CHAUVIN ARNOUX CA-6547 [3/4] Theoretical reminder

In-depth expertise …

Main applications

• Insulation measurement on cables, motors, generators, transformers…

2 levels of diagnostics:

– "Go/No go" measurement

– Qualitative measurement for preventive maintenance:

- Testing with programmed duration

- Quality ratios: polarization index (PI) & dielectric absorption

ratio (DAR)

- Insulation testing on heterogeneous or multi-layer cables

(dielectric discharge index)

- Step voltage

• Locking of test voltages: ideal when entrusting the instrument to less

experienced users

• Measurement voltage selectable from 40 to 5,100 V to deal with all

types of measurement situations

• Possibility of storing the results in the memory and exporting

the data by means of software to keep a log of the measurements

(C.A 6547 / C.A 6549)

"THEORETICAL" REMINDER

Reduced insulation may be due to

slow, gradual deterioration over a

long period of time, but also due to

sudden damage. The effects of humidity,

dirt, corrosion, penetration by chemi-

cals and even vibrations can all cause

this sort of deterioration. Its effects

are easy to document using the quality

ratios (PI-DAR-DD) available on the

whole range of 5 Kv insulation testers.

Comparison of the insulation values over

time provides crucial information for

preventive maintenance of machines.

This preventive maintenance is essen-

tial at 2 levels:

1. Safety: minimizing the risk of short-

circuits

2. Cost: avoiding the failure of impor-

tant equipment leading to high

costs in terms of production down -

time, production losses and repairs.

POLARIZATION INDEX (PI) & DIELECTRIC

ABSORPTION RATIO (DAR)

Insulation is sensitive to temperature and humidity variations.

In addition, measurement is affected by the appearance of disturbance

currents. To overcome these effects, long-term measurements must be

performed and the PI and DAR coefficients must be calculated. They will

then allow qualification of the insulants and their ageing.

TEST WITH PROGRAMMABLE DURATION

Insulation measurements sometimes take a long time to

stabilize because of transient disturbance currents. By carrying

out long-term measurements and analysing the trend curve of the insu-

lation according to the test voltage application time, you can obtain a

better assessment of insulant quality.

GRAPH R(t)

If a programmed-duration test is carried out, the instruments

automatically store the samples concerning the insulation tested,

at the rate chosen by the user. The curve R(t) can be plotted by hand on

the basis of the results, or on screen via the DATAVIEWER software.

With the C.A 6549, it is also possible to view the curve directly on the

graphic screen.

SMOOTH FUNCTION

When the measurements are unstable, the Smooth function

can be used to smooth the display of the insulation values so

that they are easier to read and can be interpreted more quickly.

REFERENCE TEMPERATURE (C.A 6549)

The value of an insulation resistance varies according to the

measurement temperature.

For accurate, reliable monitoring, it is always a good idea to express a

measurement result in terms of a reference temperature. By simply

pressing a button, the calculation can be performed automatically by

the instrument.

PRINTER (C.A 6547 and C.A 6549)

A compact serial printer can be connected for direct printouts

on site. It is also possible to use a desktop parallel printer with

a series/parallel adapter available as an accessory.

DATAVIEW SOFTWARE

This software recovers the stored data, plots the trend curve

R(t), prints the customized test protocols and creates files for

spreadsheet software.

DataView can also configure and control the instrument via an RS232

link!

DIELECTRIC DISCHARGE INDEX (DD)

This test measures the dielectric absorption of a heteroge-

neous or multi-layer insulant and will reveal the presence of

impurities or a faulty layer.

Current measured after 1 min (mA)

Test voltage (V) x Capacitance measured (F)

DD =

Var 50-5,000 V SETTING

To deal with the whole range of measurement situations

(electrical equipment, telecom installations, etc.) and measure

as accurately as possible, all 3 instruments offer the possibility of

selecting the test voltage by means of the Var 50-5,000 V setting on the

rotary switch. The voltage can be adjusted between 40 V and 1,000 V in

10 V increments and between 1,000 V and 5,100 V in 100 V increments.

PROGRAMMABLE ALARMS

A high or low alarm threshold can be memorized. If there is an

overrun, a visual warning is triggered and a buzzer sounds.

STORAGE (C.A 6547 and C.A 6549)

The C.A 6547 and C.A 6549 have an internal memory for storing

several thousand measurements. Storage is performed with

two indices, OBJ (object) and TEST (test), which store the results in an

ordered way.

STEP VOLTAGE (C.A 6549)

The resistance of a faulty insulant gradually decreases as the test

voltage rises. This test, which involves increasing the test voltage

in steps, can be used to assess the quality of the insulant by observing the

curve R(Utest) and the result in ppm/V which provides a quantitative

evaluation of the curve's slope.

CHAUVIN ARNOUX CA-6547 [3/4] Theoretical reminder

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