Table of Contents
What is the frequency of the rotor current?
The frequency of the rotor current fr = Ns x P/120, so fr = 0 if the slip is zero. If the operating speed is zero, Ns = N and the frequency of the rotor current is the same as the frequency of the stator current . f = source frequency in Hz.
What is the frequency of rotor current of a 50hz induction motor operating at 2%?
Explanation: s = 0.04, rotor frequency = s*f = 0.04*50 = 2 Hz. 6.
What is the frequency of the rotor current at full load?
(e)The frequency of rotor-currents at full-load is 1.50 Hz.
How is rotor current calculated?
For example: A 3.5-horsepower, three-phase motor nameplate lists the motor voltage as 230 volts and the locked rotor code is “K.” The range given on the table is 8.0 to 8.99 KVA. Dividing by the motor voltage of 230 volts gives the inrush current range as 34.8 amps to 39.1 amps.
How do you find supply frequency?
Assume a constant supply voltage and frequency, then Φ S = V S ω S = C t e .
What is rotor EMF?
5.3.3 Rotor induced e.m.f. and current The rate at which the rotor conductors are cut by the flux, and hence their induced e.m.f., is directly proportional to the slip, with no induced e.m.f. at synchronous speed (s = 0) and maximum induced e.m.f. when the rotor is stationary (s = 1).
Which motor has high efficiency?
Tests carried out on a 44 megawatt 6-pole synchronous ABB motor shortly before delivery showed an efficiency 0.25 percent greater than the 98.8 percent stipulated in the contract, resulting in the world record for electric motor efficiency.
When a motor is switched on the rotor frequency is?
Application: When a 3-phase induction motor is switched on, then rotor speed is equal to zero. Hence, at starting or When a 3 phase induction motor is switched on, the rotor frequency is equal to supply frequency.
What happens if fifth harmonics is given to induction motor?
It will rotates in normal operation. Either short circuit or open circuit occurs. The sinusoidal components having frequency five times of fundamental are known as fifth harmonics. Hence induction motor will rotates in reverse direction because of reverse phase sequence of fifth harmonics.
What is slip formula?
If the revolving magnetic flux’s synchronous speed & the speed of rotor are Ns & Nr in the motor, then the speed among them can be equivalent to (Ns – Nr). So, slip can be determined as. S = (Ns – Nr) / Ns.
Which induction motor has maximum speed?
Synchronous and full load speed of amplitude current (AC) induction motors Speed (rpm) Number of Poles Frequency (Hz, cycles/sec) Synchronous Full Load 2 3600 2900 4 1800 1450.
Why rotor slots are skewed?
The rotor or stator slot of the induction motor skewed through some angle so that the bars lie under alternate harmonic poles of the same polarity or other words, bars must be skewed through two pitches. The main purpose of skewing is to reduce the magnetic logging between the starter and the rotor.
How do you fix a locked rotor current?
To find LRA and starting kVA enter nominal operation voltage (such as 120 or 240), HP value, code letter from the nameplate label, and hit “Calculate” button. The general equation for single-phase devices is the following: LRA=1000*(kVA/HP)/Voltage. Note that this defines starting current at full nominal voltage.
Is Locked rotor the starting current?
Locked rotor current is basically the current drawn by the motor at its rated voltage when its rotor is kept stationary or in other words rotor is not spinning or rotating. As the rotor is at rest during starting and voltage is rated voltage, the starting current will be equal to locked rotor current.
What is locked rotor kVA?
Locked rotor indicating code letters electrical motors NEMA Code Letter kVA/HP with locked rotor Approximate Mid-Range Value A 0 – 3.14 1.6 B 3.15 – 3.55 3.3 C 3.55 – 3.99 3.8 D 4.0 – 4.49 4.3.
What happens if supply frequency increases?
So if frequency increases, the secondary voltage or emf increases. And secondary voltage decreases by the reduction of supply frequency. But with high frequency there is increase in transformer losses like core loss and conductor skin effect.
What is the supply frequency?
Keeping the frequency of our power supply constant is a delicate national balancing act that requires changes in under a second. This oscillation is known as electrical frequency. Alternating current that oscillates 50 times a second as it does in the UK is said to have a frequency of 50 hertz (50hz).
How do you find the frequency of an AC supply?
When a sinusoidal voltage is applied to an inductor, the voltage leads the current by one-fourth of a cycle, or by a 90º phase angle. XL=2πfL X L = 2 π f L , with f the frequency of the AC voltage source in hertz (An analysis of the circuit using Kirchhoff’s loop rule and calculus actually produces this expression).
What happens when slip is zero?
Zero slip means that rotor speed is equal to synchronous speed. If rotor is rotating at synchronous speed in the direction of rotating magnetic field the, there will be no flux cutting action, no emf in the rotor conductors, no current in rotor bar conductor and hence no development of electromagnetic torque.
What is the impact of slip on rotor current?
When the rotor is stationary, s = 1. Under these conditions, the per phase rotor e.m.f. E2 has a frequency equal to that of supply frequency f. At any slip s, the relative speed between stator field and the rotor is decreased.
Which type of induction motor is best for EMF?
10. Which type of Induction motor is best for e.m.f injection method? Explanation: E.M.F injection method is used to control the speed of Induction motor. It is only applicable for WRIM because WRIM rotor consists of copper windings connected in star connection.
