4/3/2023 0 Comments Excited syn![]() If we plot a curve between field current on X-axis and armature current on Y-axis, the curve so obtained is called V curves of synchronous motor. Hence the variation in excitation (field current) causes the variation in armature current. The armature current will be minimum at unity power factor and increases when the power factor decreases on either side (lagging or leading). For a constant input power and terminal voltage only increase in power factor, causes a decrease in armature current and vice versa. When the excitation of a three-phase synchronous motor taking a constant power, is varied, it changes the operating power factor of the motor. In this condition, with the change in excitation the power factor changes. Critically ExcitedĬritically excitation is defined as the excitation for which the power factor of the motor is unity. They are usually connected in parallel with the incoming power lines to the plant. Synchronous capacitors cancel the lagging KVARs of the installation with their leading KVARs. It is advantageous to raise this power factor to unity or near about.Īny increase in power factor, increases supply capacity, efficiency and improves the operating characteristics of the system. Some industrial loads run at very low power factors. Power factor correction means raising the power factor of the load from its low value to a higher value. They are used for correcting the power factor of a lagging load such as transformers and induction motors in an installation. The shaft does not extend beyond the case of the motor. Synchronous capacitors are always totally enclosed. Therefore, if the field of the synchronous motor is overexcited then its power factor will be leading.Īn over-excited synchronous motor running at no load is known as the synchronous capacitor or synchronous condenser. ![]() An over-excited synchronous motor draws leading current. ![]() If DC field excitation of a synchronous motor is such that back EMF E b is greater than applied voltage V, then the motor is said to be over-excited. An under excited synchronous motor has a lagging power factor. If the field excitation is such that back EMF E b is less than the applied voltage V, then the motor is said to be under-excited. In this case, induced back EMF E b is equal to the applied voltage V. The active component of the armature current drawn by the motor is constant because load, losses and applied voltage to the motor are constant.ĭepending on the level of excitation, the synchronous motor is capable of operating in one of the following four conditions: If the excitation of a synchronous motor is changed, keeping the load constant, the motor power factor will get automatically adjusted to keep its active component constant under all excitation conditions. Effect of Excitation on Synchronous Motor ![]() ![]() Hence the back EMF E b is proportional to or dependent on the rotor (field excitation). In the above expression, all other quantities are constant except flux φ.īut the rotor flux φ depends on the rotor excitation. This induced EMF always opposes the supply voltage according to the Lenz’s law hence called back EMF. This EMF is produced due to the stator (armature conductors) cutting the rotor flux. This induced EMF is alternating and is given by, When the rotor of the synchronous motor rotates an EMF is induced in its stator winding due to flux produced by the rotating rotor. Motor Control with Overload Protection using Solid State Relay (SSR) ![]()
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