage and the
frequency? Notice that the DC bus voltage is fixed at around 650 VDC. This voltage is representative
Figure7
the frequency range. When the current drops the drive knows where the speed is and resumes operation and brings the motor back up to speed. If the appliance that the motor is powering shakes at certain frequencies you can program the drive to skip those frequencies. And many other things.
About now you are probably asking yourself “I thought this was a trouble shooting guide. When’s he gonna get to that?” Well not yet. Now we gotta talk a little about what tells these VFDs what to do.
A few years ago these drives were pretty darned complicated. They had input boards, output boards, the control board, the power supply board, the input logic board, output relay board, the analog input board, the analog output board, the base drive board, the firing board…puleeeeze gimme a break. Trouble shooting these things isn’t quite as bad as it looks. The inputs on these things operate with a DC control voltage of some value…mostly 24 VDC. Just check from the signal common terminal to any of the input terminals for that voltage. Same thing for the analog input and
of a 460 volt three phase input. A picture is worth a thousand words. The top waveform represents a lower voltage and frequency and the lower one a higher level. The voltage is modulated in order to provide a variable voltage and frequency.
The low voltage and frequency is accomplished by switching the transistors on for short periods of time while the higher volts/hertz (frequency) levels the transistors are switched on for longer periods of time.
Let’s define Volts/hertz ratio: The voltage and frequency level at which a motor can maintain full torque at any given speed. Figure 8 is a graph representing the volts/hertz curve. The line angling up from 0 and intersecting at 460 volts and 60 hertz is the curve that I am indicating. Not much of a curve…looks pretty straight, huh. Actually it’s pretty much the way that drives are set up out of the box except for a little voltage boost at the lowest hertz level. This drawing is just an example of where the volts/hertz level is at any speed along the curve. This is what the VFD is all about.
You can do so many things VFDs. If you operate one of the positive transistors you can cause the rotor of the motor to lock down…DC injection braking. Comes in pretty handy when you need to stop a wind-milling fan or pump before you start it. You can raise the voltage some when you start the motor…torque boost. You can increase the
frequency above the 60 cycles if you need to speed up a process. Take care doing this as you my sling something apart on the rotor. You can perform a speed search when the power fails and the motor is coasting down. The drive applies a small amount of voltage to the motor throughout
60 hertz Full Speed 30 Hertz 1/2 Speed 230 Volts 460 Volts 0
output boards. If the voltage wasn’t there you would check the interface cables (the wiring from board to board). If it’s none of those things change the power supply board and maybe you were fixed. As far as all those other boards…better have some spare boards or other drives just like them so you can start swapping boards out.
The drives have gotten a lot smarter today. Most of them include the power supply board as a part of the base driver board (provides the signals to the IGBTs). The digital and analog inputs, outputs, and relay outputs are found on the control board. They still have option boards but they simply plug into the control board and use the same power supply that the control board uses. Much better way to do things. The proliferation of surface mounting technology in the circuit board manufacturing industry has really helped us here. Where would we be without the Space Program?
sees a 0 signal. What you and I see is 24 VDC, which the drive supplies, across the switch. When the switch is closed the drive then sees a 1 signal. We see a 0 VDC signal. Gosh…I guess that means that the switch is closed. The drive runs forward. The same digital thing goes for all those other switches. The difference is that all of these terminals except for S1 and SC are programmable for several different functions that require an on/off (digital) signal. S1, in this case, is always going to be a run command. There will be contacts assigned for a run command and a signal common with all drives.
The digital output signals are provided by relays mounted on and interfaced to the control board. Some manufactures choose to use transistor outputs that can be used to operate interposing relays. These outputs can be programmed to operate when you need a specific indication of something. It can indicate that the drive is running, at speed, a fault, you know…stuff like that. There can be one or more of these relay outputs depending on the brand and model of the drive.
6 Set Point
Proportional Control Time Output
Offset
The analog inputs are the inputs that tell the drive how fast to run and how to react to a changing process. A lot of today’s drives can perform process control from within their programming. The analog signals require a
control signal of some sort with 0 -10 VDC or 4 – 20 mA being typical. Also there are almost
always two analog inputs. One for actual speed control or reference (how fast do you want me to go?) and the other one for feedback (how fast am I going?). The processor in the drive compares the two inputs
Now that I have attempted an
explanation of all the scary stuff lets look at some of the signals it takes to run the VFD. First thing worth
mentioning is the digital signal. A complicated way to say an on/off signal. They further complicate this by assigning numbers to the signals. Off is a 0 and on is a 1. Lets look at
figure 6. Here we see a typical control terminal arrangement. If you apply a switch across terminals SC and S1 there is now a means to give the drive a forward command. When the switch is open the drive
Figure 9 Analog Inputs L1 L2 L3 T1 T2 T3 S1 S2 S3 S4 S5 S6 SC Forward Multi-function Input Terminals Power Supply Motor MA MB MC
Multi-function output terminal 250Vac/30VDC 1A
M1 M2
Multi-function output terminal 250Vac/30Vdc 1A AM AC Multi-function Output0-10VDC 2mA maximum Signal Common FS +15VDC FV 0-10V (20Kohms) FC Freq. Ref. Common FI Freq. Ref. 4-20 mA (250 ohms) 0-10 V available P O T Digital Inputs Digital Output Analog Output Figure 10
Figure 11
Figure 12
to is the drive looks at the offset (see fig 10… the difference between the real and desired condition ) over a period of time and then calculating a correction. It helps to stabilize the process so that the offset is as low as possible.
Fig 12 we see that the signal settles down more quickly with some derivative tweaked in. About the only time that you would want to mess with this setting is if there is a severe stability problem.
Derivative anticipates the error and puts some braking action in the signal. About all that I can really tell you about setting up an application that requires PID is that every application is different.
Sometimes there's a lot of adjusting going on and then sometimes you don't even have to touch anything.
Finally…Trouble Shooting Tips
Tips number one…If you’re not on the Internet…get there! Those of you that have not seen the light yet cannot begin to realize the information available to you on the web. Almost all of today’s drives are programmable. And everybody does it different! In order to program them you will need to have an operator’s manual. Most manufacturers have these readily available on their web site… FREE ! A lot of them will charge you if they have to ship the hard copy. I have taken the liberty of listing some of the manufacturer web sites that I know of, or can find, where you can get this
information. I can’t guarantee that these sites will be there when you look because they do change web sites from time to time:
www.drives.com/products ...Yaskawa www.baldor.com/support/literature_manuals.asp …Baldor http://www4.ad.siemens.de/csinfo/livelink.exe? func=cslib.csinfo&siteid=cs&lang=en&objid=4000957&aktprim=0&objaction=csopen ...Siemens www.ab.com/manuals/dr/index2.html#1336 ...Allen-Bradley www.abb.com/global/seapr/seapr035.nsf/viewunid/b9f108fb0c8b4410c12568fd0047d5d3! OpenDocument&v=63136&e=us …ABB
Proportional Integral Control Set point Time Output PID Control Set point Time Output
and simply speeds up or slows down the drive to keep the process running where the reference tells it to. This is PID control.
The definition of PID: Proportional, Integral, Derivative refers to the automatic means used to adjust a device that controls a process.
Figures 10, 11, and 12 walk us through each of the steps involved.
Fig 10 shows strictly proportional control. A control signal based on the difference between a real condition (feedback) and the desired
condition (setpoint) is produced. The difference is the “error”. The VFD speeds up or slows down to compensate for the error. Only problem is that different processes do different stuff and react differently to the correction.
Fig 11 shows us what takes place with proportional control along with a little integral tweaked in. It’s a math thing. What it amounts
www.reliance.com/docs_onl/online_stdrv.htm#manual …Reliance www.namc.danfoss.com/techlit/index.html …Danfoss & Graham
www.meau.com/eprise/main/Web_Site_Pages/Public/P-Home ...Mitsubishi
www.hitachi.com/products/industrial/acvarless500/index.html …Hitachi www.ch.cutler-hammer.com/NASApp/cs/ContentServer?pagename=C-H/DocumentSupport/DSMainPage …Cutler Hammer
www.squared.com/us/products/atv18.nsf/DocumentsByCategory?OpenView&count=999 …Square D www.geindustrial.com/cwc/library?famid=13 …General Electric
www.actechdrives.com/Library.htm …AC Technologies
Also…Siemens has a terrific training web site. I'm sure there are others out there. http://www.sea.siemens.com/training/step2000/courses/index.asp
Tips number two…Inside most of these operators’ manuals you will likely find some trouble
shooting flow charts. It starts out with something like “Motor won’t run”. In other words…the flow chart will take you though a comprehensive series of steps until the problem is solved, or not. I have
supplied as generic a flowchart as I can provide to help you trouble shoot AC drives. However it is better to use the manufacturers chart if it is available to you. Some of your customers even keep these manuals!
Tips number three…Fault Codes: Most of these drives will tell you what is wrong with them! Some with a simple LED blinking out different codes, to three letter codes like “uU1”, and then there are those that can even spell it out for you in plain English (or most any other language) with from one to multiple line alphanumeric displays. Some of these drives will store anywhere from the present and the previous fault to an indeterminate number of faults. Some even time and date stamp them! This can help if you have one of those “if it ain’t broke, I can’t fix it” otherwise known as “intermittent” type failures. By checking the previous fault codes you may be able to determine the problem. Chances are that you will need the operator’s manual to decipher these fault codes because, even with the elaborate alphanumeric displays, the fault can be stated in some wording that you have never heard of. So…review Tip # 1.
Tips number four …If all else fails call the manufacturer. Most drive manufacturers have a customer service phone number that you can access technical assistance from. Speaking from experience…don’t spend a whole lot of time trying to fix these things. The manufacturer pays these folks to help you and your customer fix their drives. What may take you hours or days to figure out may take one of these highly trained people a few minutes to determine with a little clear and
common sense communication from you. I hope that this article can provide you with a little of that. Tips number five…In order to keep from messing up some of the volts, amps, and ohm readings I use an analog Volt/Ohm meter (that's one with a needle for all you young folks out there). Especially when checking the output voltage. A digital meter will show the voltage really high. I know that there are digital meters out there that will indicate correctly but with all that auto scaling and stuff it can mess a guy up.
Speaking of manufacturers I want to thank Yaskawa and Siemens for the use of some of their
resources. They supplied some of the pictures and graphics. The manufacturers continue to educate us in order that we may serve their and our customers better…Sincere Thanks. The words are all mine…Don't blame them for that!
Motor will not Rotate
Check Wiring. Check control volts. Replace power supply YesAC voltage present at input terminals? Fault Code Indicated? Is run Indicated? Is stop indicated? Is run commanded? Is control voltage present at control terminals? Remove stop command. Initiate run command. Check power switch. Check operator manual for definition and correct the fault.
Is reference signal present at analog input? No No No No Yes Yes Yes No Yes Yes
Turn up the speed pot or set speed with keypad.
Check external wiring and repair.
No
No
NEXT PAGE!
Always exercise extreme caution when troubleshootingelectronic
equipment with doors open and guards removed! Voltages up to 800
VDC are present at any given time! Always follow manufacturer's
recommended safety procedures as outlined in the Operator's
Manual!
10
Is the proper voltage present at
output terminals? From Page 1
Check interface cable connections internal to drive.
2. Faulty drive.
Check interface cable connections internal to drive. 2. Faulty drive. Is voltage present at motor terminals? Check wiring to motor. Is the voltage balanced at the motor terminals? No No No Yes Yes Yes
Motor has run out of smoke.
NOTE: The main cause of over voltage trips on AC drives is inertia. Inertia is the force that resists acceleration when the motor starts Only in this case were decelerating that same force...same thing only different. The amount of inertia depends on the weight of the rotating elements. What happens is that inertia overpowers the motor when the drive decelerates the motor causing it to become an
induction generator. This in turn causes the DC bus voltage to increase to a damaging level. Typically modern drives are designed to trip at about 800 VDC (460 volt system, 400 VDC for 230 volts). This happens often on high inertia loads such as large fans and other heavy rotating loads. Even small amounts of inertia can give problems if decelerated too quickly. If the process allows, the problem can be solved by simply extending the decel time. If the process must be stopped quickly, dynamic
braking can be utilized. Dynamic breaking utilizes an internal or external braking transistor module and resistors to regulate the DC bus voltage at a safe level. When the DC bus voltage aproaches the trip level, the braking transistor module conducts redirecting the excess voltage to the resistors. In the case of really BIG inertia loads such as elevator and hoist applications there are regenerative drives available from most manufactures. A regenerative drive is capable of returning the excess energy back into the power supply lines.
Overvoltage Fault
Indication…
Does the drive trip during deceleration?
Increase decel time if process allows. Still trips from OV. Install proper dynamic braking equipment. Nuisance trips due to electrical noise.
Install snubber circuits to all coils of every contactor and every relay close by…also may need to add line
filter on drive input.
Bad control or base driver PC board. YES NO YES YES NO
*NOTE: When testing IGBTs be sure to check the gate (or base) terminal to the collector and emitter. The reading should be infinite on RX1 scale. If there is any resistance replace the base driver board. A very low DC voltage is required to fire the transistor. If the base shorts to the gate, the full DC bus
voltage is applied to the fragile gate control section of the base driver board removing all of the smoke therein. 12
Overcurrent
Fault Indication
Is output current at 200% or more?Increase accel time. Utilize current limiting function if available. Reduce load.
Load jammed.
Does over current trip occur instantly? *Check power transistors. Replace transistors if feasible.
Nuisance trips due to electrical noise?
Bad control or base driver PC board.
Install snubber circuits to all coils of every contactor and every relay close by…
also may need to add line filter on drive input. Check motor for shorted condition. Yes Must Be! Yes Yes Checks Ok Yes Yes No Replace motor. Yes
Undervoltage
Fault Indication
Check input voltage.
Is DC bus voltage within
acceptable range?
Check wiring and connections to the drive. Undervoltage trip when motor begins to run? Check for DC bus voltage drop.
Nuisance trips due to electrical noise?
Install snubber circuits to all coils of every contactor and every relay close by…
also may need to add line filter on drive input.
Bad control or base driver PC board. Yes No Ok Low Check power structure connections
internal to the drive.
Yes Yes
Yes
14
No Display.
Voltage present at AC input terminals? Apply Power. DC bus voltage present?1. Check for open precharge resistor if applicable. 2. Precharge circuit inoperable. Is control voltage present at digital control terminals? Is control voltage present at analog control terminals? Is control voltage present at analog control terminals?
Power supply or control board bad.
Check interface cables internal to drive. Yes No No No No Yes Yes No Yes OK Replace power supply board.
L1 L2 L3
+
-NORMAL ABNORMAL+
ON-
ON READING READING L1 L2 L3 _ _ _ L1 L2 L3 + + + + + + L1 L2 L3 _ _ _ L1 L2 L3 READS LIKE A DIODE -5-10 OHMS RX1 READS LIKE A DIODE -5-10 OHMS RX1 INFINITE INFINITE + _ CAP TEST - RX1 CHARGE THEN BLEED DOWN INFINITE OR SHORTED*NOTE: When testing IGBTs be sure to check the gate (or base) terminal to the collector and emitter. The reading should be infinite on RX1 scale. If there is any resistance replace the base driver board. A very low DC voltage is required to fire the transistor. If the base shorts to the gate the full DC bus
voltage is applied to the fragile gate control section of the base driver board removing the smoke therein. 16 C1A C1B C1C E1A C2A E1B C2B E1C C2C
E2A E2B E2C
G1A G1B G1C G2A G2B G2C
