Explanation:

**Interpoles and DC Motors:**

Interpoles, also known as compensating windings or commutating poles, are additional sets of field windings that are placed between the main field poles of a DC motor. They are connected in series with the armature windings and have a relatively small number of turns compared to the main field windings.

**Function of Interpoles:**

The primary function of interpoles is to improve the commutation process in a DC motor. Commutation refers to the process of reversing the current in the armature coils as the rotor rotates, ensuring that the motor continues to operate smoothly.

**Commutation Process:**

During the commutation process, as the armature coil moves under a main field pole, the current in the coil needs to be reversed to maintain the direction of torque. However, due to various factors such as armature reaction, magnetic saturation, and inductance of the coil, the reversal of current can cause sparking and arcing at the brushes.

**Role of Interpoles:**

Interpoles help in reducing the sparking and arcing at the brushes during commutation. They achieve this by creating a demagnetizing effect on the main field poles, which compensates for the armature reaction. This demagnetization reduces the flux density at the commutating region, allowing for smoother and more efficient commutation.

**Starting Above Base Speed:**

While interpoles play a crucial role in improving commutation, they are not specifically designed for starting a DC motor above its base speed. The base speed of a DC motor is the speed at which the motor operates without any external load or additional control techniques.

**Speed Control Techniques:**

To start a DC motor above its base speed, various speed control techniques can be employed, such as:

1. Field weakening: reducing the field current to decrease the flux density and increase the speed.
2. Armature control: controlling the armature voltage to vary the speed.
3. Chopper control: using a chopper circuit to control the average voltage supplied to the armature.

These techniques, along with the use of additional control devices like thyristors or transistors, allow for precise speed control of a DC motor above its base speed.

In conclusion, interpoles are not specifically used for starting a DC motor above its base speed. They are primarily employed to improve commutation and reduce sparking and arcing at the brushes. To start a DC motor above its base speed, other speed control techniques and additional control devices are utilized.