Transcript Short circuit loop measurements

EXPERIENCE AND RELIABILITY1
Short circuit loop measurements
EN 61557-3
EN 60463-4-41
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EN 60364-6
Legal requirements
• The HD 60364-6:2008 standard defines two types of inspections:
– acceptance inspections;
– periodic inspections.
• According to this standard, every system must be inspected
during assembly, after assembly and before handover to the user.
The acceptance inspection must include comparison of the
measurements results with the relevant criteria defined, among
others in the multi-sheet IEC 60364 standard, so as to check if the
requirements given there have been met. In the case of
enlargement or modifications of existing systems, the same full
scope of tests must be performed as in the case of a new system.
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EN 60364-6
Legal requirements
• During the performance of the measurements, precautions must be observed
to make sure that the inspection will not cause a hazard to persons or pets
and that it will not cause damage to the property and equipment even if the
tested loop is defective.
• The person performing the inspection should be properly qualified and
competent with regards to inspections. It must be emphasized that the
person performing the inspection is responsible for preparing the system for
tests, for conducting the tests, and for proper assessment of the test results
(E and D license).
• An acceptance inspection consists of a visual inspection and a test. A visual
inspection must be performed before the test, before the power supply of the
system is switched on.
• A periodic test consists of activities necessary to determine if the system and
all its components are in a condition that enables their continued operation.
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EN 60364-6
Frequency of periodic inspections
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EN 61557
Selection of measuring instruments
The measuring instruments and devices must be selected in
compliance with the respective parts of the EN 61557
standard:
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EN 61557 - Part 1 „General requirements”
EN 61557 - Part 2 „Insulation resistance”
EN 61557 - Part 3 „Loop impedance”
EN 61557 - Part 4 „Resistance of earth connection and equipotential
bonding”
EN 61557 - Part 5 „Resistance to earth”
EN 61557 - Part 6 „Effectiveness of residual current devices (RCD) in TT,
TN and IT systems”
EN 61557 - Part 7 „Phase sequence”
EN 61557 - Part 10 „Combined measuring equipment for testing,
measuring or monitoring of protective measures”
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EN 61557
Permissible values of measurement errors
Permissible values of measurement errors acc. to the
EN 61557 standard
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EN 61557
Permissible values of measurement errors
Displayed
value
Error
„±2%m.w”
Error
„± 4 digits”
Error
summary
Summary error in %
for particular
measurement
1,00Ω
0,02Ω
0,04Ω
0,06Ω
6%
0,50Ω
0,01Ω
0,04Ω
0,05Ω
10%
0,20Ω
0,00Ω
0,04Ω
0,04Ω
20%
0,13Ω
0,00Ω
0,04Ω
0,04Ω
30%
0,10Ω
0,00Ω
0,04Ω
0,04Ω
40%
0,05Ω
0,00Ω
0,04Ω
0,04Ω
80%
(exemplary meter with resolution 0,01Ω
and basic error ± 2% m.w. ± 4 digits)
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EN 61010-1
Categories of measuring instruments
• CAT IV – measurements performed at a low-voltage system source;
examples are measurements of equipment at overcurrent protection
devices;
• CAT III – measurements performed in systems in buildings; examples are
measurements performed at distribution boards, automatic switches,
electrical system conductors, to include cables, busbars, connectors,
power outlets in systems and equipment intended for industrial
applications and other equipment, e.g. fixed motors permanently
connected with to stationary systems;
• CAT II – measurements performed in circuits that are directly connected
with low-voltage systems; examples are measurements in home
appliances, portable tools, etc.;
• CAT I – measurements performed in circuits that are not connected
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directly to a power supply system.
Short circuit loop measurements
Electrical installation scheme in the case of failure
ZB ..................
RS .................
RE ................
If ....................
Uc ..................
Us ..................
Uf ..................
Human body impedance
Floor and shoes resistance
Earthing resistance of accessible conductive parts
Noise current
Touch voltage
Voltage drop on the floor/shoes resistance
Noise voltage (Uf=Uc+Us)
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EN 60364-4-41
Automatic power shutdown
• Basic security – insulation of active parts, covers and
fencing
– Constant insulation or gas insulation with casing or separation
– Access difficulties in places with qualified personnel supervision
• Security in case of fault – earthings, equipotential
bondings, automatic power shutdown
• Additional source of security – RCD
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EN 60364-4-41
Automatic power shutdown – disconnection times
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EN 60364-4-41
Automatic power shutdown – disconnection times
ZS  Ia  Uo
Short-circuit loop ( TN system)
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EN 60364-4-41
Automatic power shutdown – disconnection times
Z S  I a  50V
Short-circuit loop ( TT system)
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EN 60364-4-41
Automatic power shutdown – touch voltage
L1
L2
L3
PEN
Rr
I1
max280A
U1
U2
I2
UST/T(UB)
PE
Measurement of touch voltage UST
Voltage between energized object and the feet of the person in
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contact with the object
EN 60364-4-41
Automatic power shutdown – shock voltage
L1
L2
L3
PEN
Rr
I1
max280A
U1
U2
I2
UST/T(UB)
F
Probe
Measurement of shock voltage UT
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Loop measurements
L-PE, L-N and L-L
L1
L2
L3
N
PE
I2
I1 max42A
Measurement of impedance in protective circuit
(L-PE) using two-pole method
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Loop measurements
L-PE, L-N and L-L
L1
L2
L3
N
PE
L1
L2
L3
N
PE
I2
I2
I1 max42A
I1 max42A
Measurement of impedance in
L-N circuit using two-pole
method
Measurement of impedance
in L-L circuit using two-pole
method
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Calculation of short circuit
current according to Un and to Uo
Voltage ranges for which impedance is measured
180
190
230
220
260
270
340
400
380
420 440
U [V]
360
Voltage ranges for which short-circuit current is calculated
Relationship between the network voltage and the ability to
calculate the prospective short-circuit current (PSC)
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Zs and Rs
Short circuit loop measurements
Z-impedance
R-resistance
Z
X
X-reactance
R
Z R X
2
2
Short-circuit loop impedance meters
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Loop measurement
for network diagnosis
•
Loop measurements to determine aging of the network
– comparing results of measurements after each period
•
Big test current – diagnosis of diameter of cable
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Big test current and
4-wire method – big accuracy
Four-pole method - theory
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Big test current and
4-wire method – big accuracy
L1
L2
L3
PEN
Rr
I1
max280A
U1
U2
I2
Measurement of impedance in TN- system
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Short circuit loop measurements
in networks secured with RCD
Z S  I a  50V
ZS  Ia  Uo
Measurement rules and meter connection
scheme
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MEASUREMENT INSTRUMENTS
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