Siemens SIPROTEC 7SS60, Manual

Page: 87 / 134

Installation and Commissioning
7-7
7SS60 Manual
E50417-G1176-C132-A1
In models with a summation current transformer input, this measurement does not
check that the summation current transformer winding that lies in the residual current
path is correctly connected. With a symmetrical current and if all devices are correctly
connected, the residual current flowing in the neutral conductor is practically zero, so
that an interruption or polarity reversal in that circuit is not detected.
Feeders which do not carry a sufficient load current should instead be checked with
primary testing equipment.
Figure 7-1 Short-circuiting the current transformers
To allow an electrical check of this circuit as well, an artificial asymmetry of the con-
nections is created. This is achieved by short-circuiting in the tested bay successively
the secondary windings of either the main current transformers or of the matching
transformers in phases L2 and L3, and by disconnecting their outgoing leads, so that
the current L1 flows only through the primary winding of L1 and the winding N in the
zero current path of the summation current transformers.
In this circuit, the rated current on the primary side of the main current transformer cor-
responds to a current of approx. 300 mA on the secondary side of the summation cur-
rent transformer. If the N-winding were connected with reversed polarity, the rated pri-
mary current would yield only approx. 60 mA instead of approx. 300 mA. The correct
connection of the input windings of the summation current transformers can also be
checked by verifying, either visually or with a continuity test, the external connection
circuit and then injecting a suitable current, e.g. 1 A or 5 A, directly into the series-con-
nected winding of the L1 and the summation current path. This allows to perform the
test without a primary load.
DANGER!
Manipulations on the measuring current transformers must be performed with the ut-
most precaution! Short-circuit the current transformers before disconnecting any cur-
rent supply leads to the device!
N
4AM5120-3DA00-0AN2
4AM5120-4DA00-0AN2