Page 441 - ABB_Motor _Protection_and_Control_catalogue_20221216

ABB MOTOR PROTECTION AND CONTROL 3/365

—

Surge suppressors for contactor coils

The operation of inductive circuits causes overvoltages, in particular on opening of the contactor
(V) 03
1000 coil.
T (s) The electromagnetic energy stored in the coil during contactor closing is restored on opening in
0 100 the form of surges, the slope and amplitude of which may rise to several kilovolts. A number of
1000
drawbacks are observed ranging from interference on the electronic devices to breakdown of in-
0 100 sulators and even destruction of certain sensitive components.
The graph opposite reproduces the oscillogram showing voltage discharges at the terminals of a
A 884D 42 V / 50 Hz coil without peak clipping. The coil was switched by 8 series-connected poles of a
contactor relay.
Following a burst of discharges with a very steep slope a damped oscillation emerges with a peak
value of 3500 V.
Overvoltage Factor
A078 The overvoltage factor k is defined as the ratio of the maximum overvoltage peak value Ûs to the
peak value Ûc of the coil rated control voltage Uc:
Ûs max. Ûs max. Ûs max.
RC-EH k = in DC: k = or in AC: k =
Ûc Uc Uc√2

3500
For example the following is obtained for the above graph: k = ≈ 60
42 √2
To reduce the harmful effects of these overvoltages, ABB has developed a range of surge suppres-
sors designed to reduce the k factor defined above and to limit or even completely eliminate the
high pre-damping voltage frequencies.
Each case is different, but the technical data tolerances and the generous sizing of parts have en-
abled us to reduce the number of variants.
We have chosen the following solutions: transil diodes, varistors and RC blocks.
Note: A varistor is a resistor whose value decreases to a very large extent when a certain voltage is
applied at its terminals.
For contactors Rated control circuit Type Order code Pkg Weight
voltage qty (1 pce)
Uc
V AC DC kg
EK550, EK1000 48...110 ● – RC-EH800/110 SK829007-C 1 0.015
EK550, EK1000 24...125 – ● RC-EH800/110 SK829007-C 1 0.015
EK550, EK1000 220...600 ● – RC-EH800/600 SK829007-D 1 0.015