RFP_1100_MMH3047_ATT_2_v1.pdf
PDF 49 KB Posted
- Solicitation number
- RFP 1100 MMH3047
- Issued by
- Texas
About this file
This is an attachment to a Request for Proposal (RFP 1100 MMH3047) for large industrial motor repairs for Austin Energy and Austin Water, issued by the City of Austin, Texas. The document provides technical specifications and testing procedures for stator hot spot checks, a critical quality assurance process contractors must perform on stator core iron to identify shorts between laminations. The stator core testing methodology involves winding a coil through the bore and around the frame of the motor, then energizing it to generate a magnetic field that will cause damaged areas to heat faster than sound areas. The RFP does not specify quantities, response dates, or award timelines in this attachment, as it serves as a technical guidance document rather than the main solicitation terms.
The attachment establishes detailed calculations and procedures that contractors must follow, including measuring stator core dimensions (length, depth, bore diameter, and slot depth), computing effective core length at 80 percent of measured length, determining core cross-sectional area, and calculating the required voltage per turn, number of cable turns, ampere turns, and current requirements. Safety requirements are emphasized throughout, including solidly grounding the core, prohibiting probing or entry during energization, and preventing metallic objects from contacting laminations. The testing process requires constant monitoring to detect hot spots and prevent further core damage, with temperature rise between 80°F and 100°F indicating sufficient magnetic flux. Contractors may adjust the number of cable turns as needed to achieve appropriate testing conditions, removing or adding turns in increments of two to manage temperature and current levels.
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Text version
RFP 1100 MMH3047
LARGE INDUSTRIAL MOTOR REPAIRS FOR AUSTIN ENERGY AND AUSTIN WATER
ATTACHMENT B
STATOR HOT SPOT CHECK
The stator core iron shall be tested in accordance with the following, (or by using the City approved core loss tester) to determine whether there are shorts between lamination. The method is to wind a coil through the bore and around the outside of the frame. When the coil is energized, a magnetic field will be set up in the core.
If it is bad, the damaged area should heat much faster than the rest of the core. Cores can be tested with a winding in them if the leads are separated and well insulated and delta connections are opened and insulated.
For personal safety the core should be solidly grounded.
As a necessary safety precaution, do not probe the iron or enter the core with the cable energized as voltage is generated between laminations. Metallic objects, i.e., bolts or clamps, should not be allowed to contact the lamination during the test.
Contractor shall use the following as a guide to calculate the number of cable turns and the current required.
1. Measure stator core length, core depth, stator core bore diameter and slot depth (in inches).
2. Effective stator core length (C.L.) is obtained as follows:
C.L. = measured stator core length x 0.80
3. To determine core depth (C.D.):
Core depth is measured from the bottom of the coil to the core’s outer circumference.
4. To determine effective core cross sectional area:
Core area = (C.L.) x (C.D.)
5. To calculate estimated voltage per turn:
Volts per turn = 0.26 x core area
6. To determine the number of cable turns to be placed through the stator core:
Turns = Supply voltage/volts per turn
7. To determine effective stator core diameter (E.C.D.)
Stator core inside bore diameter = C.I.D.
Slot depth = S.C.
Core depth = C.D.
E.C.D. = C.I.D. + C.D. + 2 S.C.
8. To determine ampere turns (A.T.) required:
A.T. = 45 x E.C.D.
9. Current required:
Amperes: (A.T.)/Turns
10. Cable size:
Be sure cable size to be used has a nominal current rating of not less than the current required to conduct the test.
During testing a uniform core temperature of approximately 80°F to 100°F rise would indicate sufficient flux to produce hot spots. Changing the number of cable turns may be required if the temperature is less, remove turns (2 at a time) and again observe the temperature. If it is greater, add turns to reduce the current.
The test must be constantly monitored. With sufficient flux circulating hot spots may show up very rapidly resulting in further core damage if the testing is not stopped in time.
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