ABB MWD Manual de instrucciones - Página 5

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ABB MWD Manual de instrucciones
3.2

Structure and function

The POLIM® and MWK/MWD type surge arresters are constructed from metal-oxide (MO)
resistors. These MO resistors have an extremely non-linear voltage-current characteristic.
At the continuous operating voltage of U
insulator and only a small capacitive current will flow, which is in the mA range. With an
increase in voltage, the MO resistors enter a low-ohmic state practically without delay.
Thus, any further increase in voltage is limited to the specified residual voltage values.
After the decline of the overvoltage, the arrester immediately turns back to the high-ohmic
state. The surge arrester converts the energy of the surge into heat and transfers it to the
surrounding air.
The stack of MO resistors and electrodes is held together with fiberglass-reinforced plastic
elements. A directly molded silicone housing protects it against environmental influences.
Surge arresters may optionally be equipped with a disconnecting device. Such a device
disconnects automatically the surge arrester from the power network in case of an
overload.
3.3

Technical data

Performance characteristics, dimensions, weights and installation
distances of the POLIM® and MWK/MWD type surge arresters are
specified in the data sheets, see:
https://new.abb.com/high-voltage/surge-arresters/medium-
voltage-arresters
The corresponding dimensional drawings of the products and/or
their accessories are available on request.
3.3.1

Technical data on the surge arrester

Main characteristic data are partly molded into the silicone housing and partly engraved in
the electrodes.
Note: AC surge arresters are not suitable for use in DC applications. DC surge arresters have
a D at the end of their name.
Detailed information on this is given in the examples below:
POLIM-D 10-04
a
s d
POLIM-C 1.8 N D
a
s f g
POLIM-R 0.14-2 N D
a
s
h f g
MWK 24 K4
a
s j
Labeling
U
= ... kV
c
U
= ... kV
r
I
= ... kA
n
I
= ... kA
s
HA...
20...
Class IEC DH (POLIM-D)
IEEE DIST Class HD (POLIM-D .. R)
Class IEC SL (POLIM-K, MWK/MWD,
POLIM-C AC types)
Class IEC SL, SM or SH
for POLIM-I, -S or -H, respectively
DC-A/-B/-C
1HC0141361 AA | EN | Operating instructions
c
Type designation
a
U
in kV
s
c
Housing size
d
Housing type designation
f
Designation for special housing or DC type (D=DC, o ther letters
g
refer to the housing, not used if AC and standard housing)
1: one MO resistor, 2: two parallel MO resistors
h
Position only used in case of special housing (K4, KLL)
j
Meaning
Continuous operating voltage U
Rated voltage U
Nominal discharge current I
Rated short-circuit current I
Serial number (8 digits; the 'HA' might be omitted for space
reasons), also included in the QR code
Year of manufacture
Designation of arrester classification
Charge transfer class (DC types only)
, the metal-oxide material acts almost as an
in kV
c
in kV
; DC types: U
r
rms
in kA
n
for 0.2 sec in kA
s
; DC types: U
= U
rms
c
= U
c
r
rms
r
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