30020 DC Shunt and Compound Motors

The primary advantage of a DC shunt motor is that it provides excellent:

Speed Control.

DC shunt motors maintain nearly constant speed under varying loads, making them ideal where precise speed control is needed.

A DC shunt motor has the field windings connected ___ with the armature.

In parallel

The field winding is connected across (in parallel with) the armature circuit, hence “shunt.”

Which of the following is an application for a DC shunt motor?  A. Centrifugal pump  B. Cooling fan  C. Woodworking machinery  D. All of the above  E. None of the above

All of the above

All these applications require constant speed, which suits DC shunt motors.

When a shunt field is connected to a different power supply than the armature, it is called a ___ shunt field.

Separately excited

A separately excited motor has its field supplied by an independent voltage source.

The primary advantage of a DC compound motor is:

A. It provides a middle ground between a series and a shunt motor

Compound motors combine the torque of series motors with the speed regulation of shunt motors.

Which of the following is an application of a DC compound motor?  A. Conveyors  B. Punch press  C. Bending machines  D. All of the above  E. None of the above

D. All of the above

These applications need both good starting torque and moderate speed control, ideal for compound motors.

___ compound configuration is created by connecting the series and shunt windings so that their magnetic fields have the same magnetic polarity.

Cumulative

In a cumulative compound motor, both windings assist each other’s magnetic field, improving torque.

Which of the following statements is not true of a DC compound motor?  A. It has the field windings connected in series with the armature.  B. It has a field connected in parallel with the armature.  C. Both fields are connected in parallel with the armature.  D. It has two configurations in which it can be connected.

C. Both fields are connected in parallel with the armature.

In a compound motor, one field (series) is in series, and one (shunt) is in parallel, not both in parallel.

Which of the following statements is false about a separately excited shunt motor?  A. The shunt field is connected to a different power supply than the armature.  B. It allows you to vary the speed by varying the field current.  C. It requires only one power supply.  D. All of the above  E. None of the above

It requires only one power supply.

A separately excited motor specifically requires two power supplies, one for the armature and one for the field.

A self excited shunt configuration is used when fairly ____ speed is required

Constant speed. A good example of this is an elevator, you want the elevator to have roughly the same speed regardless of variety in load over time.

Disadvantage of self excited shunt configuration:

Does NOT provide high starting torque like a DC series motor.

Seperatly Excited Shunt Field

When shunt Field is connected to a power supply separate from the one connected to the armature. 

If a variable power supply is used for both controlling armature current and field current, the speed of the shunt motor can:

Be extended beyond the rated speed on the motor nameplate - one advantage of the seperatly Excited Shunt motor.

Commutation Limit

When increasing armamture current no longer increases speed. - For a self excited motor the max speed of the motor is determined by the armature current.

Field Weakening

electrical technique that allows an electric motor to exceed its base speed, or nominal speed, by reducing the strength of the motor's magnetic field. This is done by injecting a special component of current that opposes the motor's magnetic field.

Compound Configuration

Connecting both field windings, series and shunt with the armature.

Cumlative Compund

a configuration where the magnetic fields of a DC motor's series and shunt windings reinforce each other, leading to a higher overall magnetic flux and therefore increased starting torque and speed regulation benefits.

Differential Compound

the series and shunt field windings are connected so that their magnetic fields oppose each other. This opposition results in a net magnetic field that is weaker than the individual fields, causing the total flux to be reduced.