eep_super capacitors – different than others

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Super CapacitorsDifferent Than Others

(part 1)

PostedFeb 23 2013bysravankumarpadalainElectrical Lectures,Electronicswith3 CommentsTranslate

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Different then others - Super Capacitors (photo by Mr Toms World via Flickr)
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Introduction to Super Capacitors

Super Capacitor - 10F/2.5V

Capacitors storeelectric charge. Because the charge is stored physically, with no chemical or

phase changes taking place, the process is highly reversible and the discharge-charge cycle can

be repeated over and over again, virtually without limit.

Electrochemical capacitors (ECs)variously referred to by manufacturers in promotional

literature as Super capacitors also called ultra capacitors and Electri c double layer capacitors

(EDLC)are capacitors with capacitance values greater than any other capacitor type available

today.

Capacitance values reaching up to 400 Faradsin a single standard case sizeare available.

Super capacitors have the highest capacitive density available today with densities so high thatthese capacitors can be used to applications normally reserved forbatteries. Super capacitors are

not as volumetrically efficient and are more expensive than batteries but they do have other

advantages over batteries making the preferred choice in applications requiring a large amount ofenergy storage to be stored and delivered in bursts repeatedly.

The most significant advantage super capacitors have over batteries is their abil ity to be charged

and discharged conti nuously wi thout degrading l ike batter ies do. This is why batteries andsuper capacitors are used in conjunction with each other.

The super capacitorswill supply power to the system when there are surges or energy burstssince super capacitors can be charged and discharged quickly while the batteries can supply the

bulk energysince they can store and deliver larger amount energy over a longer slower period oftime.
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Construction of Super Capacitors

What makes super capacitors different from other capacitors types are the electrodes used in

these capacitors. Super capacitors are based on a carbon (nano tube) technology. The carbontechnology used in these capacitors creates a very large surface area with an extremely small

separation distance.

Capacitors consist of2 metal electrodesseparated by a dielectric material. The dielectric not

only separates the electrodes, but also has electrical properties that affect the performance of a

capacitor.

Super capacitors do not have a traditional dielectric material like ceramic, polymer f ilmsoraluminum oxideto separate the electrodes, but instead have a physical barrier made from

activated carbon that when an electrical charge is applied to the material a double electric field is

generated which acts like a dielectric.

The thickness of the electr ic double layer is as thin as a molecule.

The surface area of the activated carbon l ayeris extremely large yielding several thousands ofsquare meters per gram. This large surface area allows for the absorption of a large amount of

ions.

The charging/discharging occurs in an ion absorption layer formed on the electrodes of activated

carbon.

Figure 1 - Super Capacitor


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The activated carbon fiber electrodes are impregnated with an electrolyte where positive and

negative charges are formed between the electrodes and the impregnant.

The electric double layer formed becomes an insulator until a large enough voltage is applied

and current begins to flow. The magnitude of voltage where charges begin to flow is where the

electrolyte begins to break down.

This is called the decomposit ion voltage.

The double layers formed on the activated carbon surfaces can be illustrated as a series of

parallel RC circuits.

As shown below the capacitor is made up of a series of RC circuits where R1, R2 Rn are the

internal resistances and C1, C2, Cn are the electrostatic capacitances of the activated carbons.

Figure 2 - Equivalent circuit

When voltage is applied current flows through each of the RC circuits. The amount of time

required to charge the capacitor is dependent on the CxR valuesof each RC circuit.

Obviously the larger the CxR the longer i t wil l take to charge the capacitor.

The amount of current needed to charge the capacitor is determined by the following equation:

In= (V/Rn) exp (-t/ (Cn*Rn))


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Super capacitor is a double layer capacitor; the energy is stored by charge transfer at the

boundary between electrode and electrolyte. The amount of stored energy is function of the

available electrode and electrolyte surface, the size of the ions, and the level of the electrolytedecomposition voltage.

Super capacitors are constitu ted of two electrodes, a separator and an electrolyte.

The two electrodes, made ofactivated carbonprovide a high surface area part, defining so

energy density of the component. On the electrodes, current collectors with a high conductingpart assure the interface between the electrodes and the connections of the super capacitor. The

two electrodes are separated by a membrane, which allows the mobility of charged ions and

forbids no electronic contact.

The electrolyte supplies and conducts the ions from one electrode to the other.

Comparison of construction diagrams of three capacitors. Left: "normal" capacitor, middle:

electrolytic, right: electric double-layer capacitor

Usual ly super capacitor s are divided into two types:

1. Double-layer capacitors and2. Electrochemical capacitorsThe former depends on the mechanism of double layers, which is result of the separation of

charges at interface between the electrode surface of active carbon or carbon fiber and

electrolytic solution. Its capacitance is proportional to the specific surface areas of electrodematerial.


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The latter depends on fast faraday redox reaction.

The electrochemical capacitors include metal oxide super capacitor sand conductive polymersuper capacitors. They all make use of the high reversible redox reaction occurring on electrodes

surface or inside them to produce the capacitance concerning with electrode potential.

Capacitance of them depends mainly on the uti li zation of active mater ial of electrode.

The working voltage of electrochemical capacitor is usually lower than 3 V. Based on high

working voltage of electrolytic capacitor, the hybrid super-capacitor combines the anode of

electrolytic capacitor with the cathode of electrochemical capacitor, so it has the best featureswith the high specific capacitance and high energy density of electrochemical capacitor.

The capacitors can work at high voltage without connecting many cells in series.

The most important parameters of a super capacitor include the capacitance (C), ESRand EPR

(which is also called leakage resistance).

Will be continued

Super CapacitorsDifferent Than Others

(part 2)

PostedMar 1 2013bysravankumarpadalainElectronics,Energy and Powerwith2 Comments

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Super Capacitors - Different Then Others (on photo Super Capacitor 2.7V, Capacitance0.22~20F, E.S.R. 40~2000ohm)

Continued from fir st part:Super CapacitorsDifferent Then Others (part 1)

Content

1. Equivalent circuit2. How to measure the capacitance?

o Charge Methodo Discharge Method

3. Measure Capacitance4. Capacitor types5. Advantages of the supercapacitors

Equivalent circuit
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Super capacitors can be illustrated similarly to conventional fi lm, ceramic or aluminum

electrolyti c capacitors.

Figure 3 - First order model of a super capacitor

This equivalent circui tis only a simplified or first order model of a super capacitor. In actuality

super capacitors exhibit a non ideal behavior due to the porous materials used to make theelectrodes. This causes super capacitors to exhibit behavior more closely to transmission linesthancapacitors.

Below is a more accurate illustration of the equivalent cir cui t for a super capacitor:

Figure 4 - Model of a super capacitor

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How to measure the capacitance?

There are a couple of ways used to measure the capacitance of super capacitors:

1. Charge method2. Charging and discharging method.
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Go to Content

Charge Method

Measurementis performed using acharge methodusing the following formula:

C = t / R

t = 0.632 x Vo where Vo is the applied voltage.

Figure 5 - Charge and discharge methods

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Discharge Method

This method is similar to the charging method except thecapacitanceis calculated during the

discharge cycle instead of the charging cycle.

Di scharge time for constant cur rent discharge:

t= Cx ( V0V1 ) / I

Discharge time for constant resistance discharge:

t= CR ln ( V1 / V0 )
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Where:

tdischarge time,

V0initial voltage

V1ending voltage

Icurrent

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Measure Capacitance

Super capacitors have such large capacitance values that standard measuring equipment cannot

be used to measure the capacity of these capacitors.

Capacitance is measured per the foll owing method:

1. Charge capacitor for 30 minutes at rated voltage.2. Discharge capacitor through a constant current load.3. Discharge rate to be 1mA/F.4. Measure voltage drop between V1 to V2.5. Measure time for capacitor to discharge from V1 to V2.6. Calculate the capacitance using the following equation:

C = I * ( T2T1 )

V1V2

Where:

V1 = 0.7 Vr, V2 = 0.3 Vr (Vrrated voltage of capacitor)

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Capacitor types

We group capacitors into three family types and the most basic is the electrostatic capacitor,

with a dry separator.

This capacitor has a very low capacitance and is used to filter signals and tune radio frequencies.
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Capacitor types

The size ranges from a few pico-farad (pf)to low microfarad (uF ).

The next member is the electrolyti c capacitor, which is used for :

1. Power filtering,2. Buffering and3. Coupling.

Rated in microfarads (F), this capacitor has several thousand times the storage capacityof theelectrostatic capacitor and uses a moist separator.

How a Capacitor Works

by Dr. Oliver Winn

Cant see this video? Clickhereto watch it on Youtube.

The third type is the supercapacitor, rated in farads, which is again thousands of times higher

than the electrolytic capacitor. The supercapacitor is ideal for energy storage that undergoesfrequent charge and discharge cycles at high current and short duration.
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Faradis a unit of capacitance named after the English physicistMichael Faraday. One farad stores one

coulomb of electrical charge when applying one volt. One microfaradis one million times smaller than a

farad, and one pico-farad is again one million times smaller than the microfarad.

Engineers at General E lectri cfirst experimented with the electric doublelayer capacitor, which

led to the development of an early type of supercapacitor in 1957. There were no knowncommercial applications then.

In 1966, Standard Oil rediscovered the effect of the double-layer capacitor by accident while

working on experimental fuel cell designs. The company did not commercialize the invention butlicensed it to NEC, which in 1978 marketed the technology as supercapacitor for computer

memory backup.

It was not until the 1990s that advances in mater ialsand manufactur ing methodsled to

improved performance and lower cost.

The modern supercapacitor is not a battery per se but crosses the boundary into batterytechnology by using special electrodes and electrolyte. Several types of electrodes have been

tried and we focus on the double-layer capacitor (DLC) concept. It is carbon-based, has anorganic electrolyte that is easy to manufacture and is the most common system in use today.

All capacitors have voltage limits. While the electrostatic capacitor can be made to withstandhigh volts, the supercapacitor is confined to 2.52.7V. Voltages of 2.8V and higher are possible

but they would reduce the service li fe.

To achieve higher voltages, several supercapacitors are connected in series.

Th is has disadvantages.

Serial connection reduces the total capacitance, and strings of more than three capacitors require

voltage balancing to prevent any cell from going into over-voltage. This is similar to theprotection circuit in lithium-ion batteries.

The specific energy of the supercapacitor is low and ranges fr om 1 to 30Wh/kg. Although highcompared to a regular capacitor, 30Wh/kg is one-fifth that of a consumer Li-ion battery. The

discharge curve is another disadvantage. Whereas the electrochemical battery delivers a steady

voltage in the usable power band, the voltage of the supercapacitor decreases on a linear scalefrom full to zero voltage.

Th is reduces the usable power spectrum and much of the stored energy is left behind.

Consider the following example.

Take a 6V power source that is allowed to discharge to 4.5V before the equipment cuts off. With

the linear discharge, the supercapacitor reaches this voltage threshold within the first quarter of

the cycle and the remaining three-quarters of the energy reserve become unusable.
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A DC-to-DC convertercould utilize some of the residual energy, but this would add to the cost

and introduce a 10 to 15 percent energy loss. A battery with a flat discharge curve, on the other

hand, would deliver 90 to 95 percent of its energy reserve before reaching the voltage threshold.

Table 1below compares the supercapacitor with a typical Li-ion:

Function Supercapacitor Lithium-ion (general)

Charge time 110 seconds 1060 minutes

Cycle life 1 million or 30,000h 500 and higher

Cell voltage 2.3 to 2.75V 3.6 to 3.7V

Specific energy (Wh/kg) 5 (typical) 100200

Specific power (W/kg) Up to 10,000 1,000 to 3,000

Cost per Wh $20 (typical) $0.50-$1.00 (large system)

Service life (in vehicle) 10 to 15 years 5 to 10 years

Charge temperature 40 to 65C (40 to 149F) 0 to 45C (32to 113F)

Discharge temperature40 to 65C (40 to 149F)20 to 60C (4 to 140F)

Rather than operating as a stand-alone energy storage device, supercapacitors work well as low-

main tenance memory backupto bridge short power in ter ruptions. Supercapacitors have alsomade critical inroads into electric powertrains.

The virtue ofultr a-rapid chargingand delivery of high current on demand makes the

supercapacitor an ideal candidate as a peak-load enhancer for hybrid vehicles, as well as fuel cell

applications.

The charge time of a supercapacitor is about 10 seconds.

The charge characteristic is similar to an electrochemical battery and the charge current is, to a

large extent, limited by the charger. The initial charge can be made very fast, and the topping

charge will take extra time.

Provision must be made to limit the initial current inrushwhen charging an empty

supercapacitor.

The supercapacitor cannot go into overcharge and does not require full-charge detection; the current

simply stops flowing when the capacitor is full. The supercapacitor can be charged and discharged


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virtually an unlimited number of times. Unlike the electrochemical battery, which has a defined cycle

life, there is little wear and tear by cycling a supercapacitor.

Nor does age affect the device, as it woul d a battery.

Under normal conditions, a supercapacitor fades from the original 100 percent capacity to 80percent in 10 years. Applying higher voltages than specified shortens the life. The supercapacitor

functions well at hot and cold temperatures.

The self -discharge of a supercapacitoris substantially higher than that of an electrostatic

capacitor and somewhat higher than the electrochemical battery. The organic electrolytecontributes to this.

The stored energy of a supercapacitor decreases from 100 to 50 percent in 30 to 40 days.

A nickel-based battery self-discharges 10 to 15 percent per month. Li-ion discharges only five percent

per month.

Supercapacitors are expensive in terms of cost per watt. Some design engineers argue that themoney for the supercapacitor would better be spent on a larger battery.

We need to reali ze that the supercapacitor and chemical battery are not in competiti on; ratherthey are different products serving unique applications.

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Advantages of the supercapacitors1. Cell voltage determined by the circuit application, not limited by the cell chemistry.2. Very high cell voltages possible (but there is a trade-off with capacity)3. High power available.4. High power density.5. Simple charging methods. No special charging or voltage detection circuits required.6. Very fast charge and discharge. Can be charged and discharged in seconds. Much faster than

batteries.

7. No chemical actions.8. Can not be overcharged.9. Long cycle life of more than 500,000 cycles at 100% DOD.10.Long calendar life 10 to 20 years11.Virtually unlimited cycle life not subject to the wear and aging experienced by the

electrochemical battery.

12.Low impedance enhances pulse current handling by paralleling with an electrochemicalbattery.

13.Rapid charging low-impedance supercapacitors charge in seconds.14.Simple charge methods voltage-limiting circuit compensates for selfdischarge; no full-charge

detection circuit needed.
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15.Cost-effective energy storage lower energy density is compensated by a very high cycle count.16.Almost zero maintenance and long life, with little degradation over hundreds of thousands of

cycles.

While most commercially available rechargeable batteries can be charged 200 to 1000 times,

ultracapacitors can be charged and discharged hundreds of thousands of times with no

damage.However, in reality, they can be charged and discharged virtually unlimited number of

times, and will last for the entire lifetime of most devices and applications they are used in, thus

making them environmentally friendly.

Battery lifetime can be optimised by only charging under favorable conditions, at an ideal rate

and, for some chemistries, as infrequently as possible.

Ultracapacitors can help in conjunction with batteries by acting as a charge conditioner, storing

energy from other sources for load balancing purposes and then using any excess energy to

charge the batteries at a suitable time.

17. Increased safety since they can handle short circuit and reverse polarity. Also, there is no fireand explosion hazard.

18. Improved environmental safety since there is no corrosive electrolyte and toxicity of materialsused is low.

Rechargeable batteries on the other hand wear out typically over a few years, and their highlyreactive chemical electrolytes present a disposal and safety hazard.

19.Rugged since they have Epoxy Resin Sealed Case which is non corrosive.Go to Content

Testing and Commissioning of Substation DC

System

PostedJan 9 2013byEdvardinPower Substation,Testing and Commissioningwith1 CommentTranslate Get PDF
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Testing and Commissioning of Substation DC System (on photo: The battery assembly rated at

108V 200AH, 55 Tungstone Plante Cells all fitted with Aquagen catalytic recombination fillers,which effectively reduce topping up to less than once a year.- by prepair.co.uk)

Objective

Power substation DC systemconsists ofbattery chargerand battery. This is to verify the

condition of battery and battery charger and commissioning of them.

Test Instruments RequiredFoll owing instruments wil l be used for testing:

1. Multimeter. (Learn how to use it)2. Battery loading unit (Torkel-720 (Programma Make) or equivalent.

The Torkel-720is capable of providing a constant current load to the battery under test.
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Torkel 720 Battery Load Capacity Tester Front View

Commissionig Test Procedure

1. Battery Charger

1. Visual Inspection: The battery charger cleanliness to be verified. Proper cableterminationof incoming AC cable and the outgoing DC cable and the cable connectionbetween battery and charger to be ensured. A stable incoming AC supply to the battery

charger is also to be ensured.

2. Voltage levels in the Float charge mode and the Boost charge mode to be set according tospecifications using potentiometer provided.

3. Battery low voltage, Mains Off, charger Off etc., conditions are simulated andchecked forproper alarm / indication. Thus functional correctness of the battery charger

is ensued.4. Charger put in Commissioni ng modefor duration specified only one time during initial

commissioning of the batteries. (By means of enabling switch.)

5. Battery charger put in fast charging boost mode and battery set boost charged for theduration specified by the battery manufacturer.6. After the boost charging duration, the battery charger is to be put in float charging (trickle

charge) mode for continuous operation.

Some chargers automaticall y switch to f loat charge modeafter the charging current

reduces below a certain value.
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7. Voltage and current values are recorded during the boost charging and float-chargingmode.

NiCad Batteries being charged

This test establishes the correct operation of the battery chargerwithin the specified voltage and

current levels in various operational modes.

Calculate size of battery bank and inverterGet MS Excel Spreadsheet!

2. Battery Unit

1. Mandatory Condition: The battery set should have been properly charged as per thecommissioning instructions of the battery manufacturer for the duration specified.

2. Visual Inspection: Cleanliness of battery is checked and the electrolyte level checked asspecified on the individual cells. The tightness of cell connections on individual terminals

should be ensured.3. The load current, minimum voltage of battery system, ampere-hour, duration etc., is

preset in the test equipment using the keypad.

For (e.g.) a 58 AH battery set, 5 Hr. duration specification 11.6 A and 5 Hr. duration are

set. Minimum voltage setting is = No. of cells x end cell voltage of cells as permanufacturer specification.

4. It is to be ensured that the set value of the current and duration is within the dischargecapacity of the type of cell used. Also the total power to be dissipated in the load unitshould be within the power rating of the battery load kit.

5. Individual cell voltages to be recorded before the start of the test.6. Battery charger to be switched off/load MCB in charger to be switched off.
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7. Loading of the battery to be started at the specified current value.Individual cell voltages of the battery set are to be recorded every half an hour.

8. It is to be ensured that all the cell voltages are above the end-cell voltage specified by themanufacturer.

If any of the cell voltages falls below the threshold level specified by the manufacturer,

this cell number is to be noted and the cell needs to be replaced.9. Test set automatically stops loading after set duration (or) when minimum voltagereached for the battery set.

10.Test to be continued until the battery delivers the total AH capacity it is designed for.Value of AH and individual cell voltages to be recorded every half an hour.

Acceptance Limits

Th is test establi shes the AH capacity of battery set at requi red voltage.

The acceptance limit for the test is to ensure the battery set is capable of supplying the required

current at specified DC voltage without breakdown for the required duration.

Resource:Procedures for Testing and Commissioning of Electrical EquipmentSchnedeider

Electric

Testing and Commissioning of MV/HV

CablesPostedJan 12 2013byEdvardinTesting and Commissioningwith2 Comments

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Example of asbestos paper insulation wrap on high-voltage cable inside an underground cablevault. Several layers of the soft and friable insulation are wrapped around the cable in long, wide

strips. Originally, pure white, the discoloration is from sediment mud after formerly being

submerged in the once flooded vault; some water leakage is still present.

1. Visual and Mechanical Inspection

1. Comparecable datawith drawings and specifications.2. Inspect exposed sections of cables forphysical damage.3. Inspect bolted electrical connections for high resistance using one or more of the following

methods:

1. Use of a low-resistance ohmmeter in accordance with Section 1.2 above.2. Verify tightness of accessible bolted electrical connections by calibrated torque-wrench

method in accordance with manufacturers published data or Table 100.12.

3. Perform a thermographic survey.(NOTE: Remove all necessary covers prior to thermographic inspection. Use appropriate

caution, safety devices, and personal protective equipment.)

4. Inspect compression-applied connectors for correct cable match and indentation.5. Inspect shield grounding, cablesupports, and terminations.
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6. Verify that visible cable bends meet or exceed ICEA and manufacturers minimum publishedbending radius.

7. Inspect fireproofing in common cable areas. (**)8. If cables are terminated through window-type current transformers, inspect to verify that

neutral and ground conductors are correctly placed and that shields are correctly terminated for

operation of protective devices.

9. Inspect for correct identification and arrangements.10. Inspect cable jacket andinsulation condition.

* * Optional test

2. Electrical Tests

1. Perform resistance measurements through bolted connections with a low-resistanceohmmeter, if applicable, in accordance with Section 1.1.

2. Perform an insulation-resistance test individually on each conductor with all other conductorsand shields grounded. Apply voltage in accordance with manufacturers published data. In theabsence of manufacturers published data, use Table 100.1.

3. Perform a shield-continuity teston each power cable.4. In accordance with ICEA, IEC, IEEEand other power cable consensus standards, testing can be

performed by means of direct current, power frequency alternating current, or very low

frequency alternating current. These sources may be used to performinsulation-withstand tests,

and baseline diagnostic tests suchas partial discharge analysis, and power factor or dissipation

factor. The selection shall be made after an evaluation of the available test methods and a

review of the installed cable system.

.

Some ofthe available test methods are listed below:

.

1. Dielectric Withstand:1. Direct current (DC) dielectric withstand voltage2. Very low frequency (VLF) dielectric withstand voltage3. Power frequency (50/60 Hz) dielectric withstand voltage

2. Baseline Diagnostic Tests:1. Power factor/ dissipation factor (tan delta):

1. Power frequency (50/60 Hz)2. Very low frequency (VLF)

2. DC insulation resistance:3. Off-line partial discharge:

1. Power frequency (50/60 Hz)2. Very low frequency (VLF)

3. Test Values

3.1 Test ValuesVisual and Mechanical
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1. Compare bolted connection resistance values to values of similar connections. Investigate valueswhich deviate from those of similar bolted connections by more than 50 percent of the lowest

value.

2. Bolt-torque levels should be in accordance with manufacturers published data. In the absenceof manufacturers published data, use Table 100.12.

3. Results of the thermographic survey.(NOTE: Remove all necessary covers prior to thermographic inspection. Use appropriate caution,

safety devices, and personal protective equipment.)

4. The minimum bend radius to which insulated cables may be bent for permanent training shallbe in accordance with Table 100.22.

3.2 Test ValuesElectrical

1. Compare bolted connection resistance values to values of similar connections. Investigate valueswhich deviate from those of similar bolted connections by more than 50 percent of the lowest

value.

2. Insulation-resistance values shall be in accordance with manufacturers published data. In theabsence of manufacturers published data, use Table 100.1.Values of insulation resistance less

than this table or manufacturers recommendations should be investigated.

3. Shielding shall exhibit continuity. Investigateresistance valuesin excess often ohms per 1000feet of cable.

4. If no evidence of distress or insulation failure is observed by the end of the total time of voltageapplication during the dielectric withstand test, the test specimen is considered to have passed

the test.

5. Based on the test methodology chosen, refer to applicable standards or manufacturersliterature for acceptable values.

Tables

Table 100.12.1

Bolt-Torque Values for Electrical Connections

- US Standard Fasteners (a)

- Heat-Treated SteelCadmium or Zinc Plated (b)
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Table 100.12.1 - Bolt-Torque Values for Electrical Connections

a) Consult manufacturer for equipment supplied with metric fasteners.b) Table is based on national coarse thread pitch.

Table 100.12.2


- Silicon Bronze Fasteners (b, c)

Torque (Pound-Feet)

Torque (Pound-Feet)


24/30


c) This table is based on bronze alloy bolts having a minimum tensile strength of 70,000 poundsper square inch.

Table 100.12.3


- Aluminum Alloy Fasteners (b, c)

Torque (Pound-Feet)

Torque (Pound-Feet) - Aluminum Alloy Fasteners

a) Consult manufacturer for equipment supplied with metric fasteners.

b) Table is based on national coarse thread pitch.c) This table is based on aluminum alloy bolts having a minimum tensile strength of 55,000

pounds per

square inch.

Table 100.12.4


- Stainless Steel Fasteners (b, c)


25/30

Torque (Pound-Feet)

Torque (Pound-Feet) - Stainless Steel Fasteners


c) This table is to be used for the following hardware types:

Bolts, cap screws, nuts, flat washers, locknuts (18-8 alloy) Belleville washers (302 alloy).

Tables in 100.12 are compiled from Penn-Union Catalogue and Square D Company, AndersonProducts Division, GeneralCatalog: Class 3910 Distribution Technical Data, Class 3930

Reference Data Substation Connector Products.

Table 100.1

Insulation Resistance Test Values Electrical Apparatus and Systems

Table 100.1 - Insulation Resistance Test Values Electrical Apparatus and Systems


26/30

In the absence of consensus standards dealing with insulation-resistance tests, the StandardsReview Council suggests the above representative values. Test results are dependent on thetemperature of the insulating material and the humidity of the surrounding environment at the

time of the test.

Insulation-resistance test data may be used to establish a trending pattern. Deviations from the

baseline information permit evaluation of the insulation.

Table 100.22

Minimum Radii for Power Cable

Single and Multiple Conductor Cables with Interlocked Armor, Smooth or CorrugatedAluminum Sheath or Lead Sheath

Table 100.22 - Minimum Radii for Power Cable

ANSI/ICEA S-93-639/NEMA WC 74-2000, 5-46 kV Shielded Power Cable for Use in the Transmission and

Distribution of Electric Energy, Appendix I Recommended Bending Radii for Cables and Table I1

Minimum Radii for Power Cable.

a. 12 x individual shielded conductor diameter, or 7 x overall cable diameter, whichever is

greater.


27/30

Resource:STANDARD FOR ACCEPTANCE TESTING SPECIFICATIONS for Electrical Power

Equipment and Systems (NETA 2009)

Life cycle cost of transformers

PostedAug 6 2011byEdvardinTransformerswith2 Comments

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10kv, 20KV, 35KV oil immersed power transformer

To perform theeconomical analysisof transformer, it is necessary to calculate its life cycle cost,

sometimes called total cost of ownership, over the life span of transformer or, in other words, the

capitalised cost of the transformer. All these terms mean the samein one formula, costs ofpurchasing, operating and maintaining the transformer need to be compared taking into account

the time value of money.

The concept of the time value of money is that a sum of money received today has a higher

valuebecause it is available to be exploitedthan a similar sum of money received at some

future date.

In practice, some simplification can be made. While each transformer will have its own purchase

price and loss factors, other costs, such as installation, maintenance and decommissioning will besimilar for similar technologies and can be eliminated from the calculation. Only when different
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technologies are compared e.g. air cooleddry type transformerswith oil cooled transformers

will these elements need to be taken into account.

Taking onlypurchase priceand the cost of losses into account the Total Cost of Ownership can

be calculated by:

where:

PPis the purchase price of transformer,

Arepresents the assigned cost of no-load losses per watt,

Pois the rated no-load loss,

Bis the assigned cost of load losses per watt,

Pkis the rated load loss.

Po and Pkare transformer rated losses. A and B values depend on the expected loading of thetransformer andenergy prices. The choice of the factors A and B is difficult since they depend

on the expected loading of the transformer, which is often unknown, and energy prices, whichare volatile, as well as interest rate and the anticipated economic lifetime.

If the load grows over time, the growth rate must be known or estimated and the applicableenergy price over the lifetime must be forecast.

Typically, the value of A ranges from less than 1 to 8 EUR/Watt and B is between 0.2 and 5EUR/Watt. Below we propose a relatively simple method for determining the A and B factor fordistribution transformers.

A and B factors are calculated as follows:

(no-load loss capitalisation)

and (no-load loss capitalisation)

where:

iinterest rate [%/year]

nlifetime [years]

CkWhkWh price [EUR/kWh]

8760number of hours in a year [h/year]
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Illoading current [A]

Irrated current [A]

These formulae assume that energy prices and the loading are constant over the transformer life.

Usually, the loss evaluation figures A and B form part of the request for quotation are submitted

to the transformer manufacturers, who can then start the complicated process of designing atransformer to give the required performance. The result of this open process should be the

cheapest transformer, i.e. with the lowest total cost of ownership, optimised for a given

application.

The drawback of this process is, as mentioned, the difficulty in predicting the future load profile

and electricity costs and tarrifs with any confidence. On the other hand, these optimisation effortsdepend on material prices, particularly active materials, i.e. conductor and core material.

Dynamic optimisation makes sense when there is the different price volatility of different

materials like aluminium and copper or high and low loss magnetic steel..

For large transformers, above a few MVA, the cost of losses are so high that transformers arecustom-built, tailored to the loss evaluation figures specified in the request for quotation for a

specific project.

For distribution transformers, often bought in large batches, the process is undertaken once everyfew years. This yields an optimum transformer design, which is then retained for several yearsless so nowadays because of the volatility of metal pricesuntil energy prices and load profiles

have changed dramatically. In fact the loss levels established in HD428, HD538 and national

standards reflect established practice of preferred designs with respect to loss evaluation values.

To make the capitalisation more attractive, so that the use of TCO is easier, we propose the use

of a graph, shown in Figure 5, which allows determination of factor A.

Factor A expresses the relation between the cost of no load losses and the following:

Electricity price Discount rate or company interest rate or average cost of capital Capitalisation period or expected lifetime of the transformer

This example illustrates that for an electricity price of 100/MWh, an interest rate of 5% and a10 year capitalisation period, the cost of no load loss will be 6,75 / Watt.

Factor A is directly proportional to electricity price so the A factor can simply be scaled toaccount for electricity price changes as long as the interest rate and capitalisation period remain

unchanged.


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Figure 1. Simplified chart for calculation of factor A

It is important to note that, for small interest rates, a doubling of the capitalisation period will

result in almost doubling the cost of losses. On the other hand, applying too high a capital rate,

by making, for example, too high a provision for risk, will produce a low value of loss.

Factor B, as explained previously, is simply the product of factor A and the square of the loadingfactor. (B = A * (Loading)2) The loading factor used here is the expected average load over the

life span of the transformer, possibly taking harmonics into account.

SOURCE: Selecting Energy Efficient Distribution Transformers A Guide for Achieving Least-

Cost SolutionsSEEDT
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eep_super capacitors – different than others

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