Interview Questions.

Question 1. What Is Sensorless Vector Control?

Answer :

Sensorless vector control is a technique used in variable frequency drives to rotate the pressure vector within the motor with out the usage of a shaft role sensor. The goal of AC sensorless vector generation is to provide the user "DC-like" manage at the same time as making traditional speed or shaft role remarks from the motor pointless. Sensorless vector manipulate eliminates a main source of complexity and ability for failure, inclusive of tachometer feedback, while simplifying many AC force installations. The sensorless vector algorithm need to be tuned to suit the characteristics of the specific motor being managed via the drive. This improves torque overall performance at very low speeds compared to usual volts in keeping with hertz control.

Question 2. Does A Motor Need A Chassis Ground Connection?

Answer :

Yes, for several motives. Chassis grounding is used for protection inside the occasion of a short inside the motor that places a live voltage on its housing. Motors and different additives show off leakage currents that boom with getting old and a grounded chassis commonly emits much less electrical noise than an ungrounded one.

Digital Electronics Interview Questions
Question three. What Type Of Motor Is Compatible With Inverters?

Answer :

Inverter motor type should be a three segment AC induction motor. Preferably, you need to use an inverter-grade motor that has 800V insulation for 200V magnificence inverters, or 1600V insulation for 400V class inverters. For motor size, in practice it is tons better to locate the proper size motor to your software; then look for an inverter to healthy the motor.

Question 4. How Will I Know If My Application Will Require Resistive (dynamic) Braking?

Answer :

For new applications it is able to be tough to inform earlier than you without a doubt test a motor/drive answer. In fashionable, a few applications can rely on device losses including friction to serve as the decelerating force, or in any other case can tolerate a long decel time. These programs will no longer want dynamic braking. However, applications with a combination of a high-inertia load and a required brief decel time will want dynamic braking. 

Power Electronics Tutorial
Question 5. What Is Ringing And What Happens To The Motor When I Place It More Than 50 Feet Away From The Drive Without A Line Reactor?

Answer :

High voltage ringing (reflective voltage) happens on all VFDs. With IGBTs changing SCRs on smaller, greater less expensive drives, ringing has turn out to be extra reported. This capacitive-coupling impact is resulting from excessive speed switching (commutation). Distance significantly complements the effect. Cables at the output side of the pressure act like capacitors. When the IGBTs switch or produce the PWM output, the better frequency a part of the modern will find a path via that capacitance. Think of the cable as a capacitor that will increase in size as the cable period will increase. Ringing could be very unfavorable to cars; it weakens the primary degree rotor windings and shortens the existence expectancy of a motor. This is particularly genuine for automobiles underneath 10 hp.

Typically they're system wound, have thinner coats of varnish, and feature neither section nor give up paper (i.E., mixture insulation homes). That’s why we constantly advocate a power rated motor. Vintage and non-drive rated motors which are used with VFDs have a lifespan of unknown length. You truly can't recognize what to expect from them. Long cable runs with ringing can add 10 to 15% to the power’s modern-day rating, inflicting the force to trip out on immoderate cutting-edge. The capacitance may also reason a voltage drop that can motive velocity overall performance troubles at the lower give up of the rate scale (accelerated cutting-edge demand for demanded torque). A few trendy pointers: 

Try to reduce distances as a lot as feasible
Use an output line reactor on cabled distances extra than 50 toes
Always use a force-rated motor.
Programmable Logic Controller (PLC) Interview Questions
Question 6. Is There A Standard For Inverter Rated Motors?

Answer :

NEMA MG-1, Section IV, Parts 30 and 31. Part 30 pertains to fixed supply motors; part 31 pertains to inverter supply motors. Always speak to your motor manufacturer for additional information. Note: the worldwide preferred is IEC 60034-17.

Question 7. What Drive Power Cable Do You Recommend And Why?

Answer :

Belden 29500 – 29507 cables are in particular designed to be used with VFDs. Using the incorrect cable can boom the destructive outcomes from ringing because of capacitive coupling. Thermoplastic insulation, discovered in popular THHN cable, will smash down through the years if used to connect inverters to cars. The status waves resulting from pulse width modulation (PWM) will reason excessive voltage capacity on unmarried conductors. This renders corona (reflective/ringing voltage) in the air gaps among the conductors, that could break down and reason a device failure.

Electrical Engineering Interview Questions
Question 8. Can A Drive Replace A Softstart?

Answer :

Yes. Softstarts are used for decreased torque starting and preventing of general three-phase induction vehicles (consisting of centrifugal pumps, compressors, ball mills, jar mills, fans, blowers and saws). If the motor isn't always competently covered from surprising adjustments in rotational torque associated with beginning and preventing, the modern-day can be immoderate to the machine and the motor will surge, inflicting harm to all of the device linked to it. Over the long term, this ends in extended over-contemporary tripping and extended mechanical wear of gearboxes, clutches, transmission and conveyor structures. ANSI/IEEE Std. 141-1993 (Red Book) gives a comparison of various decreased voltage beginning strategies. An electronic softstart of VFD, despite the fact that not indexed, might have similar characteristics to the autotransformer starter.

Question nine. Can I Run My Drive At Extremely Low Speeds?

Answer :

Three major issues exist with each conventional techniques of motor control and VFD manipulate: 

When a motor is at once coupled and run at a low speed, it turns into very inefficient. You ought to go along with a high torque motor that is significantly larger than the usual and could have the equal consequences maximum of the time. 
Typical motors do no longer cool themselves properly at extraordinarily low speeds. The added warmth buildup inside the windings can motive premature motor failure. Check with the motor producer for greater information. 
The third issue is load inertia, which is greater than that of the motor. 
The results of all of these things growth greatly with a sloppy transmission machine. A pace reducer or gearbox ought to be hired to remedy this trouble. It will match the inertial modifications and increase performance. Speak with a technical useful resource about sizing the gearbox to meet your utility desires.

Power Electronics Interview Questions
Question 10. Are Variable Frequency Drives Phase Sensitive?

Answer :

The input wiring isn't touchy to segment. If you have been to trade one set of enter leads, the rotation could now not change. The opposite is genuine for the output of the power. It is sensitive to section, so converting one set of leads to the motor modifications the direction of rotation.

Question eleven. What Is A Line Reactor And What Will It Do For My Application?

Answer :

A line reactor is a special form of inductor used on the road aspect or the motor side of a power utility relying at the particular circumstances. They are used on the road aspect of the force to smooth inrush cutting-edge, lessen noise, and to act as a buffer and shield the force system. The line reactors have a 3% voltage drop based totally on impedance. This drop can be beneficial for drives on structures exceeding the rated input voltage of the drive. In this regard, the line reactor has been used to update the lots larger power isolation transformer. Line reactors are used at the motor side of the drive to protect the motor by means of smoothing the drive output waveforms and by decreasing ringing and capacitive coupling, especially with lengthy cable runs between the pressure and the motor.

DCS(allotted manage system) Interview Questions
Question 12. What Is Grounding And What Reference Material Is Available?

Answer :

Equipment or conductor-enclosure floor refers to connecting the non-modern-day-wearing steel elements of the wiring device or system to floor. This is done so the steel parts which someone may come into touch with are at or near ground capacity.

Digital Electronics Interview Questions
Question 13. What Are Some Of The Common Reasons Why Motors Fail?

Answer :

The EPRI Power Industry Study by General Electric in 1985 offered the following causes based on 6,000 application motor failures: forty one% have been bearing related, 37% had been stator related, 10% have been rotor related and 12% have been different causes. 

Question 14. My Pump Is Losing Speed; Does The Drive Have A Problem?

Answer :

Pumps are divided into three basic classes – centrifugal, rotary, and reciprocating. Take any of the 3 sorts and ruin them down further into four elements: the rotating detail, the casing, the motor, and the power. The rotating detail has a shaft, sleeves, bearings and an impeller. The casing has a pump shell, put on earrings, and shaft seals. The motor and force are intuitive. Here is a fundamental remediation list: 

the belts are slipping (if relevant)
the impeller is worn
the impeller is free at the shaft or the shaft is sheared
the casing is worn
the unique motor become replaced with a slower version or with a extra amount of motor slip
the requirements have modified beyond the design specs of the device. 
Using a guide tachometer, confirm if there may be a velocity hassle. If all of the above were investigated and a hassle nevertheless exists, then you could want to growth the maximum frequency of the pressure. Note that whatever beyond 60 Hz will bring about a shift from a steady torque to a variable torque situation. There is a low opportunity that the pressure will detrimentally have an effect on the intrinsic velocity of the machine.

Question 15. Is There A Reference For Application Help?

Answer :

NEMA standards guide “Application Guide For Adjustable Speed Drive Systems.”

DC motor Interview Questions
Question sixteen. What Is The Difference Between Torque Control And Torque Limiting?

Answer :

Torque manipulate may be accomplished with any of AutomationDirect's PID-capable drives. This might be a closed loop system the use of torque as the system variable. There have to be both a torque reference and torque remarks sign. The consumer would set up a torque setpoint and configure the pressure to maintain that setpoint. Many clients have used torque sensors, load cells, and contemporary transducers to set up an analog input to the force. Ideally, a vector drive could work higher than a volts/hertz power.

A vector power lets in tighter pace regulation and better manipulate within the decrease pace range. Torque restricting may be achieved with AutomationDirect's Hitachi SJ300 series drive. Instead of the use of an outside torque sensor, torque restricting uses the pressure's inner current sensor. The operator would set the torque restriction, and while that stage is exceeded, the power would act like a governor on a generator. The velocity could be limited till the best stage is again maintained. Mechanical devices, in addition to drives, are also employed for torque proscribing, which includes clutches, shear pins, gearboxes, and so forth.

Question 17. What Makes Joliet Technologies Different, Compared To Other Variable Speed Drive Integrators?

Answer :

As you can inform from our internet site, we're dedicated to providing as lots information as feasible concerning the goods and services we provide. We have done our high-quality to offer you the information approximately the drives we use in our systems, so you can make clean and knowledgeable choices on your precise application.

From the instant you touch us (and you could touch us in a multitude of methods, by way of cellphone, fax, email, RFQ shape or Ask a Pro shape) you may realise that our income staff and engineers have the know-how and sources to offer the force machine answers you need. We will paintings one on one with you to ensure all your questions are anwsered and all software problems are addressed. Our goal is to present you the satisfactory merchandise & offerings on the best price, it’s that easy.

Induction Motors Interview Questions
Question 18. What’s The Difference Between A Non-regenerative Dc Drive And A Regenerative Dc Drive?

Answer :

The distinction among those  types of DC drives is defined on this page, DC Drive Types.

Programmable Logic Controller (PLC) Interview Questions
Question 19. What’s The Difference Between A Variable Frequency Drive (vfd) And A Variable Speed Drive (vsd)?

Answer :

A variable frequency power (VFD) refers to AC drives most effective and a variable speed pressure (VSD) refers to both AC Drives or DC Drives.

VFD’s range the speed of an AC motor by way of various the frequency to the motor. VSD’s regarding DC cars vary the rate through varying the voltage to the motor.

Question 20. What Is The Difference Between A Vsd And A Soft Start Starter?

Answer :

The difference is the velocity that the motor can run, whilst at full velocity. With a gentle start starter, the motor is reduced voltage commenced, after which while the motor is at complete velocity, or a timing circuit has timed out, a “jogging by way of-bypass contactor” pulls in and the motor keeps to run at complete base speed. With a VSD (Variable Speed Drive) or VFD (Variable Frequency Drive) (these are the same aspect, simply one of a kind names for the identical unit), The motor will tender start, and you may vary the rate of the motor, via various the output frequency from the VSD or VFD.

So, in case you don’t need to vary the speed of the motor, once the motor is up to the mark, then the appropriate solution is a soft start starter for that motor. If the process calls for the motor pace to vary at anytime, the correct solution is a VSD / VFD.

The price for a gentle start starter is a whole lot much less than a VSD or VFD.

Scada Interview Questions
Question 21. Can A Variable Frequency Drive Replace A Softstart?

Answer :

Yes, a variable frequency power can replace a gentle begin starter, considering maximum drives come up with a contemporary limiting ramp to begin and forestall your motor. BUT, if you do no longer want to vary the manufacturing pace of your motor, then the gentle begin starter continues to be the ideal product for the application. This is due to the fact the value of the smooth start starter is much less than the fee of a variable frequency pressure.

Question 22. Are The Variable Frequency Drives Phase Sensitive?

Answer :

No, variable frequency drives are not segment touchy. You can adjust the direction of rotation of the motor, thru the software program of the force.

Question 23. Can A Variable Frequency Drive Be Used For A Fan Application, Blower Application Or A Pump Application?

Answer :

This is one of the satisfactory applications for an AC force. In maximum fan/pump packages, there may be a need to vary the output of the fan/pump. This may be very smooth to achieve with an AC force. Plus you get the benefit of reduced power fee of going for walks the motor!!!

Suitability of VFD for pumps: VFD’s are properly perfect to pumping packages. Many are manufactured to encompass motor pace/torque profiles particularly meant to optimize pump performance. However, there are a few troubles which should be considered before selecting using VFD’s:

Suitability of the motors – the motors need to be rated for inverter-obligation to withstand the higher electric stresses drives can impose. Some older cars had been no longer constructed to withstand those stresses and can fail prematurely.
Distance of automobiles from VFD’s – the VFD’s will result in voltage transients at the load connectors. If these connectors are too lengthy (manufacturers regularly recommend preserving motor lead duration to 50m or less), the voltage on the motor terminals can also increase to several factors above nominal, which also can cause premature motor failure.
VFD installation region and environmental situations – this could decide the form of enclosure and conditions underneath which the VFD’s will perform. VFD’s which must face up to excessive moisture, temperature swings, or dust can fail in advance and should be included through definitely rated enclosures.
Plc Scada Interview Questions
Question 24. How Can A Variable Speed Drive Improve Our Production?

Answer :

The pressure can be “tuned” to the software to reap most output of the device. Sometimes that is slightly under the bottom velocity of the motor, and every now and then, it's far over the bottom pace of the motor. 

Electrical Engineering Interview Questions
Question 25. What Is The Percentage Of Operating Cost Reduction After Installing A Vfd?

Answer :

This is a totally open-ended one which relies upon on many factors – load, incoming supply voltage, software expenses, and numerous others. A precise region to begin customizing the inquiry to your use would be at ABB’s web website online; they've gear for tough calculations for electricity financial savings using VFD’s.

Question 26. Can I Run A 230v, 3ph Motor With 230v, 1ph Input?

Answer :

Yes. Joliet Technologies is thrilled to announce that we've got the solution to run maximum 230V, 3Ph motors with most effective 230V, 1Ph input! Call for extra information.

Standard Template Library (STL) Interview Questions
Question 27. What Is The Best Drive For My Application?

Answer :

This isn't always an clean question to reply. Before we can come up with a complete solution to this question we can need to understand more about your application and specifications. Simply name (815) 725-9696, toll loose (866) 492-9888, fax (815) 725-9393 or email us with your utility and specifications and we can suggest the pressure that’s proper for you.

Power Electronics Interview Questions
Question 28. Can I Convert My Dc Drive Application To An Ac Drive?

Answer :

Yes, You can convert your DC force gadget; to an AC force device through changing each the motor and the power. Consideration need to take delivery of for the torque and velocity variety of the DC motor, whilst changing to AC. You will need to consider using a “Vector” AC drive for this conversion.

Question 29. Will A Variable Frequency Drive Or Variable Speed Drive Save Me Money?

Answer :

Yes, the AC force can save you money on running fee, while the load and motor speed may be various. By reducing the rate of the motor, you'll devour much less strength, with a view to lessen your electric bill.

Industrial Automation Engineer Interview Questions
Question 30. What Is The Cost Of A Vfd?

Answer :

Cost varies broadly based totally on manufacturer, voltage, ampacity, enclosure type, torque necessities, quantity of analog and digital inputs/outputs, and communications alternatives.

Question 31. Should I Replace My Old Analog Equipment With New Digital Equipment?

Answer :

DEFINITELY!!! For so many reasons. . . Hard and high-priced to get spare components, Hard to find Tech. Support / serviceability, no communications, little flexibility, etc.

Question 32. Will Joliet Technologies Train Our Staff To Operate And Maintain Our Equipment?

Answer :

We can expand a schooling application that is tailored in your corporations’ needs and area. So, while it makes experience, we will educate your personnel in our facility, or deliver the classroom on your factory, for hands on training.

Question 33. What Filters Are Used For The Vfd?

Answer :

Line-side filters are now and again set up to reduce EMI, despite the fact that current PWM drives are a good deal much less in all likelihood to generate vast noise.

On the load facet, output chokes may be hooked up to reduce power generated harmonics within the motor leads. Many drives have a few output filtration already set up and harmonics are generally not a trouble so long as wiring is effectively segregated, well grounded, and the motor leads are not excessively lengthy (normally much less than one hundred meters).

DCS(distributed control device) Interview Questions
Question 34. What Is The Best Drive Manufacturer For My Application?

Answer :

Our sales engineers are knowledgeable of what products are available from well-known manufacturers. They will propose the best power for you primarily based for your software and specifications. There perhaps numerous merchandise to be able to meet your specs.

Question 35. What Are The Maintenance Requirements Of A Vfd?

Answer :

Under everyday working conditions, VFD’s generally require little upkeep as soon as properly set up. Spare parts may be received comfortably, and some are replaceable by upkeep employees. In other cases, qualified service technicians are required.

Question 36. Is It Possible To Use The Same Soft Starter To Start Two Mv Induction Motors?

Answer :

Yes, it's miles feasible to start multiple automobiles from a unmarried tender-start. Typically, the motors are began sequentially and are identically rated. In an average MV software, extra contactor shelves are connected and manipulate-tied to the tender-start. Once the primary motor comes up to the mark, the smooth-start “Switches” to manipulate the subsequent motor in the series.

In the case of simplest two automobiles, some tender-begins are manufactured with dual settings to allow beginning of cars that have one of a kind starting characteristics, but actual motor output for the duration of ramp-up may not range a lot, being limited via the inherent performance characteristics of the gentle-begin.

Multiple simultaneous beginning of vehicles calls for that the cars be equal and that the soft-begin be sized for the full load and supplied with supplemental cooling.

DC motor Interview Questions
Question 37. What Is Exactly The Difference Between Ac And Dc Capacitor In Functionality And Manufacturing? Why A Dc Capacitor Is Required To Connect Across The Alternator Terminals?

Answer :

In essence, a “capacitor is a capacitor”, despite the fact that there are variations in layout based on topology, kind, and substances of manufacture. Sometimes capacitors will convey a twin rating, for AC and DC – the AC score for a capacitor of the equal capacitance is usually plenty decrease than its DC score (regularly at least three-4x much less considering the fact that AC max voltage height-to-peak is ~2.8x rms), to accommodate the sizeable heating inner to the cap resulting from frequency/alternating polarity. Some producers manufacture AC caps which might be essentially  DC caps in collection back-to-lower back; those limit contemporary float through both cap however their internal resistance is quite excessive, that may result in eventual destroy down due to heating as nicely.

Use of a DC cap throughout alternator terminals is regularly achieved to clear out alternator whine (noise) resulting from voltage ripple, the “AC” factor of rectified DC output. When the capacitance is well established and coupled to the frequency of the noise, it gives a low-impedance path to “divert” the voltage ripple to floor.

Question 38. What Is The Problem If I Use A 15hp Vfd For A 1hp Induction Motor Speed Control? I Set Data Of The 1hp Motor In The 15hp Vfd, Is There Any Problem Using It?

Answer :

The problem with a drastically over-sized drive is controllability, mainly at decrease speeds. Accuracy will suffer, because the drive thyristor firing angle could be so low that it is going to be hard for the drive software to manipulate. And in case you are concerned about motor safety you'll have very little due to the fact the everyday operating tiers of the motor protection parameters (overload, over-modern, and so forth.) in a 15hp drive are targeted on 15hp motor parameters; they may be ranges, of direction, however you’ll be way out on the low stop of these stages and response will go through.