Understanding Motor Stator Polarity and Consequent Poles

In an electric motor, the stator is the stationary part that contains coils. When current flows through these coils, they create magnetic poles. The arrangement and connection of these coils determine the number and polarity of the magnetic poles formed on the stator.

Typically, for a standard motor operation, adjacent stator coils are wound or connected in such a way that they produce alternate magnetic polarities (North-South-North-South, etc.) around the stator circumference. This creates a well-defined magnetic field that interacts with the rotor, causing the motor to turn.

Formation of Consequent Poles in Motors

The question describes a specific scenario: "all the stator coils of a motor are connected for the same magnetic polarity". This means that if you trace the connections around the stator, each coil is oriented to produce, for example, a North pole (N) facing inwards. However, magnetic poles always exist in pairs (North and South). You cannot have an isolated North pole or an isolated South pole.

When all designed coil groups create the same intended polarity (say, all 'North' poles), the magnetic flux lines must still complete their path. They will exit these 'North' poles and enter the stator core at points between these deliberately created poles. These intermediate points where the flux lines enter the core effectively become the 'South' poles. These poles that are formed due to the configuration of the main poles, rather than being directly wound, are called consequent poles.

Crucially, these consequent poles will always have the opposite polarity to the main poles that created them. If the main poles are all North, the consequent poles formed between them will be South. If the main poles were all South, the consequent poles would be North.

Furthermore, if you connect the stator coils to form a certain number of main poles of the same polarity (e.g., 2 North poles), an equal number of consequent poles (2 South poles) will be formed between them. The total number of poles on the stator will then be the sum of the main poles and the consequent poles.

Analyzing the Options

Let's evaluate the given options based on our understanding:

• consequent poles with opposite polarity: This aligns with our explanation. When main poles of the same polarity are created, consequent poles form between them with the opposite polarity.
• consequent poles with the same polarity: This is incorrect. Consequent poles are formed by the return path of the magnetic flux and will always have the opposite polarity to the main poles.
• rotor poles with opposite polarity: The question is about the stator coils and the polarity formed on the stator. While the rotor interacts with the stator poles, the direct result of connecting stator coils for the same polarity is the formation of poles on the stator itself, not directly on the rotor.
• rotor poles with the same polarity: Similar to the previous option, this incorrectly focuses on the rotor poles as the direct outcome of the stator coil connection described.

Therefore, connecting all stator coils for the same magnetic polarity results in the formation of an equal number of consequent poles with opposite polarity on the stator.

Revision Table: Motor Stator Polarity

Additional Information: Types of Motor Poles

Understanding how poles are created is fundamental to motor operation. Motors can have different numbers of poles, which affects their speed.

• Wound Poles (Salient Poles): These are distinct pole pieces around which coils are wound. The pole polarity is directly determined by the winding direction and current.
• Distributed Winding Poles: The coils are spread out in slots around the stator. The number and pattern of coils connected in series determine the number and location of the magnetic poles.
• Consequent Poles: As discussed, these poles are not formed by dedicated, separately wound coils for that specific polarity. Instead, they emerge between main poles (either salient or distributed) when the main poles are configured in a specific way, often involving connecting coil sections in parallel or connecting them to create identical polarities facing inwards/outwards. The number of consequent poles is equal to the number of main poles created in this configuration.

The scenario in the question specifically leads to the formation of consequent poles because the standard alternating polarity connection is bypassed in favor of connecting all coils for the same polarity.