When measuring insulator, there are a few things to consider :
1. Most insulators collect dust and get contaminated over time
with a mixture of Moisture, rain, dirt etc...
2 These contaminating matters lower the resistance of the insulator as
they are in parallel with the insulator resistance.
3. It is recommended to measure the insulator first without the guard to
verify that the total resistance is high. Should the total resistance
not be high, that could mean that the amount of dirt on the surface
of the insulator is too high and therefore, the insulator may require
cleaning.
4. Should your insulator require cleaning, follow the procedures
recommended by it’s manufacturer.
5. For final Test and Measurement, use the Guard so that leakage
surface current is collected and Insulator is intrinsically tested.
The insulator must not be connected to any live component or power source.
Use a tied copper wire arround the insulator at about its center to connect the guard.
11.1 MEASURING AN INSULATOR
11.
EXAMPLES OF MEASUREMENT
18
FIRST MEASUREMENT
MEASURE WITHOUT THE GUARD TO TAKE EVERYTHING INTO ACCOUNT AND FIND OUT IF NEED CLEANING
19
MEASURING THE INSULATION OF A CONTACTOR OR CIRCUIT BREAKER
Contactor or Circuit breaker are switching devices which when closed, must do a
good contact i.e. (have the lowest resistance possible) and when open, must be
a good insulator i.e. (have the highest resistance possible).
As they get older, their characteristics may deteriorate due to many factors.
Their material porperties may deteriorate with time and frequency of use as well
as stress put on to them.
One of the factors to be tested is their insulation when acting as an open
circuit.
Contactors or circuit breakers may also get dirty as they are utilized in heavy duty
environments, like factories, mines etc.., which have climatic conditions which
are harsh.
When they are dirty, their insulation may deteriorate due to the deposit of
contaminating matters between the terminals (see previous page about
parasitic resistance due to dirt contamination).
The Contactor or Circuit Breaker must not be connected to any live
component or power source during its testing.
MEASURING INSULATING PAINT (VARNISH) or INSULATING MATERIAL
In many applications, paint (Varnish) is utilized as an important insulating
material.
For example, transformers are painted or dipped with insulating varnish, large
power transformers are painted with High Voltage insulating paint of very high
specifications.
Many Applications uses insulating material to protect personal and equipments.
For example insulating blankets, insulating suits, insulating gloves, etc...
These materials can be quickly checked to general purpose, in day to day use, or
before sending for further more in deep tests.
Testing these can be tricky and require proper test jigs, so we will just explain the
principle of their testing for general knowledge.
11.3
11.2