Information that's needed to complete a data verification & redesign request
In the February edition of Currents, Mike Parsons provided excellent advice on contacting EASA Technical Support with questions. Mike is with Hupp Electric Motors Co. in Marion, Iowa, and is a member of the Technical Education Committee. I would like to underline one statement he made: “You are not a bother!” In fact, you are our livelihood.
Over the years, your Board of Directors has allocated resources to increase the number of technical support specialists. And in past Member Needs Assessment Surveys, members have consistently rated technical/engineering support as the number one benefit of membership. By all means, take advantage of it.
To help you get the most from the benefit, this article will explain the information required to complete the Data Verification & Redesign Request form. You can complete and submit the request online at www.easa.com/ resources/tech_support/redesign_ inquiry or you may complete and fax or email the form that is available to download from that location. See Figure 1. If the forms are filled out manually, be sure to write clearly. For example, numbers such as “1” or “7”, or “5” or “6”, can look the same if written too quickly.
Figure 1: EASA's Data Verification & Redesign Form
When completing both the printed and online forms, certain fields are marked with an asterisk (*) implying that they are required to complete your request. Sometimes all of this information is not available and should be noted so in the appropriate spot. We will then make every attempt to determine what should be done.
Starting with the company information block, the important data are your company EASA identification number, a name and contact information in case we have questions. Let us know which medium you prefer to receive your response by filling in either the fax, email, or phone area. We use information in the manufacturer block to enter into the EASA database. While helpful for future reference, it will not impede the request if it is missing.
*Hp or kW is the rating from the nameplate for the machine’s load capacity. When there are choices such as this, the correct unit should be circled. Entering rpm or poles and frequency determines the speed of the machine. Frequency, volts and amperes are also from the nameplate. If there is more than one of any of these values, all should be reported.
Core data & dimensions
One of the keys to evaluating or changing a design is to determine if the magnetic flux densities in the air gap and core iron are reasonable. This can be expressed in thousands of lines of flux per square inch (klines/in²) or Tesla (T). This is compared to the maximum values established for the air gap (65 klines/in² or 1T), core (130 klines/ in² or 2T) and tooth (130 klines/in² or 2T). They are also compared to motors with similar cores and ratings found in the EASA motor database. We can calculate the number of lines of flux per square inch using the voltage, frequency, winding data and core dimensions. The calculations require accurate measurements for each of the components as well as the number of stator slots. Figure 2 provides guidelines for these measurements.
Figure 2: Important information for taking measurements
The number of rotor bars is optional unless a speed change is requested. Depending on the number of poles, certain combinations of numbers of rotor bars compared to stator slots will produce noise, cogging or torque cusps. With the number of bars, we can check to see if the combination in your motor will be a problem. Note that if the rotor bars or stator slots are skewed, the combination should not cause these problems.
The core length should be given as the overall distance from one end of the core to the other. If there are air ducts, the number and width of these can be reported in the spaces provided. They will then be included in the evaluation.
For form coil windings, the stator slot dimensions are needed. Accurate measurements will facilitate designing the wire size and insulation to fit properly in the slot when the coil is made.
The number of groups and coils is required for the winding evaluation. Be careful with the math here. An example is a motor with 48 slots with 12 groups of 3 coils, but all the slots are equally full. Many times this will be reported as 12 groups of 4 for 48 total coils with 3 pitches in the concentric winding. Actually, there are 36 total coils and the third coil in each group has twice or nearly twice the number of turns of the other two coils in the group. In each coil group, two coils will share a slot and one of the coils will fill the slot alone. It can be confusing and often require a phone call to clarify what is really there.
The wire data section tells the number and size of the wires in hand for each turn. Remember the wire could be AWG or metric. If you are not sure, provide the micrometer readings for the wire sizes and we will make the determination. Note that if the machine is not made in North America, it well could be metric wire. Wire gauges should be avoided; they are generally not sufficiently accurate to determine the difference between half sizes or AWG versus metric sizes. Even a half wire size can make a difference. It is best practice to measure the wire with a micrometer and use the EASA Round Magnet Wire Data chart to identify the wire size.
By far the most often misreported piece in this puzzle is the connection. A good rule to remember is that if the motor has more than three leads, there is more than one connection. A discussion of this and how to determine the connection is found in the October 2011 Currents article titled “Understanding three-phase motor connections.”
Several examples should be taken to determine the number of turns in each coil; it is not uncommon for there to be different turns in the coils in the same group or for different groups. Some of these may seem odd, so it is good to count multiple coil groups until you recognize a pattern. The number of turns will equal the total number of strands (wires) in the slot divided by the number of wires in hand and the number of coil sides. For instance, in a shared slot lap winding with 90 total wires in the slot and 3#16, 2#17 the number of turns is:
90/2 = 9 turns
The pitch is the slot the first coil side falls in and the slot for the opposite side reached. See Figure 3. Such as in a pitch of 1-8, the first coil side is in slot 1 and the other side is in slot 8. A coil pitch of 1-8 spans 7 teeth, so the span = 7. All of the coils in that group will have the same space between them and then the next phase begins.
Figure 3: Coil pitch
Concentric windings will always have more than one pitch listed such as 1-8, 10, 12. This is a group of three coils that are concentrically nested as seen in Figure 4 at the right. Not all potential pitch combinations will allow the coils to be distributed evenly and therefore cannot be used. For instance, a 4-pole motor with 48 slots and 36 coils cannot use a pitch of 1-7, 9, 11; the full slot coil will fall on top of a shared slot coil and there will be empty slots.
This section contains the instructions for what you would like to accomplish. This may include changes in the horsepower, speed, frequency or voltage. The reason for the inquiry is very important so we do not need to guess. The more detail provided, especially for complicated requests, the better the results. If any of the information is not available, include a note to that effect so we can do our best to fill in the gaps.
The more complete and accurate the information provided, the more quickly and accurately the answer will be received. We very much appreciate when you submit your requests to EASA Technical Support online or using one of the downloadable forms. It seems that every facility has its own way to record this information and that is good. It does take extra time to find the information if you are not familiar with the format; submitting on standardized EASA forms expedites the process.