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Test-circuits for HVDC thyristor valves
Citation for published version (APA):Thiele, G. (Ed.), Alarovandi, G., Bonfanti, I., Cepek, M., Dumrese, H. G., & Damstra, G. C. (1997). Test-circuitsfor HVDC thyristor valves. (CIGRE technical brochure (TB); Vol. 113). CIGRE.
Document status and date:Published: 01/01/1997
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Download date: 04. Apr. 2020
Task Force 03
of Working Group 14.01
April 1997
TEST CIRCUIT
FOR HVDC THYRISTOR VALVES
113
CIGRE WG 14-01, TE 03Dielectric tests
1.INTRODUCTION
Dielectric tests for HVDC valves can be divided into die followmg categories:
- Tests betv.’een valve terminais
- Tests on multiple valves
- Tests on a valve support structure
Mostly, die tests required for HVDC valves are similar to die dielectric tests required for other high voltage
power equipment. However, die special characteristjcs of a HVDC valve mean that die test circuits must be
carefully chosen. Compared with most power equipment, HVDC valves
- have a low value, non-linear impedance in ail frequency domains;
- incorporate a designed-in feature to siiddeniy switch die valve into a conducting state when a given
voltage threshold is exceeded;
- contain complex electronics and sensitive thynstors which may require elaborate support facilities in
die form of special monitoring circuits and auxiliaiy services;
- are relatively delicate in that die thyristors are vuluerable to damage by even quite small excesses cf
voltage, current and their derivatives above die design values.
A special case cf die switching impulse test between valve terminais, die valve non-perjodic firing test, poses
a particularly chaflenging task for the test circuit designer because it requires an impulse generator capable cf
producing flot only die impulse voltage but also a precisely defined discharge current when die valve is triggered
mie conduction at die crest of die impulse.
This report discusses some of die issues involvecj and gives guidance on die selection of suitable test circuits.
2. DIELECTRIC TESTS BETWEEN VALVE TERMINALS
2.1 Test objectives
The principal objectives of die dielectric tests between valve terminais are te verify die design of die valve
regarding its voltage reiated characteristica for various types of overvokages (d.c., power frequency ac,
switching impulse, lightning impulse and steep front impulse overvoltagea). The tests should demonstrate that:
a) The valve will withstand die specified test voltages without disruptive discharge in die iusuiation of die
valve structure, cooling ducts, light guides and other insulation parts;
b) Any internai overvoltage protection circuits are effective;
c) Partial discharges will be within specified limits under any continuons operating condition. Also, that
inception and extinction voltages are above die maximum repetitive operating voltage;
d) The internai d.c. grading circuits have sufficient power rating;
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Dielectxic tes
e) The voltage distribution within die valve under various types of overvoltages is consistent with die
valve design;
f) The valve electronic circuits are immune to interference due W impulse overvoltages~ and function
correctly. (Sec appendix A for further discussion on this issue)
2.2 Test object
The test object is a complete valve which should be assembled with ail auxiliary components except for die
valve arrester. Unless otherwise specified, die valve electronics should be energized. The cooling and insulating
fluids in particular should be in a condition that represents service conditions except for flow rate which can
be reduced. If any object external to die structure is necessary for proper representation of die stresses durmg
tests it should be also included or simulated in die test.
2.3 Test circuit considerations
2.3.1 General
The characteristics of die test voltage generators for dielectric tests on a valve between valve terminais
are governed by die test objectives and die interaction of die generators with die valve. This can be
established bystudies of die equivalent circuits of die valve and test voltage generators. A typical
equivalent valve circuit is given in Fig. 1. It is mainly a resistive-capacitiVe circuit in which, depending
on die test to be carried out, either die resistive or die capacitive elements will deterinine die valve
e.quivalent circuit.
— -~
R9 Damping resistance (0.5 to 5 kc)R~ d.c. grading resistance (4 to 15 MO)C0 = Damping capacitance (200 to 20 nF)
Fast transient grading capackancc including stray capacitances (scvcral nF 10 0.1 nF)L.~ saturable valve reactor including tue stray inductances~ the effeci of stray inductances, capacitances and resistances in each brancb of the equivalent circuit may be important forlightning md steep front impulse tests.
Fig. 1: Equivalent valve circuit for dielectric type tests between valve terminais.
The higher impedance values generally correspond with valves for long distance transmission
Lv
r
cp
R~
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