Testing methods and circuits for HVDC switchgear - cigre

restmushroomsElectronics - Devices

Oct 7, 2013 (3 years and 9 months ago)

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1


A3 SP1





T
esting methods and circuits for HVDC switchgear


COLLET Michel, DUPRAZ Jean Pierre, GRIESHABER Wolfgang

ALSTOM Grid

France

Jean
-
pierre.dupraz@alstom.com





For the transportation of electrical energy over long distances, High Voltage Direct

Current links

have
definitively
demonstrated their superiority compared to alternative current links. This superiority is
especially visible regarding the level of power announced for new projects, power in excess of 7 GW
per line. In other hand, the leng
th of lines can exceed 2

000 km.

These performances were made
possible mainly through the impressive progresses in the field of large power semiconductors. Voltage
withstand capability in blocking mode exceeding 8 kV, rated current larger than 4 kA, still
increasing
reliability, are remarkable achievements. However, in the same time, the associated high voltage
substations are requiring new type of switchgear, especially design to withstand the specific
constraints and stresses inherent to direct currents a
nd voltages. These switchgears have various
functions like transferring a DC current from a former circuit to a new one, providing isolation barrier
between zones under maintenance and remaining live parts of the circuit, by
-
passing these zones in
order to

insure the continuity of service.

One other domain is requiring similar needs. We talk about
the interconnection of renewable sources of energy, like wind farms or parks of solar cells. These links
are usually done through DC cable, mostly subsea. Here ag
ain, the direct current is the technology that
brings to the best energetic efficiency.
However, brand new types of circuit breakers are required.

In both cases, the needed sw
itchgear
s

are

submitted
, during operation, to constraints that differs
significan
tly from those applied to conventional switchgear in AC networks. Among these constraints,
let’s consider, as example, the ability to withstand continuously a high level DC voltage. This
concerns supporting columns and bushings, but also the disconnecting
switches and the circuit
breakers when they are in the open position.

Testing such apparatus implies new testing methods and new test equipments. The purpose of this
report is the description of some testing circuit
submitting the switchgear under test to
the same
constraints that they will encountered in a DC network. These constraints are mostly as follows: Level
of permanent DC voltage, level of transient DC voltage, magnitude and rate of rise of DC current
during interruption or switching, etc.

Addition
ally, we have to deal with the safety of the test. Safety
of the device under test, in case of failure, but also safety of the testing equipment and circuit.


We will see, in this report, that it is possible to create testing conditions representing the tr
ue life of the
equipment, through the use of very low frequency power generators associated to oscillating circuit
properly synchronized. The notion of pure DC current is then replaced by the notion of quasi
-
stationary current. The rate of rise of the

faul
t currents are respected using high frequency oscillating
current superposed to the low frequency component.

This report will show how the safety of the systems can be granted still using conventional type circuit
breakers,

associated with oscillating circ
uits.

We know that AC circuit breakers can interrupt the
current only through current zero. This condition, which is obviously is no longer available in a pure
DC current, can be synthesized through adequate testing circuits.

We will illustrate all these c
onsideration through the example of Metallic Return Transfer Breaker and
By
-
Pass Breakers, and we will conclude with some proposals for testing DC circuit
b
reakers.


2012 Paris Session



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