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Motor Starting Software - Modeling & Simulation

ETAP power system analysis software includes motor starters such as conventional starters, soft-starters and variable frequency drive. These starters are used for dynamic motor acceleration calculation and reporting in modules such as motor starting analysis and transient stability analysis.

Conventional Motor Starters

ETAP includes the following conventional motor starters:

  • Auto-transformer
  • Stator Resistor
  • Stator Reactor
  • Capacitor, Bus
  • Capacitor, Terminal
  • Rotor Resistor
  • Rotor Reactor
  • Y/Δ  (wye/delta)
  • Partial Winding

Motor Soft Starters

A soft starter is a device used to reduce the load and torque in the powertrain of the motor during startup. Using a soft-starter reduces the mechanical stress on the motor and shaft, as well as the electrodynamic stresses on the system. ETAP includes modeling of the following motor soft-starters:

  • Current Limit
  • Current Control
  • Voltage Control
  • Torque Control

Variable Frequency Drive (VFD)

The Variable Frequency Drive (VFD), also called Adjustable Speed Drive (ASD) or Adjustable Frequency Drive (AFD) in some applications, has been enhanced to include models for motor starting control schemes, rectifier/inverter/DC-link dynamics, and harmonic spectrum. It can be used to simulate VFD behavior in normal speed control operation, during motor acceleration, and under disturbances to study its impact on system dynamics.

ETAP provides flexible representation and modeling for VFD systems. It can be inserted between a motor and its terminal bus or connected to a motor through transformers and cables to simulate long distance subsea power system. On the input side of VFD, it can be connected to multiple transformers directly to represent 12, 18 or 24 pulse VFDs.

To simulate normal operating conditions, VFD has ten operating categories allowing the user to specify different output frequency values and corresponding output voltage according to user specified V/Hz ratio. The VFD load is calculated based on VFD output frequency and load frequency characteristics. Three options for VFD input power factor are provided: VFD rated power factor, VFD output load power factor and user-specified power factor.

Two control types are provided to simulate VFD operations during motor starting for all available control schemes in today’s applications. The Frequency control scheme allows the user to freely specify VFD output frequency and Volt/Hz as functions of time. This control type can be easily used to model constant power control, constant torque control, and any other forms of controls. The Torque control scheme allows the user to specify motor torque as function of time with a maximum current limit. Voltage boost effect is also simulated in Motor Starting simulation.

The rectifier/inverter/DC-link and dynamic control modeling allows the user to simulate the impact of VFD operations on power system under disturbances, such as sudden load variations, VFD frequency change, or faults in the system.

The following gives additional features of VFD:

1. Flexible Connection
  • It can be inserted between a motor and its terminal bus to represent VFD in most of industrial applications of adjustable speed control.
  • It can be connected to a motor through transformers and cables to simulate long distance subsea power system.
  • Its input can connect to multiple transformers directly to simulate 12, 18, and 24 pulse VFD.

2. Frequency Dependent Modeling
  • VFD load is determined based on VFD output frequency and voltage, load frequency characteristics, and load torque model.
  • Frequency characteristics of transmission system below a VFD are incorporated in system computations.

3. Normal Speed Control Operations
  • Multiple options for VFD input power factor are provided: rated power factor, user-specified power factor, and calculated power factor.
  • Ten operating frequency values to simulate VFD in frequency/speed control operations.
  • User specified V/Hz ratio to determine VFD output voltage under different frequency.

4. Short-Circuit
  • Bus and load terminal fault calculations for the system power by a VFD.

5. Motor Starting
  • Frequency control scheme allows freely specifying VFD output frequency and Volt/Hz as functions of time.
  • Torque control scheme allows freely specifying VFD motor torque as a function of time.
  • It can be easily used to model constant power control, constant torque control, and any other forms of controls.
  • Voltage boost effect at low frequency during starting simulated.

6. Dynamic Simulation
  • Includes positive sequence fundament frequency rectifier (converter) model
  • Includes DC line model
  • Includes PWM inverter model
  • Includes a generic inverter output voltage and frequency control model
  • Simulate VFD system response to disturbances, such as system fault, operating frequency change and load variation.


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Electrical Power System Analysis