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Engineering Structures
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Seismic performance and restraint system of suspended 800 kV thyristor
Zhenyu Yang
, Qiang Xie
, Yong Zhou
, Khalid M. Mosalam
Department of Civil Engineering, Tongji University, Shanghai, China
Department of Civil and Environmental Engineering and the Pacic Earthquake Engineering Research Center, University of California, Berkeley, United States
Suspension equipment
Parametric analysis
Pretensioned damper
Restraint system
UHV thyristor valve
Suspended thyristor valves are widely used in ultra high voltage (UHV) direct current transmission projects all
over the world nowadays. However, the seismic performance of the 800 kV thyristor valve, which has longer
hangers, larger air clearance requirement and is heavier than its lower voltage counterparts, has not been fully
investigated. This study rstly established a nite element (FE) model of an 800 kV thyristor valve and its
corresponding hall building to evaluate the seismic response of the valve. Subsequently, a restraint system
consisting of rods, springs and viscous dampers was introduced to reduce the seismic response of the valve.
Parametric analysis was carried out on a simplied model to determine the optimal design parameters of the
restraint system. The FE model of the restrained valve, making use of the optimal parameters, was investigated.
The results show that the system with the optimal parameters can eectively reduce the horizontal displacement
of the valve. It is proposed to apply the restraint system to the valves, or other types of suspended equipment, to
reduce the horizontal displacement and accordingly increase the seismic resiliency of this types of suspended
1. Introduction
In recent years, ultra high voltage (UHV) direct current transmission
projects have experienced a rapid growth in southwest China, where
exist abundant hydropower resources. However, earthquakes fre-
quently take place in this region [1]. As the key equipment in a UHV
converter station, the thyristor valve needs to avoid structural or
functional damage during earthquakes. The seismic performance of
oor-mounted valves has been studied thoroughly [2,3] and some
performance enhancing technologies have been proposed consequently.
For example, Nakagaki et al. [4] experimentally studied the inuence of
laminated rubber bearings on the seismic responses of oor-mounted
250 kV thyristor valves. The test results shows that the bending moment
generated at the root section deceases considerably after the employ-
ment of the bearings. Because oor-mounted valves need big converter
hall buildings and large cross-sectional areas for porcelain legs, sus-
pended thyristor valves were introduced by Larder et al. [5] in the
Intermountain Power Project in 1989 and since then this kind of valve
has been widely used in many other projects. Suspension isolation can
signicantly reduce the seismic load on the valve. However, suspended
valves without any restraint system behave like a pendulum and con-
sequently experience large horizontal displacement, vertical
acceleration and vertical force response during earthquakes, which may
lead to a potential failure of the hangers [6]. For example, one hanger
of a suspended 500 kV thyristor valve in the Sylmar substation failed
during the Northridge Earthquake in 1994 [7]. Taking the tilt ground
motion into consideration, Wei et al. [8] carried out a shaking table test
on the scaled model of a hall building with one suspended valve. The
spring hanger, which has a smaller stiness than the typically used steel
rod, experiences a smaller tension during the test. Therefore, softer
hangers are recommended. Moreover, the horizontal displacement of
the suspended valve can be more than one meter according to the nu-
merical simulation by Liu et al. [9]. In order to minimize the interaction
between the valve and its adjacent installations, exible bus was
adopted in the Sylmar Substation [10]. However, the large displace-
ment of the valve may lead to insucient air clearance, especially for
the voltage upgrade in an existing converter station.
A well-designed restraint system is indeed necessary for thyristor
valves located in seismic regions. Enblom et al. [11] adopted a post
hydraulic damper for a 350 kV thyristor valve, which can decrease the
displacement from 850 mm to approximate 480 mm at the bottom of
the valve and increase the damping ratio of the valve to approximate
12%. The internal forces and displacements of the valve were obtained
by a nonlinear time history analysis and veried experimentally.
Received 9 January 2018; Received in revised form 24 April 2018; Accepted 8 May 2018
Corresponding author.
E-mail address: (Q. Xie).
Engineering Structures 169 (2018) 179–187
0141-0296/ © 2018 Elsevier Ltd. All rights reserved.
Similarly, Mahmoud et al. [12] employed post-tensioned links in par-
allel with energy dissipation components to reduce the seismic re-
sponses of suspended oor slabs in a building, which has similar
structure to the thyristor valve. As specied in IEEE 693 [6], supple-
mentary damping devices are recommended for suspended equipment
to reduce its horizontal displacement although details are not given.
Another path to alleviate the seismic response is the employment of
dynamic vibration absorber. Both the transversal and longitudinal dy-
namic absorbers, which consist of springs and damping devices, can
achieve response reduction for pendulum structures [13]. In addition,
the introduction of semi-active ono damping controller can further
improve the eectiveness of the dynamic absorber [14].
Compared with the valves with the specied voltage of less than
500 kV as mentioned above, 800 kV thyristor valves used in the UHV
direct current transmission projects have longer hangers and larger air
clearance requirement. The suspension technology successfully used in
the 500 kV thyristor valves is also applied to the 800 kV valves, but
whether they can satisfy the displacement limit under strong ground
motions has not been reported until now. Thus, it is necessary to
quantitatively investigate the seismic performance of the 800 kV UHV
valves. As the distance from the valve to the ground increases, the post
damper devices become longer, which decreases the seismic resistance
of the dampers. Therefore, for the 800 kV thyristor valves, a new re-
straint system needs to be developed.
In this paper, rstly, a nite element (FE) model including six
800 kV thyristor valves and a hall building was established and the
seismic responses of the valves were obtained by time history analyses.
Secondly, a new restraint system connecting the valve bottom to the
ground by pretensioned damper-spring joints in series with epoxy rods,
was proposed. A simplied model was introduced and then a para-
metric analysis was carried out to study the eects of the four main
parameters of the restraint system. Finally, a FE model of the thyristor
valve with the restraint system, which was modeled by a user-dened
element (UEL), was developed to evaluate the seismic performance of
the restrained valves.
2. Seismic performance of thyrister valves
2.1. Modeling of the thyristor valves and the hall building
Fig. 1 shows the side view of a typical converter hall in an 800 kV
converter station. The UHV hall building consists of the steel roof, steel
portal frames and reinforced concrete re walls. The width, length and
height of the hall building are 36 m, 86 m and 33 m, respectively. Fig. 2
shows three thyristor valves and accessory equipment in a hall building.
The thyristor valve is composed of the top and bottom shields, four
valve layers, one valve arrester, several bus bars and cooling water
pipes (Fig. 3). The 7.58 m high valve, whose layers are connected by six
6.72 m epoxy hangers, can be thought of as a pendulum. The lengths of
the hanger segments between adjacent layers vary from 1.11 to 1.7 m.
The total mass of the thyristor valve and the arrester is 8.58 t, about
3.8% of the mass of the hall building.
A FE model comprising the hall building and six thyristor valves was
established following Fig. 1. The FE package of ABAQUS [15] was used
for the development of the FE model. The modeling of the valve is quite
detail to investigate the inner stress distribution of the valve. Only the
main structural and mass components were taken into account. The top
and bottom shields of the thyristor valve supported by an aluminum
frame, were modeled as additional mass on the aluminum frame
(Fig. 4). The electronic equipment in each layer, including the thyristor
and reactor modules, was modeled by solid element. The composite
braces between layers were modeled by linear beam element. The
shields of the four intermediate layers, as the main structural compo-
in each layer, were modeled by shell element to accommodate
Fig. 1. Side view of an 800 kV converter hall (unit: m).
Fig. 2. Electric equipment in a hall building.
Fig. 3. Components of the thyristor valve.
Fig. 4. FE model of the thyristor valve.
Z. Yang et al.
Engineering Structures 169 (2018) 179–187