What is runaway condition?

Thermal runaway occurs in situations where an increase in temperature changes the conditions in a way that causes a further increase in temperature, often leading to a destructive result. It is a kind of uncontrolled positive feedback.

Which condition is used for DC series motor?

Explanation: DC series motors are used in those applications where high starting speed is required at its initial phase. Since no load operation speed of DC series motor is very high, it is always operated on some non-zero load.

Why DC series motor is not run at no load?

Thus from equation (2), it is clear that speed of DC Series Motor is inversely proportional to Armature Current Ia. Therefore if the DC Series Motor is started at No Load then the speed of DC Series Motor will become dangerously high which will definitely damage the DC Series Motor.

Which motor will run away with no load?

Pure series wound motors do suffer from potentially destructive speeds with no load on the output shaft, but that is due to the fact that with no load, as the motor accelerates, the current through the windings, both armature and field will drop.

How thermal runaway can be avoided?

Explanation: Thermal runaway is a process of positive feedback. In this process, the system gets hot and dissipated the heat in the surrounding and further gets hotter causing destructive results. It can be prevented by creating a small change in temperature to a big change in power dissipation.

How do you stop a runaway reaction?

A runaway reaction, if caught early, can sometimes be halted by adding chemicals to cancel the effect of the catalyst. Common measures include neutralization, quenching with water or other diluent, or dumping the contents into another vessel which contains a quench liquid.

What are the advantages of DC series motor?

Advantages of DC Series Motor Dc series motor have good accelerating torque. Dc series motor have a relatively huge starting torques. Dc series motor delivers high torque during an overload. The dc series motor draws less current and power from the source compared to a shunt or compound motor.

Which DC motor should never be run unloaded?

A series motor should never be started at no load. With no mechanical load on the series motor, the current is low, the counter-EMF produced by the field winding is weak, and so the armature must turn faster to produce sufficient counter-EMF to balance the supply voltage. The motor can be damaged by overspeed.

How is an electric generator like an electric motor in reverse?

A generator converts mechanical energy into electrical energy, while a motor does the opposite – it converts electrical energy into mechanical energy. What’s reversed is the flow of electricity, not the activity of the machine itself.

Why do motors run away?

Diesel engine runaway occurs when a diesel engine ingests a hydrocarbon vapor, or flammable vapor, through the air intake system and uses it as an external fuel source. As the engine begins to run off these vapors, the governor will release less diesel fuel until, eventually, the vapors become its only fuel source.

Why thermal runaway is not possible in FET?

Detailed Solution mobility decreases, i.e. 2) Since the current is decreasing with an increase in temperature, the power dissipation at the output terminal of a FET decreases or we can say that it’s minimum. So, there will be no Question of thermal Runway at the output of the FET.

Why does a DC motor run away without a load?

Because the rpm of series field DC motor tends to run away without a load. As the load goes away, the armature draws less current and that weakens the series connected field which tends to make the armature run even faster. On most small tools, the cooling fan at high rpm provides enough load to keep the rpm safe.

Why does a motor draw a small current?

When the motor is connected across the supply mains without load, then it will draw a small current from supply mains. Now question arises why small amount of current and why not high current? It is because when no load is connected on motor, torque requirement will be low.

When to disconnect a DC shunt motor?

Therefore as a thumb rule we never run series motor on less than 15% of full load. If accidentally it occurs then quickly disconnect the motor from the supply. Hope I shed some light on this beautiful topic. Thank you. Why the speed falls as load increases for a DC shunt motor?

Why is an air gap in a DC machine more than an AC motor?

When it reaches that speed, it stops accelerating, in fact if the load overruns the motor, the motor brakes the load, holding it back and in so doing also becomes a generator returning power to the DC line. Why is an air gap in a DC machine more than an AC motor?