SIEMENS
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Siemens D 11 · 2015
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Configuration
(continued)
4
SINAMICS G150
Drive converter cabinet units
75 kW to 2700 kW
Cable cross-sections for line and motor connection
It is generally recommended to use shielded 3-conductor three-
phase cables between the converter and motor – and for higher
power ratings, symmetrical cables where possible. If required,
several of these cables can be connected in parallel. There are
two main reasons for this:
•
Only then can the high IP55 degree of protection at the motor
terminal box be easily achieved. The reason for this is that
cables are routed into the terminal box through glands, and
the number of possible glands is restricted by the terminal box
geometry. Therefore single cables are less suitable.
•
With symmetrical, 3-conductor, three-phase cables, the
summed ampere-turns over the cable outer diameter are
equal to zero and they can be routed in conductive, metal
cable ducts or racks without any significant currents (ground
current or leakage current) being induced in these
conductive, metal connections. The danger of induced
leakage currents and thus of increased cable sheath losses is
significantly higher with single-conductor cables.
The cable cross-section required depends on the current being
conducted in the cable. The permissible current load capability
of cables is defined, for example in IEC 60364-5-52. It depends
partly on the ambient conditions such as temperature, but also
on the routing method. It should be taken into account whether
cables are individually routed with relatively good cooling, or
whether several cables are routed together; in this case, cable
ventilation is significantly poorer, which can therefore result in
higher cable temperatures. Regarding this topic, reference is
made to the corresponding correction factors for these second-
ary conditions in IEC 60364-5-52.
For 3-conductor copper and aluminum cables with PVC insula-
tion and a permissible conductor temperature of 70° C (e.g.
Protodur NYY or NYCWY), as well as an ambient temperature of
40° C, the cross-sections can be determined from the following
table, which is based on IEC 60364-5-52.
Current-carrying capacity according to IEC 60364-5-52 at 40° C
Cables must be connected in parallel for higher currents.
Note:
The recommendations for the North American market in AWG or
MCM must be taken from the appropriate NEC (National Electri-
cal Code) and CEC (Canadian Electrical Code) standards.
Grounding and protective conductor cross-section
The protective conductor must be dimensioned taking into
account the following data:
•
In the case of a ground fault, no impermissibly high contact
voltages resulting from voltage drops on the PE conductor
caused by the ground fault current may occur (< 50 V AC or
< 120 V DC, IEC 61800-5-1, IEC 60364, IEC 60543).
•
The protective conductor must not be excessively loaded by
any ground fault current it carries.
•
If it is possible for continuous currents to flow through the
PE conductor when a fault occurs, the PE conductor cross-
section must be dimensioned for this continuous current.
•
The protective conductor cross-section must be selected
according to EN 60204-1, EN 60439-1, IEC 60364.
Note:
The recommendations for the North American market in AWG or
MCM must be taken from the appropriate NEC (National Electri-
cal Code) and CEC (Canadian Electrical Code) standards.
•
Switchgear and motors are usually grounded separately via a
local grounding electrode. With this constellation, the ground
fault current flows via the parallel ground connections and is
divided. In spite of the relatively low protective conductor
cross-sections used in accordance with the table above, no
inadmissible touch voltages occur with this grounding system.
However, from experience gained with different grounding
constellations, we recommend that the ground cable from the
motor returns directly to the converter. For EMC reasons and
to prevent bearing currents, symmetrical 3-conductor, three-
phase cables should be used where possible instead of
4-conductor cables, especially on drives in the higher power
range. For 3-conductor cables, the protective or PE conductor
must be routed separately or arranged symmetrically in the
motor cable. The symmetry of the PE conductor is achieved
using a conductor surrounding all phase conductors or using
a cable with a symmetrical arrangement of the three phase
conductors and three ground conductors.
For more detailed
information on this topic, please refer to the SINAMICS Low
Voltage Engineering Manual.
•
Through their high-speed control, the converters limit the load
current (motor and ground fault currents) to an rms value
corresponding to the rated current. Based on this, we
recommend that the cross-section of the protective conductor
to ground the cabinets be the same as for the line conductor.
Cross-sec-
tion of 3-con-
ductor cable
Copper cable
Aluminum cable
Individual
routing
Several
cables next to
one another
1)
Individual
routing
Several
cables next to
one another
1)
mm
2
A
A
A
A
3 × 2.5
22
17
17
13
3 × 4
30
23
23
18
3 × 6
37
29
29
22
3 × 10
52
41
40
31
3 × 16
70
54
53
41
3 × 25
88
69
68
53
3 × 35
110
86
84
65
3 × 50
133
104
102
79
3 × 70
171
133
131
102
3 × 95
207
162
159
124
3 × 120
240
187
184
144
3 × 150
278
216
213
166
3 × 185
317
247
244
190
3 × 240
374
292
287
224
Cross-section, line conductor
Minimum cross-section,
external protective conductor
mm
2
mm
2
Bis 16
Minimum cross-section of line
conductor
16 ... 35
16
As of 35
Minimum half the cross-section of
line conductor
1)
Maximum nine cables may be routed directly next to one another horizon-
tally on a cable tray.
© Siemens AG 2015