ETAP PowerStation 4 - ISI Academy

141 Pages·2001·2.92 MB·English

by  Operation Technology, Inc.

ETAP

PowerStation 4.0


User Guide

Copyright  2001
Operation Technology, Inc.
All Rights Reserved

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Chapter 19

Dynamic Models

Motor dynamic models are required for dynamic motor starting, transient stability, and generator starting
studies. Generator dynamic models and some control units (exciters and governors) are only needed for
transient stability studies. In addition, load torque characteristics for different types of models are
required for both motor starting and transient stability studies. PowerStation provides a variety of
induction and synchronous machine models, plus extensive libraries for exciters and governors for you to
select from to perform your studies.

For dynamic motor acceleration studies, only the motors that are accelerated need to have a dynamic
model, i.e., generators, exciters, and governors are not dynamically modeled. For transient stability
studies, all generators, exciters, and governors are dynamically modeled. Motors, which have dynamic
models and are designated to be dynamically modeled from the study case, will be dynamically modeled.
For generator starting and frequency dependent transient stability studies, all generators, exciters,
governors, and motors have to use frequency dependent models.

This chapter describes different types of machine models, machine control unit models, load models, and
explains their applications in motor starting and transient stability studies. It also describes tools that
assist you to select those models and specify model parameters.

The induction machine models section describes five different types of induction machine models and the
frequency dependent forms of these models. Those are Circuit Models (Single1, Single2, DBL1, DBL2)
and Characteristic Curve Models. In the synchronous machine models section, descriptions of five
different types of synchronous machine models and the frequency dependent forms of these models are
given. Those are Equivalent Model, Transient Model for round-rotor machines, Sub-transient Model for
round-rotor machines, Transient Model for salient-pole machines, and Sub-transient Model for salient-
pole machines. Motor starting and transient stability studies also require the utility tie system to be
modeled as an equivalent machine. A description of the modeling of power grid systems is found in the
section Power Grid. Different types of exciter and automatic voltage regulator (AVR) models, including
standard IEEE models and vendor special models, are defined in the Exciter and AVR Models section.
Governor-turbine models that are also based on both IEEE standards and vendors’ product manuals are
listed in the Governor-turbine Models section. Finally, different types of load models are described in the
Mechanical Load section.
Operation Technology, Inc. 19-1 ETAP PowerStation 4.0
Dynamic Models Induction Machine
19.1 Induction Machine
PowerStation provides five different types of induction machine models, which cover all commonly used
induction machine designs. These models are:

• Single1 CKT Model
• Single2 CKT Model
• DBL1 CKT Model
• DBL2 CKT Model
• Characteristic Curve Model
• Frequency Dependent Model

In general, Single1, Single2, DBL1, and DBL2 are referred to as CKT (circuit) models, because they all
use equivalent circuits to represent an induction machine stator and rotor windings. These models can be
used for both dynamic motor starting and transient stability studies. Characteristic models use machine
performance curves specified at some discrete points to represent an induction machine. It can be used
for dynamic motor starting studies, but is not suitable for transient stability studies.

Note that the models described in this section are also employed by synchronous motors for motor
starting studies since, during starting, synchronous motors behave similarly to induction motors. This
modeling procedure is approved by the industrial standards.
Notations and Symbols
The following notations are used in defining various parameters for induction machine models:

R = Stator resistance
s
X = Stator reactance
s
X = Magnetizing reactance
m
R = Rotor resistance
r
X = Rotor reactance
r
X = Locked-rotor reactance ( = X + X X / (X + X) )
lr s m r m r
X = Open-circuit reactance ( = X + X )
oc s m
T ’ = Rotor open-circuit time constant ( = (X + X) / (2πfR) )
do m r r
X/R = Machine X/R ratio

Plus the notations used in the machine electrical and mechanical equations:

E = Machine internal voltage
It = Machine terminal current
ω = Machine synchronous speed
s
ω = Machine mechanical speed
m
s = Machine slip ( = (ω - ω) / ω)
s m s
f = Synchronous frequency
H = Machine shaft inertia
D = Damping factor (this value is negligible)
P = Mechanical output power
m
P = Electrical input power
e
Operation Technology, Inc. 19-2 ETAP PowerStation 4.0
Dynamic Models Induction Machine
19.1.1 Single1 Model
This is the least complex model for a single-cage induction machine, with no deep-bars. It is essentially
using a Thevenin equivalent circuit to represent the machine. The rotor circuit resistance and reactance
are assumed constants; but the internal voltage will change depending on the machine speed.

Parameters for this model are:

• E Machine internal voltage
• Xlr Locked-rotor reactance ( = X + X X / (X + X) )
s m r m r
• Xoc Open-circuit reactance ( = X + X )
s m
• Tdo’ Rotor open-circuit time constant ( = (X + X) / (2πfR) )
m r r
• X/R Machine X/R ratio

Note that the X/R value is obtained from the library and is not the same X/R used for short-circuit
calculations.
Operation Technology, Inc. 19-3 ETAP PowerStation 4.0
Dynamic Models Induction Machine
19.1.2 Single2 Model
This is the standard model for induction machines, representing the magnetizing branch, stator, and rotor
circuits, and accounts for the deep-bar effect. The rotor resistance and reactance linearly change with the
machine speed.

Parameters for this model are:

• Rs Stator resistance
• Xs Stator reactance
• Xm Magnetizing reactance
• Rrfl Rotor resistance at full load
• Rrlr Rotor resistance at locked-rotor
• Xrfl Rotor reactance at full load
• Xrlr Rotor reactance at locked-rotor
Operation Technology, Inc. 19-4 ETAP PowerStation 4.0
Dynamic Models Induction Machine
19.1.3 DBL1 Model
This CKT model represents double cage induction machines with integrated bars. The rotor resistance
and reactance of each cage are constant for all machine speeds; however, the equivalent impedance of the
two rotor circuits becomes a non-linear function of the machine speed.

Parameters for this model are:

• Rs Stator resistance
• Xs Stator reactance
• Xm Magnetizing reactance
• Rr1 Rotor resistance for the first rotor circuit
• Rr2 Rotor resistance for the second rotor circuit
• Xr1 Rotor reactance for the first rotor circuit
• Xr2 Rotor reactance for the second rotor circuit
Operation Technology, Inc. 19-5 ETAP PowerStation 4.0
Dynamic Models Induction Machine
19.1.4 DBL2 Model
This is another representation of double cage induction machines with independent rotor bars. The same
as the DBL1 model, the rotor resistance and reactance of each cage are constant for all machine speeds,
and the equivalent impedance of the two rotor circuits is a non-linear function of the machine speed. The
DBL2 model has a different characteristic than the DBL1 model.

Parameters for this model are:

• Rs Stator resistance
• Xs Stator reactance
• Xm Magnetizing reactance
• Rr1 Rotor resistance for the first rotor circuit
• Rr2 Rotor resistance for the second rotor circuit
• Xr1 Rotor reactance for the first rotor circuit
• Xr2 Rotor reactance for the second rotor circuit
Operation Technology, Inc. 19-6 ETAP PowerStation 4.0
Dynamic Models Induction Machine
19.1.5 Characteristic Curve Model
This model provides the capability to model induction machines directly based on machine performance
curves provided by the manufacturer. Although only a discrete set of points is required to specify each
curve, PowerStation uses advanced curve fitting techniques to generate continuous curves for calculation
purposes.

Curves specified in this model include:

• Torque vs. Slip
• Current (I) vs. Slip
• Power Factor (PF) vs. Slip

Note that this model is only used for motor starting studies. For transient stability studies you can use the
Machine Parameter Estimation program to convert this model into one of the CKT models.
Operation Technology, Inc. 19-7 ETAP PowerStation 4.0
Dynamic Models Induction Machine
19.1.6 Frequency Dependent Model
In generator starting and frequency dependent transient stability studies, the frequency dependent models
of induction machines are used. PowerStation provides the frequency dependent forms for the four types
of circuit models (Single1, Single2, DBL1, DBL2). In these models, the stator and rotor reactance and
slip of machine are functions of system frequency. The following is the equivalent circuit for a double
cage induction machine model with independent rotor bars (DBL2).

Rs ωsLs

i
s

ωL ωL
s r1 s r2
Vs ωsLm

R /s R /s
r1 r2

Parameters for this model are:

• Rs Stator resistance
• Ls Stator inductance
• Lm Magnetizing inductance
• Rr1 Rotor resistance for the first rotor circuit
• Rr2 Rotor resistance for the second rotor circuit
• Lr1 Rotor inductance for the first rotor circuit
• Lr2 Rotor inductance for the second rotor circuit
• ω System speed
s
• s Motor slip

The data interface and library for the frequency dependent forms of the four types of induction machine
models (Single1, Single2, DBL1, DBL2) are the same as the corresponding regular induction machine
models. PowerStation internally converts the reactance in machine interface to inductance.

The model also can be expressed as the following equivalent circuit in terms of transient inductance and
transient internal electromagnetic-force.
Rs ωsL’

i
s

ωE’
s
V
s

Parameters in the circuit are:

• L’s Transient inductance
• E’ Transient internal electromagnetic-force
Operation Technology, Inc. 19-8 ETAP PowerStation 4.0
Dynamic Models Synchronous Machine
19.2 Synchronous Machine
PowerStation provides five different types of synchronous machine models to choose for transient
stability studies and frequency dependent models for generator starting and frequency dependent transient
stability studies. The complexity of these models ranges from the simple Equivalent Model to the model
that includes the machine saliency, damper winding, and variable field voltage. These models are:

• Equivalent Model
• Transient Model for Round-Rotor Machine
• Transient Model for Salient-Pole Machine
• Subtransient Model for Round-Rotor Machine
• Subtransient Model for Salient-Pole Machine
• Frequency Dependent Model

Synchronous generators and synchronous motors share the same models. In the following discussion, the
generator case is taken as an example.
Notations and Symbols
The following notations are used in defining various parameters for synchronous machine models:

Xd” = Direct-axis subtransient synchronous reactance
Xd’ = Direct-axis transient synchronous reactance
Xd = Direct-axis synchronous reactance
Xq” = Quadrature-axis subtransient synchronous reactance
Xq = Quadrature-axis synchronous reactance
Xq’ = Quadrature-axis transient synchronous reactance
Xl = Armature leakage reactance
Ra = Armature resistance
X/R = Machine X/R ration (= Xd”/Ra)
Tdo” = Direct-axis subtransient open-circuit time constant
Tdo’ = Direct-axis transient open-circuit time constant
Tqo” = Quadrature -axis subtransient open-circuit time constant
Tqo’ = Quadrature -axis transient open-circuit time constant
S100 = Saturation factor corresponding to 100 percent terminal voltage
S120 = Saturation factor corresponding to 120 percent terminal voltage
H = Total inertia of the shaft
D = Shaft damping factor
Operation Technology, Inc. 19-9 ETAP PowerStation 4.0