Procedure of Installation of dummy Insulators & Pollution
Measurements
Dummy insulator string installation
Dummy insulator string consists of 10 number disc insulators. Such strings
are mounted in each of the locations identified for pollution level monitoring
at height as possibly close to the actual live (energized) insulator so that no
shutdown is required for the mounting and dismounting of the strings
(Ideally at the same height of energized insulator strings) for ESDD/NSDD
and layer conductance measurements.
One string shall be mounted at location where only ESDD/NSDD
measurement has to be conducted and at locations where both the
NSDD/ESDD and layer conductivity measurement has to be conducted two
(2) Strings shall be mounted.
The insulator strings are given a unique identification number (UID) for
each of the locations (This shall be assigned by CPRI at the stage of
finalization of the location). Each locations geographical co- ordinates are to
be noted. The ESDD and NSDD measurements are carried out periodically
as per the procedure follows.
The Format to be filled by the Central Transmission Utility/State
Transmission Utility on identification of site for ESDD/NSDD
Measurements is attached.
Necessary equipment and accessories required to measure pollution at
site shall be provided. These are:
*De mineralized water (this shall not be provided)
*Measuring cylinder
* Surgical gloves
* Container
* Cotton/ cotton cloth
* Conductivity meter with cell. Cell constant= 1
* Temperature probe
* Filter paper
* Funnel
* Desiccator/ drying oven
* Weighing balance
Procedure for ESDD/ NSDD Measurement
The site pollution severity can be determined by measuring the equivalent
salt deposit density (ESDD) and Non soluble deposit density (NSDD) of the
polluted insulators.
Pollution Measurement Procedure (for ESDD)
1.
Each of the insulators shall be dismantled carefully. The insulators in
the string shall be numbered from 1 to 10. Line end (bottom most)
Insulator in the string is numbered as 1 and ground end (Top most)
insulator in string is numbered as 10.
2.
The top and bottom surface of each insulator shall be cleaned
separately with known volume (eg: 250 ml) of de-mineralized water.
3.
Temperature of the de-mineralized water has to be noted using
thermometer.
4.
250 ml (or the amount of water required to cleanse the surface) of demineralized water shall be measured using a measuring jar and then
put in a container. A cotton wool or small piece of cotton cloth shall
be used to clean the polluted surface of the insulator. After the
cleaning the cotton wool or small piece of cotton cloth shall be
immersed in the de-mineralized water.
5.
The conductivity of the polluted water then shall be measured using
the conductivity meter. Figure: 1 shows the cleaning process of top
and bottom surface pollution.
6.
After the measurement the readings has to be put in the format that
shall be provided by CPRI later.
7.
The polluted water shall then be used for the NSDD measurement.
Note:
1.
2.
3.
4.
5.
The conductivity of de mineralized water shall be within the range of 0.01 milli
Siemens.
The pollutant on the top and bottom surface of the insulator shall be cleaned using
the DM water separately.
Cotton with pollutant shall be put back in to the water container after cleaning the
surface of insulator.
The volume conductivity of top and bottom surface are measured separately
Care shall be taken not to lose any water during the measurement.
6. Surface area calculations are very important to calculate the ESDD of the insulator.
The procedure for the calculation of surface area shall be taught during the
conduction of the training program by CPRI. However, it is advised to bring one
sample each of all the different types of insulators that shall be installed as dummy
insulators at the training venues so that the area of the insulators are calculated by
the CPRI personnel then and there.
Figure 1. Washing of top and bottom surface of insulator
The procedure till above shall be conducted by the STU/CTU personnel
at site and the readings shall be duly filled in the provided format after
this following formula shall be used to calculate ESDD, by CPRI
Knowing the surface area of top and bottom surfaces of the insulator the
ESDD of top surface and bottom surface ESDD can be calculated using the
formula
ESDD = (SA X V)/A mg/cm2
Where SA = (5.7 X σ 20) 1.03 kg/m3
V = volume of water used.
A = surface area of the insulator
σ 20 = volume conductivity of polluted water at 20 degree centigrade.
Correction factor shall be applied when the ambient temperature is more
than 20 degree centigrade using the formula
Pollution Measurement Procedure (for NSDD)
1. Weight of dry filter paper shall be taken using the digital weighing
balance.
2. The polluted water after measuring ESDD shall be filtered using a
funnel.
3. The filter paper shall be then dried using Desiccator/ drying oven.
4. The filtered paper containing pollutants, which is now dried, shall be
weighed using the digital weighing balance.
5. After weighing, the dried filter paper alongwith the pollutant shall be
sent to CPRI for chemical analysis. The complete procedure for the
chemical analysis sample collection is described in the next section.
6. Figure 2 shows the process for measurement of non- soluble deposit
density.
Figure 2: Process for measurement of NSDD
The procedure till above shall be conducted by the STU/CTU personnel
at site and the readings shall be duly filled in the format provided after
this following formula shall be used to calculate ESDD, by CPRI
The NSDD can be calculated using the formula
NSDD= Wf – Wi /A
mg/cm2
Where,
Wf, is the wt. of pollutant with filter paper under dry conditions in milligrams
Wi, is the Initial wt. of filter paper under dry condition in milligrams
A, is the surface area of the insulator in cm2
Pollution Measurement Procedure (for Chemical analysis of the
pollutant)
1. After the NSDD measurement is completed the dried filter paper
alongwith the pollutant shall be packed in a small plastic sachet.
2. Care must be taken that no pollutant falls off from the plastic sachet.
3. A label should be pasted on the sachet indicating the UID, transmission
line name and tower no.
4. The sample shall then be sent to CPRI for chemical analysis.
5. Only one sample from each location has to be sent to CPRI during the
entire pollution mapping exercise (i.e. during the course of 6
measurements or 2 years)
Then at lab CPRI shall conduct chemical analysis on the sample. The
analysis can be useful to identify chemical components of non-soluble salts.
Pollution Measurement
measurement)
Procedure
(for
Layer
conductance
Figure 3: Schematic diagram for layer conductivity measurement
1.
Approx. 2 kV (or 1.5 kV) Voltage shall be applied and the resulting
leakage current has to be measured at every 5 minutes. This shall then be
tabulated and sent to CPRI.