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AQ: 1:1 ratio transformer

A 1:1 ratio transformer is primarily used to isolate the primary from the secondary. In small scale electronics it isolates the noise / interference collected from the primary from being transmitted to the secondary. In critical care facilities it can be used as an isolation transformer to isolate the primary grounding of the supply from the critical grounding system of the load (secondary). In large scale applications it is used as a 3-phase delta / delta transformer equipment to isolate the grounding of the source system (primary) from the ungrounded system of the load (secondary).

In a delta – delta system, the equipment grounding is achieved by installing grounding electrodes of grounding resistance not more 25 ohms (maximum or less) as required by the National electrical code. From the grounding electrodes, grounding conductors are distributed with the feeder circuit raceways and branch circuit raceways up to the equipment where the equipment enclosures and non-current carrying parts are grounded (bonded). This scheme is predominant on installations where most of the loads are motors like industrial plants, or on shipboard installations where the systems are mostly delta-delta (ungrounded). In ships, the hull becomes the grounding electrode. Electrical installations like these have ground fault monitoring sensors to determine if there are accidental line to ground connections to the grounding system.

AQ: Sensorless control

I am curious about the definition of “sensorless control”.  When you talk about sensorless control, are you in fact meaning a lack of physical position sensor such as e.g. a magnet plus vane plus hall effect? i.e. not having a unit whose sole objective is position detection.
Is the sensorless control based around alternative methods of measurement or detection to predict position using components that have to exist for the machine to function (such as measuring or detecting voltages or currents in the windings)?

I had long ago wondered about designing a motor, fully measuring its voltage and current profiles and phase firing timings for normal operation (from stationary to full speed full load) using a position sensor for getting the motor to work and to determine the best required phase firing sequences and associated voltage/current profiles then program a microprocessor to replicate the entire required profile such that I would attempt to eliminate the need for any sensing or measurement at all (but I concluded it would come very unstuck for any fault conditions or restarting while it was still turning). So in my mind don’t all such machines require a form of measurement (i.e. some form of “sensing”) to work properly so could never be truly sensorless?

A completely sensor-less control would be completely open-loop, which isn’t reliable with some motors like PMSMs. Even if you knew the switching instants for one ideal case, too many “random” variables could influence the system (just think of the initial position), so that those firing instants could be inappropriate for other situations.

Actually, induction machines, thanks to their inherent stability properties, can be run really sensor-less (i.e. just connected to the grid or in V/f). To be honest, even in the simple grid-connection case there is an overcurrent detection somewhere in the grid, which requires some sensing.

But there can also be said the term sensorless relates to el. motor itself. In another words, it means there are not any sensors “attached” to the el. motor (which does not mean sensors cannot be in the inverter, in such a case). In our company we are using the second meaning, since it indicates no sensor connections are needed between the el. motor and the ECU (inverter).

AQ: Design and Implementation

The owner of the system should provide clear requirements of what the system should do and should define what constitutes “maintainability” of the system. This places a burden on the owner of the system to consider the full life-cycle of the system.

1. You need good design documentation.

2. All source code should be well-documented.

3. Coders should be trained on the techniques used and mentored,

4. The use of “templates” helps ensure that coders and maintenance alike are familiar with routine functions.

5. The HMI should provide clear indication of faults and interlocks.

6. The HMI should provide clear indication of equipment statuses.

7. Any code that is hidden must “work as advertised”. This means that it must be completely and unambiguously documented for all inputs, outputs, statuses, and configurations. It must be thoroughly tested and warranted by the vendor,

8. All code should be well-tested. (I have found that the first line of defense is to simply read the code!)

Post-Startup
1. The owner should have a change-control procedure to manage modifications.

2. All users and maintenance support personnel should have adequate training. Training needs to be periodically refreshed as it can become stale through lack of use.

AQ: Benefits of Having products and services in the same company

Having products and services in the same company can either be treated as an opportunity or as a constraint. I strongly believe that having services and products in the same company should be treated as an opportunity, and that any potential constraints should be eliminated.

Here are the things that I have learned.

First: Never limit the product sales to the capacity of your service organization:
I see some companies that develop products that are so great that they want to be the only organization delivering, implementing and maintaining them. They believe that the products are a competitive advantage that will allow them to dominate the services market. This almost always fails; your example from Xerox is one of many. One of two things tend to happen: Either the product does not reach its full market potential due to limited services capacity, or the product organization limits their innovation and product development so that it can continue a lucrative services business. Both may be good short term, but fails on a longer term basis.
My recommendation is that companies that have both products and services should allow their products to be delivered, implemented and maintained by other companies that compete with themselves in the services market.

Second: Never limit the services that you offer to the products that you have in your own portfolio:
Service organizations are typically focused on delivering, implementing and maintaining solutions for their customers. They deliver more than just the product. If you limit the services to only focus on the products in the in-house portfolio, then you are either going to miss opportunities to sell services or you are going to get a portfolio that is too broad. Neither of them is good.
My recommendation is that companies that have both products and services should allow their services organization to deliver products from everywhere, even products that directly compete with the products in their own portfolio. This will ensure that the services organization stays competitive.

Third: Leverage the synergies between products and services:
You may ask “why have both products and services in the same organization if they need to be kept separate?”. The answer lies in the synergies. Companies need to create a culture where the product and services organizations can collaborate even though they are independent. Good organizations can make good decisions about when to expand their own portfolio and when to solve the same customer problems through services and/or third party products. I have seen great innovations come from organizations that master this.

Having products and services in the same organization creates a great foundation for innovation. The key to success is to have the right company culture.

AQ: Operate low speed generator and high speed generator in the same terminal

Can we operate low speed generator and high speed generator in the same terminal? Is there a mechanical effect?

First, specify that this is an isolated system with two generators feeding the same bus. Operation of an isolated system is different than a grid connected system, and the mode setting of the governors have to be set to accommodate this. Depending upon the prime mover type and governor model, improper tuning will manifest itself in speed variations. The size of the two machines relative to each other, as well as their size relative to the load, can have measurable impact as well. The best way to tell whether it is mechanical or electrical in nature is to look at the time-frame of the phenomena relative to the time constants of the various control and response loops.

Second, “…In large power system, generators are not connected in the same terminal…” is not generally true, there are many power plants where multiple generators feed the same bus before the power is utilized.

Third, “…frequency oscillation is about 1.5-2 Hz…”, if you mean that the frequency swings between 48 and 52 Hz routinely, that usually indicates a governor setup/tuning problem or a non-uniform load.

Fourth, reactive current compensation takes place in quadrature from real power and should have minimal effect on real power and only affect the terminal voltage if not set properly. Droop compensation is the means for ensuring that the AVRs do not fight with each other since you cannot have two independent controllers attempting to control the same control variable.

Fifth, regarding different types of prime movers, some are inherently more likely to induce mechanical vibrations, especially reciprocating engines, especially if they are not all of the same size and/or number of cylinders. The same is true of the loads, non-uniform, cyclic loads can cause very severe problems especially on isolated systems where the load is a significant percentage of the prime movers’ output power. The analysis of, and solution to, such problems is an interesting area of study.

AQ: Why we need Engineers?

Even the humble motor car runs diagnostics that the garage read to see the problems with your car. This doesn’t involve technicians looking at the code that controls the car but is 100% driven by the faults flagged by the car’s management system programs. These could even be displayed to the users, the drivers like me and you but the manufacturers don’t want amateurs hacking around their management systems and you know that is exactly what we would do.

Do we ask for this functionality from our car manufacturer? Do we complain about it and ask for them not to fit it? Would we like to go back to the “golden age” of motoring where we spent as much time under the hood as we did on the road?

You do?…. Yeah right and neither do I nor do I want a plant where I need a guy with a laptop to diagnose a blown fuse, sticking valve, overload trip, etc .

We need to change as Engineers by selling systems to customers that fulfill their needs, that are safe and reliable, that follow industry and international best practices and are user friendly. The notion of having to wait for a blank cheque from the customer to fulfill these goals is really a cop out, you either do what is right or just walk away because at the end of all this it is you who are under scrutiny when things go wrong not the customer who will plead ignorance.

AQ: DC Drives Parameter Setting / Programming

Programming parameters associated with DC drives are extensive & similar to those used in conjunction with AC drives. An operator’s panel is used for programming of control setup & operating parameters for a DC drive.

SPEED SETPOINT
This signal is derived from a closely regulated fixed voltage source applied to a potentiometer. The potentiometer has the capability of accepting the fixed voltage & dividing it down to any value, For example, 10 to 0 V, depending on where it’s set. A 10-V input to the drive from the speed potentiometer corresponds to maximum motor speed & 0 V corresponds to zero speed. Similarly any speed between zero & maximum can be obtained by adjusting the speed control to the appropriate setting.

SPEED FEEDBACK INFORMATION
In order to “close the loop” & control motor speed accurately, it’s necessary to provide the control with a feed back signal related to motor speed. The standard method of doing this in a simple control is by monitoring the armature voltage & feeding it back into the drive for comparison with the input setpoint signal. The armature voltage feedback system is generally known as a voltage regulated drive.

A second & more accurate method of obtaining the motor speed feedback information is from a motor mounted tachometer. The output of this tachometer is directly related to the speed of the motor. When tachometer feedback is used, the drive is referred to as a speed regulated drive.

In some newer high-performance digital drives, the feedback can come from a motor-mounted encoder that feeds back voltage pulses at a rate related to motor speed.

These pulses are counted & processed digitally & compared to the setpoint, an error signal is produced to regulate the armature voltage & speed.

CURRENT FEEDBACK INFORMATION
The second source of feedback information is obtained by monitoring the motor armature current. This is an accurate indication of the torque required by the load.

The current feedback signal is used to eliminate the speed droop that normally would occur with increased torque load on the motor & to limit the current to a value that will protect the power semiconductors from damage. The current-limiting action of most controls is adjustable & is usually called current limit or torque limit.

MINIMUM SPEED
In most cases, when the controller is initially installed the speed potentiometer can be turned down to its lowest point & the output voltage from the controller will go to zero, causing the motor to stop. There are, how ever, situations where this is not desirable. E.g.,, there are some applications that may need to be kept running at a minimum speed & accelerated up to operating speed as necessary. The typical minimum speed adjustment is from 0 to 30 percent of motor base speed.

MAXIMUM SPEED
The maximum speed adjustment sets the maximum speed attainable. In some cases it’s desirable to limit the motor speed (and machine speed) to something less than would be available at this maximum setting. The maximum adjustment allows this to be done.

IR COMPENSATION
Although a typical DC motor presents a mostly inductive load, there is always a small amount of fixed resistance in the armature circuit. IR compensation is a method used to adjust for the drop in a motor’s speed due to armature resistance. This helps stabilize the motor’s speed from a no-load to full-load condition. IR compensation should be applied only to voltage-regulated drives.

ACCELERATION TIME
As its name implies, the acceleration time adjustment will extend o

AQ: Power industry engineers

The power industry has many tentacles. Energy production is one key subset, the design, manufacture, installation and operation of hydro, nuclear, fossil, renewables, etc is continuing to grow especially in the renewable area. Then there is the transmission of energy which includes the design/manufacture/construction/maintenance of substations, protection and control systems, overhead and underground lines, series and shunt compensation, etc. Last there is the distribution of the energy to the customers at the lower voltages which includes many of the transmission opportunities but introduces other niche areas like power quality, smart metering, distributed generation, etc.

It’s not as simple as stating you want a PHD in the power industry with hands on experience without first knowing the ins and outs of the business. As has been previously mentioned, get your BS in EE with a slant toward power. Get a job in a utility and learn the business top to bottom so you can actually make an intelligent decision on what area of the business floats your boat. Once you know that then pursue an advanced degree in that specific area (the real bonus is most companies will pay for it).

AQ: Systems Development Life-Cycle

Step 1. Initiation
Step 2. System Concept Development
Step 3. Planning
Step 4. Requirements Analysis
Step 5. Design
Step 6. Development
Step 7. Integration and Test
Step 8. Implementation
Step 9. Operation and Maintenance
Step 10.Disposition

There are three major players present in this model; Customer (client), System Integrator, and Machine or device manufacturer.

In many instances, the result of step 4 (Requirements Analysis), is an RFQ for the system implementation has been issued to one or more systems integrators. Upon selecting the system integrator, step 5 (Design) begins. Upon completing step 5 (Design), the system or process flow is defined. One of the major outputs from step 5 are the RFQs for the major functional components of the finished system. Based on the RFQ responses (bids), the Machine or device manufacturers are chosen.

Steps 6, 7, and 8 are where all the individual functional components are integrated. This is where the system integrator makes sure the outputs and feedback between to machines or devices is defined and implemented. Step 8 ends with a full systems functional test in a real manufacturing situation is demonstrated to the customer. This test includes demonstrating all error conditions defined by the requirements document and the systems requirements document. If a specific device or machine fails its respective function it is corrected (programming, wiring, or design) by the manufacturer and the test begins anew.

Each of the scenarios presented is correct. The technician role being presented (customer, integrator, or manufacturer) is not clear. System diagnostics are mandatory and need to be well defined, even in small simple machines. There should be very few and extreme conditions under which the customer’s technician should ever have to dig into a machine’s code to troubleshoot a problem. This condition usually indicates a design or integration oversight.

(You can find a complete description here, http://en.wikipedia.org/wiki/Systems_development_life-cycle)

AQ: DC Drives Field Voltage Control

To control the speed of a DC motor below its base speed, the voltage applied to the armature of the motor is varied while the field voltage is held at its nominal value. To control the speed above its base speed, the armature is supplied with its rated voltage & the field is weakened. For this reason, an additional variable-voltage field regulator is needed for DC drives with field voltage control. Field weakening is the act of reducing the current applied to a DC motor shunt field. This action weakens the strength of the magnetic field & thereby increases the motor speed. The weakened field reduces the counter emf generated in the armature; therefore the armature current & the speed increase. Field loss detection must be pro vided for all DC drives to protect against excessive motor speed due to loss of motor field current.

DC drives with motor field control provide coordinated automatic armature & field voltage control for extended speed range & constant-horsepower applications. The motor is armature-voltage-controlled for constant-torque, variable-horsepower operation to base speed, where it s transferred to field control for constant-horsepower, variable-torque operation to motor maximum speed.