Gas Turbine Generator Cycles

A combustion gas turbine is a rotary engine that extracts energy from the combustion gas stream. It has an upstream compressor coupled to a downstream turbine, and a combustion chamber in-between. It has an upstream compressor coupled to a downstream turbine, and a combustion chamber in-between. Energy is added in the combustor, where fuel is mixed with air and ignited. Energy added in the combustion chamber, where fuel is mixed with air and ignited. Combustion increases the temperature, velocity and volume of the gas flow. Combustion increases the temperature, velocity and volume of gas flow. This is directed through a nozzle over the turbine's blades, spinning the turbine and powering the compressor. It is directed through a nozzle over the turbine blades, spinning the turbine and the compressor turned on. Energy is extracted in the form of shaft power the which is used to drive an electric generator. Energy is extracted in the form of shaft power is used to drive an electric generator.

Combined Cycle

A combined cycle is a power producing engine or plant employs more than That one thermodynamic cycle. Combined cycle is a power producing engine or plant that employs more than one thermodynamic cycle. Gas turbine engines are only Able to use a portion of the fuel generates Their energy. gas turbine engines can only use a portion of fuel energy to produce. The remaining heat from combustion is Generally wasted. Residual heat from combustion is generally wasted. Combining two or more "cycles", Such as the Brayton cycle (gas turbine) and Rankine cycle (steam turbine, condenser, cooling tower), results in improved overall efficiency. Combining two or more "cycles", such as the Brayton cycle (gas turbine) and Rankine cycle (steam turbines, condensers, cooling towers), resulting in improved overall efficiency. In a combined cycle power plant, a gas turbine generator generates electricity and the exhaust, waste heat is used to the make steam to generate additional electricity using a steam turbine; this last step enhances the efficiency of electricity generation. In a combined cycle power plant, gas turbine generator generates electricity and gas waste, the waste heat is used to make steam to generate additional electricity using steam turbines; this last step increases the efficiency of electricity generation.

Simplified Combined Cycle (SCC)

SCC technology gas turbine combustion similarly Captures waste heat and turns it into steam, creating additional power without the need for a steam turbine, condenser or cooling tower. SCC technology also captures waste heat of combustion gas turbine and convert it into steam, creating additional power without the need for a steam turbine, condenser or cooling tower. Like the combined cycle, capturing this waste heat results in Increased production of kWh without additional fuel being burned. Such as combined cycle, this result captures waste heat in the increased production of kWh without additional fuel is burned. Because injected steam cools the combustor's hot gases, it is possible to burn additional fuel and stay in compliance with the thermal limits of the engine. Because the steam injected gas cools the hot combustion chamber, it is possible to burn extra fuel and live according to the thermal limit of the machine. The result is Increased capacity and improved efficiency. The result is increased capacity and improved efficiency.
SCC achieves emissions improvements by pre-mixing of steam and fuel before injection into the combustor. SCC emissions improvements achieved by pre-mixing steam and fuel prior to injection into the combustor. The result is a smaller, cooler flame the which reduces NO x. The result is a cold, a small fire which reduces NO x. NO x of less than 5 ppmvd has been Achieved in the field, while in rig tests of NO x atmospheric levels of less than 2 ppmvd have been Achieved. NO x is less than 5 ppmvd has been achieved in the field, while in the test rig atmospheric NO x levels of less than 2 ppmvd have been achieved.
The low NO x levels are Achieved Because CO stays below 10 ppmvd, while steam injection is Increased to levels not achievable without a very homogeneous mixture of steam and fuel. NO x is achieved due to low levels of CO remained below 10 ppmvd, while the steam injection to increase to levels that can not be achieved without a highly homogeneous mixture of steam and fuel. The ability to Produce the NO x and CO allows Greater turndown while maintaining compliance. The ability to produce NO x and CO allow greater turndown while maintaining compliance.
Usually, SCC reduces the turbine inlet temperature and hot gas path extends the Time Between Overhaul by at least fifty percent. Typically, SCC reduces the turbine entry temperature and extend the time path of hot gas between the improvement by at least fifty percent.
Faster start requiring less fuel is possible Because steam can be injected in the gas turbine as Quickly as it is produced, avoiding the steam turbine warm-up requirements. Quickly began to require less fuel is possible because the steam can be injected in a gas turbine as fast as produced, avoiding the steam turbine heating requirements.
 

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Calculation of Electric Motor Safety

Basically the "Motor protection" and "motor circuit protection" are two different things and requires a different calculation.

To prevent the motor burning, we have to prepare a way to protect it from overcurrent (overload, short circuit, or ground-fault). Before we go into further discussion, there should not be confused with a motor protection and circuit protection. Motor protection is a safety system tehubung motor with the motor power circuit. While the protection circuit is a safety system for power series rather than the motor itself.


Please refer to the NEC 430.1 pictures to help you see clearly the difference of the two. There are described the requirements for the motor overload protection and the requirements of Chapter III short-circuit protection and ground-fault in Chapters IV and V.

Table or nameplate? To determine the CRC (or ampacity capability Flow Conductivity) minimum from power supply conductor motor, you should know clearly how much current will flow when the first traction motor. But there also exist various kinds of currents in motor applications (see "Current Motor Basics" on page 80). Full load current / full-load current (FLC) or ampere full load / full-load amperes (FLA) Which we use to calculate your motor?

In the NEC standards are not permitted use of the Full Load Ampere / FLA marked on the nameplate to determine the CRC / ampacity of conductors or cables used size, branching circuit short-circuit and ground-fault size overcurrent device, or even the amperage rating disconnecting switches [430.6 (A) (1)]. But here we must use the value of the motor FLA to determine the size of the motor overload-protection separately in accordance with Part III Alenia 430 [430.6 (A) (2)]. Note the following exceptions:

• If you calculate the motor overload protection separately for the motor torque, locked rotor current use value on the nameplate [430.6 (B)] 
• If there is a variable-frequency drive (inverter) as motor controllers, use the maximum operating current marked on the nameplate (motor or control). If the value is not found on the nameplate, use 150% of the value found in the table NEC [430.6 (C)]. 
• Motor with High Torque (generally made and to operate under the speed of 1.200 rpm) typically have a larger value of FLC compared with multispeed motors. For motor like this, use the current rating stamped on nameplate [430.6 (A) (1)]. 
• For a listed motor-operated appliance, use the FLC marked on the nameplate of the appliance (rather than the horsepower rating) to determine the ampacity (or rating) of the disconnecting means, branch-circuit conductors, controller, and branch-circuit short -circuit and ground-fault protection [430.6 (A) (1) Ex 3].

Overload protection. Overload protection shall be in accordance with Chapter III 430. Overload protection device size is based on the rating indicated on the motor nameplate (this serves to protect the motor windings due to the current damage incurred by the locked-rotor or the rotor jams / drag / jamming) [430.31].

Fig. 4. Branch-circuit conductors are protected against overloads by the overload device.
You can use a single overcurrent device, sized per 430.32 requirements, to protect a motor from overload, short circuit, and ground faults

Branch-circuit conductor size. Branch-circuit conductors to a single motor must have an ampacity of not less than 125% of the FLC as listed in Tables 430.247 through 430.250 [430.6(A)(1), 430.22(A)].

When selecting motor current from one of these tables, note that the last sentence above each table allows you to use the ampacity columns for a range of system voltages without any adjustment. Select the conductor size from Table 310.16 according to the terminal temperature rating (60ºC or 75ºC) of the equipment [110.14(C)].

THHN/THWN is a common conductor insulation type that can be used in a dry location at the THHN 90ºC ampacity, or in a wet location at the 75ºC ampacity for the THWN insulation type. Regardless of the conductor insulation type, size the conductor per 110.14(C).

In 110.14(C)(1)(a), we read that equipment terminals are rated 60ºC for equipment rated 100A or less (unless marked 75ºC). Today, most equipment terminals are rated at 75ºC. Look for that specification, so you can use the 75ºC column if your conductors are also rated for 75ºC. If this is the case, you may save considerable money on your project. If you can’t find that specification, use the rules of 110.14(C).

Test your knowledge by answering this question: What size branch-circuit conductors are required for a 7½-hp, 3-phase, 230V motor (Fig. 1 on page 76)?

The motor FLC from Table 430.248 is 22A. The conductor is sized no less than 125% of motor FLC: 22A 3 1.25 = 27.50A. As per Table 310.16, a 10 AWG conductor is rated 30A at 75ºC.

The minimum size conductor permitted for building wiring is 14 AWG [310.5]; however, some local codes and many industrial facilities require branch-circuit conductors to be 12 AWG or larger.

Feeder conductor size. Perform feeder conductor size calculations the same way as for branch circuits, but use the different ampacity rules provided in 430.24. Conductors that supply several motors must have an ampacity of not less than:

(1) 125% of the highest rated motor FLC [430.17], plus
(2) The sum of the FLCs of the other motors (on the same line). Find the FLC in the NEC Tables [430.6(A)(1)].

The highest rated motor is the motor with the highest FLC [430.17]. Determine the “other motors in the group” value by balancing the motor FLCs on the feeder being sized, then select the line that has the highest rated motor on it (Fig. 2 on page 78).

Branch-circuit short-circuit and ground-fault protection. Each motor branch circuit must be protected against short circuit and ground faults by an overcurrent device sized no greater than the percentages listed in Table 430.52. The motor branch-circuit short-circuit and ground-fault protective device must be capable of carrying the motor’s starting current, and it must comply with 430.52(B) and 430.52(C).

A branch-circuit short-circuit and ground-fault protective device protects the motor, the motor control apparatus, and the conductors against short circuits or ground faults, but not against overload [430.51] (Fig. 3 on page 78).

It bothers many electrical practitioners to see a 14 AWG conductor protected by a 30A circuit breaker, but branch-circuit conductors are protected against overloads by the overload device (Fig. 4). That device is sized between 115% and 125% of the motor nameplate current rating [430.32]. See 240.4(G) for details.

Where the branch-circuit motor short-circuit and ground-fault protective device values derived from Table 430.52 don’t correspond with the standard overcurrent device ratings listed in 240.6(A), you can use the next higher overcurrent device rating. The “next size up protection” rule for branch circuits [430.52(C)(1) Ex 1] doesn’t apply to the motor feeder overcurrent device rating (Part II).

Keeping it straight. Articles 430 and 250 are the largest of the NEC Articles, and arguably the most misapplied. Something else these two Articles have in common but not with the other Articles is a “Figure 1” you can use as a guide.

In the case of Art. 430, this figure is a simple representation of the motor system with the correct Part of Art. 430 noted for each area of application. At the beginning of this article, we said that using Figure 430.1 will help you to not confuse motor protection with circuit protection when in actuality it can do much more. Spend some time working with it, and you’ll see how useful it really is.

If you base each motor project on Figure 430.1, you will reduce — if not eliminate — Art. 430 application errors.

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Testing Current Transformers

CT or current transformer is an intermediate flow measurement, which limits the ability to read gauges. Suppose the system of high voltage lines, the current flowing is the 2000A while the gauges are only limited to 5A. CT is needed to transform a representation of the actual value of 2000A at 5A so that the field be read by the measuring instrument.

CT is generally only used as a medium readings are also used in power system protection system. Protection systems in electrical power systems are so complex that CT itself was made to the specifications and classes that varied according to the needs of the existing system.

Specifications on CT include:

1. CT ratio, CT ratio is the basic specifications that must be present on CT, where the representation of the current value on the ground in calculating the size of the CT ratio. Eg CT 2000/5A ratio, the measured value in the secondary CT is 2.5A, then the actual value of current flowing in the conductor is 1000A. Presentation or the magnitude of the error ratio error (% err.) Can affect the magnitude of error in measuring instrument readings, the error rate calculation, and fault protection system operation.
2. Burden or a maximum value of power (in VA) that can be borne by the CT. The value of this power must be greater than the measured value of the CT secondary terminal to the relay coil protection work. If smaller, then the relay protection will not work for mengetripkan CB / PMT when an interruption occurs.
3. Class, class of CT to determine whether the type of protection system for the CT core. Eg used for overcurrent protection 5P20 class, for class use tariff metering class 0.2 or 0.5, busbar protection system used for Class X or PX.
4. Kneepoint, is the point of saturation / saturation when CT did excitasi voltage. Busbar protection is generally used as the driving coil voltage. Voltage can be generated by CT when CT secondary impedance is given as it appears on Ohm's Law. Kneepoint only in CT with a Class X or PX. The magnitude of the voltage can reach 2000Volt kneepoint, and of course kneepoint magnitude depending on the value or the desired design.
5. Secondary Winding Resistance (RCT), or impedance in CT. Impedance in CT are generally very small, but in the Class X this value is determined and must not exceed the values ​​listed there. For example: <2.5Ohm, the impedance of the Class X CT should not be more than 2.5Ohm or CT were returned to the factory to do the replacement.

Based on the above criteria, then the CT testing can be done as follows:

These examples along with a description in this article I took from my experience doing SAT on CT and HV Equipments Project: Cikarang Listrindo 4x60MW Gas Power Plant Project, Inalum 275kV OHL Prot'n Panel Replacement Project, and Muara Karang 2x250MW Gas Power Plant Project. 

Ratio Test

Example: CT Ratio = 2000/5A
To perform the test that is true if the value of the CT secondary rated current of the primary line 2000a is 5A, the current injection device is needed here that can divert the current of 2000A. Of course this tool is very rare and very large.
Commonly used alternative way is to inject a smaller device, such as 500A. To get the 2000a then we can make as many rolls or loops 2000A/500A = 4 times roll.

Of course the value is not exactly as it appears on the calculator but at least that value can be achieved. Metering or instruments attached to show the value of approximately 2000A.

In the general case that occurred in the field, it kind of test tool that can generate large amounts of current are quite hard to find (because it is expensive so generally we rent from my friends)

Behind it was a lot of the CT measurement results are not linear / or not directly proportional to the ratio indicated. In other words, the percentage of error-reading of his varied and generally the smaller the applied current, the percentage of error, the greater his reading beyond the specifications listed on the nameplate CT. Though to some of the protection system such as Distance Relay using the current parameter readings at a low value.

Then IEC standardization issue that must be linear CT measurement values ​​of at least s / d 10% of current value or the nominal current rating indicated. Of course, this beneficial for me as the SAT and commissioning team. To test required enough current 2000A CT by 10% x 2000A = 200A only. Hmm .. consequently ujinya tool was not too heavy and not many places to eat. Hot smile "still loading luggage for souvenirs nyimpen ..".

Then how to test and calculation error presentation-reading it how?

 

Example for 2000A :

• CT 2.1 - Core # 3 
• Serial No. CT: 0805451CT primary terminal and secondary terminal 
• Tap terminal is used 3S1 ~ 3S3
• Class 0.5 Security Factor (FS) <20, a maximum of% err. is 0.5% 
• Ratio 2000/5 A 
• Injection current of 200A, the current measured on the primary side of CT were: 199.96 A, of course there are losses in the cables and connections on the primary side. 
• Rated current on CT secondary side is: 501.55 mA
• With the above formula, the value of primary current is: 2000A and skundernya current value is 5.0165 A 
• So that% err. = 0.33% [OK]

Because the count is less hobby, so I've made in the form of Excel formulas, and the result will be like this. Simply insert the actual value of primary current and secondary current actual value. Pretty simple is not it?

 Secondary Winding Resistance Testing (RCT)

CT Secondary Winding testing generally refers to the standard IEC 60076-1. Formula and test systems should be based on the setandar. Testing out the standard unauthorized and does not meet the criteria for standard CT testing.

Based on IEC 60076-1, the measurement of elements that must be taken when testing CT Secondary Winding is as follows:

• IDC: DC current is injected into the actual CT secondary terminal. I usually use the current value is of type 5A to 5A nominal CT secondary output. 
• VDC: measured voltage generated by the injection of DC current in the coil / winding CT. 
• Meas R: The value of winding resistance or resistance in the CT, which is obtained from the calculation VDC / IDC (Ohm's Law). 
• Time: Total time spent in testing. 
• Dev: deviation angle is expressed as% of maximum and minimum values ​​are measured and evaluated at least 10 seconds of measurement. Results declared stable if the Dev <0.1%. 
• Tmeas: ambient temperature or room temperature 
• TREF: operating temperature of CT, most commonly used value is 75 ° C. FAT Data should refer to the reference manual from the manufacturer or CT.

  Formulation so that the calculation of CT Secondary Winding Burden can be made as follows:

Secondary testing burden is quite significant, given that this test was also a CT to check on the circuit load such as relay panels, metering, buspro, logger, etc.. The series of CT must always be closed (short-circuit) in order to mengasilkan flow.

Circuit impedance should not be any large or even cut off, in case the current can not flow and CT into heat and overload. As a result the CT can be damaged, broken, or even explode. This testing while ensuring decent conditions rangkain CT operated or not.

CT or CT excitations testing Kneepoint

In the test CT saturation point or kneepoint there are three types of standards are set, all three have different values ​​kneepoint but all three are considered legitimate, depending on what standard to be used at least a CT Manufacturer and End-User use the same standard.

• IEC / BS - According to IEC 60044-1, the knee point is defined as the point on the curve where a voltage increment of 10% increases the current by 50%. 
• ANSI 45 ° - According to IEEE C57.13, the knee point is the point where, with a double logarithmic representation, the tangent line to the curve forms a 45 ° angle.Applies to current transformer cores without an water gap. 
• ANSI 30 ° - Like ANSI 45 ° but forming a 30 ° angle.Applies to current transformer cores with an the water gap.

In Indonesia generally refers to the IEC Standard, as a standard of high and medium voltage intalasi.

To conduct CT testing, it would require an AC voltage source is capable of being used to test the CT Class X, where its value could reach kneepoint 2000Volts. Excitation voltage is supplied to the secondary terminals of each Core-CT at her, then the voltage was increased slowly to reach the nominal current value of CT. Current measurements can be done by placing the Ampere-meter with a linked series of injections or the use of a clamp meter on the output cable voltage injection devices.

Model testing is generally I use is as below:

Any significant change in the current or any multiple of how many volts of voltage, measurement and recording can be done simultaneously in order to chart a smooth and precise. Examples of such graphs is as follows:

 


If you created a graph in Excel, then the graph it will be shaped like this:

 

Unfortunately, not all manufacturers or rarely mentioned CT Kneepoint value that is obtained when the done FAT (because not everyone is easy to determine and understand the value of the measurements obtained). Usually the only manufacturer to attach a data value with the value of excitation current in the can and attach the graph.

The key core excitation voltage on CT testing is only to determine the value of what the Volt, CT has reached saturation point and did not produce significant changes in flow.

Eg CT specification is Vk> 1.7 kV excitation voltage is 1.7 kV CT must exceed to produce 5A, 5A reached at least 2kV. Thus CT has specifications as stated.

Isolation or Megger Testing

Tests on a whole is to determine that the CT is feasible to operate the system design specifications and current measurement errors do not occur exactly where CT is an element metering and protection.

To determine whether CT voltage is feasible or not, it must be done or Megger Insulation testing. 5kV Megger is used for the primary side and secondary side to 1kV.

The point of testing can be done is:

• Primary to Ground terminal should not be any relationship 
• Primary to secondary terminals should not be any relationship 
• Secondary to the Ground terminal should not be any relationship

Physical checks

CT time comes and when installed must physically check diulakukan first as a quality control form. There should be no cracks, or even a transformer oil seepage.

"Hopefully, the article mentioned above were able to add insight and improve the quality control of products or development projects of electricity infrastructure in Indonesia. Electricity is better for the future, and let air-Save Energy."

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Insulation Testing May Rescuing Prisoners Electric Motor

Insulation resistance test on the equipment is simple but important preventive measures which can significantly reduce maintenance cost.

You probably already familiar with the insulation resistance test (more commonly known as a megger). This test plays an important role in the maintenance of the cable, but do we realize that it can also help us in preventing unexpected motor failure? Not only is the motor insulation is susceptible to excessive temperatures, moisture, dirt, corrosive vapors, vibration, oil, and aging, but also be able to withstand the normal surge and inrush current VFD. An insulation resistance test program that can consistently deliver substantial savings and increased service life of / uptime motors.

Testing also reduces the waste of resources for maintenance. For example, stamping and assembly plant to replace the motor 250hp Plant Air System with motor rewinding purchased from a local store. After struggling to put the motor into place, termination or cable connection, and setting the position of the clutch, the maintenance crew tried to start the motor, but it turns out the motor does not respond at all. Service electric motor repair shop turned out to have been wrong to send a similar model which is actually still need to be re rewindning. Finally, the motor must be disassembled and transported back to the electric motor service shop. Maintenance staff of these cases could prevent delays in the replacement of the motor is happening there as well as loss of production time by just doing simple insulation resistance test as a condition of receiving an electric motor before it is installed.

 

Testing Automated vs Testing Manual

Insulation resistance tests automatically (online) can save maintenance time = saving money, but the automated tests can not replace the need for manual testing. For example, you have to perform insulation resistance tests when we receive new or rewinding motors. Each time take the motor out of the garage service, we should always test the motor windings before the motor cable termination. If you do maintenance to the power outage, manual testing is the best choice.

Test results are automatically or manually, the data of test results should be stored in order to produce an electric motor performance trend graphs. In this process the manual method can be very long to find a graph of test results and test methods can be used automatically, can use the "CMMS" or similar software. Always use only the results of tests performed on the same test voltage for the same period, and under conditions of temperature and humidity are similar to results obtained graph is always valid, comprehensive and easy to analyze the existing discrepancies.

 

Voltage Test

In today's world, megohmmeters mostly been using DC voltage or simply by batteries. The main advantage of the DC assay test kits one of which is smaller and lighter, test equipment does not damage the object being tested (nondestructive testing), and be able to compile historical data / records a history of the results of the tests that have been made.

Testing with AC voltage test voltage value is usually two times the voltage on the nameplate plus 1.000V. When using a DC voltage, megohmmeters that we use today, just a test voltage at twice the nameplate voltage. The table (right) gives the test voltage is recommended. However, you should still contact the manufacturer to find out the recommended test voltage value.

 

Test Connections

Before starting the test, kebumikan / ground the starter terminal, frame, and the motor shaft. If you test DC motors, lifting the brush out. Discharge / charge field waste on rolls with membumikannya / grounding. Then remove the grounding of the motor windings and connect to the line (-) on megohmmeter. Connect the terminal (+) to the grounding. You also have to measure the stator in the same way.

 

Spot Reading Test

Perform this test only when the winding temperature above the dew point. Megohmmeter connect to each one of transverse roll insulation. Apply test voltage for a certain period (usually 60 seconds). Then note the reading of test equipment. Use the same duration for all tests performed as a comparison.

Spot measurements can be meaningful only if we compare the test results have been deposited with trend graphs developed from previous tests. A declining trend charts typically show a loss of insulation resistance due to unfavorable conditions such as humidity, dust accumulation, and oil penetration. Showed a sharp decline in insulation failure.

 

Dielectric Absorption Test

This test serves to compare the absorption characteristics of the insulation is still good until the parts are wet with moisture. During the test, applying the test voltage for an extended period, usually 10 minutes. Take the measurements every 10 seconds for the first minute and a per-minute for the next nine minutes. Then you can create a trend graph of insulation resistance value over time.

The slope of the curve indicates that the isolation conditions tested. Good insulation will show continuous improvement in the resistance, as shown in curve D in Figure (right). Contaminated, damp insulation, or the crack will produce a curve similar to curve E.

Polarization Index (PI) can we find by dividing the value of the 10-minute readings by 1-minute readings. This index shows the slope of the curve. A low PI usually indicates excessive moisture and contamination. For large motors or generators, are generally found values ​​as high as 10.

 

Step Voltage Test

Apply a test voltage of two or more in a few steps. The recommended ratio is 1:5 for each stepnya. At each step, test voltage is given for the same period of time, usually 60 seconds. This will create a pressure on the electrical insulation area of the cracked / brittle. The test voltage greater is intended to reveal the onset of aging and damage to internal insulation which though looks relatively dry and clean insulation where damage can not be detected by low voltage or nominal.

Compare some of the measurements taken at different voltage levels, then find where is the reduction of excessive insulation resistance value at a higher voltage level. Isolation of a dry, clean, and undamaged should have a resistance value of the fixed / stable despite the changes in the voltage level of a given test. Resistance values ​​are substantially decreased when tested at a higher voltage level indicates the quality of the insulation begins to deteriorate.

Many people choose not to test insulation resistance testing because they fear it will actually damage the insulation, but in fact this is not true. By testing the motor on a regular basis, we will be able to analyze and correct the failure of insulation that will come before the turmoil on the production system is more severe.

The research was conducted by: John Kolibri, AEMC :: Hummingbird is a product development manager AEMC Instruments, Foxborough, Mass.

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