Dynamic Interaction of High-Voltage Power
Transformer Bushings, Turrets, and Tanks
Guo-Liang Ma,
a)
M.EERI, Qiang Xie,
b)
and Andrew Whittaker
c)
High-voltage (HV) bushings are attached to a power transformer tank either
directly or indirectly via turrets. Turrets are used to achieve electrical performance
requirements, but their potential impact on the seismic performance of the sup-
ported bushings has not been considered. Earthquake simulator testing and finite-
element analysis were used to quantify the amplification of ground shaking
through tanks (220- and 500-kV) and turrets to the points of attachment of
roof- and sidewall-supported bushings. Substantial amplification of motion
was seen in both physical experiments and numerical simulations. Sample bra-
cing schemes external to the transformer tank were investigated to potentially
reduce the motions experienced by the bushings. Bushing tip displacements
were reduced in all stiffening cases studied, but the outcomes for bending
moment at the bushing-turret connection were mixed, with no change in
some cases and significant reductions in others. The physical and numerical stu-
dies described in this paper make clear the importance of dynamic interaction of
bushings, turrets, and the power transformer tank. The methods currently used to
address the amplification of input motion from the base of a tank to the points of
attachment of its bushing are inadequate. The seismic design of HV power trans-
former tanks and turrets should be supported by finite-element analysis of vali-
dated models to avoid dynamic interaction in the bushing-turret-tank system, to
minimize seismic demand on the transformer bushings, and to minimize the risk
of substation damage in earthquakes. [DOI: 10.1193/091416EQS148M]
INTRODUCTION
Power transformers, which are mainly composed of a tank, turrets and bushings, are key
pieces of equipment in electrical substations that have proven to be vulnerable to the effects of
earthquake shaking, including the 2008 Wenchuan (Yu et al. 2008, Xie and Zhu 2011) and 2013
Lushan (You and Zhao 2013) earthquakes in China; the 2010 earthquake in Chile (Araneda
et al. 2010); the 2010 Baja California earthquake in Mexico (Johnson and Iliev 2012, Cochran
2015); the 2010 Haiti earthquake (Fujisaki et al. 2014, Goodno et al. 2011); the 2010 and 2011
Canterbury earthquakes in New Zealand (Kwasinski et al. 2014); and the 2011 Tohoku
earthquake in Japan (Eidinger et al. 2012, Tang 2017). In these earthquakes, HV power
a)
Ph.D candidate, Department of Structural Engineering, Room 806 Civil Building A, Tongji University, Shanghai
200092, China; email: mgldut@163.com
b)
Professor, Department of Structural Engineering, Room 807 Civil Building A, Tongji University, Shanghai
20092, China; email: qxie@tongji.edu.cn
c)
Professor and MCEER Director, Department of Civil, Structural and Environmental Engineering, State
University at Buffalo, Buffalo, NY 14260
Earthquake Spectra, Volume 34, No. 1, pages 397421, February 2018; © 2018, Earthquake Engineering Research Institute
397
transformers experienced a variety of damage from global overturning, fracture of porcelain
bushing insulators and cast aluminium flanges, to oil leakage (e.g., Yu et al. 2008, Yuan
and Sun 2008, Xie and Zhu 2011, Eidinger et al. 2012, Fujisaki et al. 2014).
HV bushings are insulated conductors that pass electricity between HV conductors and
power transformer tanks. Transformer bushings can be attached directly to the roof or side-
walls of a transformer tank. However, to achieve electrical performance goals, an increasing
percentage of HV transformer bushings are mounted on turrets to increase the physical dis-
tance between the upper tips of adjacent bushings and the upper tips of the bushings from the
ground. All of the power transformers tested or analyzed by Bellorini et al. (1998), Villaverde
et al. (2001), Saadeghvaziri et al. (2010), Platek et al. (2010), and Zareei et al. (2016)
involved turret, not tank, mounts. Figure 1 shows damage to turret-mounted HV bushings
in the 2008 Wenchuan earthquake. It has long been suspected that these turrets
(i.e., cylindrical canisters in the figures) amplify the effects of earthquake shaking to the
point of attachment of the bushing and thus increase the seismic vulnerability of the bushings
for a given level of ground shaking.
Figure 1. Damage to turret-mounted HV bushings in the 2008 Wenchuan earthquake: (a) two views
of failed porcelain bushings of the same tank; (b) slip of air-side porcelain units and oil leakage.
398 G.-L. MA, Q. XIE, AND A. WHITTAKER
Studies on the seismic performance of HV power transformers have been reported
since the 1971 San Fernando earthquake. In 1984, the Institute of Electrical and
Electronics Engineers (IEEE) in the United States developed guidelines (IEEE 693)
for seismic testing and qualification of electrical equipment which have been regularly
updated (IEEE 2006). After the 1994 Northridge earthquake, ASCE drafted guidelines to
improve the earthquake performance of electric equipment (Schiff 1998). Wilcoski and
Smith (1997) performed seismic qualification and fragility testing of a 500-kV transfor-
mer bushing that was mounted on a small braced frame and tested using artificial waves.
Gilani et al. (1998, 1999a, 1999b) and Whittaker et al. (2004) studied the seismic per-
formance of 196-kV, 220-kV, and 550-kV porcelain t ransformer bushings by physical
testing and numerical analyses. They investigated the effect of ta nk roof flexibility on the
seismic responses of tank-mounted bushings. Bellorini et al. (1998) used forced vibr ation
tests to determine the frequencies and damping ratios of a 230-kV power transformer and
conducted finite-element analysis on the tested systems to estimate ground motion ampli-
fication to the point of attachment of the bushing. Villaverde et al. (2001) conducted field
tests and analyses of 230- and 550-kV bushings mounted on two 500-kV power trans-
formers, and quantified ground motion amplification to the point of attachment of the
bushing. Ersoy and Saadeghvaziri (2004) analyzed the seismic response of HV power trans-
former-bushing systems. Filiatrault and Matt (2005, 2006) conducted experimental and
numerical studies on the seismic performance of HV power transformers. Reinhorn et al.
(2011) performe d numerical analysis of tra nsformers. Koliou et al. (2013a, 2013b) studied
how stiffening the roof of a transformer tank affected the seismic performance of HV trans-
formers. Zareei et al. (2016) generated seismic fragility curves for a 400-kV power trans-
former. Ersoy et al. (2001) and Saadeghvaziri et al. (2010) studied the use of the Friction
Pendulum isolator (Earthquake Protect ion Systems, Vallejo, CA) to seismically protect
power transformers. Murota et al. (2006) conducted shaking tab le tests on a power trans-
former model protected by a hybrid base isolation system. Oikonomou et al. (2016) tested a
model of a transformer isolated with triple concave Friction Pendulum bearings and lead-
rubber bearings. Ki tayama et al. (2016) compared the seismic response of nonisolated, hor-
izontally isolated, and three-d imensional (3-D) isolated transfo rmers.
Although each of these studies contributed important information in terms of reducing the
seismic vulnerability of electric substations and their equipment, none addressed the dynamic
coupling of the bushing-turret-tank system, which affects the amplitude of shaking experi-
enced by vulnerable porcelain transformer bushings. This dynamic coupling or interaction is
the subject of this paper, the remainder of which is organized into five sections: construction
of HV tank-turret-bushing systems, earthquake simulator testing of a HV tank-bushing
system, numerical analysis of the test specimen, mitigation of the effects of turret flexibility
on bushing response by local stiffening, and numerical study of the seismic response of an
in-service 500-kV power transformerturretbushing system, including the effects of turret
stiffening.
HV POWER TRANSFORMERS
Figure 2 is a schematic of a typical three-phase HV (500-kV) power transformer
(see also Figure 1a) used in China. The oil conservator, the radiator, the stiffeners on
the tank roof and sidewall, and the low-voltage bushing-turret assemblies are not
DYNAMIC INTERACTION OF HIGH VOLTAGE POWER TRANSFORMER BUSHINGS, TURRETS, AND TANKS 399