Control Techniques Mentor II User Manual page 103

Emission
For installation in the "second environment",
ie, where the low voltage supply network does not supply domestic
premises, no filter is required in order to meet IEC61800-3 (EN61800-3).
Operation without a filter is a practical cost-effective
possibility in an industrial installation where existing
levels of electrical noise are likely to be high, and any
electronic equipment in operation has been designed
CAUTION
for such an environment. There is some risk of
disturbance to other equipment, and in this case the
user and supplier of the Drive system must jointly take
responsibility for correcting any problem which
occurs.
Figure 12-1 shows wiring guidelines to achieve minimum emission in a
typical installation. When used with the recommended filter the Drive
will meet the conducted emission limits required by the generic emission
standard EN50081-2.
Motor cable length should not exceed 300m to ensure that the industrial
limit is met with adequate margin.
The limits for conducted emissions required by the generic standards
are summarized in the following table:
Standard Description Frequency
range
EN50081-2 Generic 0.15-0.5MHz 79dBµV quasi peak
emission
standard for
0.5-5MHz
the
industrial
environment
5-30MHz
Recommended filters
Two methods are shown in Figure 12-1 for suppressing the conducted
emission into the power supply line for the main thyristor converter.
Method 1
A low cost technique using high value capacitors between power lines
and earth which makes use of the suppression provided by the standard
line reactors. Component values are given in the following table:
Drive Line
reactors
La, Lb, Lc
(µH)
M25, M25R 200
M45, M45R 200
M75, M75R 100
M105, M105R 100
M155, M155R 75
M210, M210R 75
M350, M350R 35
M420, M420R 27
M550, M550R 25
M700, M700R 23
M825, M825R 19
M900, M900R 17
M1200, M1200R 13
M1850, M1850R 8.6
Mentor ll User Guide
Issue Number: 12
Limits Applica-
supply
66dBµV average
73dBµV quasi peak
60dBµV average
73dBµV quasi peak
60dBµV average
Line to Discharge Discharge
earth resistors resistor
capacitors Ra, Rb, Rc power
Ca, Cb, Cc (kΩ) rating
(µF) (W)
4.7 470 0.5
4.7 470 0.5
10 220 0.5
10 220 0.5
13 150
13 150
29 68
37 56
40 56
44 47
53 39
59 33
77 27
116 18
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The capacitors must be wired in as close as possible approximation to a
'Kelvin' connection, minimising the length of the wiring between the
capacitors and the power circuit.
An assembly of low-inductance capacitors, designed for direct mounting
to a bus-bar, is available from Steatite Ltd with the part number
CON9020250. The capacitance value in this box is 10µF per phase. A
number of these assemblies can be used together to give the required
capacitance. Because of their low inductance, the next higher multiple of
10µF above the required value can be used.
The total capacitance line to earth must be within +/-10% of the value
given in the table. If lower value line reactors are used then the
capacitors must be increased in proportion. It is important that the
capacitors are rated at 440V AC and are suitable for connection to
normal industrial supplies. They should also be designed to have a low
series inductance.
Suitably rated resistors should be used to discharge the capacitors when
the supply is disconnected from the installation. The resistors given in
the table are calculated to discharge the network to less than 60V within
5s, based on a 440V supply.
The capacitor network will cause a high leakage current to flow to earth.
The leakage current may be calculated using the following expression,
assuming the three phase supply is balanced with respect to earth and
line to line:
= V × 2π × f × C × a
I
E
tion
Where:
V is line to earth voltage
AC
f is supply frequency
C is line to earth capacitance
lines
a is capacitor tolerance.
Example: M210 Drive operating on a 400V 50Hz supply
Use 10µF + 4.7µF in parallel = 14.7µF between each line and earth
(13µF is required).
Select capacitor tolerance to be 10%.
= 400 × 2π × 50 ×14.7 × 10
I
E
= 185mA
In the event of a phase loss the leakage current will be higher. It can be
calculated from the following expression:
× 2π × f × C
I = V
EPL LE
= (400/√3) ×2π × 50 ×14.7 × 10
= 1.07A
The capacitors cause a high earth leakage current. A
permanent fixed earth connection must be provided,
and subjected to regular testing.
WARNING
If high earth leakage currents are unacceptable then an RFI filter must
be used instead of capacitors. The filter uses lower values of
capacitance, achieving the necessary attenuation by inductance.
1
1
3
3
3
3
4
4
6
9
-6 × 0.1
-6
99