What is static Kramer drive?
Definition: The static Kramer-drive is the method of controlling the speed of an induction motor by injecting the opposite-phase voltage in the rotor circuit. By changing the injected voltage, the resistance and speed of an induction motor are controlled. …
What is Kramer system?
Kramer System is a cascade connection of slip ring or Wound rotor Induction motor. Once motor is started using rotor resistance starter, the rotor terminals are thrown to. three phase bridge rectifier.
What are the advantages of static Kramer drive?
What are the advantages of static Kramer system? i. The drive system is very efficient and the converter power rating is low, because it has to handle only the slip power.
What are the causes of harmonic currents in static Kramer drive?
19. Harmonics in a Static Kramer Drive The rectification of slip-power causes harmonic currents in the rotor which are reflected back into the stator. This results in increased machine losses.
What are the two types of static Scherbius system?
Operating Modes of Static Scherbius Drives
- Sub-synchronous Motoring – In this mode of operation the slip and torque both are positive and hence the injected voltage is in phase with rotor current.
- Super-synchronous Motoring – When the speed of the motor is above the synchronous speed, then the slip is negative.
What are the advantages of V F control?
The advantage of using V/F for speed control of three phase induction motor is as follows [2]: ● The current required at the starting is reduced. The motor runs more in stable region. Instead of simply running at its base rated speed the motor can be run typically from 5% of the synchronous speed up to the base speed.
Which drive will give both sub synchronous and super synchronous speed?
A cycloconverter allows power flow in either direction making the drive operate at both sub and super synchronous speeds.
What are the advantages of static rotor resistance control?
Compared to conventional Rotor Resistance Control of Induction Motor, static rotor resistance control has several advantages such as smooth and stepless control, fast response, less maintenance, compact size, simple closed-loop control and rotor resistance remains balanced between the three phases for all operating …
Where is the V F Control used?
Applications of V/F Control When changing the frequency, we should control the output voltage of AC drive, in order to keep constant flux and avoid weak magnetic and magnetic saturation phenomenon. This control method is commonly applied for fans and pumps.
Which benefit is for VFD?
The most significant benefit to using a VFD is energy savings. By matching system capacity to the actual load throughout the entire year, major savings in system motor energy use are achieved. Another benefit of the units is reduced wear and tear on the motors.
What is super synchronous motor?
Such a motor involves the use of external resistance and changing the connections of the secondary from a polyphase starting net work to a singlephase synchronous field winding. It also inherently has lower efficiency, due to the higher core losses and the greater exciting energy required.
What are the disadvantages of static rotor resistance control?
Because of low cost and high torque capability at low speeds, rotor resistance control is employed in cranes, Ward Leonard Ilgener Drives, and other intermittent load applications. Major disadvantage is low efficiency due to additional losses in resistor connected in the rotor circuit.
What is the slip power of static Kramer Drive?
By changing the injected voltage, the resistance and speed of an induction motor are controlled. The static Kramer-drive converts the slip power of an induction motor into AC power and supply back to the line. The slip power is the air gap power between the stator and the rotor of an induction motor which is not converted into mechanical power.
What kind of motor does a Kramer Drive use?
The static Kramer drive is shown in Figure 19.27. The drive comprises a slip-ring (wound rotor) induction motor together with an uncontrolled converter, d.c. smoothing reactor and a fully-controlled converter in the rotor circuit. Figure 19.27. Static Kramer drive
What is torque equation for static Kramer Drive?
Considering the torque equation for slip energy recovery: when motoring, torque is positive, when generating torque is negative. In this mode, operation is similar to that obtained with a static kramer drive. Slip and torque are both positive, therefore injected voltage must be in phase with rotor current.
How is a three phase diode bridge used in static Kramer?
1) The rotary conversion is replaced by an uncontrolled diode bridge and the DC motor is replaced by a three phase SCR bridge. 2) The slip power is drawn from the rotor of motor. The three phase rotor induced voltage is rectified by a three phase diode bridge.