Application considerations for gapped silicon-carbide arresters installed on utility high voltage systems part II: Energy consumption

Abstract

There has been increased global interest recently in identifying opportunities to conserve energy by reducing consumption, both in the residential and commercial areas. One such energy savings opportunity, in the utility environment, relates to the large number of gapped Station and Intermediate Class silicon-carbide (SiC) arresters still installed on utility high voltage systems. These gapped SiC arresters represented state-of-the-art protection during the 30+ years that they were installed (1950s thru 1980s). Application considerations regarding these gapped SiC arresters versus modern gapless metal oxide (MOV) arresters were presented previously in reference[1], which focused primarily on protection and durability concerns. The intent of this paper is to extend this initial effort and focus on energy consumption issues and energy savings opportunities associated with replacement of these high voltage gapped SiC with MOV arresters.

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Application Considerations for Gapped Silicon-Carbide Arresters
Installed on Utility High Voltage Systems
Part II: Energy Consumption

Dennis Lenk, Fellow, IEEE

Abstract: There has been increased
global interest recently in identifying
opportunities to conserve energy by
reducing consumption, both in the
residential and commercial areas. One
such energy savings opportunity, in the
utility environment, relates to the large
number of gapped Station and
Intermediate Class silicon-carbide (SiC)
arresters still installed on utility high
voltage systems. These gapped SiC
arresters represented state-of-the-art
protection during the 30+ years that they
were installed (1950s thru 1980s).
Application considerations regarding
these gapped SiC arresters versus
modern gapless metal oxide (MOV)
arresters were presented previously in
reference[1], which focused primarily on
protection and durability concerns. The
intent of this paper is to extend this
initial effort and focus on energy
consumption issues and energy savings
opportunities associated with
replacement of these high voltage
gapped SiC with MOV arresters.

I. Introduction

In 2004, we participated in a joint
venture with a US utility to evaluate a
quantity of old style Station Class high







voltage gapped silicon-carbide (SiC)
arresters recently removed from the
utility’s operating system. The utility
was concerned about the electrical
integrity and protective characteristics of
these arresters. In total, 28 arresters were
returned. Evaluation consisted of 60 HZ
electrical testing and disassembly of a
limited quantity of arresters, typically
those with electrical test values different
from the norm. 60 HZ testing included
sparkover, Internal Ionization, grading
current, and rated voltage watts.

This utilities interest in old style gapped
silicon carbide (SiC) arresters, combined
with continuing inquiries from other
utilities, prompted writing reference [1].
This paper addressed
considerations related to upgrading surge
protection by replacing existing in-
service gapped SiC arresters with new
MOV arresters. Discussion focused on
protective margin, pressure relief, and
energy improvements provided by new
MOV arresters versus design limitations
associated with gapped SiC designs.
This paper did not address energy
consumption issues associated with the
gapped SiC arrester’s highly conductive
grading structure.

The intent of this paper is to provide the
utility with a quantifiable summary of
potential energy savings that can be
achieved by upgrading from gapped SiC
to MOV arresters across their high
voltage system.

technical
978-1-4244-6547-7/10/$26.00 © 2010 IEEE

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While the energy savings estimates are
based solely on one manufacturer’s
Intermediate and Station Class gapped
SiC arresters, it is the author’s opinion
that all manufacturers of gapped SiC
arresters during this era faced similar
design issues, mainly control of the
sparkover characteristic
sometimes quite tall, arresters. All
manufacturers relied
components, oriented along the length of
the gap stack, to counteract the
influences of stray capacitance and
external contamination affects. The
amount of energy each design consumed
is directly correlated to the conductivity
of the individual manufacturer’s arrester
resistance grading circuits.

II. Discussion

While utilities understand that the new
MOV arrester designs provide technical
improvements in the form of improved
protection and durability characteristics,
many have not
economically justify updating surge
protection, based solely on these
improvements.

From this 2004 joint testing and
disassembly effort, it became obvious
that these older style gapped SiC
Arresters were in good operating
condition, even the early vintage (Series
3) arresters manufactured from 1957
thru 1966.

Electrical tests did indicate, however,
that these gapped
conducted high levels of grading current
and dissipated significant watts when
energized at their rated voltages. While
the SiC arrester gap conducts no
continuous current, the grading structure
located in parallel with the gaps does
of these,
on grading
been able to
SiC arresters
conduct continuous levels of grading
current. The simple gap configuration of
the early vintage Series 3 design
required a highly conductive grading
resistor structure, connected in parallel
with the gaps. This “stiff” grading was
necessary to control the sparkover
characteristic of the long Series 3
arresters under all service conditions.

The design improvements incorporated
in the later vintage Series 5 Station Class
arrester (introduced in 1966) included
the addition of external gap capacitors
which allowed for the use of lower
conductivity resistors. This redesign
resulted in a marked improvement in the
Series 5 protective
(versus Series 3) and also provided more
energy efficient performance in the form
of lower watts dissipation.

In comparison to the gapped SiC
arresters, the MOV gapless arresters, by
design, conduct low levels of grading
current continuously through the MOV
disc column resulting in even lower
levels of watts dissipation.

III. Purpose of Study

This analysis quantifies potential annual
energy (KWHr) savings associated with
the replacement of old style gapped high
voltage SiC arresters with new gapless
MOV designs. This analysis is based on
measurements made during the joint test
program and recent laboratory tests to
characterize the non-linearity exponent
of the Series 3 and Series 5 arrester
grading resistors. This data was used to
predict gapped SiC arrester watts loss as
a function of applied voltage.

To make the analysis relevant to the
utility, the watts loss calculations are
characteristics

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based on arresters applied at specific
system voltages. Arrester watts loss
values were estimated for both gapped
SiC and proposed replacement gapless
MOV designs. The difference between
the gapped SiC and MOV arrester watts
loss was converted to an annual KWHr
savings.
IV.
Results of Study

Tables 1, 2, and 3 summarize the results
of this effort.

Table 1 estimates expected energy
savings associated with replacement of
Series 3 Intermediate Class arresters
with equivalently
Intermediate Class MOV arresters. Note
that the Series 3 gapped Intermediate
SiC arrester was manufactured and
installed on utility systems from 1957
thru 1982.
rated gapless

Table 1

Estimated Annual Energy Savings Associated with Replacement of
Gapped Intermediate SiC Series 3 (1957-1982 Vintage) with Gapless MOV
Intermediate Arresters
Gapped
SiC
Series
3 Arr
Watts
@ Max
Sys
kVL-g
48.3 27.9
29 36 31.7
31.5 39 24.4
36.5 45 15.3
72.5 41.9 42 54 47.6
48 60 33.8
57 72 18.7
121 69.9 70 90 79.9
76 96 64.8
145 83.7 84 108 95.3
98 120 67.7
169 97.6
98 120 129.7
Max
Sys
kVL-L
Max
Sys
kVL-g MCOV Rating
Nominal
Estimated
MOV
Watts @
Max Sys
kVL-g
1.26
0.86
0.45
2.85
1.17
0.62
4.75
2.58
5.70
2.13
6.65
Watts
Reduction by
Replacing
Gapped SiC
with Gapless
MOV
30.4
23.6
14.9
44.8
32.7
18.1
75.1
62.2
89.6
65.5
123.1
Estimated
Annual KWHr
Savings from
Intermediate
arrester
replacement
effort
266
206
130
392
286
158
658
545
785
574
1078

Table 2 estimates expected energy
savings associated with replacement of
old Series 3 Station Class arresters with
equivalently rated gapless MOV Station
arresters. Note that the Series 3 gapped
Sic Station arresters were manufactured
and installed from 1957 thru 1966.

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Table 2

Estimated Annual Energy Savings Associated with Replacement of
Gapped Station SiC Series 3 (1957-1966 Vintage) with Gapless MOV
Station Arresters
Gapped
SiC
Series 3
Arr Watts
@ Max
Sys kVL-g
kVL-g
27.9 29 36/37 31.7
31.5 39/40 24.4
36.5 45 15.3
41.9 42 54 47.6
48 60 33.8
57 72/73 18.7
69.9 70 90 79.9
76 96/97 64.8
83.7 84 108/10995.3
98 120/12167.7
97.6
98 120/121129.7
106 132/13395.2
115 144/14571.7
139.7 140 172 185.2
144 180/182159.7

152 192/195 129.5

Max
Sys
kVL-L
48.3


72.5


121

145

169


242


Max
Sys
kVL-g MCOV Rating
Nominal
Estimated
MOV
Watts @
Max Sys
Watts Reduction
by Replacing
Gapped SiC with
Gapless MOV
29.2
21.9
12.8
43.7
29.9
14.8
73.3
61.0
87.4
64.3
120.8
90.0
67.7
172.6
149.2
121.7
Estimated Annual
KWHr Savings from
Station arrester
replacement effort
255
192
112
383
262
130
642
534
766
563
1058
789
593
1512
1307
1066
2.52
2.52
2.52
3.94
3.90
3.86
6.6
3.8
7.9
3.4
8.9
5.1
4.0
12.6
10.5
7.8


Figure 1 illustrates the resistive grading
structure used to control the Series 3 gap
sparkover and stability characteristic.

Table 3 estimates expected energy
savings associated with replacement of
newer vintage Series 5 Station Class
arresters with equivalently rated gapless
MOV arresters. Note that the Series 5
gapped SiC Station arresters were
manufactured and installed from 1966
thru 1982.









Figure 1

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Table 3
Estimated Annual Energy Savings Associated with Replacement of
Gapped Station SiC Series 5 (1967-1982 Vintage) with Gapless MOV
Station Arresters
Gapped
SiC
Series
5 Arr
Watts
@ Max
Sys
kVL-g
48.3 27.9 29 36 5.56
31.5 39 4.02
36.5 45 3.00
72.5 41.9 42 54 8.6
48 60 6.9
121 69.9 70 90 14.4
76 96 12.5
145 83.7 84 108 17.1
98 120 12.4
169 97.6
98 120 22.0
106 132 18.1
115 144 13.8
242 139.7 140 172 33.1
144 180 28.7
152 192 23.5
Max
Sys
kVL-L
Max
Sys
kVL-g MCOV Rating
Nominal
Estimated
MOV
Watts @
Max Sys
kVL-g
2.52
2.52
2.52
3.94
3.90
6.6
3.8
7.9
3.4
8.9
5.1
4.0
12.6
10.5
7.8
Watts
Reduction by
Replacing
Gapped SiC
with
Gapless
MOV
3.0
1.5
0.5
4.6
3.0
7.8
8.8
9.3
9.0
13.1
12.9
9.8
20.5
18.2
15.7
Estimated
Annual KWHr
Savings from
Station arrester
replacement
effort
27
13
4
41
26
68
77
81
79
115
113
86
180
159
137

Examination of Tables 1 and 2 reveal
that the utility can expect significant
energy savings by replacing any in-
service Series 3 Intermediate or Station
Class arresters with similarly rated
gapless MOV arrester. The energy
savings is not as pronounced on Table 3
which summarizes energy dissipated by
the Series 5 gapped Station Class
arresters.

The minimal improvement in energy
savings shown on Table 3 relates to the
improved Series 5 gap/grading design
when compared with the grading
structure of the original Series 3 design.

Figure 2 shows the resistor and capacitor
grading structure incorporated into the
Series 5 arrester gap design


Figure 2

The
associated with the reduction of arrester
watts on (2) intermediate and (1) station
arrester rating (bolded and highlighted in
Tables 1 thru 3) are summarized in
Figures 3 thru 5.
manufacturing time frames