HT JUPITER User Manual

JUPITER
IT - 40
9.3. LOOP AND CALCULATION OF ASSUMED SHORT-CIRCUIT CURRENT
Purpose of the test
“Fault ring" (Loop) indicates the circuit run through by the current generated by an
insulation fault to earth (dead short). The fault ring includes:
 The phase winding of the transformer.
 The line conductor, up to the fault point.
 The protective conductor from the fault point to the star center of the transformer.
Once impedance has been measured, it is possible to determine the earth dead short
current (assumed short-circuit current Isc) and to evaluate whether the protection devices
against overcurrents are correctly coordinated for protection against indirect contacts.
Parts of the system to be checked
The test must necessarily be performed on TN and IT systems not protected with
differential devices.
Allowable values
The purpose of this measurement is to check that the tripping current of the automatic
protection device Ia satisfies one of the following relationships:
LPE
PEL
a
Z
U
IscI


For measuring Line/Loop L-PE impedance
LN
NL
a
Z
U
IscI


For measuring Line/Loop L-N impedance
LL
LL
a
Z
U
IscI


For measuring Line/Loop L-L impedance
where:
U
L-PE
= Rated voltage L-PE set on the instrument (see § 4.2.11)
U
L-N
= Rated voltage L-N set on the instrument (see § 4.2.11)
U
L-L
= Rated voltage L-L set on the instrument (see § 4.2.11)
Z
LPE
= Loop impedance L-PE measured by the instrument
Z
LN
= Loop impedance L-N measured by the instrument
Z
L
= Loop impedance L-L measured by the instrument
I
SC
= Assumed short-circuit current measured by the instrument

HT JUPITER Specifications

General

Brand	HT
Model	JUPITER
Category	Measuring Instruments
Language	English