IEEE Electrical Insulation Magazine | Year: 2012
Partial discharges (PD) are small electrical sparks that can occur in liquid or solid insulation systems in high-voltage equipment, and can eventually cause failure of the equipment -. Partial discharge testing has been used for more than 80 years as a factory quality control tool to find manufacturing defects that could eventually lead to equipment failure. We believe that Johnson was the first to measure PD on operating high-voltage equipment, in the 1940s . His aim was to find an online method to determine whether stator winding coils or bars were vibrating excessively in the stator magnetic core. These vibrating coils lead to abrasion of the high-voltage electrical insulation and to eventual failure. A symptom of the insulation abrasion process was that PD (or what he referred to as slot discharge) occurred between the surface of the coil and the stator core. By measuring the PD online, he could indirectly detect the movement of coils, which indicated that failure was likely. The measurement had to be made online because, if the generator were not operating, no magnetic forces would be acting on the coils; thus, the air gaps that are a necessary precursor of PD would not be as large. Johnson was successful in identifying those generators that were suffering the most from this problem, which was caused by the introduction of the first thermoset insulation systems and by workmanship variations that were magnified by an inadequate method of securing the coils in the stator slots for the novel insulation system. The success of the Johnson online PD measuring system inspired other machine manufacturers and even a few utilities to develop their own methods , . The main reason Johnson needed online PD measurement was that loose windings do not produce as much PD when the motor or generator is not operating. Thus one of the important reasons for performing online PD tests is to monitor the condition of the equipment under normal operating electrical, thermal, and mechanical stresses. However, with the current emphasis on extending times between maintenance outages, and the push to reduce testing costs in general, the main reason now given for online PD measurement is to avoid shutdown of the equipment, which would be necessary for an off-line PD test or other diagnostic test. Although we believe online PD monitoring was first applied to rotating machines, the same reasons are valid for other electrical equipment, such as oil paper cable joints or terminations, distribution class switchgear, gas-insulated switchgear, and power transformers , . © 2006 IEEE.
IEEE Transactions on Dielectrics and Electrical Insulation | Year: 2013
Condition-based maintenance (also called predictive maintenance) requires diagnostic tools to determine when significant insulation aging has occurred, and thus when maintenance is necessary to avoid an in-service failure. Over the years many off-line diagnostic tests and on-line monitoring systems have been proposed and implemented, especially on critical motors and generators. In the past decade, most of the research has concentrated on improving existing off-line diagnostic tests and on-line monitoring such as magnetic flux, partial discharge, temperature, endwinding vibration, etc. However, some newer tests such as polarization/depolarization current, dielectric spectroscopy and on-line leakage current monitoring have been introduced. These tests and monitoring systems are reviewed. Tests and monitoring systems for rotor winding insulation and stator winding insulation are addressed separately. © 2013 IEEE.
Qualitrol | Date: 2012-08-01
In accordance with the present invention, there is provided a hybrid mechanical and electrical transformer temperature monitor. The mechanical sensing mechanism drives mechanical switches, a local display and a sensing input to the electrical side of the monitor. The electrical portion of the temperature monitor has the ability to calculate winding temperature (with an additional current sensor), data log, actuate electrical switches and has a local display for winding temperature.
Qualitrol | Date: 2012-12-31
A port assembly is receivable in an opening allowing access to the interior of a transformer. The port assembly includes a body and a port cover. The body is receivable in the opening and has a substantially axial opening therethrough. The axial opening allows access to the interior of the transformer through the port. The port cover is disposed on the interior of the transformer and is movable relative to the body between a sealed position sealing the axial opening and an open position allowing access to the interior of the temperature well. The port cover is biased toward the sealing position and moves to the open position upon being acted upon by an elongate tool inserted into the temperature well through the axial opening in the port.
Qualitrol | Date: 2011-03-31
The invention provides a sensor assembly for a sensor having a semiconductor element for measuring hydrogen concentration in an insulating fluid in electric power generation, transmission, and distribution equipment having a temperature well that has a tubular portion extending into the equipment providing access to the interior of the equipment, the temperature well having a movable valve at an end of the tubular portion. The tubular portion includes a first flange, a tubular housing member attached to the first flange having one end adapted to be telescopically received in the temperature well. The tubular portion further includes a housing body having one end thereof connected to the tubular housing member having a substantially uniform cross section extending from the tubular housing member wherein at least one wire receiving opening extends through the housing body. The tubular portion also includes a cover closing an end of the housing body distal from the one end, a first seal disposed between the tubular housing member and the tubular portion of the temperature well for blocking the flow of insulating fluid in the space between the housing member and the temperature well wherein said tubular housing member is long enough so that when fully extended into the temperature well, the tubular housing causes the movable valve to open.