High frequency AC noise suppression within transformers

A transformer configured for use in connection with a variable speed motor drive includes primary windings and secondary windings. The secondary windings are configured as wye-windings and a ground lead and a plurality of phase leads. The transformer includes a ferrite blocking circuit connected to the ground lead.

FIELD OF THE INVENTION

This invention relates generally to power supply systems, and more particularly, but not by way of limitation, to an improved transformer for providing power to an electric pumping system.

BACKGROUND

Pumping systems are often deployed into wells to recover petroleum fluids from subterranean reservoirs. Typically, the submersible pumping system includes a number of components, including one or more electric motors coupled to one or more high performance pumps. Each of the components and sub-components in a submersible pumping system is engineered to withstand the inhospitable downhole environment, which includes wide ranges of temperature, pressure and corrosive well fluids.

The electric motor is often driven by a variable speed drive located on the surface. The variable speed drive produces an alternating current that is transferred to the electric motor through a power cable. In some applications, the voltage of the current provided by the variable speed drive to the motor must be increased by a step-up transformer to reach the design voltage for the electric motor. In other applications, transformers are used to adjust the input voltage to the variable speed drive.

Inductors are sometimes used to create a reactance ground on transformers. To comply with ratings established by the International Electrotechnical Commission (IEC), inductors placed on the ground lead of transformers must be configured to handle electrical shorts. Often, this requires the conductor of the inductor to be oversized to minimize temperature increases in the event of a short circuit. Additionally, when an inductor is used with transformer, a ground fault indicator (GFI) must be used to verify that the equipment is properly ground referenced. The use of oversized conductors and ground fault indicators increases cost and complexity to the transformers. It is to these and other deficiencies in the prior art that the present invention is directed.

SUMMARY OF THE INVENTION

In some embodiments, the present invention includes a transformer that has primary windings and secondary windings, where the secondary windings include a ground lead and a plurality of phase leads. The transformer also includes a ferrite blocking circuit connected to the ground lead.

In another aspect, the present invention provides a pumping system that has an electric motor, a power supply, a variable speed drive, and a transformer connected to the variable speed drive. The transformer includes primary windings and secondary windings, where the secondary windings include a ground lead. The transformer further includes a ferrite blocking circuit connected to the ground lead of the secondary windings.

In yet another embodiment, the present invention includes a transformer that has primary windings and secondary windings, where the secondary windings include a ground lead and a plurality of phase leads. The transformer further includes a ferrite blocking circuit connected to the ground lead, where the ferrite blocking circuit has a ferrite element and a conductor coupled to the ground lead and extending through the ferrite element.

WRITTEN DESCRIPTION

In accordance with exemplary embodiments of the present invention,FIG. 1shows a perspective view of a pumping system100attached to production tubing102. The pumping system100and production tubing102are disposed in a wellbore104, which is drilled for the production of a fluid such as water or petroleum. As used herein, the term “petroleum” refers broadly to all mineral hydrocarbons, such as crude oil, gas and combinations of oil and gas. The production tubing102connects the pumping system100to a wellhead106located on the surface. Although the pumping system100is primarily designed to pump petroleum products, it will be understood that the present invention can also be used to move other fluids. It will also be understood that, although the pumping system100ofFIG. 1is depicted in a deviated or non-vertical wellbore104, the pumping system100and methods disclosed herein will find also utility in traditional vertical wellbores.

The pumping system100includes a pump108, a motor110and a seal section112. The motor110is an electric motor that receives power from surface facilities114through a power cable116. When energized, the motor110drives a shaft (not shown) that causes the pump108to operate. The seal section112shields the motor110from mechanical thrust produced by the pump108and provides for the expansion of motor lubricants during operation. The seal section112also isolates the motor110from the wellbore fluids passing through the pump108.

The surface facilities114provide power and control to the motor110. The surface facilities114include a power source118, a variable speed drive (VSD)120and a step-up transformer122and an input transformer124. The power source118includes one or both of a public electric utility126and an independent electrical generator128. Electricity is fed by the power source118, through the input transformer124to the variable speed drive120. It will be appreciated that in some applications, it may not be necessary to deploy both the step-up transformer122and the input transformer124.

Turning toFIG. 2, shown therein is a functional depiction of the input transformer124and the variable speed drive120. The input transformer124may be configured as a three-phase transformer that includes a dielectric fluid-filled tank with an input throat and an output throat for making electrical connections with adjacent equipment. The output from the input transformer124is carried to the variable speed drive120. In accordance with well-established motor drive technology, the variable speed drive120may include a converter130and an inverter132. The output voltage from the input transformer124is coupled to the converter130, where the alternating current is converted and coupled to a direct current (DC) bus. The inverter132is utilized to convert the DC bus voltage to a variable frequency AC signal, in response to motor drive control commands in the variable speed drive120. In some configurations, the output from the inverter132is provided directly to the motor110or to the intermediate step-up transformer122. During normal operation, the variable speed drive120can be configured to produce a pulse width modulated (PWM) current at a selected frequency. In some embodiments, the inverter132of the variable speed drive120is configured to produce a six-step commutation sequence that can be adjusted manually or automatically to adjust the operating parameters of the pumping system100.

As depicted inFIG. 2, the input transformer124is a delta-wye transformer that includes delta-connected primary windings134and wye-connected secondary windings136. In alternate embodiments, the primary windings134are also configured as wye-connected windings. The wye-connected secondary windings136include phase leads138a,138b,138cand a ground lead140. The phase leads138a,138b,138care connected through the output throat to the variable speed drive120. It will be appreciated that switches, sensors, fans and other customary equipment may be included within the input transformer124.

Unlike prior art designs in which the ground lead of a transformer is provided with an inductor, the input transformer124includes a ferrite blocking circuit142connected to the ground lead140. The ferrite blocking circuit142is configured as a high-frequency, noise-absorbing and blocking circuit that is connected in parallel with the ground lead140or connected in series with the ground lead140.

In an exemplary embodiment depicted inFIGS. 3 and 4, the ferrite blocking circuit142includes a ferrite element144through which a conductor146extends. As depicted inFIGS. 3 and 4, the ferrite element144is a ferrite cylindrical body that surrounds a portion of the conductor146. In other embodiments depicted inFIGS. 5 and 6, the ferrite element144includes one or more ferrite rectangular or prism bodies that are connected to, or in close proximity with, the conductor146and that extend in a substantially parallel orientation with the conductor146. In the embodiment depicted inFIGS. 5 and 6, the ferrite element144can be secured to an exterior surface of the conductor146with banding148.

The ferrite blocking circuit142on the ground lead140provides noise-filtering without impeding the AC signal, without resistive or reactive losses, and without generating temperature during operation. Unlike prior art inductors, the ferrite blocking circuit142does not make use of looped conductors, which raise compliance issues with IEC standards and require ground fault indicators.

Although the ferrite blocking circuit142is disclosed in connection with the input transformer124, it will be appreciated that the ferrite blocking circuit142could also be applied to the ground lead140within the step-up transformer122. Additionally, it will be appreciated that the combination of the ferrite blocking circuit142and ground lead140could be applied to wye-connected windings in other transformers, including in industrial power applications.