miércoles, 9 de noviembre de 2011

PARTICULAR NATURE´S ELECTRICITY

Electricity is a form of energy particularly flexible and adaptable. Can be converted into other forms of energy: heat, light, mechanical energy and in other ways: electromechanical, electronic, acoustic and visual techniques are based on modern telecommunications, information technology and entertainment.

Electricity, as supplied to customers, has several features that may vary and affect their usefulness to users of the network. This standard describes the characteristics of the AC voltage electricity. Given the use made of electricity, it is desirable that this alternating voltage supplied at a constant frequency, according to a perfect sine wave and a constant amplitude. In practice this does not allow many factors. Unlike standard products, the use made of it is one of the main factors determining the variation of its "features".

The power supply to equipment users in the network causes electrical currents roughly proportional to the demand of users. When these currents flow through the network drivers, give rise to voltage drops. The amplitude of the voltage supplied to a user at any time is a function of accumulated voltage drops across all network elements through which the user feeds, and is determined both by individual demand and the simultaneous demand from other users. Since each customer demand is constantly changing along with additional variation depending on the match between the demands of different users, also vary the voltage supplied. For this reason, this standard deals with the voltage characteristics in terms of statistics and probability. Economic benefit of the customer, the standard corresponds to normal conditions rather than under unusual circumstances such as an unusual degree of overlap between the demands of multiple devices or users.

The electricity reaches the customer through a system of production, transportation and distribution. Each network element can be subjected to damage or failure caused by electrical stresses, mechanical and chemical, due to various factors such as extreme weather conditions, normal wear, aging, external causes due to human activities, the birds , animals, etc.. Such damage can affect or even disrupt the power of one or more users.

To maintain constant frequency, it is necessary to have a production capacity in each time adapted to the demands of all users simultaneously. As the production capacity and the load likely to vary discretely, particularly in the case of failures in the generation and transmission or distribution, there is always a risk of imbalance that causes an increase or decrease the frequency. However, this risk is reduced if many networks are grouped in a large interconnected network whose production capacity is very large with respect to any changes which may occur.

Many other features can disrupt or damage the user's computers and even network user itself. Some of these characteristics are linked to unavoidable transients inherent to the network itself, caused by the misconduct, maneuvers or atmospheric phenomena (lightning). Other features, however, are the result of various uses of electricity directly modify the waveform voltage, impose a particular value of the amplitude or voltage signal superimposed information. Coincidentally, the recent proliferation of equipment which produces these effects is accompanied by an increase in the number of equipment sensitive to these disturbances.

This European Standard defines, when possible, the variations of the features normally expected. In other
cases, the standard gives a quantitative estimation, the best of what you find in practice.

Due to the diversity of structures of distribution networks in different regions resulting from the differences of charge density, dispersion of the population, local topography, etc.., Many users of the network can find variations the voltage characteristics well below the values ​​indicated in this statement.

One of the properties of electricity is that, with respect to some of its characteristics, its quality depends more on the user to the supplier or producer. In such cases, the user is thus an important partner of the supplier to strive to maintain quality of electricity.

It should be stressed that this issue has been addressed in other standards already published or under development: the emission standards of customer devices define levels of electromagnetic interference that these teams are authorized to issue. Immunity standards define levels of disturbance tolerated by the equipment without causing excessive damage or stop functioning. A third type of standards concerning electromagnetic compatibility levels can coordinate and harmonize standards of emission and immunity, in order to ensure electromagnetic compatibility.

Although there are obvious links with the levels of compatibility, it is important to note that this standard deals with the characteristics of the voltage. This is not a standard for compatibility levels. It is important to note that the performance of a team can degrade if feeding conditions are more severe than those defined in the relevant product standard.


viernes, 21 de octubre de 2011

CHARACTERISTICS IN LOW VOLTAGE II

Interharmonic voltages; interharmonics level increases due to the development of inverters and other similar equipment and command control. Because of the limited experience in this field, levels of interharmonics are to be studied.
In some cases, interharmonics, even weak level, causing the lamp flashing or interference with ripple control systems.

Transmission of signals through the network information; In some countries, the general distribution network can be used by the distributor to transmit signals. The voltage value of the transmitted signals, averaged over 3 s, must not exceed the values ​​indicated by Figure 1 in a time period equal to 99% overnight.


















Nite :
Facilities customers can use carrier-current signals at frequencies between 95 kHz and 148.5 kHz. Although the overall network utilization is not authorized for the signal transmission between clients must be taken into account tensions at these frequencies that reach up to 1.4 V rms in the general distribution network in BT. Because of the possibility of mutual interference between signal transmission facilities nearby, it may be necessary for the client to protect or ensure proper immunity to installation of transmission.

lunes, 3 de octubre de 2011

CHARACTERISTICS IN LOW VOLTAGE I

Frequency ; the nominal frequency of the voltage supplied is 50 Hz normal operating conditions, the value
half of the fundamental frequency measured in periods of 10 s should be placed in the following ranges:
- Coupled network for synchronous connections to an interconnected system:

50 Hz ± 1% (ie 49.5 Hz to 50.5 Hz) for 99.5% a year
50 Hz +4% / - 6% (ie 47 Hz to 52 Hz) for 100% of the time

- No network connection to an interconnected system synchronous (eg food webs that exist in
certain islands):

50 Hz ± 2% (ie 49 Hz to 51 Hz) for 95% of one weeks
50 Hz ± 15% (ie 42.5 Hz to 57.5 Hz) for 100% of the time

Amplitude of the voltage supplied

A standard nominal voltage for low voltage general networks is A = 230 V, both phase-neutral
and between phases

- In the case of a three-phase 4-wire:
A = 230 V between phase and neutral;

- In the case of a three-phase 3-wire:
A = 230 V between phases.
NOTE In low voltage systems and the declared voltage rating equal.

Variations of the voltage supplied
Requirements
Voltage variations should not exceed ± 10%.
This excludes situations like that arise following faults or voltage interruptions, beyond the
reasonable control of the parties involved.

NOTE 1
Experience has shown that voltage deviations maintained within ± 10% over a long period of time are extremely unlikely, but theoretically could be within the limits given in paragraph 4.3.2.
For this reason, in accordance with product standards and associated facilities and the application of IEC 60038, the end user's computers are usually designed to tolerate variations of ± 10% of the rated voltage of the system, which is enough to cover most of the conditions of supply. It is assumed that is neither technically nor economically feasible to have teams that are capable of working with voltages higher tolerances to ± 10%. If it were the case in which this occurs, the magnitude of the voltage supplied may deviate from this limit for a long period of time, additional measures should be taken in collaboration with the local network operator, depending on the risk analysis. The same applies in cases where specific devices have a sensitivity that increases with voltage variations.

NOTE 2

In case of electricity supply in remote areas with no long lines or a line connected to interconnected, the voltage may
be outside the range of +10% / -15%. Network users should be aware of the conditions.

Test Method
In normal operating conditions:
- For each period of a week, 95% of the effective values ​​of the voltage supplied averaged over 10 min
should be in the range of ± 10%, and
- All effective values ​​of the voltage supplied averaged over 10 min should be in the range A + 10% / -15%.

Fast voltage variations
Sporadic fast voltage variations
The rapid variations of the voltage supplied essentially from variations in load
facilities for users of the network or the network maneuvers.
In normal operating conditions, a rapid variation of the stress generally not exceeding 5% of A but, in certain circumstances, variations may occur which reach up to 10% of A for a short while, several times on the same day.
NOTE
A decrease in the tension that results in a voltage less than 90% of A is regarded as a voltage dip.

Flicker severity
In normal operating conditions for each period of one week, the level of severity of long duration
flicker due to voltage fluctuations should be Plt! 1 for 95% of the time.
NOTE
The flicker response is subjective and can vary according to the causes of perception and by duration.
In some cases, Plt = 1 can
lead to trouble, while in other cases, higher levels of Plt not the cause.

Voltage dips
The voltage dips are generally caused by faults that occur on the premises of the users of the network or grid. These random events are fundamentally unpredictable. Its annual frequency depends mainly on the type of distribution network and the observation point. In addition, their distribution in a year can be very irregular.

Indicative values:
In normal operation, the expected number of voltage dips in a year can go a few tens to a thousand. The majority of voltage sags with a duration of less than a second and a voltage
than 40% residual. However, sometimes sags can occur from a depth and duration
superior. In some places, it often sags occur with a residual voltage between 85% and
90% of A, which are caused by load switching facilities of the network users.

Interruptions of the supply voltage
Indicative values:
During normal operation, the annual number of interruptions of the voltage supplied can
vary from several tens to several hundreds. The duration of approximately 70% of interruptions
may be less than 1 s.
NOTE
In some documents, it is considered that the duration of interruptions not exceeding 1 min.
But sometimes systems are used
control with active run times up to 3 min, to avoid long breaks.

Long interruption of the voltage supplied
Accidental interruptions are generally caused by external causes or events that can not be prevented by the operator of the distribution network. It is not possible to indicate typical values ​​for the annual frequency and duration of long interruptions. This is due to considerable differences in the architecture of networks in different countries, as well as the unpredictable effects of adverse weather conditions and external causes.

Indicative values:
In normal operating conditions, the annual frequency of voltage dips exceeding 3 min
may be less than 10 or as high as 50, depending on the region.
Indicative values ​​of planned outages do not occur on the grounds that are announced in advance.

Temporary surges in the network between conductors and earth
A temporary surge in the frequency of the network is usually during a free kick in the overall network distribution or in a user facility and disappears at the time of disposal of such failure. Under these conditions, the voltage can reach the value of phase voltage (up to 440 V in networks
230/400 V), due to the residual voltage three-phase network, depending on the actual value of the degree of
load imbalance, and the impedance is maintained between the conductor and ground failure.
The length is limited by the time it takes the protection and medium voltage circuit breaker
clear the fault, usually not more than 5 s.
Under certain conditions, a failure that occurs upstream of a transformer can temporarily produce
overvoltages in the low voltage side for the duration of the fault current. Such surges do not exceed
usually 1.5 kV rms.

Overvoltages between live conductors and earth
The surge generally not exceed 6 kV (peak value).
NOTE 1
The rise time can vary from less than a few microseconds to several milliseconds.
However, for physical reasons, the
longer duration transients typically have much lower amplitudes. Therefore, the coincidence of high amplitudes
with long rise times is extremely unlikely.

NOTE 2
The energy content of a surge varies considerably according to their origin.
An induced voltage due to lightning is characterized by a higher amplitude and a lower energy content of an overvoltage caused by maneuvers, because the latter generally last much longer.

NOTE 3
Low voltage installations and equipment from end users are usually designed according to the Standard EN 60664-1, for
withstand surges in most situations. When necessary, according to IEC 60364-4-44, should be selected protective devices shock waves, according to IEC 60364-5-53, to take into account the real situations. It is assumed that this would cover both induced overvoltages due to lightning as maneuvers.

Unbalance of the voltage supplied
In normal operating conditions for each period of a week, 95% of the effective values ​​averaged over 10 min from the reverse component (fundamental) of the supply voltage must be between 0% and 2% of the direct component (fundamental). In some areas where facilities for users of the network are partially monophasic or biphasic, imbalances can reach 3% in the three-phase supply points.
NOTE
This European Standard does not suggest any values ​​that correspond to the inverse of the stress component, which is essential for any
damage to the equipment connected to the network.

Harmonic voltages
In normal operating conditions, during each period of a week, 95% of the RMS values ​​of each harmonic voltage averaged over 10 minutes must not exceed the values ​​given in Table 1. Elevated voltages to give a given harmonic may be due to resonances.
In addition, the rate of total harmonic distortion of the supply voltage (THD) (including all harmonics up
the order 40) should not exceed 8%.
NOTE
The limit of order 40 is by convention.







jueves, 22 de septiembre de 2011

QUALITY STANDARDS´ HONDA- DEFINITIONS II

Flicker Severity:
Intensity of the discomfort caused by the flicker-defined measurement method UIE-IEC flicker and evaluated according to the following amounts: - Short-term severity (Pst) measured over a period of 10 min; - Severity of long-term (Plt) calculated from a sequence of 12 Pst values ​​at an interval of 2 h, using the following formula:








Hollow supply voltage:
Sudden decrease of the supply voltage to a value between 90% and 1% of the declared voltage Uc, followed by the restoration of voltage after a short period of time. By convention, a voltage dip lasts 10 ms to 1 min. The depth of a voltage dip is defined as the difference between the minimum rms voltage during the voltage dip (residual stress) and the declared voltage. Voltage variations do not reduce the supply voltage to a value less than 90% of the declared voltage Uc are not considered as voltage sags.

Power interruption:
Condition in which the voltage at the supply points is less than 1% of the declared voltage Uc. A disruption
supply can be classified as:
- Planned network when users are informed in advance to allow the execution of works
programmed in the grid, or
- Accidental, when caused by permanent or fugitive failures, most often linked to events
external to equipment failure or interference. An accidental interruption can be classified as:
• long interruption (lasting more than 3 min);
• brief interruption (up to 3 min).

NOTE 1 The impact of a planned interruption can be minimized by the network user to take appropriate action.
NOTE 2 accidental interruptions are unpredictable and essentially random events.
Temporary overvoltage at industrial frequency:
Overvoltage of relatively long duration at a given location (see Technical Report CLC / TR 50422, Chapter 3
for more information).
NOTE
Surges are usually due to temporary or minor maneuvers (eg, sudden reduction of the charge, single-phase faults, not
nonlinearities).

Surge:
Oscillatory or oscillatory surge of short duration usually strongly damped and lasts as
most a few milliseconds. [IEV 604-03-13 modified].
NOTE surges are usually caused by lightning, maneuvers, or the operation of fuses. The rise time of the front
of transient overvoltages can vary from less than 1 microsecond to several milliseconds.

Harmonic voltage:
Sinusoidal voltage whose frequency is an integer multiple of the fundamental frequency of the supply voltage.
Harmonic voltages can be evaluated:
- Individually, according to their relative amplitude (Uh) relative to the fundamental voltage U1, where h represents the
order of harmonic
- Globally, ie by the value of the rate of total harmonic distortion (THD) calculated using the formula
following:








NOTE harmonic voltage power network are mainly due to nonlinear loads connected network users at all levels of tension in the mains. Harmonic currents flowing through the circuit impedances result in harmonic voltages. The harmonic currents, impedances of the network and therefore the harmonic voltages in the supply points vary over time.

Interharmonic voltage:
Sinusoidal voltage whose frequency is between the frequencies of the harmonics, ie, the frequency is not a
integer multiple of the fundamental frequency.

NOTE
At the same time interharmonic voltages may appear to have very close frequencies then forming a broadband spectrum.

Voltage imbalance:
Condition in a polyphase system in which the effective values ​​of the line voltages (fundamental component), or phase angles between consecutive line voltages are not equal. The degree of inequality is usually expressed as the ratio of zero sequence components and component inverse and direct sequencing.
[IEV 161-08-09 modified].

NOTE 1
In this European Standard, the voltage imbalance is seen only in three-phase systems and in relation to the component only reverse sequence.

NOTE 2
Several approaches give reasonably accurate results for the levels normally encountered imbalance (ratio of
reverse sequence component and the component of direct sequence), for example










Where U12, U23 and U31 are the three line voltages.

Information signals transmitted by the network:
Signal superimposed on the voltage supplied, in order to transmit information over the network and general distribution the facilities of the network users. The three types of signals on the network can generally be classified as follows way:
- Ripple control signals: superimposed sinusoidal voltage in the range of 110 Hz to 3000 Hz;
- Carrier Current signals: superimposed sinusoidal voltage in the range from 3 kHz to 148.5 kHz;
- Dial-wave signals: pulses (transients) of short duration superimposed on moments chosen on the
voltage wave.

lunes, 5 de septiembre de 2011

QUALITY STANDARDS´ HONDA- DEFINITIONS

Normative references; the rules listed below are indispensable for the application of this standard. For dated references, only the edition cited applies. For undated references the latest edition of the standard (including any amendments).
IEC 60050-161 International Electrotechnical Vocabulary. Chapter 161: Electromagnetic Compatibility.

Definitions
For purposes of this document, the terms and definitions:

Network user:
Party that is supplied or supplies electricity to a distribution network.

Operation of the distribution network:
Party responsible for operating, ensuring the maintenance and, if necessary, the development of network
distribution in a given area, to ensure network capacity to meet long term demands reasonable
distribution of electricity.

Points of delivery:
Point in a distribution network so designated and fixed by contract, in which energy is exchanged
power between the parties that have signed the contract.
NOTE: This item may be different, for example, the measuring point or point of common connection.

Supply voltage:
RMS value of the voltage present at a given supply point, measured in a time interval
given.

Rated voltage (Un):
Voltage that designates or identifies a distribution network which refers to certain characteristics of
operation.

Declared voltage (Uc):
The declared voltage Uc is usually a nominal voltage distribution network. If, as
following an agreement between the operator of the distribution network and the network user, the supply voltage
applied across the terminals differs from the nominal, then the tension corresponds to the supply voltage
Uc declared.

Low Voltage (LV):
In the scope of this European standard nominal voltage whose rms maximum is 1 kV.

Medium Voltage (MV):
In the scope of this European standard voltage whose effective value of greater than 1 kV and less than 35 kV.

Normal Operation:
Conditions that may respond to the demand of the load and generation, network maneuvers and
elimination of faults with automatic protection systems in the absence of exceptional conditions due
external influence or force majeure.

Conducted Disturbance:

Electromagnetic phenomenon spread across the conductors of the lines of a distribution network. In some
cases, an electromagnetic phenomenon spreads through the windings of the transformers and, therefore, between networks of different voltage levels. These disturbances can degrade the performance of an appliance, equipment or system, or cause damage.

Frequency of the voltage supply:
Repetition rate of the fundamental component of the voltage measured during a time interval
given.

Variation of stress:
Increase or decrease in voltage, usually caused by load variations.

Rapidly varying voltage:
Variation of rms voltage maintained between two consecutive time intervals
defined but not specified (for details see EN 61000-3-3).

Voltage fluctuation:
Series of voltage variations, cyclic variation of the envelope of the stress.
[IEV 161-08-05].

Flicker (Flicker):
Impression of unsteadiness of visual sensation due to a light stimulus in which the brightness or
spectral distribution fluctuates over time. [IEV 161-08-13].

NOTE The voltage fluctuations cause variations in luminance of the lighting, which produces the phenomenon called blinking eye. Above a certain threshold, flicker becomes annoying. This discomfort increases rapidly with the amplitude of the fluctuation. For some repetition, even the weak amplitudes can be annoying.

domingo, 28 de agosto de 2011

HONDA QUALITY STANDARDS - SCOPE AND PURPOSE

Scope; this standard defines, describes and specifies the point of delivery to the network user, the main features of the voltage supplied by a global network of low voltage distribution and medium voltage under normal operating conditions. This standard describes the limits or values ​​to be expected to remain the constant voltage across the general distribution network and does not describe the typical situation is usually an individual user on the network.

This European Standard does not apply to abnormal operating situations, including the following:

- Temporary conditions designed to maintain power supply to network users after a failure or during maintenance work or construction on the network, or to limit the extent and duration of a power interruption;
- In case of non-compliance of the facility or equipment of a network user to the applicable rules or technical requirements of connecting, established, either by administration or by the operator of the distribution network, including the limits emission of conducted disturbances;

- Exceptional circumstances, in particular:
• exceptional weather conditions and other natural disasters;
• interference from third parties;
• decisions of public authorities;
• strikes (subject to legal requirements);
• force majeure;
• interruptions due to external causes.

The voltage characteristics given in this standard are not intended to be used as levels of support
(EMC) or emission limits of conducted disturbances user for general networks
of distribution.

The voltage characteristics given in this standard are not intended to be used to specify the requirements
teams in product standards and facilities.

This rule can be replaced in whole or in part by the terms of a contract between a user
individual network operator and distribution network.

Object

The purpose of this European standard is to define and describe the characteristics of the supply voltage supplied,
such as:
- The frequency;
- Size;
- The waveform;
- The symmetry of the line voltages.

These features are subject to change during the normal operation of a power system due to load changes, disturbances emitted by certain equipment, and the occurrence of faults due mainly to external causes.
Features vary randomly in time with reference to a given supply point, and randomly in space, with reference to a given instant. Because of these variations, the levels of the characteristics may be exceeded once.
Certain phenomena which have an impact on blood are particularly unpredictable which makes it very difficult to give useful values ​​corresponding definitive. The values ​​given in this standard for these phenomena, such as voltage sags and voltage interruptions are to be interpreted accordingly.

martes, 9 de agosto de 2011

ACCURACY ,REPEATABILITY AND REPRODUCIBILITY

Accuracy
The accuracy of a test method is the proximity of different experimental results obtained in samples the same. The calculation of accuracy is given by the repeatability r and reproducibility R, both defined in ISO 5725-1. The calculation methods are given in ISO 5725-2, ISO 5725-3 and ISO 5725-4.
R r values of dissipation factor of an insulating liquid depend on the nature of the liquid tested, whether the fluid is new or used and the temperature, these values are altered and is very low (Less than 10-4), as is the case in highly insulating liquids, which are altered significantly by the impurities, handling, cleaning the test cell, and so on.

Repeatability (r)
If obtained in a laboratory two measures A and B, at room temperature, can be considered acceptable if the absolute difference !A - B! satisfies the equation:





Where
Min (A, B) is the smaller of the two values A and B.
For new insulating liquids: l== 0.2
For insulating liquids used: l= 0.1

Reproducibility (R)
If you get two different laboratories in two steps A and B, at room temperature, the above relationship is still the following valid values l
For new insulating liquids: l = 0.35
For insulating liquids used: l = 0.20

Examples of R and R
The following table gives examples of r and R values, net of inter-laboratory trials conducted with insulating mineral oil at room temperature:


jueves, 28 de julio de 2011

EXPRESSION OF RESULTS AND REPORT OF TEST

Expression of results
Results are calculated using the following equation:







Where
G is the conductance, in siemens (S);
C is the capacity, in farads (F);
W is the angular frequency in radians / second (rad / s) = 2πf
F is the frequency used in Hertz (Hz).

NOTE - Assuming that the relative permittivity temperature measurement is known, the conductivity of the liquid can be calculated by the following equation:






Where








REPORT OF TEST
The report must include the following:
- Identification of the sample;
- test temperature;
- measured values of G and C;
- As calculated values

domingo, 10 de julio de 2011

SAMPLING,LABELLING AND PROCEDURES

SAMPLING
The insulating fluid samples should be taken by qualified personnel in accordance with IEC 60475. During his storage and transport, samples should be protected from direct light.

LABELLING
Insulating liquid samples must be properly labeled before being sent to the laboratory.
The following information is required:
- Customer or facility;
- Fluid identification (type and class);
- Identification of the equipment;
- The date and time of sampling;
- Temperature during sampling;
- sampling point;
- Other relevant information.

PROCEDURES
In order to obtain a meaningful measure of the dissipation factor is essential to follow exactly the rules with respect to:
- Careful cleaning of the test cell;
- Careful filling test cell and the careful handling of liquid samples and the very test cell.

Cleaning test cell
Procedure. Depending on the cleanliness of the test cell and the level of conductivity liquid to be analyzed, the cleaning of the test cell will be more or less sophisticated and more or take less time.
If the cleanliness of the cell is unknown, or if there is any doubt, you should have a cleaning process.
You can follow many cleaning procedures if they prove to be effective.

Checking the cleanliness of the empty cell. For a significant extent, it is necessary that
Cell electrical losses are much smaller empty the fluid to be measured.

Checking the cleanliness of the full cell for measurements at room temperature. If the cell trial is perfectly clean and fluid temperature is constant, and are independent of time. The measure can therefore be performed as soon as practically possible. In fact, this can be done in less 1 min. Moreover, a single measurement of a single sample is sufficient to obtain the correct value.
It may happen that, at constant temperature, conductivity(or so to increase or decrease over time, but no more than 2% at two minutes to fill the cell. In this case can be seen that the cell is sufficiently clean and the first measured value, ie a minute or so to fill the cell, can be registered.
Otherwise, it is recommended after cleaning the cell again, take a second sample of the same liquid and a second measure. It is considered the lowest value of the two, as recommended in IEC 60247.

Checking the full cell for measurements at temperatures above room temperature.
Before taking any action at high temperatures, make sure that the temperature of the liquid in the cell is constant. Except in cases in which the cell is perfectly clean, the measurement result depends on the way in which the cell and the liquid had been heated.
If the test cell is perfectly clean and the liquid temperature is constant, conductivity and are independent of time. The measure can thus be made immediately. In practice, the measure may do as soon as the temperature may be considered constant. Moreover, a single measurement of a single sample is enough to get the correct value.

It can happen, even if the liquid and the cell are at a constant temperature, conductivity (o de tan increase or decrease over time. This may be due to different causes: for example, heating to high temperatures can alter the composition of certain liquids, or modify the moisture content of the particles.
In practice, the temperature is not perfectly constant and their variations induce variations or conductivity,liquids varies more or less depending on the temperature nature of the liquid, typically up to 5% per degree centigrade. Therefore, the origin of variations.
If the test cell is not perfectly clean, the heating time affects the measured values, even the first, because the cell impurities dissolve in the liquid. The first measured value should, therefore, be discarded and the cell must be cleaned again.

Precautions when filling the test cell
When the cell is filled with liquid, you must ensure that the ambient atmosphere is, as far as possible, free of gas fumes that can be dissolved in the liquid.
The electrodes must be completely submerged in the liquid.


Test temperature
The measurement of conductivity and dissipation factor of a liquid can be made at any temperature.
Room temperature is recommended for its simplicity and time savings. Since the ambient temperature is essentially variable, you must remember a fixed value (eg 25 ° C).
There is nothing to stop the test is done at higher temperatures (eg 40 ° C 1 ° C, 90 ° C 1 º C or more).

Methods of heating
To make a measurement at high temperatures can be used several methods of heating. The time required to reach the test temperature depends on the method used and typically varies between 10 min and 60 min. If the test cell is not perfectly clean, the increase in conductivity due to the dissolution of impurities will depend on the duration of heating and the measured conductivity will depend, in turn, the heating method.
Thus, heating test cell as quickly as possible.
A suitable method to achieve this can be heated separately from the test cell and the liquid in a clean container. Another method is to rapidly heat the liquid in the test cell itself.

Measure
Fill the sample cell with avoiding contamination of the fluid or the cell (see 8.2).
Cleaning is checked as described in 8.1.3 or 8.1.4. If the cell is clean enough (see 8.1), is
Note the values of G and C.

sábado, 25 de junio de 2011

APPLIANCES

To perform this measurement method can be used specially constructed devices or constituted by individual items conveniently assembled. The block diagram shown in Figure 2 and elements described in the following sections illustrate appropriate equipment.

Block diagram of measuring apparatus









Keys

1. Test cell
2. Heating System
3. Square wave generator
4. Measurement chain
5. Meter
6. Recorder

Test Cell
The test cells of three terminals, designed according to the recommendations of IEC 60247, are generally appropriate for these measures.

You can use an additional type of cell in which there is no bridge, made by any solid insulating material, between the measuring electrodes, as shown in Figure 3. This cell type is often more accurate with highly insulating liquids.

Example of a cell test designed for highly insulating liquids













Keys

1. Cover
2. Internal electrode
3. External electrode
4. Stainless steel container
5. Thermocouple or thermometer to measure temperature
6. Electrical connections for BNC terminals

The typical distance between the inner and outer electrodes is 4 mm, the minimum distance should not be less than 1 mm.

The recommended material for the electrodes is stainless steel. As an example, the diameter of the outer electrode is 43 mm, the outer electrode is 51 mm, the length of the electrodes is 60 mm, and the diameter of the container Stainless steel is 65 mm.

This type of test cell is designed to minimize the effects of contamination of surfaces

Contact: although the contact surface is large, the relationship ÷ = "electrode surface" / "fluid volume" is relatively small (÷ = 2.6 cm-1) due to the large volume of liquid (v = 200 cm3).NOTE - It is recommended restricting the use of a given cell to a particular type of liquid.

Heating System
The heating system must be adequate to maintain the temperature of the measuring cell to within
±1 ºC of set point. This can be a forced draft oven or in an oil bath controlled thermostatically controlled and equipped with a bracket to hold the cell.
The heating system must be shielded electrical connections on the cell.

Square wave generator

The square wave generator must provide a quasi-rectangular voltage highly stable. The following features are appropriate:

- Amplitude: 10 V to 100 V;

- Frequency: 0.1 Hz to 1 Hz;

- Ripple: <1%;

- Rise time of tension: 1 ms to 100 ms.

Measurement Chain

The IR conduction current through the measuring cell, is measured in the second part of each half-wave and averages for a number of periods depends on the range of measures. The chain of measures gives the conductance G test cell.




As an example, the range of measured values ​​of conductance is 2 x 10-6 S a 2 x 10-14 S with a margin of error less than 2%.

The capacity C of the test cell is deduced from the measured current during the voltage rise. The values measurable capacity is between 10 pF and 1000 pF with an uncertainty of less than 1%.

As an example, for a liquid relative permittivity r = 2, a conductance value of 2 x 10-14 S gives

as ä = 0,8 x 10-6 a 50 Hz.

 
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