Methods and apparatus for rendering electrical cables safe
1. A safe grounding apparatus for attachment to a motor lead end electrically coupled to a permanent magnet motor comprising:
- the motor lead end including a plurality of electrical conductors enclosed within a layer of insulation;
a plurality of clamps adapted to pierce the layer of insulation and be selectively electrically coupled to the plurality of electrical conductors of the motor lead end;
a plurality of shorting conductors adapted to electrically couple to the clamps and extend therefrom; and
the shorting conductors adapted to electrically couple to a bus bar to electrically short the shorting conductors.
A “safe grounding apparatus” (SGA) for safely grounding or neutralizing the electrical conductors for permanent magnet motor (PMM) powered artificial lift systems and methods of practicing the same are disclosed. The SGA of the present invention ameliorates some of the dangers associated with PMM'"'"'s. Methods of shorting, grounding, testing and monitoring the electrical conductors of a permanent magnet motor in order to safely manipulate the conductors are also disclosed.
|Sheath bonding arrangement for fiber optic cable splices|
Patent #US 6,591,055 B1
Current AssigneeATT Inc.
Sponsoring EntityATT Inc.
Patent #US 4,201,433 A
Current AssigneeHubbell Inc.
Sponsoring EntityFargo Manufacturing Co. Inc.
|HIGH TEMPERATURE POTHEAD|
Patent #US 20120052721A1
Current AssigneeSchlumberger Technology Corporation
Sponsoring EntitySchlumberger Technology Corporation
- 1. A safe grounding apparatus for attachment to a motor lead end electrically coupled to a permanent magnet motor comprising:
the motor lead end including a plurality of electrical conductors enclosed within a layer of insulation; a plurality of clamps adapted to pierce the layer of insulation and be selectively electrically coupled to the plurality of electrical conductors of the motor lead end; a plurality of shorting conductors adapted to electrically couple to the clamps and extend therefrom; and the shorting conductors adapted to electrically couple to a bus bar to electrically short the shorting conductors.
- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
- 10. A method for rendering a motor lead end coupled to a permanent magnet motor safe, the method comprising:
providing a plurality of clamps; selectively electrically coupling the clamps to a plurality of electrical conductors of a plurality of power cables of the motor lead end; electrically coupling the clamps to a plurality of shorting conductors; electrically coupling the shorting conductors to a bus bar; and monitoring at least one condition of at least one of the motor lead end and the permanent magnet motor.
- View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21)
This application is a continuation of U.S. patent application Ser. No. 15/422,368, filed Feb. 1, 2017 now U.S. patent Ser. No. 10/079,457, which is herein incorporated by reference.
The present invention relates in general to artificial lift systems used to pump fluids from wells and, and more particularly, to an apparatus and method for rendering a MLE of a motor safe from electrical shock hazards.
Hydrocarbon reservoirs produce fluid from boreholes drilled therein when the reservoir pressure is greater than the flowing pressure at the point of entry to the borehole necessary to lift the fluid to surface. When this condition is not attained it is known in the prior art to operate electric motors to drive pumps downhole, in situ, a method generally known as electric submersible pumping (ESP). The pump increases the flowing pressure sufficiently to lift the fluids to surface.
Most prior art motors used to drive ESPs have been of the three-phase alternating current asynchronous squirrel cage induction type. A power cable including electrical conductors extends from a power source at the surface and runs along the production tubing downhole to the motor. The electrical conductors of the cable are affixed to the motor before installation utilizing a connection commonly referred to as a “pot head”. The section of the power cable that includes the pot head is commonly referred to as the motor lead end (MLE). The MLE is typically spliced in the field to one or more sections sometimes referred to as the power cable. Such splices are well known in the industry, such as those described in United States Patent Application number 20130052055, the disclosure of which is incorporated herein in its entirety.
There exist other embodiments of ESP systems in the prior art that utilize permanent magnet motors such as those described in U.S. patent application Ser. No. 15/356,167, the disclosure of which is incorporated herein in its entirety. Such permanent magnet motors may also use three-phase AC power and similar MLEs, pot heads and power cables. However, ESP systems utilizing permanent magnet motors differ from induction motor systems in that when the motor shaft rotates (in the absence of supply power) it acts as a generator and can impress a significant voltage across the cable conductors, resulting in an electrical shock hazard for anyone touching the conductors. The motor may be rotated by, among other things, fluid running through the pump in certain situations such as while running the system in hole, removing the system from the hole or simply the draining of the production fluid from above the pump during a power failure or power shutdown. In addition, unlike centrifugal pumps, progressive cavity pumps do not pass fluid freely and breakout friction must be overcome in order to rotate. When running in, the tubing connected to such progressive cavity pumps remains essentially void of fluid and at low pressure, while well pressure builds on the bottom of the pump. At some depth the friction may be overcome and the pump will suddenly turn. The aforementioned hazards during running in are infrequent and may not occur and therefore makes the hazards sudden and unexpected. In such situations a technician or operator may be unaware that the motor is rotating and may be producing significant voltage. It should be appreciated by those skilled in the art that in such situations the manual manipulation of the electrical conductors of the cable, such as during a splicing operation, of a permanent magnet motor poses a significant risk of electrical shock and sparking. Sparking may even cause explosions if certain gases are present in the environment near the splicing operation.
What is needed is an apparatus and method that renders a power cable of a permanent magnet motor ESP system safe for splicing and other operations.
In accordance with some aspects of the present disclosure, systems and methods related to a novel artificial lift system are disclosed.
Various embodiments of an apparatus for attachment to a plurality of power conductors electrically coupled to a permanent magnet motor are disclosed.
In some aspects of the present invention, the apparatus is a safe grounding apparatus (SGA) and includes a plurality of shorting conductors electrically coupled to the power conductors; and a connection for electrically shorting the shorting conductors.
In still other aspects of the present invention, the SGA includes a ground connector for grounding the power connectors to earth.
In yet other aspects of the present invention the SGA includes a module for monitoring physical conditions of the permanent magnet motor including voltage, resistance, speed and frequency.
In yet other aspects of the present invention a method includes rendering a plurality of conductors electrically coupled to a permanent magnet motor safe.
In still other aspects of the present invention a method includes rendering a plurality of power conductors electrically coupled to a permanent magnet motor safe includes electrically coupling a plurality of shorting conductors to the power conductors and shorting the shorting conductors. The method further includes grounding the shorting conductors.
In still further aspects of the present invention a method includes monitoring the power conductors for various electrical attributes.
So that the manner in which the above-recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
In the following detailed description of the embodiments, reference is made to the accompanying drawings, which form a part hereof, and within which are shown by way of illustration specific embodiments by which the examples described herein may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the disclosure.
The examples disclosed herein relate to a “safe grounding apparatus” (SGA) for safely grounding, neutralizing (or shorting), testing and monitoring the electrical conductors for permanent magnet motor (PMM) powered artificial lift systems and methods of practicing the same. The SGA of the present invention ameliorates some of the dangers associated with PMMs. The present invention provides a method of shorting, grounding and monitoring the electrical conductors of a permanent magnet motor in order to manipulate the conductors, for example, to splice the motor lead end (MLE) of a cable to a power cable. Referring to
Now referring to
It is known in the prior art to mechanically connect PMM 16, ESP 12 and at least a few sections of production pipe 14 at the surface. It is further known to attach pot head 22 to PMM 16 and MLE 23 to the side of ESP at the surface. With the various components assembled at the surface as described, an operator lowers the assembly into well 18. There are various situations within the art that necessitate the placement of a splice connection 21 in the embodiment described. For instance, a first splice connection 21 between MLE and power cable 20 is typically made on site as ESP 12 and PMM 16 are positioned within well 18. An operator further attaches successive sections of production pipe 14, continues to lower the assembled components into well 18, and makes splice connections 21 as needed until ESP 12 is positioned at a predetermined depth within the well. In addition, MLE 23 may be damaged, either during installation in the well or thereafter, and necessitate that a splice connection 21 be placed to restore electrical connectivity to PMM 16. A typical splice connection 21 may comprise any known connector including as described herein above with reference to US20130052055.
As described herein above, and with reference to
Referring now to
As discussed herein above, and as will be appreciated by those skilled in the art, that while splicing MLE 23 to power cable 20 the conductors 38 are exposed and present hazards such as shock and sparking. The primary voltage hazard arises when contact is made across two conductors 38. It is an aspect of the present invention that if conductors 38 are shorted together there can be no voltage across them. If the shaft of PMM 16 is rotating, the internal generator voltage of the motor will however drive a current through a short circuit of conductors 38, limited by the impedance of the motor winding and the shorted conductors. The present invention takes advantage of the known characteristic of permanent magnet motors, that this current flow will result in a braking torque and advantageously a reduction in the speed of the motor and pump. The current flow may be detected as hereinbelow described so as to provide an indication of rotation and hence a warning to stop work as a further safety precaution.
Still referring to
Given the aforementioned description of SGA 50 if the exemplary pair of conductors 38 are isolated from earth, and only one conductor is touched by an operator then no shock or sparking hazards can result. However, if an earth fault on one of the conductors 38 occurs in PMM 16 or MLE 23 during work on the MLE then a hazard exists from the other conductors to earth 62. It should be appreciated that this secondary fault case is well known in electrical installation practice using the “IT” floating power system. In normal electrical installations this secondary fault is not immediately hazardous and an insulation monitor may be used to detect and warn of its occurrence. It should be further appreciated however that when working on conductors 38 in utilizing the present invention there may be an immediate touch hazard. Therefore, certain embodiments of the present invention preferably includes a further step of shorting the conductors 38 to ground 62 via conductor 61. Although armor 30 is inevitably in contact with metallic parts of the production tubing, and therefore likely in contact with ground, it is preferable to explicitly ground it as with conductor 58.
The reliability of splices and other means of connection is an essential part of the economics of artificial lift systems and ESP'"'"'s in particular, wherein the loss of production and rig costs associated with a repair are extremely costly. Therefor it is a further objective of the present invention to allow existing established practice for induction type motors to be followed as closely as possible when permanent magnet motors are used. The splicing operation of the exemplary method described herein below closely resembles that practiced in the art of induction motor driven ESP systems.
An exemplary method of employing the SGA 50 of the present invention is illustrated with reference to
Referring now to
Power cable 20 may be comprised of the same or similar components as MLE 23 as described herein above. The same operation of preparing power cable 20 for splicing may typically performed on each end the power cable at least to expose the conductors. In the art it is common practice, and necessary for safely practicing the present invention, to short the conductors of the uphole end of power cable 20, using a terminal block for instance. If a second SGA is used in place of the terminal block, the present invention has the advantage of monitoring the splice during the completion of the splice. Once SGA 50 is installed as described, power cable 20 may be brought into position as shown in
The embodiment of SGA 50 in
With reference to
It should be appreciated by those skilled in the art that in the shorted system of the present invention, for each motor phase there is a continuous loop through the motor winding, the motor star point and back up through the other phase connections. Taking advantage of these inherent properties, various conditions of PMM 16 may be realized, monitored, measured and otherwise employed to provide further safety to operators.
As an example of the foregoing, for continuity one of the shorting conductors, say 55 for example, may be passed through the core of a small transformer (not shown). The transformer primary can be energized by a simple oscillator circuit, causing current to be induced in a phase conductor, returning via the other shorting conductors 56, 57. A low value resistance, perhaps only a few milliohms, can be inserted in series with each of the shorting conductors 56, 57, and the voltage drops across them may be sensed using known methods. There will no voltage on a connection that is open circuit. The frequency of the oscillator should be high enough for the transformer to work well but low enough that the series inductance of the motor windings presents too high an impedance to allow a measurable current flow.
Again, and as another example, for detection of rotation of the shaft of PMM 16, it will be apparent a rotating motor shaft will generate current into a short circuit in proportion to its internal voltage (emf) and series impedances. This alternating current is measurable from the voltage drop across the aforementioned resistances. The current readily reaches many amperes and can be distinguished from the continuity circuit by frequency range and large amplitude. It is known that the frequency of the current from PMM 16 is inherently an exact indicator of speed. An alternative embodiment to utilizing resistances, other current transducers such as flux gate and hall effect sensors as made by LEM (lem.com) may be used.
An important aspect of all the aforementioned methods of motor current measurement is that they work continuously from DC through the maximum frequency of the motor. These methods work for ESP systems using permanent magnet motors having used for PCPs as well as centrifugal pumps. As an example, a 4-pole motor rotating at 1800 rpm generates current at a frequency of 60 Hz but at 180 rpm it is only 6 Hz. A motor wound for say 600V operation at 180 rpm would produce a hazardous 60V at 18 rpm (48V being a widely accepted maximum safe voltage). However at 18 rpm the frequency of the current would be only 0.6 Hz. This example shows the advantages of the features of module 80 of the present invention. Conventional widely available handheld meters would be ineffective at performing such monitoring in that are designed to either measure DC or to measure AC above a few Hz. Even on DC+AC ranges the same limitation applies. At 0.6 Hz there may be a slight indication when set to DC or DC+AC but on AC there will no reading at all.
It should be noted that the present invention further includes the termination of a MLE 23 with a “touch safe” connector (not shown) that would in itself be connected to the electrical connectors and allow manipulation and connection of the MLE to the power cable with minimal risk of electrical shock or sparking. The present invention further includes a removable terminating connector (not shown) for connecting with the touch safe connector and safely terminating MLE 23 thereby. It is within the scope of the present invention that the terminating connector includes the features and components of monitor 80 described herein above.
While the foregoing is directed to embodiments of the present invention for use in conventional tubing deployed ESP systems, other systems utilizing permanent magnet motors where a similar risk of shock hazard exists such as electric drilling, rigless completions, coiled tubing and the like are within the scope of the present invention.
While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.