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IEEE Transactions on Power Systems, Vol. 10, No. 1, February 1995 3
A STUDENT DESIGN PROJECT TO IMPROVE POWER QUALITY FOR A COMMERCIAL FACILITY
Roby C. Lentz Frank J. Mercede Joseph N. Mercede, Jr.
(Student Member) (Member)
Department of Electrical Engineering Mercedes Electric Company, Inc.
Widener University Philadelphia, PA 19134
Chester, PA 19013
Keywords: power engineering education, power quality, power system transients, power system harmonics
Abstract - A recent paper (cf. Ref. I ) reported on the success of The branch circuits of sensitive, microprocessor-based loads are
industry-sponsored student projects to promote power quality fed from the same panelboard with other loads that produce
education. One such project, sponsored by BCM Engineers in power line disturbances (e.g.. vending equipment, ice machine,
Plymouth Meeting, PA, was entitled "Power Quality Survey of a microwave oven, photocopying machine, electric discharge sign
Commercial System." The results of the survey confirmed the lighting, heating equipment, paper shredder and other switched
suspicion that power line disturbances (i.e., normal-mode and inductive loads such as refrigeration equipment and ventilation
common-mode impulses and "noise") were responsible for the fan motor).
outages, premature failures and data communication errors of critical
microprocessor-based equipment (e.g., terminals, workstations, Sensitive, microprocessor-based loads share the same branch
network file servers, teleconferencing video equipment, etc.). As a circuit with other general purpose loads which produce power
follow-up to this project, this paper reports on the results of a line disturbances (e.g., space heater, coffee maker, toaster,
student design project to develop a cost-effective implementation vacuum cleaner and other housekeeping equipment, electric
plan to mitigate the causes of the BCM power quality problems (i.e., typewriter, electric pencil sharpener, hair dryer, electric razor,
grounding. wiring methods, load configurations, surge protection, portable refrigerator, etc.).
and employee practices). Since BCM only leases several floors of
the commercial building, it was important that the design be C
Many branch circuits for F terminals and other sensitive,
cost-effective and unobtrusive to the other tenants in the building. microprocessor-based equipment are run without a separate
The design presented is simple and effective, and it conforms to the insulated equipment grounding conductor via 2-conductor (Type
NE@ 121 and accepted industry practice 131. The students have AC) armored cable 17, Fig. 31. Equipment grounding is only
benefited from this experience by being exposed to real-world effected by the outer armor of the cable, which presents a
constraints on power quality design which cannot be taught in the relatively poor (i.e., high impedance) return path to actuate
classroom. branch circuit overcnrrent protection on ground faults.
INTRODUCTION On each floor, the panelboard is tapped from a 600 amp, 208 /
120 volt bus duct riser. The method of equipment grounding
BCM is a multi-million dollar environmental consulting firm from the bus duct to the panelboard is effected via mechanical
which provides engineering, scientific and financial services to the connection to the bus duct enclosure rather than to a separate
nation's leading industries. Its operations depend heavily on the use ground bus-bar from the main service entrance panel in the
of microprocessor-based equipment, such as personal computer 7
basement of the building 1 , Fig. 31. This method of equipment
(K)terminals, local area networks (LANs), computer-aided design grounding poses potential power quality problems. (The
(CAD) workstations, televideo conferencing equipment, etc. for following discussion is paraphrased from the correspondence by
applications such as financial forecasting, engineering design, the reviewer of Ref. 4.) One such problem is the vertical voltage
project management and scientific analytical studies. The BCM divider effect, which is caused in this case by each floor being
office in Plymouth Meeting, Pennsylvania, has been experiencing tapped into the bus duct over the entire nine stories of the
unplanned and costly outages and failures of microprocessor-based building. The problem is that electronic computer / data
equipment, such as network outages brought about by file server processing equipment on each floor may also be interconnected
shutdown, lock-ups of mail server hardware, lock-ups of by data I / 0 cables that are run between the floors.
teleconferencing video equipment, catastrophic and repeated Consequently, any voltage drop across the bus duct route could
hardware failures of PC terminals at particular sites. and electric cause conducted circulating currents to flow in the interconnecting
shock hazards from network cabling connectors and enclosures of equipment grounding and data I / 0 cable grounding conductors.
microprocessor-based equipment. This is a common-mode "noise" current problem of significant
A previous student project conducted a power quality survey of proportion. In addition, since the bus duct has no dedicated
the BCM electrical system in order to ascertain whether the outages equipment safety grounding conductor (i.e., "greenwire"), one
and failures were due to the quality of the electric power that must rely solely on the bus duct enclosure for the equipment
supplies these microprocessor-based loads. The results of the (safety) grounding path. This path is "noisy" under many
survey (cf. Ref. I ) confirmed the suspicion that power line conditions, and an equipment safety grounding conductor would
disturbances (i.e., normal-mode and common-mode impulses and be needed to bond around the usual sources of this noise (e.g.,
"noise") were responsible for the outages, premature failures and loose and / or rusted joints, fittings, terminations, etc.).
data communication errors of essential microprocessor-based Although transient voltage surge protecting (TVSS) multi-outlet
equipment. Some of the specific causes of the BCM power quality power strips are utilized at the load level, the type being used
problems are listed below. does not provide a monitor / indicating light of effectiveness
status of the suppressors (i.e., metal oxide varistors).
9 4 WM 237-8 PWRS A paper recommended and approved
by the IEEE Power Engineering Education Committee of On every BCM-occupied floor, a power monitor was connected
the IEEE Power Engineering Society for presentation at the electrical panelboard to record the phase (i.e.,
at the IEEE/PES 1994 Winter Meeting, New York, New phase-to-neutral) voltages. phase currents, neutral-to-ground
York, January 30 - February 3, 1994. Manuscript sub- voltage and neutral current for the feeder conductors from the bus
mitted July 30, 1993; made available for printing duct to the electrical panelboard and the branch circuit load
December 15, 1993. currents II I. The feeder conductors supply a significant
percentage of nonlinear phase-to-neutral loads (e.g., PC
terminals) 114, Chap. 5; 16, Chap. 71, which accounts for the
observed harmonic current distortion (i.e., triplen harmonic
components) in the phase and neutral conductors and the
0885-8950/95/$04.00 0 1994 IEEE
4
relatively large amplitude of the neutral current IS). (In theory, BCM is prepared to sponsor only those modifications to its
the fact that these harmonic components of the phase currents are electrical system which are absolutely necessary to achieve
additive at the wye point of a balanced three-phase, four-wire adequate power quality for essential computing facilities. In other
system accounts for the fact that the neutral current could
-
approach v'3 1.73 times therms value of the phase current 181.)
Finally, the phase-to-neutral voltages exhibited harmonic
words, it is not cost-effective to completely rewire all sensitive
branch circuits on every BCM-occupied floor in the building.
Instead, only those sensitive, microprocessor-based loads which
distortion called "flat-topping,'' which can affect the performance have been experiencing reliability problems or else are critical to
of microprocessor - based loads (i.e., digital power supplies) the business will be rewired and incorporated into the plan.
whose operation depends on peak sensing of the voltage
waveform [5, p. 61 I. BCM does not want its power quality to be affected by the other
tenants in the building.
As a follow-up to this project, this paper reports on the results of
a student design project to develop a cost-effective implementation The proposed modifications to the BCM electrical system are
plan to mitigate the causes of the BCM power quality problems (i.e., subject to approval by Building Management.
grounding, wiring methods, load configuration, surge protection,
and employee practices). The students have benefited from this
experience by being exposed to real-world constraints on power On every floor, the existing electrical panelboard is located in the
quality design which cannot be taught in the classmom. electrical utility closet: therefore, space limitations will have a
significant impact on the final design. The implementation of the
DESIGN CONSTRAINTS proposed design must not cause serious disruptions to daily
business operations.
The purpose of this project is to design a cost-effective
implementation plan to mitigate the causes of the BCM power The design must conform to the NE@ 1 1 and any other local
2
quality problems. The design is subject to the following constraints. ordinances.
THREE-PHASE,
600 AMP,
2081 120 VOLT
BUS DUCT
RISER
EXISTING
PANELBOARD
FOR GENERAL-
PURFOSE LOADS
BUS-BAR, SG-ESGC BUS-BAR KIT,
& IC-ESCC BUS-BAR KIT.)
Figure 1 - Physical Layout in Utility Closet
5
In order to satisfy the design constraints it is imperative to accept Plue-in. Fused Disconnect Switch - Pnmary overcurrent protection
the fact that the proposed design cannot protect sensitive, of the isolation transformer is provided by 3 - 20 amp, class RK I.
5
microprocessor-based equipment from every possible cause of dual-element. current-limiting fuses. The rating of the fuses is less
power quality problems. For example, a more effective strategy than 125 % of the rated primary current of the transformer (i.c., 208
might be to run a dedicated branch circuit from a dedicated amperes). in conformance with NE@ 450-3(b)( I ) 121.
panelboard to every microprocessor - based load on the BCM -
occupied floor. However, for this application the cost of such a K-Factor Rated, Shielded Isolation Transformer - The reader is
plan would be prohibitive. directed to the literature 13. Secs. 8.2.1 and 9.17: 12: 14, pp. 38 and
65: 16, p. 761 for the advantages of using a locally installed K-factor
APPROACH rated. shielded. isolation transformer to serve sensitive.
microprocessor - based loads.
Fig. 1 presents a physical layout of a typical electrical utility closet
on a BCM-occupied floor of the nine-story building. The additions The following specifications of the transiormer are based on the
which constitute the design are shaded and include the following: requirements of the installation and recommendations from the
literature: ventilated self-cooled (class A A ) dry type: 208 V.
* Plug-in, fused disconnect switch delta-connected primary - 2oR v. / 120 v. wye-connected secondary:
75 kva. based on 8 volt-amperes per square foot design criterion for
* K-factor rated, shielded isolation transformer: computer-intensive offices 19, p. 3.51; 3 - 5 % impedance 13. Sec.
9.17.41; K-13factor 1131; provide at least a single-layer electrostatic
* Industrial-rated, dedicated panelboard with up-sized neutral (Faraday) shield of primary-secondary intenvinding type 13. Sec.
bus-bar and ground bus-bar kit to serve only sensitive, 9.17.1 I; UL-listed; 150°C temperature rise, 220(C UL component
microprocessor - based loads: recognized insulation system 1121; copper windings: standard basic
lightning impulse insulation level (BIL) rating of IO kV: and four
* Panelboard-mounted, shunt-connected transient voltage surge 2.5 % taps - two above and two below rated voltage.
suppression (TVSS) with line-to-neutral and neutral-to-ground
protection modes; Fig. 2 shows the wiring diagram of the shielded. isolation
transformer. The transformer secondary neutral (i.e., Xo)terminal.
* Supply and return ventilation ducts, whose fire dampers are shielding, transformer core and enclosure, and insulated equipment
controlled by a smoke detector in the electrical utility closet; grounding conducton (into and out of the transformer enclosure, are
all connected to the NEC required ac system grounding electrode
Additional details o the proposed design are presented in Figs. 1
f path. which consists of an ac system grounding bus-bar in the
through 4 and are discussed in this section. transformer enclosure and its connection via a grounding conductor
3 0 KCMILTHHNWHITENEUTRAL
5
'1
c- 5 - 1 12 AWG T H "
yw INSULATED
SrRANDED
BUS -BAR WITH COPPER
X 20 TAPPED HOLES FROM PANEL
STEEL CHASE NIPPLE
WITH BONDING-TYPE SG - ESGC BUS
LOCKNUTS
I
NEC AC SYSTEM
GROUND SG-ESGC -1 LIG-ESGC
GREEN WIRES GREENlYELLOW
WIRE
Fig. 2 - Wiring Diagram for Isolation Transformer, Surge Protection and Dedicated Panel
6
(i.e., separately derived) to the nearest "effectively grounded" Fig. 3 is adapted from Fig. 9 of Ref. 10 and shows the N e
structural steel [2, Article 2M. 3, Sec. 9.10.11; 14, Fig. 7-4; 16, [2] required equipment grounding practice for a complete IG form of
Chaps. 4 and 5 . Note that the bonding strap which is furnished
1 grounding for a dedicated branch circuit, which extends from the ac
with the transformer may be undersized and flimsy; in which case, it system grounding bus-bar in the transformer enclosure to the IG
is recommended that every grounding connection be made with an style receptacle. The IG style receptacle includes a TVSS module
insulated conductor of the same size as the phase conductors [6, p. with audible alarm I indicating light status of the suppressors (i.e.,
4 1 (i.e., t 3 I O THHN copper).
5 metal oxide varistors). The dedicated branch circuit is employed to
serve a vital microprocessor - based load (e.g., file server and mail
It is important to note that the noise attenuation capability of the server hardware, CAD workstation, minicomputer, televideo
shielded isolation transformer is affected by the length (i.e., conferencing equipment, etc.). Personnel must be reminded never
inductance) of the conductor used to bond the shield to the ac system to connect general purpose loads (e.g., space heater, coffee maker,
grounding bus-bar 14; 14, p. 651. Finally, conduit connection to the toaster, vacuum cleaner and other housekeeping equipment, electric
transformer is permitted only below a designated point on the typewriter, electric pencil sharpener, hair dryer, electric razor,
enclosure and is not recommended on the top cover, rear or front portable refrigerator, etc.) into these important outlets.
cover, or ventilation screen 13, Sec. 9.17.71.
Fig. 4 shows the equipment grounding practice for a single-phase
Dedicated Panelboard for Sensitive. MicroDrocessor - Based Loads branch circuit which supplies a "cluster" of four nearby receptacles
for the PC network terminals in the cubicles. Clearly, a more
On every BCM-occupied floor, it is recommended that the effective strategy would be to run a dedicated branch circuit for
secondary of the isolation transformer directly feed a dedicated '
C
every F network terminal. However, due to the large number of
electrical panelboard to supply only sensitive, microprocessor - terminals on the computer network, the cost of such a plan would be
based loads [3, Sec. 9.3.21. prohibitive. Likewise, this practice is implemented only when an
existing terminal has been suffering from power quality problems or
The dedicated panelboard shall not supply heavy-duty loads that else the installations are new; otherwise, the existing wiring for
produce serious power line disturbances (e.g., vending equipment, these outlets is undisturbed. Once again, cost prohibits rewiring all
ice machine, microwave oven, electric discharge sign lighting, PC network terminal outlets on every floor.
heating equipment, paper shredder, and other switched inductive
loads such as refrigeration equipment and ventilation fan motor). Finally, it is important to note that the phase-to-neutral,
microprocessor-based load is supplied by a single-phase branch
The panelboard shall be the industrially-rated style for power or circuit with separate neutral conductor instead of a three-phase
lighting applications and not be the lighter-duty "load center" type branch feeder system with a shared neutral. The latter method is
13, Sec. 9.14 14, p. 391. It shall be painted orange and include a avoided because it could cause excessive current to flow in the
clearly visible unauthorized nameplate. The panelboard should be shared neutral conductor, even when the load is balanced 121; 221.
directly mounted to building steel 13,Sec. 9.14.4; 14, p. 401.
The dedicated panelboard supplies sensitive, nonlinear
phase-to-neutral loads (e.g., PC terminals) which produce triplen-
harmonic components in the phase currents. Since these harmonic
components of the phase currents are additive at the wye point, the
current rating of the shared neutral conductor from the transformer
to the panelboard is upsized by about 170 % with respect to the PANELBOARD
phase conductors (i.e., 350 kcmil THHN copper) 13, Sec. 9.17.3; (SEE FIGURE 2)
14, p. 381 and the neutral bus-bar assembly of the panelboard is
upsized by the same percentage with respect to the line bus-bars (3,
Sec. 9.14.2; 14, p. 391. Many microprocessor-based loads are
supplied by dedicated branch circuits. Therefore, the neutral and
ground bus-bars in the panelboard should provide an adequate IO - ESGC
GREEN I YELL0
I
number of termination points r3, Secs. 9.14.2 and 9.14.3; 14, p.
401. WIRE
Wiring Methods - Solid-wall, ferrous conduit is used in Fig. 1 to
shield the feeder conductors from unwanted coupled fields 13, FACILITIES ( W C )
-
SG ESGC
GREEN WIRE
Sec.9.20.1; 14, p. 411. TYPE A C T "
In Fig. 2, note that there are two types of EQUIPMENT SAFETY
GROUNDING CONDUCTOR (ESGC) which originate at the ac
system grounding bus-bar and terminate at particular grounding
bus-bars in the dedicated panelboard SOLID GROUNDING (SG -
ESGC) and INSULATED I ISOLATED GROUNDING (1G -
ESGC). The insulation color of the SG - ESGC is solid green, and
it serves a the NE@ [21required equipment grounding conductor
s
for electrical safety. The insulation of the IG - ESGC is color-coded
by applying green and yellow tapes next to each other at both ends
of the conductor 13, Sec. 9.10.12.6.11. It serves to connect the IG -
ESGC bus-bar in the dedicated panelboard to the ac system
grounding electrode [3, Fig. 9-3(a); IO, Fig. 9; 15, Sec. 4.171.
Since the IG - ESGC bus-bar is insulated from the panelboard, the 2-POLE, 3-WIRE, 15 AMP, 125 VOLT
purpose of this connection is to ground the "isolated" grounding ISOLATED GROUND (IO) STYLE
poles of 1G receptacles to the ac system grounding electrode. The RECEPTACLE WITH TVSS MODULE
I form of grounding is intended to reduce the effects of
G & AUDIBLE ALARM I INDICATING
common-mode noise on ac supply circuits. The actual effectiveness LIGHT STATUS OF SUPPRESSORS.
~~ ~.~ . .
~ -
..~~~ ~. . . ~~ .-~...
from using IG wiring is dependent on the overall length of the IG ORANGE FACE COLOR. UL 1449 I CSA LISTINO.
path: IG forms of grounding may have minimal effect on short NOTE: IG STYLE HAS NO
lengths and maximum effect on longer lengths, and the actual effects CONNECTION TO BOX.
are often reversed for the return currents of internal LC filter and
suppression networks of the electronic computer I data processing Fig. 3 - Grounding Practice for Dedicated
equipment (IO, Conclusions]. Branch Circuit
7
Figure 4 - Grounding Practice for Receptacle
Cluster of Network Terminals
M 20 AMP, SINGLE-POLE CIRCUIT
BREAKER IN DEDICATED PANELBOARD
NOTE: BALANCE RECEPTACLE CLUSTERS
ON THREE PHASES OF PANEL.
BUS IN DEDICATED
BUS IN DEDICATED PANELBOARD
- 1 TYPE ME'ITALIC JUNCTION BOX SO - ESGC BUS - BAR
MOUNTED ON STRUCTURAL STEEL IN DROP DIRECTLY SCREWED
IG-ESGC BUS-BAR INTO TAPPED HOLES
INSULATED PROM CEILING. PAINTED ORANGE WITH CLEARLY ON JUNCTION BOX.
JUNCTION BOX. VISIBLE UNAUTHORIZED NAMEPLATE.
- The reader is directed to the literature [3, Secs. The panelboard-mounted, shunt-connected TVSS is shown in
3.4.3 and 4.5: 16, Chap. 6 to understand the importance of surge
1 Fig. 1. As an example, the following specifications are provided for
protective devices for normal mode protection of sensitive, the Joslyn Model 1455-1I Medium Duty Subpanel Surge Protector
microprocessor-based loads. Sec. 9.1 1 of Ref. 3 and Refs. 17 (cf Refs. 17 -19).
through 19 discuss the recommended design and installation
practices for TVSS devices which serve sensitive, micropmessor - nominal line voltage: 208 Y I 120 volt, 60 Hz,3Q, Qwire
based loads.
listinp: Underwriters Laboratories (a) 1449
"Having a TVSS unit at the end of a branch circuit is a good idea, technolopv: multiple Metal Oxide Varistors (MOVs)
especially if it can be brought together with the TVSS unit to protect with individual fusing
the data I I O cables at the equipment to form a truly commonly maximum continuous ooeratine voltaee: I50 volts (line-to-neutral)
modes of motection: line-to-neutral and neutral-twground
shared ground point of low impedance. Usually, this means
mounting the ac power and signal TVSS units on the same small max. single-suree ratine m r uhase (8I 2 0 ps waveshape): 16 kA
piece of sheet metal to act as an inter-TVSS ground plane. Or, the surge enerev cambility (8 I 20 ps waveshape.): 1920Joules
two TVSS units may simply be screwed one to the other in direct (total rating o all MOVs)
f
fashion. (The use of wire jumpers is not recommended due to the peak let-through voltaee (measured 1 inch outside &using)
large inductance that results across the bond.) This practice is very ANSlllEEE C62.41-1991 and C62.11-1987 waveshapes:
important since it prevents most of the surge current, being Category A (200 amp, 100 kHz ring wave) - 400 volts
exchunged between these two related pathways, from flowing Category B (500 amp, 100 kHz ring wave) - 440 volts
through the victim equipment itself. Instead, the majority of it flows
across the diversionary path provided between the two Category B (3 kA, 8 I 2 0 ps combination wave) - 400 volts
groundedbonded TVSS units." 1 1 4 Category C (10 kA,8 I 20 ps) - 630 volts
8
Category C (20 kA, 8 / 20 ps) - 1080 volts (61 B. Epstein, "Bridging today's power quality gap: one view of
power quality problems - part two of a two-part feature,"
surge life uer phase: 3 kA,8 / 20 ps - > 800 operations Electrical Contractor, National Electrical Contractors
(120 volts ac applied) 10 kA, 8 I20 ps - z 50 operations Association, Bethesada, MD, pp. 43-6, June 1991
comwnent resuonse time: < 1 nanosecond 171 G. Porter, "Power quality: more than just a pretty waveform,"
ouerating temoerature: - 40 OC to 65'5 Proceedings of the First International Power Quality
&:
r LEDs on - suppressors operational Conference, lntertec International, Ventura, CA, Oct. 1989,
3 year warranty pp. 96-107
# 14 AWG THHN stranded wires - 18 inches i 1 inch long 8
11 T.M. Gruz, "Harmonic distortion in electric power systems,"
Proceedings of the Second International Power Quality / ASD
Conference, Intertec Communications, Ventura, CA, pp.
CONCLUSIONS 13745, Oct. 1990
191 B. Lundgren, "Designing branch circuits for the computer -
This paper has reported on the results of a student design project intensive office," Electrical Construction and Maintenance,
to develop a cost-effective plan to mitigate the causes of power
quality problems for a computer-intensive commerical facility. Intertec Publishing, Overland Park, KS,pp. 35-44, Feb. 1993
Since the customer only leases several floors of the commercial [IO] Warren H. Lewis, "The use and abuse of insulated / isolated
grounding (E)," Paper No. P-33012, Proceedings of
IEEE
building, it was important that the design be cost-effective and the 1987 IEEE Industry and Applications Society Annual
unobtrusive to the other tenants in the building. The desi Meeting, Atlanta, CA
presented herein is simple and effective and conforms to the NEC%
121 and accepted industry practice 13, Chap. 91. The students have 1111 M. Waller, "Work station planning for power quality and
benefited from this experience by being exposed to real-world safety," Proceedings of the Fourth International Power Quality
constraints on power quality design which cannot be taught in the / PRONCON Conference, Intertec International, Ventura, CA,
classroom. Sept. 1991, pp. 225-35
1121 J. Frank, "The how and why of k-factor transformers,"
Electrical Construction and Maintenance, lntertec Publishing,
Finally, it is important to note that the design was based on the Overland Park, KS, pp. 79-82, May 1993
results of a power quality survey by another undergraduate senior 113) J.M. Moravek and E. Lethert, "The k factor: clearing up its
design project, which were reported in Ref. 1. In addition, a future
*
senior design project will investigate the effectiveness of the mystery," Electrical Construction and Maintenance, lntertec
proposed design, by conducting a follow-up survey, once it is fully Publishing, Overland Park, KS,pp. 65-77,June 1993
implemented by BCM. 1141 Power Oualit Reference Guide, Electrical Contracting
ACKNOWLEDGEMENTS 1151 R. Momson and W.H. Lewis, Grounding and Shielding in
Facilities, John Wiley, New York, 1990
We wish to take this opportunity to thank the supporters of the 1161 A. Berutti and R. M. Waggoner, editors: Practical Guide to
student project. First, due to limited space in the title block, only the Oualitv Power for Sensitive Electronic Eauimnent, Electrical
Construction and Maintenance, Intertec Publishing, Overland
group leader of the student project is listed. The other student Park, KS, 1993
members of the group were Skip Garrison, Mike Hagen, Jon 1171 H. Steinhoff, "Transient voltage protection in the real world,"
Palahnuk, and Brian Silvestri. Finally, we would like to express Proceedings of the Fourth International Power Quality /
our sincere appreciation to Mr. Norbert J. Kubilus, Vice President
and Chief Information Officer, for renewing the support of BCM PRONCON Conference, lntertec International, Ventura, CA,
Engineers in the Senior Project Design program at Widener Sept. 1991, pp. 32-8
University. In addition, we wish to acknowledge the other 1181 0. Melville Clark, "Multilocation surge protection for
supporters from BCM of this recent project: Ray Middleton, Tom commercial and industrial environments," Proceedings of the
Bender, Tom Moyer, Mike Falcone, Guy Spears and Barry Second International Power Quality / ASD Conference,
Thompson. Intertec International, Ventura, CA, Oct. 1990, pp. 17480
[I91 H. Steinhoff, "Selecting a low voltage ac surge arrestor,"
Finally, we wish to express our appreciation to Mr. Warren H. Proceedings of the International EMC / ESD Conference, pp.
Lewis, a leading authority on the subject of powering and grounding 41-6, April 22-24, 1992
of sensitive electronic equipment, for reviewing the original [201 D.H. Wilfong, "Selecting transient suppressors," Proceedings
manuscript and identifying several important modifications and of the Second International Power Quality / ASD Conference,
corrections (cf. Ref. 4). However, it must be emphasized that the lntertec International, Ventura, CA, Oct. 1990, pp. 117-22
review by Mr. Lewis in no way implies his approval of the final I211 W.H. Lewis, "Branch circuits and feeders - shared or
design nor does it guarantee satisfactory system performance upon dedicated ?" Proceedings of the First International Power
implemenation. Quality Conference, Intertec International, Ventura, CA, Oct.
1989, pp. 402-25
I221 J.F. McPartland, "Common neutral versus separate neutrals
REFERENCES for 3-phase, 4-wire branch circuit," Electrical Design and
Installation, McPartland Publishing, Englewood Cliffs, NJ,
I 1IM.A. Aniba, et. al., "Industry-sponsored student projects to vol. 2, no. 2, pp. 48-51, Feb. 1991
promote power quality education," IEEE Transactions on
Power Systems, vol. 7, no. 4, pp. 1550-8, Nov. 1992 BIOGRAPHIES
121 ANSI / NFPA 70 - 1993, National Electrical Code, National
Fire Protection Association, Quincy, MA Robv C. Lentz was born in Beaumont. Texas in 1969. He was the
r31 IEEE Std. 1100-1992, IEEE Recommended Practice for group leader of this student design project. Mr. Lentz received his
Powering and Groundin- Sensitive Electronic Eauioment, B.S.E.E. degree from Widener University in 1992. He is pursuing
IEEE, New York, First Printing, 1991 a career in the nuclear power industry with Asta Engineering and has
participated in projects for Niagra Mohawk Power Company and
141 Private correspondence dated August 18, 1993 by Warren H. Public Service Electric and Gas.
Lewis (Ref. #LCE930818-01), Review of first manuscript of
"A student design project to improve power quality for a Frank J. Mercede received his B.S.E.E. (first honors, magna cum
commercial facility," Lewis Consulting and Engineering, San laude), M.S.E.E. and Ph.D. in electrical engineering from Drexel
Juan Capistrano, CA, 92675 University (Phila., PA) in 1981, 1983 and 1989, respectively.
1 1 B. Epstein, "Bridging today's gap: one view of power quality
5 From 1 9 8 1 to 1983 he was an Electrical Project Engineer in the
problems - part one of a two-part feature," Electrical Corporate Engineering Division of Scott Paper Company (Phila.,
Contractor, National Electrical Contractors Association, PA). There he participated in the design of industrial control and
Bethesada, MD, pp. 60-4, April 1991 power systems. In 1988 he joined the faculty of Widener
9
University where he is currently Assistant Professor of Electrical
Engineering. His recent work is in the areas of power quality and
power system protection. Dr. Mercede is a registered professional
engineer in the state of PA. He and his wife, Anne, are the proud
parents of three children: Michael (age 6),Maryanne (age 4) and
Christine (age 2).
Joseoh N. Mercede. Jr. graduated from Mastbaum Vocational
Technical High School in 1977, specializing in industrial electrical
construction. Over the next eight years, Mr. Mercede gained
extensive experience with Gowder Electric Company (industrial and
FD
commercial electrical construction), Reliance Electric R ’ Division
(maintenance, testing and troubleshooting of medium-voltage
switchgear), and the SEWA Electric Traction Department (catenary
distribution of the commuter rail system). In 1985 Mr. Mercede
founded Mercedes Electric Company, which specializes in industrial
and commercial electrical construction. Mr. Mercede is a licensed
contractor for the City of Phila. and is a member of the National fire
Protection Association and Delaware Valley Independent Electrical
Contractors Association. He is active in community affairs, sewing
as architect for his development and auditor for Birmingham Chester
County township. He and his wife, Laurie, are the proud parents of
two children: Mathew (age 2) and Ashley (age 1).
10
Discussion An alternative arrangement which avoids the need of a fifth
TVSS module is shown below. This arrangement is taken from
Warren € . (Lewis Consulting & Engineering. San Juan
Lewis
I Fig. 4.3b. page 97 of Reference 15 and shows the NEC required
Capistrano, CA): I have looked at your paper per your letter of Dec. G
grounding for a partial I form of grounding, which extends only
16, 1993 and specifically at referenced figure 2. You have correctly from the IG receptacle to the dedicated panelboard. The feeder to
identified one of the problems with the use of the IG form of wiring the dedicated panelboard is no longer configured to be an IC form -
- what do you do with the TVSS and the IG wire ? If you do not it is an SG form. The grounding I bonding jumper between the IC -
clamp the 1 wire in the same manner as the neutral wire, the IG
G ESGC and SG - ESGC grounding bus-bars is for the purpose of
wire may go to an unwantedly high potential under surge permiting measurements to be taken via the collective current to
conditions. Therefore, 811 additional TVSS stage needs to be "ground" from all of the IG branch circuits. If this feature is not
shown on Figore 2 with the TVSS element connected desired, the 1 - ESGC and SG - ESGC bus-bars may be one and
G
from the [panelboard] IG bns-bar to the equipment the same, and it must be directly screwed into tapped holes on the
enclosore [i.e., panelboardl via the [panelboard] SG panelboard.
bos-bar. Persons who use the IC method all the way back to the
service entry often find that the IG circuit in the branch circuit's auap
M n s i meived April 19,1994.
receptacle box goes to a very high potential in relation to the box and
local "ground" in the area where the load is installed. This causes
damage to equipment unless the IG circuit is also clamped.
Manuscript received February 14, 1994.
FRANK I. MERCEDE I wish to thank the reviewer for identifying
an important correction to Figure 2. In Figure 2, the IG form of
grounding extends from the IG receptacle all the way back to the
isolation transformer (i.e., seperately derived ac system). The
correction to this arrangement requires a fifth TVSS module to be
connected between the 1 - ESGC and SG - ESGC bus-bars in the
G
dedicated panelboard of figure 2. The cost of this arrangement is the
need of a fifth TVSS module.
NEUTRAL BUS
ESGC
GREEN WIRE
SG - ESGC
GREEN WIRES
TAPPED HOLES
NEC AC SYSTEM ON PANEL
GROUND
-
Figure 2a: Partial IG Form of Grounding from IG Receptacle to Panelboard
IEEE Transactions on Power Systems, Vol. 10,No. 1, February 1995 11
A Transient Stability Simulation Package(TSSP)
for Teaching and Research Purposes
Z. Ao, student Member IEEE R.J. Fleming, Senior Member IEEE T. S . Sidhu, Member IEEE
Power System Research Group
University of Saskatchewan
Saskatoon, Saskatchewan
Canada S7N OW0
Abstrwt-This paper describes a simulation package for implemented on an IBM PC has been developed at the
performing transient stability study of a power system. The University of Saskatchewan. 'Ihis package has been utilized
package includes four parts which are a fast decoupled load to perform stability studies of the WSCC system [9] and the
flow program, a short circuit calculation program, a transient New England Test system. A classroom project associated
simulation program and a plotting program. The simulation with a power system modeling and control course using the
program consists of a coordiitor and many modules, each of WSCC system is discussed. As a research tool, the package
which simulates a power component, a controller or a physical has also been used to conduct a stability investigation of a
process. Simulated results can be displayed OII the screen by longitudinal power system having 69 buses and 12-
identifying the components and variables. The package is rich machines [lo]. The results of this research are briefly
in providing modules for nonlinear representations of power discussed in this paper.
components, though user-defined modules can also be easily The following is a list of tasks that can be p e r f o d
interfaced into the package. The three data mes are designed using the TSSP
in such a way that maximum convenience in data preparation
is achieved. The package can be used for teaching and doing 1) Machine modeling of varying complexity
research related to power system dynamics and control. 2) Transient simulation of induction motors
Application examples and experience gained with the use of 3) Modeling of symmetrical and asymmetrical
the package are discussed. disturbances
4) Variousload modeling
I. INTRODUCITON 5) Modeling of AVR, AGC and PSS
6) Interfacing of user-defined modules
Time domain simulation of power system stability has 7) Load flow studies
been a classical tool for various purposes of studies and 8) Short circuit calculations
popular for decades [1,2,3,4]. Various large scale
simulation packages such as the EPRI-ETMST (Extended 11. c- R€QmEums
Transienmid Term Stability Program) and the PTI-PSSE
(power System SimulationE Program) are in wide use. A The package is written in the F O R W language and
number of educational softwares are also reported in the run on an IBM compatible PC. A minimum of 410K
literature [5,6,7,8]. conventional memory is required to conduct a stability
It is felt that every simulation package has its own study for a power system of 100 buses. A CGA, EGA or
advantages and shortcomings. A package available to one VGA graphics card is also required to run the plotting
may not have all the features and flexibility that one wants program. A hard disk should be used if it is required to
for either education or research purpose. The possibility of store a large amount of numerical results from simulation.
changing the capability of the package is often limited if The purpose of the package is to provide researchers
not impossible. During the last two years, we have felt the and university students easy and wide access of it through
urgent need of a package that has the capability of fulfilling personal computer while retaining the capability of
most requirements in both teaching and research. In modeling power components with desired complexity. The
answering this call, a transient stability simulation package only limitation to the application of the package is imposed
by the PC, not by the package itself. That limitation is the
94 SM 383-0 PWRS A paper recommended and approved size of the system to be studied. A small to medium sized
by the IEEE Power Engineering Education Committee of system can be handled on the PC.
the IEEE Power Engineering Society for presentation
at the IEEE/PES 1994 Summer Meeting, San Francisco,
CA, July 24 - 28, 1994. Manuscript submitted July
D
I .MODEUNG
DFSCRIPTION
30, 1993; made available for printing April 6, 1994. The transient behavior of a power system component or
a controller is modeled by a set of fust order differential
equations. Based on the implicit integration method [ll],
this set of differential equations can be simulated by
0885-8950/95/$04.00 0 1994 IEEE
