This extensive simulation tool explores the performance characteristics of a separately excited DC motor delivering information about speed, torque, current relationships and their rapid changes via interactive visualizations and real-time measurements.

Objective

The simulation is meant to meet the several major learning objectives:

Simulate Performance

Model the entire operational function of an independently stimulated DC motor under different load conditions.

Analyze Characteristics

Check the motor’s speed, torque and current relationships using the dynamic measurements.

Validate Theory

Confirm theoretical links between the electrical and mechanical factors using the simulation data.

Study Transient Activity

Study how the motor functions during startup and changes between the steady states.

Framework 

An independently excited DC motor is a basic electric motor arrangement.

This DC motor has an externally driven field winding different from the armature circuit. 

Electrical isolation has many advantages:

1). The independent field circuit accurately controls magnetic flux which affects motor speed and torque. 

2). Operators can regulate the speed well in many conditions by changing the field voltage independent of the armature voltage.

3). Machine tools, rolling mills & traction systems use these design for the variable-speed operation. 

4). This motor type is ideal for applications that requiring accurate speed control and dynamic reaction since it controls field and armature circuits separately.

Motor Specifications

The simulation utilizes the following basic parameters:

Control Settings:

Armature Voltage:

Field Voltage: 

Step Load Torque: 

Step Time: 

Motor Parameters

Ra (Armature Resistance): 1.5 Ω

La (Armature Inductance): 0.032 H

Rf (Field Resistance): 150 Ω

Lf (Field Inductance): 8 H

Ke (Back EMF Constant): 0.8 V·s/rad

Kt (Torque Constant): 0.8 N·m/A

Real-Time Measurements

The simulation allows a constant monitoring of the essential operating parameters:

Electrical Measurements

Armature Current (I)

Measure (monitor) the current flowing via the armature circuit in Amps (Amperes).

Field Current (J)

Monitors the field winding current in amperes (A).

Mechanical Measurements

Speed

Displays the motor rotational speed in RPM (revolutions per minute).

Torque 

Displays the electromagnetic torque generation in Newton-meters (N·m).

Angle

Measure the rotor’s angular location in degrees.

Power Measurements

Back EMF

Back EMF indicates the counter-electromotive force created in volts.

Power 

Power calculates the instantaneous power output in kilowatts.

Time

Records the elapsed (delayed) simulation time in seconds.

Scope Outputs (Time Domain Analysis)

The simulation produces three important time-domain plots:

Speed vs Time

This graph depicts how motor speed varies from startup to steady state. 

Primary findings include a progressive increase in speed during startup due to mechanical inertia & the effect of load torque application on speed drops & final stability at the steady-state operating speed.

Armature Current vs Time

The armature current profile demonstrates the transient electrical activity. 

During startup a large initial current flows to overcome inertia & accelerate the motor. 

As the back EMF increases the current drops (decreases) and stabilizes. 

When load torque is applied the current increases in order to sustain the electromagnetic torque.

Electromagnetic Torque vs Time

This characteristic shows how the motor generates torque in response to the electrical input & mechanical load. 

The relationship between current & torque is evident for confirming the proportional relationship given by the torque constant.

Motor characteristics (XY graphs)

Speed-Torque Characteristic (N-T curve)

This is the important characteristics showing an inverse linear connection between the motor speed & load torque. 

The simulation indicates that as load torque increases the motor speed drops (decreases) correspondingly. 

This dropping characteristic is typical of DC motors and is caused by a voltage drop across armature resistance as the current demand increases.

Speed-Current Characteristic (N-Ia Curve)

The N-Ia curve shows how the armature current fluctuates with motor speed and also loading conditions. 

At no load only a small amount of current is required to maintain spinning. 

As the mechanical load increases so do the current and rate of speed decreases. 

This feature is important for determining the motor efficiency and identifying the optimal operating conditions.

Key Observations

The simulation explains a number of fundamental working principles:

Startup Dynamics

Mechanical inertia causes the motor speed to gradually increase during startup. 

The rate of acceleration is directly proportional to the difference between electromagnetic torque and load torque divided by the moment of inertia.

Current Behavior

During startup the armature current exhibits high initial values before stabilizing at steady level. 

This feature is essential for selecting safety devices & starting circuits.

Field Current Development 

Because of the huge field inductance (8 H) field current increases out gradually. 

This property provides natural dampening but it also causes delay in field-dependent control techniques.

Load Application Response

Applying step load torque results in a rapid decrease in speed and increase in current. 

As the system approaches its new equilibrium point it exhibits first-order transient response characteristics.

Speed-Torque Linearity

The speed-torque characteristic shows linear dropping motion which is typical of DC motors which renders them predictable & controllable in industrial applications.

Validated Theoretical Relationships

Back EMF Equation 

E_b = K_e × ω × I_f

The back EMF rises correspondingly with speed (ω) confirming the fundamental relationship. 

The back EMF opposes the applied voltage & establishes the equilibrium operating point.

Electromagnetic Torque Equation

T = K_t x I_f x I_a

The simulation shows that electromagnetic torque is directly proportional to armature current (at a constant field current). 

This linear relationship is essential for torque control techniques.

Speed Regulation

Speed regulation is dependent on both load torque & armature resistance. 

The voltage equation 

V_a = E_b + I_a x R_a

defines steady-state speed. 

Increasing current creates a higher voltage drop and lower back EMF resulting in slower speed.

Transient Response

The system exhibits first-order response governed by electrical time constants (L_a/R_a & L_f/R_f) & mechanical time constant (J/B). 

These settings govern how quickly the motor reacts to changes in voltage (or) load.

Steady-State Operation

At constant voltage and steady condition speed is inversely proportional to the load torque. 

This state makes individually excited DC motors ideal for applications that requires constant and steady speed-torque relationships.

Power Relationships

The simulation expresses the power equation 

P = T x ω

using real-time measurements illustrating the conversion of an electrical input power to the mechanical output power while considering for losses.

Practical Applications

Considering these characteristics is important for:

1). Selecting suitable motor ratings for certain applications.

2). Creating speed and torque control techniques.

3). Sizing Overload Protection & Starting Circuits.

4). Operating motors at optimal efficiency locations.

5). Diagnosing motor disorders via characteristic analysis

Conclusion

This simulation is a thorough tool for understanding individually excited DC motor activity linking theoretical concepts to real data. 

The established relationships and characteristic curves serve as important references for 

• Motor application, 
• Control system design and
• Performance analysi

in electrical engineering education & industry practice.