Sunday, March 17, 2013

Variable Frequency Drives - Toshiba

Variable Frequency Drives - VFDs / ASD's ~ Inverters for Electric Motors

Toshiba Drives from Sords Electric provide Excellent Motor and Pump control.

General discussion on uses and how they work.

You can divide the world of electronic motor drives into two categories: AC and DC. A motor drive controls the speed, torque, direction and resulting horsepower of a motor. A DC drive typically controls a shunt wound DC motor, which has separate armature and field circuits. AC drives control AC induction motors, and-like their DC counterparts-control speed, torque, and horsepower.

Variable Frequency Drives (VFD's)  also known as Adjustable Speed Drives, are used to vary the speed of an electric motor. They do this by changing the frequency of the electric power going to the motor. They work only with three-phase power. Today they are very economical.
In the United States, normal electric power is supplied at 60 cycles per second, sometimes called 60 hertz (Hz). At this frequency motors run at 1,800 rpm, 3,600 rpm, 1,200 rpm, or 900 rpm, depending on how they are wound. The number of poles in the winding determines its speed. For example, four-pole motors run at 1,800 rpm, and two-pole motors run 3,600 rpm.
The actual motor speed, as read on the motor nameplate, is a little lower than these theoretical figures because of slippage that occurs.
The speed of the motor changes in direct proportion to the hertz. Thus, a four-pole motor running at 45 hertz will turn 1,350 rpm, and a six-pole 1200-rpm motor at 40 hertz will run 800 rpm. A motor can be sped up, also: a four-pole motor running at 90 hertz will turn 2,700 rpm.
Most VFD's come with a preset limit of 60 Hz. This can be easily changed.
When a motor is slowed down, the cooling fan that is mounted on the motor shaft also slows down. Thus, motors have a tendency to overheat at low speeds like 10 Hz or 15 Hz. Feel the motor to see that it is not overheating. A Toshiba premium efficiency motor will overheat less. Low speeds are fine for a trial, but they may not be suitable for extended operation.
VFD's have a built-in circuit breaker that shuts down the motor if the amps get too high for the speed at which the motor is being run. This provides excellent (the best we know of) electrical protection for a motor and the machine it is driving.
It is best to have a VFD that is rated for more horsepower than the motor being driven. This gives more flexibility. However, where electrical overload protection is deemed important, the rating of the actual motor being driven should be loaded into the VFD. Otherwise the VFD might put out enough power, if called for, to burn up the motor.
It is very easy to install a VFD. They work only on three-phase power output, some Toshiba S15's have single phase power in. So there are four wires coming from the power control panel: white, black and (usually) red power wires and a green ground wire. The three power wires are hooked to the L1, L2 and L3 terminals. There are three output terminals, labeled T1, T2 and T3 (sometimes U, V, and W), to which you connect the power wires going to the motor.
When you turn on the motor, it may be running backwards. It is usually easy to change the direction of rotation with the VFD itself. Most VFD's have a simple toggle command for forward and reverse.
Unfortunately, when the motor is shut down and later restarted, it will restart running backwards again. To correct this permanently it is necessary to switch two of the power leads. It is a little tricky to change the direction of rotation of a motor with a VFD. Simply switching leads at the main circuit breaker in the motor control panel will not work. Instead, it is necessary to switch the leads coming out of the VFD, the ones going to the motor.
Once a VFD is wired up, there may be frustration trying to get the motor to start. The solution usually is to toggle from the Remote to the Local operation, then hit the Start button.
To change the speed (frequency), get into the frequency adjustment display (next to the actual frequency output display). Toggle the speed up or down, then hit the enter button.
Amps can be read by toggling the menu button to the amps display. Amps reading are a little peculiar with VFD's. They are no longer directly in proportion to the power being consumed. So, use them as a reference only.
Please do not let water and electricity to mix around a VFD. It is very easy to fry a VFD, and they are not worth trying to repair when you do. Be sure to have a plastic bag or sheet over the VFD. Protect the VFD from dripping pipes, rain, and wash-down water. Also, use GFCI's if necessary for human protection in wet areas.
VFD's are good for only one voltage, either 208-220-240 volts or 440-480 volts. Be sure you know what voltage you are working with. There are more sophisticated VFD models that work on both voltages.
For advanced students we offer the following: Basically, with a VFD set below 60 Hz, the motor drops maximum horsepower output and instead holds constant torque. Above 60 Hz, the horsepower is limited to the motor nameplate maximum, which means there is a reduction in torque. Some VFD's can be set for overload trip on either amps or torque; set it on torque for the best overload protection.
The input section of the drive is the converter. It contains six diodes, arranged in an electrical bridge. These diodes convert AC power to DC power. The next section-the DC bus section-sees a fixed DC voltage.
The DC Bus section filters and smoothes out the waveform. The diodes actually reconstruct the negative halves of the waveform onto the positive half. In a 460V unit, you'd measure an average DC bus voltage of about 650V to 680V. You can calculate this as line voltage times 1.414. The inductor (L) and the capacitor (C) work together to filter out any AC component of the DC waveform. The smoother the DC waveform, the cleaner the output waveform from the drive.
The DC bus feeds the final section of the drive: the inverter. As the name implies, this section inverts the DC voltage back to AC. But, it does so in a variable voltage and frequency output. How does it do this? That depends on what kind of power devices your drive uses. If you have many SCR (Silicon Controlled Rectifier)-based drives in your facility, see the Sidebar. Bipolar Transistor technology began superceding SCRs in drives in the mid-1970s. In the early 1990s, those gave way to using Insulated Gate Bipolar Transistor (IGBT) technology, which will form the basis for our discussion. Toshiba manufacturers their own IGBT's and thus has complete control and quality measures for their drives.

The drive's control board signals the power device's control circuits to turn "on" the waveform positive half or negative half of the power device. This alternating of positive and negative switches recreates the 3 phase output. The longer the power device remains on, the higher the output voltage. The less time the power device is on, the lower the output voltage. Conversely, the longer the power device is off, the lower the output frequency. The speed at which power devices switch on and off is the carrier frequency, also known as the switch  frequency. The higher the switch frequency, the more resolution each PWM pulse contains. Typical switch frequencies are 3,000 to 4,000 times per second (3KHz to 4KHz). (With an older, SCR-based drive, switch frequencies are 250 to 500 times per second). As you can imagine, the higher the switch frequency, the smoother the output waveform and the higher the resolution. However, higher switch frequencies decrease the efficiency of the drive because of increased heat in the power devices. 

Drives vary in the complexity of their designs, but the designs continue to improve. Drives come in smaller packages with each generation. The trend is similar to that of the personal computer. More features, better performance, and lower cost with successive generations. Unlike computers, however, drives have dramatically improved in their reliability and ease of use. And also unlike computers, the typical drive of today doesn't spew gratuitous harmonics into your distribution system-nor does it affect your power factor. Drives are increasingly becoming "plug and play." As electronic power components improve in reliability and decrease in size, the cost and size of VFDs will continue to decrease. While all that is going on, their performance and ease of use will only get better. 

Please contact us at 800-929-2845 or use our contact form.

Thursday, March 7, 2013

Heating with Compressed Air

Sords Electric and Convectronics offer Compressed (flameless) Air Heating, up to 1400 degrees F.

The energy (kW) requirement is calculated from the following formula:


KW = SCFM x (Texit – Tinlet) (ΔT) / 2500

SCFM = Air flow in Standard* Cubic Feet per Minute
Tinlet = Inlet Air Temperature (°F) (typically 70°F)
Texit = Desired Exit Air Temperature (°F)
[The temperature difference is also know as delta T (ΔT) ]

Example: Heating 10 SCFM from ambient temperature (70°F) to 800°F:
KW = 10 SCFM x (800°F – 70°F) / 2500 = 2.9 kW

Conversion Formulas:

(Liters per Minute)/28.3 = Cubic Feet per Minute
°C = 5/9 (°F – 32)
°F = 9/5°C + 32

Using an Air Heater:

If used properly, heater life of 5000 hours or greater can be expected. To ensure long heater life and safe operation, follow these guidelines. Also read and understand your heater Operating Manual before use. Failure to follow these guidelines can result in heater damage, failure, or personal injury. 

Air Sources:

In general, compressed air, and air from regenerative blowers may be used to supply Convectronics flameless air heaters. Your air source should be clean and dry. Dirt, grease, oil, or oil vapors, or corrosive or reactive gases will damage an air heater. Also, use air or inert gas only. Do not use with volatile or combustible gases.

Regenerative Blowers:

Regenerative blowers are compact and inexpensive clean air sources. They can provide large amounts of low-pressure air for your air heating system. 

Compressed Air:

Compressed air is commonly available in most factories. It is high-pressure regulated air (typically to 100psi), and often contains oil for lubricating pneumatic valves and equipment. You must filter this oil to prevent fouling and damage to Convectronics electric air heater elements.

When measuring compressed air flow rates, be sure you are measuring Standard CFM or Standard LPM units. The "Standard" means that the units are measured at standard temperature and pressure. Many flow meters are labeled SCFM, but this is incorrect at the higher pressures produced by compressed air. For accurate flow measurements, you must consult your flow meter manual for converting CFM to "Standard" CFM. In the diagram below, the flow meter reading (CFM) is converted to SCFM using a Dwyer ball-type flow meter conversion.


A good control system is critical for long heater life. Before turning your control system on, you must have sufficient airflow through the heater before applying power. (Applies to heaters without over-temperature protection.) Only qualified individuals should install Convectronics heaters and controls. Follow all applicable electrical codes and use proper wiring, fusing and safety procedures.

Open-Loop (Manual) Control:

This simple method of control uses a manually operated power controller to apply a fixed voltage to the heating element. Using this system, the operator manually adjusts the controller to change heater temperature. Note that if the airflow is suddenly interrupted, the element could fail. The open-loop controller is generally used with Convectronicss Series heaters.

Closed-Loop (Feedback) Control:

A closed-loop heater control system uses a power controller, temperature controller, and thermocouple to provide a constant output temperature, regardless of changes in airflow. The temperature controller also provides a convenient display of your process air temperature.

Power Controller:

Phase angle fired SCR (Silicon Controlled Rectifier) power controls will provide the smoothest power regulation for  Air Heaters.

Temperature Controller:

Use only digital temperature controls with type-K thermocouple inputs. The temperature control output must match the input of the power control. (i.e. 4-20mA, or 0-10VDC).
A standard PID-type control with a wide proportional band setting will work best to minimize temperature overshoot. PID parameters may be auto-tuned, but only at temperatures well below the maximum of the heater. If the temperature rises too high during auto-tune, turn power off immediately.
When using a Solid State Relay power control, the temperature controller cycle time should be set for 100ms or less.


Use only a fine-wire (.030" max wire dia.), exposed-junction, type-K thermocouple placed within 1" of the heater exit for accurate temperature readings. Other thermocouple styles, or varying the distance from the heater exit will result in temperature measurement errors and/or heater failure.

Air Flow Conversions:

SCFM = SCFH / 60 = SLPM / 28.3
SLPM = SCFH / 2.12
SCMH = SCFH / 35.3
SCFM = (Pounds of Air Per Minute) / (.080 lbs/ft3)

SCFM = Standard Cubic Feet per Minute
SCFH = Standard Cubic Feet per Hour
SLPM = Standard Liters per Minute
SCMH = Standard Cubic Meters per Hour

Single Phase Wiring:

V = I x R (Volts = Amps x Ohms)
I = W / V (Amps = Watts / Volts)
W = V2/R (Watts = (Volts x Volts) / Ohms)

Use our Ohms Law Calculator

Three Phase Wiring:

Delta Configuration:

R = R1 = R2 = R3
Wdelta = 3(VL2)/R
Wdelta = 1.73 x VL x IL
IP = IL/1.73

Wye Configuration:

R = R1 = R2 = R3
Wwye = (VL2)/R = 3(VP2)/R
Wwye = 1.73 x VL x IP
VP = VL/1.73

Percent Loss of wattage with lower than rated voltages applied:

230-volt heater on 208 volts - 82% (18% loss)
240-volt heater on 208 volts - 75% (25% loss)
480-volt heater on 277 volts - 33% (66% loss)
480-volt heater on 440 volts - 84% (16% loss)
480-volt heater on 318 volts - 44% (56% loss)
550-volt heater on 480 volts - 76% (24% loss)

To convert KiloWatts to BTUs:

Multiply  KW x 3413 = BTUs

°F (Farenheit)=(9/5°C) + 32
°C (Celsius)=5/9 (°F - 32)

For application help, please call Sords Electric - 216-765-4230

Monday, March 4, 2013

Chromalox Watlow Cross Reference for Strip Heaters

Chromalox Strip Heaters and Watlow Strip Heaters Cross Reference

Sorted by Chromalox part number. Please note that some Watlow parts cross reference to two Chromalox strip heaters.  Watlow uses an Aluminized Steel sheath good to 1100 degrees to cover both the Chromalox Iron Sheath (750) and Chrome Steel Sheath (1200) heaters.

Watlow Chromalox Watts Volts
SGA1J7JO1 OT-715 150 120
SGA1J7JO2 OT-715 150 240
SGA1J7JO3 OT-702 200 240
SGA1J8AO1 OT-815 150 120
SGA1J8AO5 OT-815 150 240
SGA1J8AO2 OT-802 200 120
SGA1J8AO8 OT-802 200 240
SGA1J10JO8 OT-1003 350 120
SGA1J10JO5 OT-1003 350 240
SGA1J10JO6 OT-1004 400 120
SGA1J10JO7 OT-1004 400 240
SGA1J10JO1 OT-1025 250 120
SGA1J10JO2 OT-1025 250 240
SGA1J12AO1 OT-1202 250 120
SGA1J12AO2 OT-1202 250 240
SGA1J12AO5 OT-1203 350 120
SGA1J12AO6 OT-1203 350 240
SGA1J12AO3 OT-1205 500 120
SGA1J12AO4 OT-1205 500 240
SGA1J12AO1 OT-1225 250 120
SGA1J12AO2 OT-1225 250 240
SGA1J14AO3 OT-1405 500 120
SGA1J14AO4 OT-1405 500 240
SGA1J14AO2 OT-1430 300 120
SGA1J14AO1 OT-1430 300 240
SGA1J15EO4 OT-1505 500 240
SGA1J15EO2 OT-1532 325 120
SGA1J15EO1 OT-1532 325 240
SGA1J17RO10 OT-1801 1000 120
SGA1J17RO3 OT-1801 1000 240
SGA1J17RT2 OT-1807 750 120
SGA1J17RT3 OT-1807 750 240
SGA1J17RO4 OT-1835 325 120
SGA1J17RO5 OT-1835 325 240
SGA1J17RO6 OT-1837 375 120
SGA1J17RO7 OT-1837 375 240
SGA1J17RO1 OT-1850 500 120
SGA1J17RO2 OT-1850 500 240
SGA1J19JO1 OT-1901 1000 240
SGA1J19JO7 OT-1905 750 120
SGA1J19O4 OT-1905 750 240
SGA1J19JO8 OT-1907 750 240
SGA1J19JO6 OT-1935 325 240
SGA1J19JO7 OT-1950 750 120
SGA1J19O4 OT-1950 750 240
SGA1J21AO3 OT-2107 750 120
SGA1J21AO4 OT-2107 750 240
SGA1J21AO1 OT-2150 750 120
SGA1J21AO2 OT-2150 750 240
SGA1J23NO7 OT-2401 1000 120
SGA1J23NO3 OT-2401 1000 240
SGA1J23NO5 OT-2405 750 120
SGA1J23NO6 OT-2405 750 240
SGA1J23NO1 OT-2407 750 120
SGA1J23NO2 OT-2407 750 240
SGA1J23NO6 OT-2450 500 240
SGA1J23NO1 OT-2475 750 120
SGA1J23NO2 OT-2475 750 240
SGA1J25JO5 OT-2501 1000 240
SGA1J25JO3 OT-2507 750 120
SGA1J25JO4 OT-2507 750 240
SGA1J25JO1 OT-2550 500 120
SGA1J25JO2 OT-2550 500 240
SGA1J25JO3 OT-2575 750 120
SGA1J25JO4 OT-2575 750 240
SGA1J26NO2 OT-2601 1000 240
SGA1J26NO1 OT-2670 700 240
SGA1J30JO2 OT-3007 750 120
SGA1J30JO3 OT-3007 750 240
SGA1J33JO1 OT-3307 750 240
SGA1J33JO1 OT-3375 750 240
SGA1J35RO3 OT-3601 1500 240
SGA1J35RO4 OT-3610 1000 120
SGA1J35RO3 OT-3610 1000 240
SGA1J38JO2 OT-3801 1000 120
SGA1J38JO2 OT-3810 1000 120
SGA1J42JO1 OT-4815 1500 240
SGA1J47RO1 OT-4822 2250 240

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