50 Hz vs 60 Hz
50 Hz and 60 Hz power sources are most often used in international power systems. Some countries (regions) commonly use 50Hz power grid while other countries use 60Hz power grid.
- Alternating current (AC) is changing the direction of the current periodically.
- Cycle is the time of a cyclical change of the current.
- Frequency is the times of the current changes per second, unit Hertz (Hz).
- AC current direction changes 50 or 60 cycles per second, in accordance with 100 or 120 changes per second, then the frequency is 50 Hertz or 60 Hertz.
WHAT IS HERTZ?
Hertz, in short Hz, is the basic unit of frequency, to commemorate the discovery of electromagnetic waves by the German physicist Heinrich Rudolf Hertz. In 1888, German physicist Heinrich Rudolf Hertz (Feb-22, 1857 to Jan-1, 1894), the first person confirmed the existence of radio waves, and had a great contribution in Electromagnetism, so the SI unit of frequency Hertz is named for him.
WHAT IS Hz USED FOR?
Hz (Hertz) is the frequency unit of the vibration cycle time of electric, magnetic, acoustic and mechanical vibration, i.e. the number of times per second (cycle/sec).
WHAT IS 50 HERTZ?
50 Hertz (Hz) means the rotor of the generator turns 50 cycles per second, the current changes 50 times per second back and forth, direction changes 100 times. That means the voltage changes from positive to negative, and from negative to positive voltage, this process converts 50 times/second. The electricity 380V AC and 220V AC, are both 50 Hz frequencies.
The speed of 50 Hertz 2 poles synchronous generator is 3000 rpm. AC power frequency is determined by the pole number of the generator p and speed n, Hz = p*n/120. The grid standard frequency is 50 Hz, which is a constant value. For a 2-pole motor, the speed n = 50 * 120 / 2 = 3000rpm; for a 4-pole motor, the speed n = 50 * 120 / 4 = 1500rpm.
WHY USE 50 HERTZ?
When the frequency increases, the copper and steel consumptions of the generator and transformer decrease, along with the reduction of weight and cost, but will make the inductances of the electrical equipment and transmission line increase, reduce the capacitances and increase losses, thereby reducing the transmission efficiency. If the frequency is too low, the electrical equipment's materials will increase, along with heavy and high cost, and will make lights flashing obviously. Practices have proved using 50 Hz and 60 Hz frequencies are appropriate.
CAN A 50 HERTZ MOTOR RUN ON 60 HERTZ?
Since the formula for governing the synchronous speed of a three-phase motor is n = (120 * Hz)/p if this is a 4-pole motor then at 50 Hz the speed would be 1,500 RPM whereas at 60 Hz the speed would be 1,800 RPM. Since motors are constant torque machines then by applying the formula that HP = (torque*n)/5252 then you can see that with a 20% increase in speed the motor would also then be able to produce 20% more horsepower. The motor would be able to produce rated torque at both 50/60 Hz frequencies only apply if the V/Hz ratio is constant, meaning that at 50 Hz the supply voltage would need to be 380 V and at 60 Hz the supply voltage would need to be 460 V. In both cases the V/Hz ratio is 7.6V/Hz.
WHAT IS 60 HERTZ?
At 60 Hz, the rotor of the generator turns 60 cycles per second, the current changes 60 times per second back and forth, direction changes 100 times. That means the voltage changes from positive to negative, and from negative to positive voltage, this process converts 60 times/second. The electricity 480V AC and 110V AC, are both 60 Hz frequencies.
The speed of 60 Hz 2-pole synchronous generator is 3,600 RPM. AC power frequency is determined by the pole number of the generator p and speed n, freq. = p*n/120. The grid standard frequency is 60 Hz, which is a constant value. For a 2-pole motor, the speed n = 60 * 120 / 2 = 3,600 RPM; for a 4-pole motor, the speed n = 60 * 120 / 4 = 1,800 RPM.
HOW TO CHANGE 60 Hz TO 50 Hz
A frequency converter can convert fixed frequency (50 Hz or 60 Hz) AC power to variable frequency, variable voltage power through AC → DC → AC conversion, output pure sine wave, and adjustable frequency and voltage. It is different with variable frequency drive, which is special for motor speed control only, and also different with ordinary voltage stabilizer. Ideal AC power supply is stable frequency, stable voltage, resistance is approximately zero and the voltage waveform is pure sine wave (without distortion). Frequency converter output is very close to the ideal power supply, hence, more and more countries use frequency converter power supply as a standard power source in order to provide the best electrical power supply environment for appliances to estimate their technical performance.
50 Hz vs. 60 Hz IN OPERATING SPEED
The primary difference between 50 Hz (Hertz) and 60 Hz (Hertz) is simply that 60 Hz is 20% higher in frequency. For a generator or induction motor pump (in simple terms) it means 1,500/3,000 RPM or 1,800/3,600 RPM (for 60 Hz). The lower the frequency, the lower will be the iron losses and eddy current losses. Lower the frequency, speed of induction motor and generator will be lower. For example with 50 Hz, generator will be running at 3,000 RPM against 3,600 RPM with 60 Hz. Mechanical centrifugal forces will be 20% higher in case of 60 Hz (rotor winding retaining ring has to bear centrifugal force while designing).
But with higher frequency, output of generator and induction motors will be higher for same size of motor/generator because of 20% higher speed.
50 Hz VS 60 Hz ON EFFICIENCY
The design of such magnetic machines is such that they are really one or the other. It may work in some cases, but not always. To change between different power supply frequencies will certainly have an effect on efficiency, and may mean de-rating is necessary. There is little real difference between 50 Hz and 60 Hz systems, as long as the equipment is designed appropriately for the frequency.
It is more important to have a standard and stick with it. The more significant difference is that 60 Hz systems usually use 110V (120V) or thereabouts for the domestic power supply, while 50 Hz systems tend to use 220V, 230V etc. for different countries. This has the impact that house wiring needs to be twice the cross section for the 110V system for the same power. However the optimum system is accepted as around 230V (wire size and power required versus safety).
IS 60 Hz BETTER THAN 50 Hz?
It is no big difference between 50 Hz and 60 Hz, nothing is bad or good basically. For independent power equipment like ships, aircraft or isolated area like gas/oil installation, any frequency (like 400 Hz) can be designed based on suitability.
50 Hz OPERATION OF 60 Hz MOTORS
To obtain optimum performance, motors used for 50 Hz applications should be specifically engineered and manufactured for 50 Hz. Frequently, the delivery of 50 Hz products is such that an alternate course of action, utilizing 60 Hz products, is desirable.
The general guidelines for operating 60 Hz motors on 50 Hz systems relate to the fact that the volts per cycle have to remain constant with any change in frequency. Also, since the motor will operate at only five sixths of 60 Hz speed the output horsepower capability of 50 Hz is limited to a maximum of five sixths of nameplate H.P.
Source: U.S. Motors http://www.usmotors.com/TechDocs/ProFacts/50Hz-Operation-60Hz.aspx
THINGS TO CONSIDER WHEN OPERATING 50 Hz EQUIPMENT AT 60 Hz?
Machinery imported into the United States is often rated at an operating frequency of 50 Hz—unless engineered for operation at 60 Hz.. This can be problematic for electric motors. This is especially true when operating pump and fan loads.
Often, the distributors and purchasers of this machinery assume that the Original Equipment Manufacturer has taken this into consideration. This is recognized when motors are received for repair roasted out from overload.
A Variable Frequency Drive (VFD) can be used to properly address the issues associated when operating 50 Hz equipment at 60 Hz.
Motor speed is directly proportional to the operating frequency. Changing the operating frequency on a pump or fan increases the operating speed, and consequently increases the load on the motor. A pump or fan load is a variable torque load. A variable torque load varies by the cube of the speed.
A 50 Hz motor operating on 60 Hz will attempt to rotate at a 20% increase in speed. The load will become 1.23 (1.2 x 1.2 x 1.2) or 1.73 times greater (173%) than on the original frequency. Redesigning a motor for that much of a horsepower increase is not possible.
One solution would be to modify the driven equipment to decrease the load. This may include trimming the diameter of the fan wheel or impeller to provide the same performance at 60 Hz as the unit had at 50 Hz. This will require consultation with the OEM. There are other considerations associated with an increase in speed besides the increase in load. These include mechanical limitation, vibration limits, heat dissipation, and losses.
The best solution is to operate the motor at the speed for which it was designed. If that is 50 Hz., then a variable frequency drive can be installed. These drives will convert the 60 Hz line power to 50 Hz at the motor terminals.
There are numerous other benefits that will be realized with this solution. These benefits include:
- improved efficiency
- power regulation (often better than the utility will supply)
- motor over current protection
- better speed control
- programmable output to perform other tasks
- improved performance.
Source: Precision Electric, Inc., By Craig Chamberlin, November 25, 2009