HT instruments MACROTEST G3 - Manual (Page 34)

MACROTESTG3 - COMBIG3
EN - 33
6.4.1. Test types
The protection of electrical lines is the essential part of a project so as to guarantee the
correct functionality and avoid damages to persons or property. To this purpose, the safety
guidelines impose on electrical designers also to design the electrical installation in order to
reach:
1. The protection from short-circuits, that’s to say:
 The breaking capacity of the protection device must be not lower than the supposed
short-circuit current in the point in which the device is installed
 In case of short-circuit in any point of the protected line, the protection device must
trip on quickly enough to avoid that the insulation materials assume excessive
temperatures
2. The protection from indirect contacts.
In order to verify the a.m. conditions, the instrument performs the following functions:
Check of protection from indirect contact – According to the type of
distribution system (TT, TN, IT) set by the user, the instrument performs the
measurement and verifies the condition imposed by the guidelines. Should it
be reached, the instrument gives a positive outcome (see § 12.6, § 12.7,
§12.8)
kA Check of protection’s breaking capacity – The instrument detects the value
of the line impedance upstream to the measurement point, calculates the
maximum value of short-circuit current and gives a positive outcome if the
value is lower than the limit set by the user (see § 12.5)
I 2 t Check of protection from short-circuits – The instrument detects the value
of the line impedance upstream to the measurement point, calculates the value
of short-circuit current and the corresponding value of the trip out time (t) of the
protection device and gives a positive outcome if the value of specific energy
passing through the protection device is lower than the specific short-circuit
energy bearable by the cables according to the known relationship (see §
12.10):
 
t I S K
2 2
*

where K and S are parameters of the cable, set by the user, that’s to say:
K= parameter indicated by the guideline depending on the type of conductor
material and on the material of the insulating sheath
S = section of the cable
To completion of the above checks, the instrument performs also :
Check of the coordination of protections – The instrument detects the value
of the line impedance upstream to the measurement point, calculates the
minimum value of short-circuit current and the corresponding value of the trip
out time (t) of the protection device and gives a positive outcome if the value is
lower than the limit set by the user (see § 12.9)
STD Generic test
The IMP57 optional accessory allows the instrument to perform both individual and high
resolution (0.1m
) Line/Loop impedance measurements