AIR LOAD BREAK SWITCH DESIGN PARAMETERS
Doctoral thesis
Date
2015Metadata
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- Institutt for elkraftteknikk [2338]
Abstract
Current interruption is vital in the power system, as this makes it possible to
control the use of different loads, change the grid configuration, and minimize
damage when faults occur. This thesis presents a study of the different switch
design and test circuit parameters involved in medium voltage air load break
switching and how they affect the thermal interrupting capability. Mediumvoltage
load break switches are common in the distribution grid, and are a
cheaper option than installing circuit breakers.
Medium voltage load current ratings are typically in the range of 6 – 36 kV
and 400 A up to around 1 kA (50 Hz). Air is considered an environmentally
benign alternative as an interrupting medium compared to SF6 for these ratings,
and is also thought to be cost-competitive compared to vacuum. However, no
compact air load break switch for 24 kV is currently available for commercial
use. Thus, it is necessary to have a good understanding of the design parameters
involved, and how they affect the interrupting capability of the switch.
This thesis addresses medium-voltage load current interruption in air. It is
an empirical study based on an extensive test program in a medium voltage test
lab, and the main results and contents of this thesis are presented in five papers.
The two first are switch design parameter studies. Using a test switch that is
simple and axisymmetric, yet in many aspects similar to commercial puffer
devices, one test switch parameter has been changed at a time to find the air
flow over-pressure needed for successful interruption. The test circuit settings
are also varied to find how the interrupting capability changes with load currents
in the range 400 – 880 A, and with a transient recovery voltage corresponding to
IEC’s 24 kV ”mainly active load” test duty. Only the thermal phase of current
interruption has been considered, i.e. the first tens of microseconds after current
zero. The over-pressures needed to interrupt the load currents were typically
from 0.2 to 0.4 bar.
The third paper presents a logistic regression analysis of all the conducted
interruption tests, with the goal of describing the interruption performance as
a function of the main test switch design parameters and transient recovery
voltage stresses. More than 3 000 interruption tests are used as input data for
this analysis, which produce a mathematical expression that summarizes all the
empirical results.
The nozzle-to-contact diameter ratio has been found to be an important
design factor. Low ratios require a substantially lower air over-pressure than
high nozzle-to-contact diameter ratios in order to interrupt successfully. The
choice of contact diameter important as well, where larger contact diameters
require lower over-pressures, but higher mass flow rates. The nozzle length does
not influence the interrupting capability very much, but the chance of successful interruption is greater when the pin contact has moved out of the nozzle at
current zero. The interruption becomes more difficult with increasing current
and the rate of the voltage build-up across the contacts after interruption.
The other two papers are based on the current interruption experiments
mentioned above, but concern details of the arc behavior and arc voltage under
different currents, test design variations and air flow conditions. For typical
medium-voltage and load current ratings, the arc greatly affects the air flow
during current interruption. The flow through the tulip contact and nozzle
is clogged during the high current part of the half-cycle, even for moderate
currents and relatively large contact dimensions. The typical over-pressures
needed for successful interruption correspond to air velocities that are well below
supersonic level. The arc voltage is a function of several parameters, and rises
with increasing air over-pressure, decreasing current, and a larger contact gap.
There is also a clear visible difference in the arc appearance when it is either
subjected to forced cooling or not. The typical arc voltage is a few hundred
volts.
Has parts
Paper 1: Jonsson, Erik; Aanensen, Nina Sasaki; Runde, Magne. Current interruption in air for a medium-voltage load break switch. IEEE Transactions on Power Delivery 2014 ;Volum 29.(2) s. 870-875, Is not included due to copyright available at http://dx.doi.org/10.1109/TPWRD.2013.2280300Paper 2: Aanensen, Nina Sasaki; Jonsson, Erik; Runde, Magne. Air-Flow Investigation for a Medium-Voltage Load Break Switch. IEEE Transactions on Power Delivery 2015 ;Volum 30.(1) s. 299-306. Is not included due to copyright available at http://dx.doi.org/10.1109/TPWRD.2014.2334360
Paper 3: Aanensen, Nina Sasaki; Runde, Magne; Jonsson, Erik; Teigset, Anders Dall'Osso. Empirical Relationships Between Air Load Break Switch Parameters and Interrupting Performance. IEEE Transactions on Power Delivery 2015 , Authors postprint is published and available at http://dx.doi.org/10.1109/TPWRD.2015.2435804 (c) 2015 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works."
Paper 4: Aanensen, Nina Sasaki; Runde, Magne. Air Flow Measurements During Medium-Voltage Load Current Interruptions. Plasma Physics and Technology 2015 ;Volum 2.(1) s. 83-87 Is not included due to copyright available at http://fyzika.feld.cvut.cz/misc/ppt/ppt2015.html#number2
Støa-Aanensen, Nina Sasaki; Runde, Magne; Teigset, Anders Dall'Osso. Arcing voltage for a medium-voltage air load break switch. I: Electrical contacts - 2015 : proceedings of the sixty-first IEEE Holm Conference on Electrical Contacts. IEEE conference proceedings 2015 ISBN 9781467393416. s. 101-106