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A New Approach to Creating Dynamic Models for Industrial Facilities
Xiaodong Liang, Shengqiang Li, and Wilsun Xu
University of Alberta
Edmonton, Alberta, Canada
Abstract
This paper presents a new approach to construct dynamic models for large industrial and commercial
facilities connected to power transmission systems. These facilities typically draw large amounts of power
and have complex dynamic responses to power system disturbances. Traditional load modeling
approaches such as those based on load composition or site measurement are not adequate to produce
dynamic models for such facilities.
A common situation encountered by utilities planers can be described as follows: A manufacturer contacts
a utility company and plans to develop an X-type industrial facility in a particular location. The facility
needs about Y-MW power and could be in service after a few years. The basic information of the facility,
such as single-line diagrams, load composition, loading factors etc, is commonly not available. The
utility, however, must include the future facility model in its planning study since the load can be large, in
hundreds of MWs.
Only a limited number of research works addressed this load modeling gap. Rogers presented a method of
creating equivalent models for industrial facilities assuming the electrical system structure of the facility
is known [1]. Morison proposes an industrial load model that consists of about 76% small and large
motors and 24% static load [2]. A few utility companies have adopted very crude approaches such as the
WECC modeling guide [3], [4]. This guide suggests that an industry facility can be modeled as 80% static
loads and 20% induction motors. If this approach is used, an oil refinery will have a response similar to
that of a steel mill in power system dynamic studies. This is clearly not acceptable when more and more
accurate models are being developed for aggregate loads and other power system components such as
generators.
In this paper, a facility template-based load modeling technique along with template scaling/equivalence
algorithms is proposed to solve the facility load modeling problem. The technique requires minimal user
input and can be implemented in a database program for generating user desired models for a wide variety
of facilities.
The basic idea is derived from the consideration that each type of facilities has a common electrical
system configuration, called a facility template. The configuration includes, but is not limited to, industry
processes and their electric circuits, the number of circuit branches and voltage levels, load types and load
composition, common motor sizes for different processes, motor voltage levels, and types of distribution
lines/cables, etc. One can create a template database for different types of facilities.
The template needs to be scaled up or down to match the size of a specific facility to be modeled. For
example, if a template represents a 100MW facility and a model of 75MW facility of the same type is to
be created, the template scaling method will be used and a size-specific facility configuration is thus
created. Template scaling is the process to modify template circuits and loads automatically so that the
scaled facility consumes approximately the expected amount of power. Scaling is based on a set of
scaling criteria that are developed according to different manufacturing processes.
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The third aspect of the proposed method is the facility model equivalence or reduction. The size-specific
template full (TF) model created through the template scaling process often contains hundreds of buses
and motors, which is still large and complex. To further simplify the model to be suitable for power
system dynamic studies, equivalent models are constructed by aggregating/reducing the TF model.
Industrial facilities are constructed according to their production processes and there are usually several
processes involved in one facility. If all loads in one process are reduced into one equivalent load, it will
lead to an equivalent model that has each of its processes represented as one equivalent load, which is
called the “Equivalent Process (EP) model”. In subsequent steps, several or all processes can be
aggregated into one load and called the “Equivalent Facility (EF) model”, which leads to the simplest
equivalent model of the facility under study. Electric systems of the majority of industrial facilities have
radial (tree) configurations. At the tip of the system are multiple motors (or other types of loads)
connected to the same buses. Several such branches are often connected to a higher voltage bus through
transformers and cables/lines. A bottom-up machine load aggregation scheme for radial networks is
developed for this purpose (Fig. 1).
(a) Original model
(b) Model with two groups of induction motors equivalenced
Fig. 1 Bottom-up load aggregation approach
The modeling of Paper Mill facilities are used as an example to illustrate the proposed load modeling
technique in this paper. Based on general categories of Paper Mill facilities, four types of facilities are
summarized. The template and template scaling rules for Kraft Paper Mill facilities, which are most
popular type among Paper Mill facilities, are proposed. As a case study, the load modeling of an 88MW
Kraft facility is employed using the proposed template for this type facility, and a size-specific template
full (TF) model is created. By applying the proposed equivalence methods to the TF model, the equivalent
models for this sample facility are obtained.
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By conducting simulation for the case study, it is found that dynamic responses of the full and equivalent
template-based models have good agreements, which confirms the accuracy of the model equivalence
method. The template-based models are also compared with the real facility model and a WECC
guideline model (Fig. 2). The dynamic responses of the template-based models have good agreements
with that of the real facility model, while have large discrepancies with that of the guideline model. This
verifies that the template-based model provides an adequate representation of an industry facility.
The main contributions of this paper can be summarized as follows: It has proposed a new concept and
associated procedures for modeling an important class of loads in power systems.
Fig. 2 Active power, reactive power, and voltage responses at Utility main bus for real facility, templatebased EF model, and WECC guideline model for the 88MW Kraft-type paper mill facility
References:
[1] Graham J. Rogers, John Di Manno, Robert T.H. Alden, “An Aggregate Induction Motor Model for
Industrial Plant”, IEEE Transactions on Power Apparatus and Systems, Vol. PAS-103, No. 4, April
1984, Page(s): 683-690.
[2] Kip Morison, Hamid Hamadani, Lei Wang, “Practical Issues in Load Modeling for Voltage Stability
Study”, IEEE Power Engineering Society General Meeting, Vol. 3, 13-17 July 2003, Page(s): 13921397.
[3] Dmitry Kosterev and Anatoliy Meklin, “Load Modeling in WECC”, 2006 IEEE PES Power Systems
Conference and Exposition (PSCE '06), Oct. 29 -Nov. 1 2006, Page(s):576 – 581.
[4] A. Ellis, D. Kosterev, and Anatoliy Meklin, “Dynamic Load Models: Where Are We?”, 2005/2006
IEEE PES Transmission and Distribution Conference and Exhibition, 21-24 May 2006, Page(s):1320
– 1324.
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