IEEE 1434-2014 pdf download
IEEE 1434-2014 pdf download.IEEE Guide for the Measurement of Partial Discharges in AC Electric Machinery.
The radio noise voltage appearing on conductors of electric equipment or circuits, as measured using a radio noise meter as a two-terminal voltmeter in accordance with specitied methods as are described in CISPR 16-1-2 ed2.0 (2014-03).
random partial discharges (PDs): Discharges that recur infrequently with a repetition rate of less than one per second.
repetitive voltage impulses: Impulses that occur due to switching of power electronic devices at a carrier or driven frequency.
resistance temperature detector (RTD): A temperature detector that is usually a three-terminal resistor, either 10 12 copper at 25 °C or 100 12 platinum at 0 °C, whose sensing element is about 25 cm in length, which is encapsulated within an insulating substrate of suitable thermal rating. RTDs are usually installed between top and bottom bars (coil legs) in a given slot. The measuring leads should be positioned such that they do not interfere with the stress control coating.
semiconducting slot coating: A coating, applied on the insulation surface of the slot parts of winding. The semiconducting coating, compound, or tape in which the powder filler or portion of powder litter is a semiconductive material and the electrical surface resistivity of this coating in such that when converted into a semiconducting solid layer, is in the range of 1 x 102 to 5 x i05 ohms per square. This semiconducting slot coating must have uniform tight contacts with the grounded walls of the stator slot. This coating provides minimum voltage between the surface of the coil or bar and the grounded stator core.
signal attenuation: A decrease in signal magnitude from one point to another.
signal reflection: The result of a mismatch in the characteristic (surge) impedances of the signal transmission path in which a portion of the incident signal is reflected in the direction opposite to the incident signal.
signal transmission: The process by which the signal travels in a medium in the same direction as the incident signal.
slot discharges: Discharges that occur between the outer surface of a coil or bar and the grounded core steel.
NOTE Sec Johnson [[37], Wilson [[310].
spectrum analysis: Measurement of a signal over a range of frequencies using a detector having a defined bandwidth resolution.
stress control coating: The paint or tape on the outside of the groundwall insulation that extends several centimeters beyond the serniconducting slot coating in high-voltage stator bars and coils. The stress control coating often contains silicon carbide particles that tend to linearize the electric field distribution along the coil or bar end turn. The stress control coating overlaps the serniconducting coating to provide electrical contact between them.
4. The nature of PD in machine windings
4.1 Sources of PD
In most ac electric machines, there are numerous potential sites of PDs. Machine design, materials of construction, manufacturing methods, operating conditions, and maintenance practices can profoundly affect the quantity, location, characteristics, evolution, and the significance of PDs.
One of the most common sources of discharges in a stator is internal discharge which occurs inside small cavities trapped within the groundwall insulation. This activity can be constantly present from the first day of operation until the end of life without reducing the expected life of’ the machine. It is considered as normal PD activity and it is important to be able to differentiate between this activity and other more deleterious discharges.
Groundwall delaminations and cavities that develop as a result of machine misoperation, thermal aging, bar vibration, and PD erosion may exhibit characteristics that are very different from the characteristics of cavities in new insulation. PD sites may also be present or develop at the interface between the conductor and the groundwall and between the groundwall and the semiconducting treatment on the surfaces of’ stator winding elements. Other potential sites of PDs may occur within girth cracks, mechanical disruptions of insulation caused by overheating, sites of impact damage, insulation fractures, and abraded areas.
Slot discharge sites may occur as the result of certain semiconducting coating conditions that either are present when the machine is new or develop in operation. These conditions include discontinuities in the semiconducting slot coating, high resistivity values of’ the coating such that it does not function as intended. porosity, separations, migration defects, and erosion or abrasion defects. Slot discharge sites may also be caused by or extinguished by certain types of’ chemical contamination.
