Difference Between Induction Motor vs Synchronous Motor

In industries and workshops, motors run almost every machine. They look similar from the outside but work differently on the inside. The two most common types are the induction motor and the synchronous motor.

Both turn electrical energy into motion, yet the way they achieve that rotation isn’t the same. Understanding the difference between induction motor and synchronous motor helps in choosing the right type for each job.

What is Induction Motor 

What is induction motor? An induction motor is the most common motor type used in factories, fans, pumps, and compressors. It runs on alternating current (AC). The basic idea is simple. When AC power flows through the stator winding, it creates a rotating magnetic field. This field passes through the rotor and induces current inside it. The induced current then produces its own magnetic field, and both fields interact to create rotation.

In simple terms, the rotor turns because the stator’s magnetic field drags it along. However, the rotor never reaches the same speed as the rotating field. That’s why it’s called an asynchronous motor. The small difference in speed is called “slip,” and it’s what allows torque to be produced.

A 3 phase induction motor is widely used in industrial machines because it’s reliable, simple to maintain, and efficient.

What is Synchronous Motor 

Let’s understand what is synchronous motor in detail. A synchronous motor also runs on AC power but works differently from the induction type. In this motor, the rotor turns at the exact same speed as the rotating magnetic field - there’s no slip. That’s why it’s called synchronous.

The rotor in a synchronous motor usually carries a DC excitation, either from slip rings or permanent magnets. This creates a constant magnetic field. When the AC current energizes the stator, its magnetic field locks in step with the rotor field. As both rotate together, the rotor speed stays perfectly synchronized with the supply frequency.

Because of this property, synchronous motors are often used where speed must remain constant, regardless of the load.

Synchronous Motor vs Induction Motor: Basic Concept 

The synchronous motor vs induction motor comparison begins with one major point - how the rotor reacts to the stator’s magnetic field. In an induction motor, the rotor current is induced by the stator field. In a synchronous motor, the rotor’s magnetic field is created separately using DC excitation or magnets.

One depends on induction, while the other stays synchronized through direct magnetic coupling.

Difference Between Induction and Synchronous Motor 

Here’s a detailed look at the difference between induction and synchronous motor based on working, speed, and construction.

From this table, it’s clear that both have strengths suited to different needs.

Induction Motor vs Synchronous: Speed and Control 

When elaborating induction motor vs synchronous, speed is the biggest difference between the two. In an induction motor, the speed changes slightly with load because of slip. As load increases, the rotor slows down just a little to produce more torque. In a synchronous motor, the speed remains steady no matter what. Load or no load, it runs at the same speed as the magnetic field set by the supply frequency.

For example, a 4-pole motor on a 50 Hz supply has a synchronous speed of 1500 rpm. The induction motor might run at around 1450 rpm, while the synchronous motor will stay fixed at 1500 rpm.

This is why synchronous motors are preferred where timing and speed accuracy matter.

Construction Differences 

Both motors have two main parts - stator and rotor - but their designs differ slightly.

• Induction Motor: The stator carries a set of windings that create a rotating magnetic field. The rotor is either squirrel cage type or wound type. Current is induced inside the rotor bars when the stator field passes over them.

• Synchronous Motor: The stator is similar to the induction motor, but the rotor carries a separate DC coil or permanent magnets. Brushes and slip rings may be used to supply DC. Once running, the magnetic fields of rotor and stator stay locked in position.

So, the induction motor depends on induction to get the rotor moving, while the synchronous motor already has a magnetic field that locks in instantly after starting.

Operation and Starting Method  

An induction motor starts automatically when power is applied. The magnetic field induces current and the rotor begins to turn on its own. A synchronous motor needs help at first. Since the rotor doesn’t produce torque until synchronized, it uses an external motor or damper winding to reach near-synchronous speed. Once close, the DC excitation is applied and the rotor locks with the stator field.

This is why synchronous motors are said to be “not self-starting.”

Synchronous Motor and Induction Motor Difference in Performance 

In terms of performance, both have unique qualities:

• Induction Motor: More rugged, cheaper, and simpler. It tolerates overload and fluctuating supply.

• Synchronous Motor: Delivers constant speed, better efficiency at full load, and can improve the system’s power factor.

The synchronous motor and induction motor difference is mainly about precision versus flexibility. One gives stability, the other gives adaptability.

Applications of Synchronous Motor and Induction Motor 

Each motor fits certain types of work. Here are the main application of synchronous motor and induction motor categories:

Induction Motor Applications  

• Pumps, fans, compressors- Induction motors are commonly found here because the work itself is repetitive and steady. Water keeps flowing. The air keeps moving. The motor doesn’t need exact speed control. It just needs to run, often for hours, sometimes all day, without needing attention or fine adjustments. That simplicity is why maintenance teams trust them in everyday systems.

• Elevators and conveyors- In elevators and conveyors, reliability matters more than perfection. Loads change. Starts and stops happen frequently. Induction motors handle this without complaint. They don’t demand complex controls and continue working even when conditions are not ideal, which is why they are trusted in daily-use systems. Their predictable behavior keeps operations moving without frequent shutdowns.

• Mixers and grinders- Mixing and grinding rarely stay consistent. Materials change. Resistance changes. Induction motors cope with this naturally. They slow slightly under load and recover without damage. This behavior suits kitchens, workshops, and small industries where conditions aren’t perfectly controlled every time. The tolerance helps avoid unnecessary motor failures.

• Industrial blowers and machine tools- Blowers and basic machine tools need endurance more than precision. Induction motors provide steady output without requiring careful monitoring. Dust, vibration, and long operating hours don’t affect them much, which explains why they remain common in workshops and factory floors. They simply keep running when conditions are not comfortable.

Synchronous Motor Applications 

• Power factor correction in large plants- Some plants don’t install synchronous motors for motion at all. They install them to balance electrical systems. When adjusted properly, these motors help reduce reactive power. This quietly improves efficiency and avoids penalties without changing how production equipment operates. Most people notice the savings only on electricity bills.

• Rolling mills and crushers- Here, speed consistency matters. Materials push back hard. Loads change suddenly. A synchronous motor keeps its speed steady anyway. The stability helps protect mechanical parts and ensures the output stays uniform, which is critical in heavy processing environments. Even small speed variations can affect product quality here.

• Textile mills- Textile processes depend on coordination. If one machine drifts in speed, the whole line suffers. Synchronous motors help avoid that. They keep timing aligned across systems, which reduces errors, material waste, and interruptions during continuous production runs. Consistency matters more here than raw motor power.

• Constant-speed drives for timing systems- Some systems care more about time than force. Clocks, recorders, and similar setups rely on motors that don’t drift. Synchronous motors follow supply frequency closely, which makes them useful wherever steady timing matters more than load flexibility. Accuracy over long periods becomes the main advantage here.

In short, induction motors handle daily mechanical tasks, while synchronous motors take on special jobs needing constant speed or controlled power factor.

3 Phase Induction Motor 

The 3 phase induction motor is the most common of all. It uses three alternating currents, each out of phase by 120 degrees. This creates a continuously rotating magnetic field. Because of this design, it runs smoothly, produces uniform torque, and is efficient. These motors are found in almost every industrial setting - from pumps to conveyors and compressors.

The simplicity of construction and reliability make the 3-phase version the backbone of industrial drives.

Efficiency and Power Factor 

Induction motors usually operate at lagging power factors because the current lags the voltage due to inductance. Synchronous motors, however, can operate at unity or even leading power factors by adjusting excitation. This helps industries correct overall power factor and reduce penalties from utilities.

That’s one of the biggest reasons large factories often use synchronous motors alongside induction ones.

Also Read: Everything You Need To Know About Motor Controllers

Conclusion 

Both the induction motor synchronous motor are vital for electrical and mechanical systems. Knowing the difference between induction and synchronous motor helps in selecting the right type for specific needs.

For general drives and variable loads, the induction motor is best. For steady, precise motion and better power factor, the synchronous motor is preferred. Together, they cover nearly every application - from small tools to heavy industrial machinery - proving how crucial these two motor types are in powering modern life.

FAQ

Q1. Can synchronous motors improve power factor?

Ans. In many cases, yes, and that’s often why they are installed in the first place. They are not always added for motion alone. When adjusted properly, they quietly help balance the electrical system. Most people don’t notice this directly. They notice only later, when power-related issues reduce.

Q2. Which motor provides constant speed under load?

Ans. Synchronous motors tend to hold their speed steady once they are running. Even when the load changes, the speed doesn’t drift much. That’s why they’re chosen in places where timing matters. It’s less about flexibility and more about staying exactly where the system expects.

Q3. Why are induction motors preferred for industrial applications?

Ans. Industries usually choose induction motors because they don’t demand attention. They start, run, and keep going. Even when conditions aren’t perfect, they continue working. That reliability matters more than fine control in many factories where machines are expected to run daily without surprises.

Q4. Which industries commonly use induction motors?

Ans. They are used almost everywhere without much discussion. Manufacturing floors, water plants, warehouses, and processing units all rely on them. Any place that needs simple rotation, fans, pumps, conveyors, ends up using induction motors because they fit in easily and don’t complicate setups.

Q5. What is the lifespan of an induction motor?

Ans. There isn’t a fixed number. Some run for years without issues, others much longer. It depends on how they are treated. Clean surroundings, proper loading, and basic care usually matter more than age. Many motors stop only because systems change, not because they fail.

Q6. Are synchronous motors compatible with VFDs?

Ans. They can be, but it’s not always straightforward. Synchronous motors need careful coordination when paired with VFDs. When done properly, the setup works well. When rushed, problems appear. This is why this combination is planned carefully rather than installed casually.