Megger BTDR1500 Guia Del Usuario página 12

7.1 CONNECTIVITY
When you use the BTDR in bridge mode all four of the terminals can be used; the exact
configuration required depends on the test in progress according to the following diagrams:
Insu latio n Test
YELLOW - C YELLOW -
GREEN - B
GREEN - B
Faulty Line
RED - A RED - A
100V
BLACK - E BLACK - E
Good Line
YELLOW -
Far
Good Line
end
GREEN - B
s traps
Faulty Line
RE D - A
Fault
BLACK - E
Note: Earth connection not
required on loop tests
measurement of the resistance (and hence distance) to the strap without making any
assumptions and so can give a more accurate fault position.
12
2-Wire Test Method
Good Line
Far
end
Faulty Line
stra p
Not e: Earth connection not
required on loop only tests
The 2-wire test method assumes that the Good
Line and the Faulty Line are of the same gauge
wire and approximately equal in length. Then the
assumption that the strap is at half the total loop
distance is valid. However, it is preferable to use a
second return wire if possible to make use of the 3-
wire testing method. Each of the Good Lines can
be of different resistances and lengths compared
with the Faulty Line. This can allow for a direct
7.2 Auto Test
The Auto Test automatically runs through a series of tests to calculate the resistance to a fault.
These calculations and measurements are based on the bridge principle given that the
location of the fault will be the point of the lowest insulation resistance. Hence, by measuring
the insulation resistance, the loop resistance (in 2-wire mode) or leg resistances of the faulty
wire (in 3-wire mode), the instrument can then inject current through the fault resistance to
measure and derive the following:
Resistance to Fault (RTF)
Resistance to Strap (RTS)
Resistance of the Strap to Fault (STF)
From this resistance, and by knowing some other conversion factors – the gauge of wire and
its temperature – the distance to fault can be calculated and displayed as:
Distance to Fault (DTF)
Distance to Strap (DTS)
Distance of the Strap to Fault (STF)
7.2.1. Auto test – Insulation
When Auto is selected, the screen briefly indicates the sequence of tests that is to be run
before starting the insulation test. Then while the insulation test is taking place, the screen
indicates between which terminals the insulation test is performed (E to A).