If there are interference sources around the variable frequency drive, they will invade into the filter on variable frequency drive input side to reduce high harmonics, thereby to reduce the noise impact from the power lines to the electronic equipment; and install radio noise filter on VFD output side to reduce its output line noise for the same.
All motors have a “torque vs speed” characteristic.
DC machines are very simple: constant torque from zero speed to some “base speed”, and then a “constant power” ranging from base speed to top speed. In the constant torque range, acceleration is dependent on applied voltage, with the field under constant full current excitation. In the constant power range, voltage is held constant and the field current is reduced, thereby achieving an increase in speed (hence the term “field weakening”).
AC machines are somewhat more complex, since the curves are nowhere near as linear. The key points are:
– “starting torque”, which is the torque achieved at the locked rotor (zero speed) condition
– “pull in torque”, which is the available machine torque at the point where the machine pulls into synchronism (synchronous machines only)
– “pull out or breakdown torque”, which is the peak torque the machine can sustain momentarily before stalling
– “load torque”, which is the amount of torque actually required by the process at any operating point
– “accelerating torque”, which is the difference between what the machine is capable of producing and the load torque
A machine is rated for the “full load torque” condition which is the rated torque performance of the machine. In imperial (lb.ft) units, that would be 5252 * HP / RPM. It can produce this torque continuously, provided it has the rated conditions of applied terminal voltage and applied terminal current (for both rotor and stator, as applicable).
The time required to start a motor is dependent primarily on the accelerating torque available and the combined inertia (motor + remainder of drive train).
Note that available starting and pull-in torque during the transient operation of starting is proportional to the square of the applied voltage – if the voltage dips below 1.0 per unit, the available torque will be significantly reduced.
1) Overload protection: the soft starter has current control loop to track and detect of the changes of the electric motor current. Achieve overload protection by increasing overload current settings and inverse time control mode, to cut down the thyristor and send alarm signals when motor is overload.
2) Phase loss protection: soft starter detects changes in the three-phase line current all the time, to make phase loss protection response once the current off.
3) Overheating protection: the soft starter detects the thyristors internal radiator’s temperature by its thermal relay, automatic cut down and send alarm signal once the radiator’s temperature exceeds the allowable value.
4) Other features: achieve lots of mixed protection functions by combination of the electronic circuits.
In electric motor stop, the traditional control ways are accomplished by momentary power cutting off. But in lots of applications, it’s not allowed the motor instant shutdown. For example: high-rise buildings, building’s water pump system, it will appear huge water hammer during instant shutdown, to damage the pipe, even the pumps. To reduce and avoid “water hammer” phenomenon, the pumps motor need be shut down gradually, that is soft stop. The soft starter can meet such requirements. In pumping station, soft stop technology can avoid the pump door damaged of the pumping station, to reduce maintenance costs and maintenance works. The soft stop function in soft starter is, when the thyristor gets stop instruction, decrease conduction angle gradually from full conduction, and achieve full closed after a certain time. Stopping time can be adjusted according to actual requirements within 0 – 120s.
Induction motor is inductive load, the current lags the voltage, most electrical appliances are the same. In order to improve the power factor we need to use capacitive load for compensation, parallel capacitors or with synchronous motor for compensation. Reduce motor excitation current also can improve the power factor (HPS2 saving function, reduce excitation current by reducing voltage at light loads, to increase COS∮). Energy-saving operation mode: decrease voltage in light loads to reduce excitation current, the motor current divides into the active component and reactive component (excitation component), to increased COS∮.
Energy saving operation mode: when the motor load is light, the soft starter working at energy-saving conditions, PF switch to Y position, under the current feedback action, the soft starter reduces the motor voltage automatically, to reduce excitation component of the motor current. Thereby improving the power factor of the motor (COS∮). If the contactor in bypass state, this feature cannot works. TPF switch provides energy saving features with two reaction times: normal speed and slow speed. The soft starter operation in energy saving state automatic (In normal and slow speed), saving 40% energy in no-load and 5% with load.
1: Torque boost: this function is the variable speed drive increases output voltage (mainly in low frequency) to compensate the torque loss due to voltage drop in the stator resistance, thereby improving the motor output torque.
2: Improve the motor insufficient output torque in low speed
“Vector control” can make the motor output torque at low speeds, such as (without speed sensor) 1Hz (for 4-pole motor, the speed is about 30r/min), same as the torque output at 50Hz power supply (maximum is approx 150% of rated torque).
For the V/F control variable speed drive, the motor voltage increases relatively as the motor speed decreases, which will result in lack of excitation, and make the motor can not get sufficient rotational force. To compensate this deficiency, the variable speed drive needs to raise voltage to compensate for the voltage drop in motor speed decreases. This feature called “torque boost”.
Torque boost function is to improve the variable speed drive output voltage. However, even if the drive increases voltage, the motor torque and current does not increase corresponding. Because the motor includes the torque and other components (such as the excitation) which generated by the motor.
“Vector Control” allocates the motor current value to determine the motor torque current component and other current component (such as the excitation component) values.
I have a generator of 3 hp, and it outputs 230 V, and I have a submersible Electric Pump, the motor of which is rated to operate at 460 V, Can I use a step up transformer to increase the voltage output from my generator and power the pump? What more parameters do I need to know of in this case?
Check to see if the generator has 3 phase power output. A typical home generator will provide 230 volt single phase output. You will not be able to step up to 460 volt and start a 3 phase motor with single phase. The only way at that point to generate 3 phase would be to use a VFD with single phase input capability and use the drive to generate 3 phase. You will still need to use a transformer. Variable frequency drives won’t normally behave well on generator power but may for an intermittent load like a submersible pump.
For the MW range of Synchronous generators, there is no terminology of “interturn fault” on the stator winding. There could only be coil to coil fault on the stator for such size of machine design.
There are possibilities of having inter-turn faults on the rotor winding: when the insulation positioned between adjacent conductors break (electrically) over time under certain mechanisms. These mechanisms can include; turn to turn movement caused by thermal expansions (during starts/stops cycles), rotor coil shortening, end strap elongation, inadequate end-turn blocking or conductive bridging formed by contamination. The protection of avoiding the interturn insulation is a function of how well the machine is designed, maintained and operated. The OEM of the generator usually provides recommendations to avoid any inter-turn fault during the lifecycle of the machine. Saying this, there are ways to monitor the interturn fault indication; such as data acquisition (air gap flux probe, air gap search coil), as supportive monitoring (RSO, Shaft voltage, shaft vibration levels, excitation current etc.). Ideally, you have to be knowledgeable with the machine design to interpret the acquired data to make valuable predictions.
If you start by contemplating what kind of symptoms inter-turn faults could give rise to, you will be part of the way.
While machine is at standstill, you could do some reflected-wave analysis. All phases should show (near) identical responses.
During operation, you could have non-identical current and voltage waveforms on the three phases (you must compensate for unequal load).
You may experience strange sounds, in the supersonic range. Changing for different locations around the stator. You can continue the list, and settle on systems that may be able to detect any anomalies, so you can react accordingly.
Motor starter (also known as motor soft starter) is a electronic device integrates soft start, soft stop, light-load energy saving and various protection functions for motor controls. Its main components are the three phase reverse parallel thyristors between power supply and being controlled motor and related control circuits. Control the conduction angle of the three phase reverse parallel thyristors by different methods, to achieve different functions by the changeable of the input voltage on the controlled motors.
Soft starters and AC motor speed control, it can change output voltage and frequency at the same time; actually, soft starter is a regulator for motor starting, only changes output voltage but not the frequency. The frequency inverter has all the features of soft starter, but its price is much more expensive than the soft starter, and the structure is much more complex.
Frequency inverter allows the AC motor smooth start up, control startup current growing from zero to motor rated current, reduce impact to the power grid and avoid the motor being burned out, also provide protection in motor running process. Besides these functions, the main function of frequency inverter is adjusting the motor running speed according to actual operation conditions, to achieve energy saving effect.
Heating and cooling capacity to determine the variable frequency drive output current capability, thus affect its output torque capability.
Carrier Frequency: generally the variable frequency drive rated current is the continuous output value under the highest carrier frequency, the maximum ambient temperature. Reduce carrier frequency won’t affect the motor current, but will reduce electronic devices heating.
Ambient temperature: like will not increase VFD drive protection current when detect relative low ambient temperature.
Altitude: altitude increases will affect both heating and insulating property of the variable frequency drive. Generally it’s fine in below 1000m, and derate 5% per 1000meters for above.