Author: ABBdriveX

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AQ: What is SynRM motor?

Many others thirty years ago, synchronous reluctance motors (SynRM) have finally replacing the traditional AC induction motors in the industry. ABB has claimed achieving IE4 efficiency with SynRM, a great improvement from IE2 efficiency with the traditional induction motors, for the same motor envelope size and input power.

A SynRM is a true AC machine with or without permanent magnets on the rotor. It is totally different from the closed-loop controlled, permanent magnet brushless DC machines (BLDC) in that one would never be able to get rid of torque ripples as that have been achieved in commonly used BLDC machines.

The difference is on the rotor: copper or aluminum bars for inductance motor (squirrel cage after joining end disks) vs. flux barriers (air pockets) in SynRM. The SynRM rotor can be further enhanced by inserting permanent magnets in the air pockets for a machines called PM assisted SynRM. High efficiency is achieved for two reasons: 1) no copper loss due to the lack of rotor bars and end disks; and 2) high inductance difference between d- and q-axes (Ld-Lq) because of flux barriers and motor torque linearly proportional to (Ld-Lq).

In comparison with the traditional AC induction motor, a SynRM motor needs a frequency inverter and when permanent magnets are present in the rotor, a rotor position feedback sensor. The drawbacks of SynRM are the motor torque ripples due to switching operation, inherited small air gap, etc.

AQ: India renewable energy

Refer to the REI seminar, wherein Government of India representative stated that the VGF payment is spread over 5 year period.

1) Any profit Making Company, must have had the benefits from the Government (subsidies etc) / Eco system.

The profit must be taxed for the improvement of the Economy of the Country.

2) Present renewable energy policy is allowing these profit making companies to avoid paying taxes, and own the assets due to such FREE EQUITY, which belongs to the Government, thus Accelerated Depreciation (AD) is a killer of Economy.

Thus, we are unable to develop the NICHE technology as unrelated industries are owning the project due to avoidance of paying taxes and just to own the assets due to such loop hole in the policy, later making an early exit to make quick money without serving the Nation.

AD promotion is not a level playing field apart from Tax loss to the Government.

3) The Tax thus saved, is again allowed to earn 19 to 24% Return On Equity (ROE), which is very unfair (actually this should have been disallowed to have rs.3/kwh less tariff), due to a fact that, this is public money, hence, should not be allowed to have such wind fall gains.

4) By loading ROE, showing high CAPEX and taking back more than 30% project equity, getting EXIM Bank or such low cost funding to reduce the interest burden, but, Tariff claimed of rs.18 or 15 or 10/kwh is once again a kind of Tariff subsidy, thus, a common man is paying more money for RE power tariff, which is a great killer of economy and making people poor.

5) Viability Gap funding in addition to AD will be an Economic suicide as a project promoter will be allowed to take back 60 to 70% of project cost without paying tax on profit earned !!

This is likely encourage poor equipment buying / its maintenance due to such immediate undue / windfall gains.

6) Despite taking such huge wind fall gains, again these project promoters will be allowed to sell the project to others, to make further wind fall gain to make few existing companies to get undue benefits due to such wrong policy guidelines, despite many representations made to the Government, which states that they have go clearance from Finance Ministry to further ruin the Economy !!

AQ: Negative Impact of Accelerated Depreciation on the Indian Economy

For argument sake or as an illustration, if we assume that 1 MW solar will generate 1.6 Mkwh and rs. 1.2/kwh is rebate for AD taken by the investor = 16 x 1.2 = Rs. 19.2 lakhs/year

[Now, Adani and Tata Power have been negotiating the firm Contract PPA to get more, like wise biomass people who based their PPA on LCOE, but, are asking more money from Government, hence, Solar PV developers may also follow the same route after few years, wherein this rebate of AD given will not have any meaning!!]

Total rebate given = 19.2/year x 25 years = Rs. 480 lakhs = Rs. 4.8 Crore (that too year wise depreciated / devaluated rupee value, which has no meaning !)

But, the tax saved is = 80% of investment = 0.8 x 10 cr = 8 Crore, upfront, right in the first year, which is great value, which government would have used as Equity to develop many more MWs.

Is this POLICY of providing 80% Accelerated Depreciation correct by any standards and why Finance Secretaries or policy makers can’t take note and issue corrective measure for INDIA FIRST Culture??

MNRE, in its Draft policy has proposed 20 to 40% Viability Gap Funding, which will further worsen the LOSS to the government !!

If Mahagenco (with 50% subsidy) goes ahead with the proposed business model, then, how and why State and hence Central government has to take the burden due to such errant policies??
We must put an end to the Scrupulous Project Development, which avails the Capital Subsidy (or Viability Gap Funding) and the Accelerated Depreciation and then the Promoters Sell the Project to a prospective buyer, who in turn approaches the Government for the Tariff hike in the 25 years tenure (please note the Politics dynamics or change of administrative set up will hamper the sustainability), thus, the nation is a great loser

Policies and the enabling tax advantages to few promoters (who claimed Capital Subsidy without creating good quality asset or with NON functional biomass power plants) have made a big dent on Indian Economy without any good results esp in Renewable energy sector.

Government or its administration through such policy (without checks or being accountable) transferred the Public Property to the Private Companies in the Form of Renewable Energy Generation through Capital Subsidy (or Viability Gap Funding) coupled with Accelerated Depreciation along with Low cost Debt fund to these Corporate companies (like EXIM etc) / Project Developers – entrepreneurs, which are not paid back as few of these projects are not functioning and still no action taken to recover the Capital Subsidy paid or Tax recovery which was availed through Accelerated Depreciation (AD).

If Government would have established all these projects from the Tax collections (which are doled out as free through AD), it would have needed only a fraction i.e only Rs. 51,504 Crores, which could have been managed from the taxes of Rs.137,344 Crores while retaining the land and property in Government’s name and could have generated lot of employment.

But, by giving an opportunity to Private sector, many have failed to deliver and no Action to recover the Capital Subsidy or the Debt (due to Tribunals etc…. Please be informed that Indian Parliament had to pass an act in Dec 2012 to recover debt (through wrong business cases of Project Promoters, approved by many banks which were certified by National and International Advisors or Consultants) which is around a whopping 40 Billion USD!!)

Total estimated Renewable energy project capacity = 12% of total installed 220GW = 26000 MW
Cost/ MW Investment Equity Debt Cap Sub AD
Source MW installed Total 30% 70% Rs(Cr) 80%adj
Biomass 6 4,500 27,000 8,100 18,900 6,750 21,600

Wind 7 20,160 131,040 39,312 91,728 104,832

Solar PV 10 1,300 13,000 3,900 9,100 VGF? 10,400
(Ground)

AQ: Solar power

On a purely theoretical level and ignoring interrelated economics and energy usage, it makes sense to charge EVs during the day – though never in non-distributed environments, IMO.

In reality, and the reality for likely the rest of my life, it makes more economic and particulate emissions sense to distribute solar power during the day to decrease, and ultimately decommission, fossil fuel sources used for peak demand supply that occurs during the day.

Thus, using solar output distributed to offset the dirtiest, most expensive and most distribution grid loading power enhances and optimizes the value and worth of that solar generated power – both economically and ecologically. Attempting, therefore, to do all of ones’ EV charging off peak is the optimal solution until the mix of energy sources changes dramatically – likely a 20 plus year process even in the most environmentally friendly “energy generation mix” regions of the world. Even if one charges during “peak”, it is better to simply charge from the grid as the distributed energy is allowed to go to areas of peak demand. Again, for at least my lifetime, I don’t project a more optimal use of that generation even assuming the archaic state of most “grids” persist.

Right now, even for a 1 story commercial building, solar cannot supply the energy needs used in the office, much less a manufacturing facility. In fact, it can normally only supply 1/3 or less for the most energy and resource intensive commercial environment in a UV intense region (and that is quite an optimistic calculation, more likely 1/5th). Once you get to two or more stories on the building, one is not even close. On a modest tower with a tower parking garage, the footprint is likely to small to even generate the needs on a theoretical basis. Distributing the energy to location of greatest needs will allow us to dial down and decommission peak sources, which again are the dirtiest and most wasteful.

At some point, we will hit a new equilibrium where the energy generation mix is much cleaner, solar generation specifically is much more efficient, and peak power generation is handled more efficiently and ecologically cleaner. I still believe, however, that distributed power is better than “off grid” type of scenarios as it allows the energy to go where it is being demanded at the moment, decreasing the need for redundant sourcing. And, even in the cleanest energy generation mix, redundancy means building more of something and is by definition more energy wasteful and ecologically wasteful than a scenario where the redundancy buffer that is required is lesser.

Much of this type of debate reminds me of the consumer sort recycle versus the destination sort recycle debate. Even with the advances in trash collection and recycling processes, 20 years later we are suboptimizing the recycling process. Much of the reason for that is the “style” statement, making people feel like they are contributing by sorting themselves. It may make some people “feel” better by imagining “independent” off grid or semi off grid solutions. In reality, however, we live in an interconnected world where “sharing” or distributing solutions to leverage scale and minimize redundancies is far more advantageous, economic, and a faster route to a solution to both particulate emissions issues and energy independence for groups of people.

AQ: Resistance to ground

Resistance to ground is greatly influenced by the ambient conditions and the state of the motor when tested.

Factors Affecting Insulation Measurement:
First, it is important to understand that we are measuring a motor circuit. We are connecting our test instrument at a point where we can measure the majority of the de-energized circuit. As such, we do not necessarily know where an insulation anomaly is located when identified. We also have the motor circuit potentially exposed to differing environments. Ambient temperature and humidity can have a significant effect on any insulation measurements. When a motor circuit’s insulation is tested is also a major variable. Testing a motor circuit immediately after shut down will most likely yield good results. This is because the motor is warm and dry. Testing a motor after it has been shut down for a while may indicate insulation problems, but if the motor is allowed to reach ambient temperature, the insulation integrity may appear normal. This is because while cooling, particularly in somewhat humid conditions, moisture (condensation) will accumulate within the motor and lessen ground resistance. Is this a problem? Yes, particularly if starting from a partially cooled state. Most motor failures occur during starting. This is when the insulation is exposed to the most stresses. If your motors are only down for a few hours at a time, then this is when insulation testing should be conducted.

When conducting insulation testing, the most important consideration is consistency. Always test at the same location, use the same test voltage, perform the test for the same amount of time, and use the same test instrument. It is also important to note the motor temperature, ambient temperature, and relative humidity. It is also helpful to compare like motors and the motors that are operating within the same environment.

Insulation testing is somewhat ambiguous. Although there are reference standards, they cannot be rigidly followed because they do not factor in all of the potential variables that may be encountered. Temperature is the biggest variable. Temperature of the motor and the ambient temperature are of primary concern. One method to help negate the influence of temperature is performance of a “Timed Resistance Test.” This testing is comprised of “Dielectric Absorption,” “Polarization Index,” and “Step Voltage” testing. Dielectric Absorption is a 1 minute test. The resultant values at 30 seconds and 1 minute are logged and the ratio of the 30 second value divided into the 1 minute value, is a relative indicator of insulation integrity. A polarization index is a 10 minute test with the resultant ratio derived from the 1 minute value divided into the 10 minute value.

So, if ground resistance is low after prolonged shutdown and it is at ambient conditions, then you probably have an insulation issue. Conditioning of the insulation may be required. A motor shop can perform a “Clean, Dip and Bake.” process which will prolong the motor longevity. If the motor is several years old you may want to HiPot the insulation but if you are not using one of the newer units that automatically shut down upon a jump in current, you may cause insulation failure and that would necessitate a rewind.

AQ: Rotary Tube Furnace Efficiency

There are many factors that govern the performance of rotary tube furnaces. A direct fired rotary unit has a potential for much higher thermal efficiency due to the direct contact of the hot gases with the material in process. Cement kilns are the most common large scale unit operation with direct fired units. Any articles you find on this will be helpful. Thermal efficiency can be estimated by dividing the inlet temperature minus the outlet temperature by the inlet temperature minus the ambient temperature in absolute scales either Rankine or Kelvin. Then there is the issue of co-current versus counter-current firing and heat recovery from the hot material and the exit gas for which standard designs are available. Indirect fired rotary kilns have heat transfer limitations due to the thickness and alloys needed for high temperature calcination >500 C. There is no simple way to measure the equivalent of the inlet and outlet temperatures on a direct fired unit. There are simply exit gas temperatures from each zone and an approximate shell temperature on the hot side of the shell which is lower than the zone exit gas temp. These are useful for control purposes and consistent operation. The higher the temperature the material requires to achieve conversion the higher the shell side fired temperature has to be to provide the delta T necessary to drive heat through the shell into the material zone.

Some materials further limit heat transfer by adhering to the inside of the shell and acting as an insulator! This requires trial and error application of “knockers” at the ends of the shell or sometimes internally secured chains that bang around and knock the adhering material loose. This is a potential nightmare as the learning curve to install chains so that the securing lugs and the chains themselves will stay attached for acceptably long service before failing and ending up in the take off conveying equipment with usual breakage and downtime is an uncertain one. From Perry’s one can find thermal efficiencies for indirect fired rotary’s given as less than 35%. The bed fill can be 10-30% depending on the heat demand of the material and the heat transfer limitations. You will want to have real time gas usage metering on the burners so that you know the theoretical energy input. From that you can subtract the theoretical heat needed to complete your reaction and compare that to the input to see how efficiently you have used the energy input.

The few large high temperature direct fired rotary kilns I have seen had view ports for measuring the local wall temperatures by optical pyrometer. It can be a challenge to get a protected thermocouple sheath down into the moving bed for an actual bed temperature and even just to hang it in the gas streams at the outlet or inlet area. See if you can contact cement kiln suppliers for some configurations of temperature sensing elements for your application. Bed fill effects on heat transfer are related to several parameters. Above ~500 C gas and refractory liner temperatures, the main heat transfer mode will be radiative as far as the surface of the bed material. Within the bed it will be conduction and some convection at the surface. A thin bed will reach max. temperature in shorter time, but this reduces through put for a given gas temperature. If you increase bed fill to increase production you will have to increase the firing temperature and the outlet temperature will probably increase lowering your thermal efficiency. This becomes a trade off between production rate and energy efficiency. Countercurrent firing usually maintains the highest driving force for heat transfer along the bed and gives the highest temperature of the bed just before exit of the bed material.

Perry’s may have a useful section on direct fired rotary kilns and lime or cement manufacturing references may help you as well. Please make sure lead emissions to air are properly captured

AQ: Frequency Inverter Direct Digital Control

Modulating Supply & Return Fans are used as a means of providing proper variable air volume (VAV) control as well as building pressurization. Many such VAV systems are still largely pneumatic with static to the downstream boxes being maintained by inlet guide vanes. To provide increased energy savings and energy comfort, these systems can be easily converted to frequency inverter fan control of the supply and return fans and Direct Digital Control (DDC) to coordinate any increased energy saving strategies. Figure 1 shows such a system.

Frequency Inverter Direct Digital Control

To increase energy savings, the DDC controller can be programmed to reduce the flow from the return & supply fans for short periods of time. Coordinated with the building pressurization system, any temporary loss of space temperature may be avoided.

In Figure 1, the supply fan is controlled by the duct static pressure sensor, via the DDC, while the outside air and mixed air dampers are optimized to provide economizer control.. The return fan is modulated to stabilize building pressure at a slight positive. For simple supply and exhaust systems the building pressure and static pressure sensors may be connected directly to the frequency inverter with an internal PID controller.

Typical Energy Savings are realized from converting pneumatic (or electromechanical) control to DDC control with frequency inverter in the following ways:

  • Locking inlet guide valves mechanically open to allow the frequency inverter to fully modulate the fans.
  • Free cooling by accurately modulating the economizer dampers and sequencing the mechanical equipment.
  • Controlling static and resetting the static pressure during short periods of time.
  • Accurate building pressurization.
  • Implementing other energy saving measures which include supply air reset, and night purge routines.

CONTROL CONSIDERATIONS

  • Placement of the indoor static pressure sensor is important as it should provide a stable signal. Entrances, dock, and other areas where large , sudden static pressure changes may occur should be avoided.
  • The outside reference static tip should be shielded from wind and rain.
  • When the exhaust fan is frequency inverter controlled, consider a 2-position air damper to prevent the outside air from entering the building (infiltration) when the exhaust fan is off or a very low speeds.
  • For simple VAV systems, consider using frequency inverters with built in PID controls such as the Iacdrive frequency inverters.. This minimizes hardware and installation costs. Static sensors provide a 0-10vdc control signal directly to the frequency inverter.
  • Duct mounted static pressure sensor should be mounted 2/3 of the distance of the distribution system.

AQ: Variable Air Volume System Optimization

Variable Air Volume Systems (VAV) can be optimized to increase energy savings by maximizing the efficiency of the equipment at part-load conditions. The goal with the optimization strategy is to run each subsystem (chiller, cooling tower, Airhandler, etc) in the most efficient way possible while maintaining the current building load requirement.

VAV System Optimization

As each Variable Air Volume terminal controls the space temperature – based on flow – the “worst case” zone can easily be identified by an automation system. The supply fan speed can be reduced by resetting the static pressure (see following page). As the load drops and the fan meets a preset minimum flow, the system resets the air temperature up, so less chilled water is needed. In a variable flow chiller system, this reduces pumping energy.

If the system load continues to drop, the system will reset the chiller supply water temperature upward which will then reduce the energy requirements of the chiller. Changes in the chiller head pressure and loads can then reset the cooling tower fan speed.

The key to optimizing the system operation is communication and information sharing through the entire system equipment. With the reduced cost of variable frequency drives and Building Automation Systems, (BAS) complete system optimization can be implemented as a cost effective option.

In VAV systems where the individual VAV boxes and the AHU are on a building automation system, additional savings can be achieved by implementing static pressure reset. The static pressure sensor in a VAV system is typically located two-thirds of the way downstream in the main supply air duct for many existing systems. Static pressure is maintained by modulating the fan speed.

When the static pressure is lower than the setpoint, the fan speeds up to provide more airflow (static) to meet the VAV box needs, and vice-versa. A constant set point value is usually used regardless of the building load conditions.

Under partial-load conditions the static pressure required at the terminal VAV boxes may be far less than this constant set point. The individual boxes will assume a damper position to satisfy the space temperature requirements. For example, various VAV box dampers will be at different damper positions, (some at 70% open, 60% open, etc) very few will be at design, ie 95% -100% open.

RESET STRATEGY
Essentially, resetting supply air static pressure requires that every VAV box is sampled with the static reset set to the worst case box requirement. For example, each box is polled, every 5 minutes. If no box is more than 95% open, reduce duct static pressure set point by 5%. If one or more boxes exceed 95% open, increase static pressure set point by 5%.

With a lower static set point to maintain, fan speed reduces. The result is increased energy savings in the 3 to 8% range. See figure below. If the BAS system is already installed, implementing this strategy is relatively free.
Variable Air Volume System energy savings

AQ: Why companies don’t invest in variable frequency drive control

Investing in energy efficient variable frequency drives (VFD) seems like an obvious path to cutting a company’s operating costs, but it is one that many companies ignore. This article explores some possible reasons for this reluctance to invest in VFD.

There is a goldmine of savings waiting to be unlocked by controlling electric motors, but the reluctance to take advantage of this is a very puzzling phenomenon. Motors consume about two thirds of all electrical energy used by industry and cost 40 times more to run than to buy, so you would think optimizing their efficiency would be a priority. The reality is that this good idea is not always turned into good practice and many businesses are missing out on one of the best opportunities to boost profits and variable frequency drive growth.

It might surprise you to learn that your average 11kW motor may cost about £500 to buy but £120,000 to run at 8,000 hours per year over a 15-year lifetime (and that isn’t even accounting for inevitable increases in energy prices). It’s worth considering the payback on any investment in motor control that will reduce this significant running cost, such as using VFDs to control speed, or implementing automated starting and stopping when the motor is not needed. Payback times can often be less than 1 year and, of course, the savings continue over the lifetime of the system, particularly as energy costs rise.

The question that often arises when I talk about this subject to people is: “If the savings are so great, why don’t more people do this?” It would appear to be something that fits into the nobrainer category, however there are three main barriers to the wider uptake of motor control with variable frequency drive, none of which should stop common sense from prevailing – but all too often they do.

The first barrier is a lack of awareness of how much energy is being consumed, and where, in a business. A surprising number of companies do not have a nominated energy manager, still less have energy management as a dedicated job function or have a board member responsible for this significant cost. Those that do measure their energy consumption often have a financial rather than technical bias, so solutions tend towards renegotiating supply contracts, rather than reducing consumption.

The second barrier stems from the economic climate and the level of uncertainty about future events and policies. Businesses are still reluctant to invest in improvement projects, despite short payback periods and the ongoing benefits. The short-term focus is on cutting costs, not on spending money, even to the detriment of future growth. This make-do-and-mend attitude is often proudly touted as a strength, but it is ultimately a false economy. Saving money by cutting capital budgets, reducing staff and cancelling training is damaging to a business and to morale, making it difficult to grow again when the opportunity arises. Saving money by reducing energy consumption makes a business more competitive, while keeping hold of key skills and resources.

The third barrier is a focus on purchase cost, rather than lifetime cost. Whenever a business invests in a machine, a production line or a ventilation system, you can be sure they will have a rigorous process for getting several quotes, usually comparing price, with the lowest bid winning. Something that is not often evaluated is the lifetime energy cost of the system. Competing suppliers will seek to reduce the capital cost of the equipment but without considering the true cost for the operator, including energy consumption. What if the cost of automation and motor control added £700 to the purchase cost? Many suppliers will consider cutting this from the specification. But what if that control saved £1,400 per year in energy? It co

AQ: Variable Frequency Drive Harmonics

For the AC power line, the system (VFD + motor) is a non-linear load whose current include harmonics (frequency components multiples of the power line frequency). The characteristic harmonics generally produced by the rectifier are considered to be of order h = np±1 on the AC side, that is, on the power line (p is the number of pulses of the variable frequency drive and n =1,2,3).Harmonics Thus, in the case of a 6 diode (6 pulses) bridge, the most pronounced generated harmonics are the 5th and the 7th ones, whose magnitudes may vary from 10% to 40% of the fundamental component, depending on the power line impedance. In the case of rectifying bridges of 12 pulses (12 diodes), the most harmful harmonics generated are the 11th and the 13th ones. The higher the order of the harmonic, the lower can be considered its magnitude, so higher order harmonics can be filtered more easily. As the majority of VFD manufacturers, Iacdrive produces its low voltage standard variable frequency drives with 6-pulse rectifiers.

The power system harmonic distortion can be quantified by the THD (Total Harmonic Distortion), which is informed by the variable frequency drive manufacturer and is defined as:

THD = √(∑∞h=2 (Ah/A1)2)

Where
Ah are the rms values of the non-fundamental harmonic components
A1 is the rms value of the fundamental component

The waveform above is the input measured current of a 6-pulse PWM variable frequency drive connected to a low impedance power grid.

Normative considerations about the harmonics
The NEMA Application Guide for variable frequency drive systems refers to IEEE Std.519 (1992), which recommends maximum THD levels for power systems ≤ 69 kV as per the tables presented next. This standard defines final installation values, so that each case deserves a particular evaluation. Data like the power line short-circuit impedance, points of common connection (PCC) of variable frequency drive and other loads, among others, influence on the recommended values.

Voltage harmonics
Even components 3%
Odd components 3%
THDvoltage 5%

The maximum harmonic current distortion recommended by IEEE-519 is given in terms of TDD (Total Demand Distortion) and depends on the ratio (ISC / IL), where:
ISC = maximum short-current current at PCC.
IL = maximum demand load current (fundamental frequency component) at PCC.

Individual Odd Harmonics
(Even harmonics are limited to 25% of the odd harmonic limits)
Maximum harmonic current distortion in percent of IL
ISC/IL <11 11<h<17 17<h<23 23<h<35 35<h TDD
<20 4 2 1.5 0.6 0.3