If you are looking for more details, kindly visit .
Rotation is an essential part in the act of pumping thus making the motor an essential component of any pump. The purpose of the electric motor is to create this rotation by converting electrical energy into mechanical energy. This webcast is an introduction into how motors work. Viewers will learn the basic principles of magnetism, electromagnetism, and magnetic flux; how the two primary components, the stator and rotor, form the basic operating principle of an induction motor; the operating principles for 3-phase and single-phase motors; the difference between synchronous and asynchronous motors; and motor torque and power—where torque and speed come from.
Presenter Reece Robinson, senior technical training specialist, Grundfos Pumps Corp., responded to questions not answered during the live Electric motor basics webcast on Sept. 27, 2017.
Moderated by Jim Swetye, technical training expert, Grundfos Pumps Corp.
Question: What materials are used for laminations? Which is best for producing the strongest field of magnetism?
Reece Robinson: Laminations are made of steel, specifically silicon steel, also known as electrical steel. The addition of silicon to steel makes the steel more efficient and faster in terms of building and maintaining magnetic fields.
Q: I’ve read that motors act as generators during a fault. What exactly happens during a fault that causes the motor to act as a generator?
Robinson: Actually, when the motor spins in the opposite direction, it essentially becomes a generator. Some controls use braking to slow motors down, which can cause a fault or trip of the control. In pump applications, if water flow is going back through a pump discharge, this can cause the pump to spin in the opposite direction. This can be due to a check valve not functioning or in some cases, sever water hammer can cause a sudden reverse of pump shaft direction.
Q: What is the reason again to use variable frequency drives (VFDs) for permanent magnet synchronous motors (PMSMs)?
Robinson: PMSMs are not designed for across-the-line starting, and require a drive. To provide the right amount of torque at a given current, the rotor position must be known. Currently, there is research being done for line-start permanent magnet motors.
Q: Are PMSMs single-phase or 3-phase?
Robinson: The motor itself is based on 3-phase power but the control (VFD) can be designed for single-phase or 3-phase input. For commercial pumps, for example, PMSMs are available for single-phase supply from fractional size motors to 3 hp; 3-phase sizes range up to around 15 hp.
Q: For PMSMs, do you need to install stray current protection for the motor/pump bearings?
Robinson: I have seen no evidence showing that PMSMs reduce or eliminate problems associated with bearing currents. I will say that bearing damage due to these stray currents (called “fluting”) occurs predominantly in larger motors (above 50 hp). Fluting also is more common in equipment that is poorly grounded and/or has a flexible type coupling between the driven equipment and motor. Many flexible type couplings result in a break in the metal-to-metal contact, which results in having a poor path to ground for those stray currents.
Q: Did you say it is not necessary to worry about motor overheating at low speeds, and did you mean lower than 25% speed?
Robinson: For variable torque loads (centrifugal pumps and fans), the torque reduces with the square of the speed, so, even though the fan at the end of the motor shaft is only spinning at 25% of the motor’s rated speed, the torque has been reduced to only 6.25% of the full-load torque. Motor overheating concerns have originated from constant torque type applications where high torque is required at all speeds.
Q: Can you discuss implications running a 50 Hz, 380 V induction motor at 460 V, 60 Hz and vice versa?
Robinson: If a motor is rated/nameplated at 50 Hz/380 V, it should not be operated at 60 Hz/460 V. For example, if the motor was rated at 10 hp (7.5 kW) at 50 Hz/380 V and had a rated speed of 2,900 rpm, it could certainly overload at 60 Hz/460 V as it would be spinning at approximately 3,480 rpm. The horsepower increases with the cube of the speed so that 10 hp (7.5 kW) could become 17.3 hp (12.9 kW). It’s generally more feasible to go down from 60 Hz/460 V to 50 Hz/380 V, especially because most modern induction motors are rated for variable speed. When controlled by a VFD, a 60 Hz/460 V motor will periodically operate at 50 Hz/380 V during the normal duty cycle. Many motors have dual ratings, both at 50 Hz and 60 Hz. It is always best to consult the motor manufacturer and also check with the driven equipment manufacturer as well to ensure operation is advisable.
Q: All other things being equal, which has a higher initial cost: an 1,800-rpm motor or a 3,600-rpm motor?
Robinson: A 4-pole (1,800 rpm) motor will require more material and cost to produce therefore will have a higher initial cost. The 1,800-rpm motor will also be heavier, which may incur a higher shipping cost as well, as possible increased cost to mount and support. But on the other hand, 4-pole (1,800 rpm) motors generally are more efficient, from 1% to 2% higher than 2-pole (3,600 rpm) motors. But remember that the initial cost and efficiency of the driven equipment must also be taken into consideration.
Q: How does the switching frequency/carrier frequency of the VFD affect motor operation and expected life?
Robinson: When the switching/carrier frequency of a VFD is increased, this will result in a rise in temperature for both the motor and drive, which will result in lower efficiency for both as well. The most common reason for increasing the switching frequency is to decrease the audible noise (sometimes known as “VFD whine”). If the equipment is of good quality and sized to allow for some wiggle room, carrier frequencies can be adjusted up with only minor impacts on added heat or loss of efficiency. As always, it is best to consult with the drive and equipment manufacturers (or industry experts) before making those changes.
Q: How do you determine a motor’s load?
Robinson: The load on the motor is based on the equipment connected to the motor. So, if the motor is connected to a pump, there will be a corresponding brake horsepower curve for that pump. If the pump is driven by a 10 hp (7.5 kW) motor for example, the actual load on the motor might only be 8 hp (6 kW). The amount of flow going through the pump will determine the load on the motor and that load will be shown on the pump performance curve (or fan curve if you’re looking at fans). If you’re evaluating a motor in the field for example, you can get an idea of the approximate load on the motor by measuring the current and voltage. If the full load amps (FLA) of a motor is 10 and the average current draw on each phase is 8, then that motors is running somewhere between 7.5 and 8.5 brake horsepower (bhp). There are formulas to determine motor performance in publications such as the Electricians Handbook and the Cameron Hydraulic Data Book, etc. Most motor suppliers can supply a motor performance curve that shows volts, amps, efficiency, rpm, and power factor as a function of load.
Do you have experience and expertise with the topics mentioned in this content? You should consider contributing to our CFE Media editorial team and getting the recognition you and your company deserve. Click here to start this process.
A: Specific types of winding temperature detectors include thermostats, RTD’s, thermistors, and thermocouples. Following is a brief description of each.
Winding Thermostats
Winding thermostats are snap action, bi-metallic, temperature actuated switches. Their purpose is to activate a warning device, or simply shut down the motor upon excessive winding temperatures, when wired into the motor control circuit.
Thermostats are made either with contacts that are normally closed (open at high temperatures) or contacts that are normally open (closed at high temperatures). The thermostat temperature switch point is pre-calibrated by the manufacturer and is not adjustable. Reset is automatic after a decrease in temperature. Thermostats are normally installed in the connection end turns of the motor winding. Standard procedure is to wire three thermostats together in a set, with one thermostat embedded in each phase of the winding. Open thermostats are normally wired in parallel, while closed thermostats are wired in series. Refer to the figure below for further explanation
As seen in the figure above, only two leads come out to the motor outlet box. The leads of a normally closed (N.C. thermostat) are marked P1 and P2. Those of a normally open thermostat are marked P3 and P4.
Refer to the table below (Table 6) for thermostat alarm and shutdown temperatures.
Table 6: Thermostat Temperature Chart
Temperatures shown in ° C
Service Factor
1.00
1.15 and up
Purpose
Alarm
Shutdown
Alarm
Shutdown
Temp. Rise Class
A
B
F
A
B
F
A
B
F
A
B
F
Open Motors
N.O.
95
118
140
106
132
150
106
132
150
118
140
160
Without
N.C.
100
120
140
110
130
150
110
130
150
120
140
160
Ducts:
N.C. (R&T)
100
120
140
110
130
150
110
130
150
120
140
160
Open Motors
N.O.
106
132
150
118
140
160
118
140
150
132
150
160
With Ducts &
N.C.
110
130
150
120
140
160
120
140
150
130
150
160
TEFC Motors:
N.C. (R&T)
110
130
150
120
140
160
120
140
150
130
150
160
RTD’s (Resistance Temperature Detectors) are precision, wire-wound resistors, with a known temperature resistance characteristic. We use flat, molded strip type RTD’s that are only .030 inch thick. RTD’s are installed in the slot portion of form wound motors, and in either the slot or end turns of mush wound motors.
RTD’s used in motor windings are either 10 ohm, 100 ohm, or 120 ohm. Each type of RTD has its own specific resistance characteristic. The basic detectors are listed below in Table 7.
Table 7: Winding RTD’s
OHMS
ELEMENT
# LEADS
10 Ohms at 25° C
Copper Wire
3
100 Ohms at 0° C
Platinum Wire
3
120 Ohms at 0° C
Nickel Wire
2*
* Also available with 3 leads.
All the RTD leads are brought out to a motor outlet box. RTD’s leads are identified in sets, using C1, T1, T1, and C11, T11, T11 for the same phase. Since leads are always brought to terminal strips, the leads are terminated with fork-tongue terminals.
See alarm and trip temperatures based on the motor service factor, HP rating, and class of temperature rise.
Winding Thermistors
A thermistor is a non-linear resistance temperature detector, made from semi-conducting material. We utilize positive temperature coefficient (PTC) type thermistors, which have a resistance that increases with increasing temperature. Each individual thermistor has its own unique resistance vs. temperature characteristic. Thermistors are normally installed in the end turns of the motor. Depending upon the controller, they are wired either in series or in a ‘common lead circuit’. Both circuits are shown below.
The following is a brief description of the controllers and thermistors supplied by various companies:
Power Control Corporation (PCC)
In the past, we supplied PCC 600, 900, 8000, and 9000 series thermistors. We now use only the 8000 series thermistors. A maximum of three PCC 8000 series thermistors are installed in the common lead circuit configuration. Do not install them in series, or false tripping will result. PCC makes numerous controllers, including a special controller for the therma-sentry system. The PCC controller brand name is ‘MOTOGUARD’. For non-therma-sentry PCC thermistors, the thermistors are internally wired in the common lead configurations with the leads marked TM5, TM6, TM7, and TM8. Lead TM5 is the common lead.
Texas Instrument (TI)
TI currently uses 4BA and 7BA series, PTC thermistors. The 4BA series thermistors are normally used on new and rewound motors and contain a copper heat collector for a fast response time. The 7BA series is normally used on existing motors, and contains only a small thermistor bead to ease installation. TI thermistors are wired in series. Three thermistors may be installed in series without false tripping the controller. Our procedure is to bring out all six leads and make the series connection in the outlet box. The thermistor lead pairs are marked TM1, TM2, and TM3. The standard TI controller is a 50AA control module.
Siemens
We presently use a Siemens Q63100-P, PTC thermistor. Siemens thermistors must be wired in series. Six thermistors may be wired in series without false tripping the controller. Our standard procedure is to install three thermistors in series and bring all six leads out, making the series connection in the outlet box. The thermistor lead pairs are marked TM1, TM2, and TM3. The Siemens standard controller is a 3UN tripping unit control module, which has an N.O. and an N.C. contact.
The following table (Table 8) shows alarm and shutdown temperatures (in ° C) for 1.0 and 1.15 SF thermistors, based on the required class of temperature rise.
The new Thermasentry® system utilizes Siemens B59100M thermistors connected in series and a Siemens 3RN1010 controller.
Table 8: Thermistor Temperature Setting Chart
Temperatures shown in ° C
Service Factor
1.0
1.15 - UP
Purpose
ALARM
SHUTDOWN
ALARM
SHUTDOWN
Class of Temp. Rise
A
B
F
A
B
F
A
B
F
A
B
F
Open Motors w/o Ducts
PCC, PTC 8000
105
115
145
115
125
155
105
125
155
115
135
165
TI, 4BA Series
105
115
145
115
125
155
105
125
155
115
135
165
TI, 7BA Series
105
115
145
115
125
155
105
125
155
115
135
165
Siemens
100
120
140
110
130
155
110
130
155
120
140
160
Open w/Ducts and TEFC Motors
PCC, PTC 8000
105
125
155
115
135
165
115
135
155
125
145
165
TI, 4BA Series
105
125
155
115
135
165
115
135
155
125
145
165
TI, 7BA Series
105
125
155
115
135
165
115
135
155
125
145
165
Siemens
110
130
150
120
140
160
120
140
155
130
150
160
Thermocouples
A thermocouple is a pair of dissimilar conductors joined at one point, in a way that causes an electromotive force (EMF) to develop due to the thermoelectric effects. Any given set of thermocouple wires has a known EMF vs. temperature characteristic. Thermocouples are only able to generate a low-voltage, low-power signal in the millivolt range. There are many types of thermocouples. Standard types include copper-constantan, chromel-constantan, and iron-constantan. Thermocouples are normally installed in the slot between coil sides, on both mush wound and form wound motors. However, if necessary, they can also be installed in the end turns. The standard quantity of thermocouples is six, installed two per phase. If quantity-3 thermocouples are specified, leads are marked TC1, TC2, and TC3. If quantity-6 are specified, leads are marked TC1, TC2, TC3, and TC11, TC22, TC33, such that TC1 and TC11, etc. are in the same phase.
See alarm settings for alarm and trip temperatures based on the motor service factor, HP rating, and class of temperature rise.
You can find more information on our web, so please take a look.
If you want to learn more, please visit our website outdoor led video wall for sale.